EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)
CERN-SHiP-NOTE-2015-005 SHiP-TP-2015-A3-v1.1 2 May 2016
Extraction and beam transfer for the SHiP facility
B. Goddard, M. Fraser, J. Borburgh, B. Balhan, B. Todd, G. Le Godec, B. Puccio, M. Zerlauth, J. Bauche, D. Tommasini, V. Kain, K. Cornelis, J. Wenninger, L. Jensen CERN
Abstract
This document summarises the key feasibility issues associated with the SPS extraction and beam transfer systems required for the SHiP facility. It describes the expected performance limits of the electrostatic septa, the expected beam losses during extraction and consequences, the design of the new beamline geometry and equipment systems and the expected extracted spill structure.
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Page 2 of 43 HISTORY OF CHANGES REV. NO. DATE PAGES DESCRIPTIONS OF THE CHANGES
0.1 2015-03-01 43 Version 0.1 completed, distributed for checking
0.2 2015-04-08 47 Version 0.2 complete included all comments.
1.0 2015-10-29 43 Updated erroneous proton loss data from 2007.
1.1 02.05.2016 43 Update of figures. PDF conversion problem.
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Page 3 of 43 TABLE OF CONTENTS Extraction and beam transfer for the SHiP facility ...... 1 1. Introduction to beam transfer for SHiP ...... 5 2. Electrostatic extraction septa ZS performance limits ...... 5 2.1 Slow extraction ...... 6 2.2 ZS electrostatic septa ...... 6 2.3 Potential ZS performance limitations at SHiP intensities ...... 7 2.3.1 WIRE HEATING ...... 8 2.3.2 SEPTUM BEAM CONDITIONING ...... 8 2.3.3 HIGH VOLTAGE FEEDTHROUGHS ...... 8 2.3.4 AVERAGE BEAM POWER AND ANODE HEATING ...... 9 2.3.5 HIGH SPARK RATES AND CATHODE DAMAGE ...... 9 2.4 Improvements and testing ...... 10 2.5 Conclusion on ZS performance limits ...... 10 3. Beam Losses During Extraction ...... 10 3.1 Beam Loss Mechanism During Extraction ...... 11 3.2 Comparison with SPS Operation During WANF ...... 11 3.3 High-Level Dosimetry ...... 12 3.4 Activation ...... 13 3.5 Impact of Increased Activation ...... 15 3.6 Possible mitigation measures ...... 15 3.7 Conclusion on beam losses during extraction ...... 17 4. Beam Line Design ...... 17 4.1 Beam Line Design ...... 18 4.2 Conclusion on beamline design ...... 21 5. Beam instrumentation for SHiP extraction and beamline ...... 21 5.1 Existing instrumentation ...... 21 5.1.1 POSITION AND PROFILE MONITORING ...... 21 5.1.2 BEAM INTENSITY MONITORING ...... 22 5.1.3 BEAM LOSS MONITORING ...... 23 5.2 Changes needed to the existing instrumentation ...... 24 5.3 New instrumentation needed for the new section of SHiP beamline ...... 24 5.4 Conclusion on beam instrumentation ...... 25 6. Design and powering of new splitter magnets ...... 25 6.1 Design requirements ...... 26 6.2 Magnet coil design ...... 26 6.3 Magnet yoke design ...... 27 6.4 Splitter powering ...... 28 6.5 Schedule and lead times ...... 28 6.6 Conclusion on new splitter magnet and powering ...... 28 7. Beam Dilution ...... 29 7.1 Sweep profile over target ...... 29 7.2 Dilution magnets ...... 30
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7.3 Conclusion on dilution sweep...... 30 8. Interlocking ...... 31 8.1 Hardware interlocking design requirements ...... 31 8.2 Hardware interlocking concept ...... 31 8.3 Magnet current surveillance ...... 33 8.4 Fast Magnet Current Change Monitor Interlocks ...... 34 8.5 Hardware interlock user inputs ...... 34 8.6 Software interlocks ...... 34 8.7 Conclusion on interlocking ...... 35 9. Spill structure and control ...... 35 9.1 Slow extraction servo spill ...... 36 9.1.1 EFFECTIVE SPILL DURATION ...... 36 9.1.2 LOW FREQUENCY HARMONIC CONTENT OF SPILL FROM MAINS RIPPLE ...... 37 9.1.3 MEDIUM FREQUENCY VARIATIONS ...... 37 9.1.4 RESIDUAL 200 MHZ BEAM STRUCTURE ...... 38 9.2 Conclusion on spill structure ...... 39 10. Machine Development Studies ...... 39 10.1 Foreseen program of studies ...... 40 10.2 Conclusion on machine development studies ...... 40 11. Conclusions and R&D activities ...... 41 12. References ...... 41
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1. Introduction to beam transfer for SHiP The SHiP experiment requests an intense beam of protons with a momentum of 400 GeV/c delivered to its target station foreseen to be located in the North Area at the SPS. After consideration of different extraction techniques, a slow-extracted spill over 1 second was chosen as the baseline scenario considering the maximum acceptable instantaneous particle flux at the experiment and other constraints given by the maximum beam power accepted by the design of the SHiP target. A nominal intensity of 4.0×1013 p/cycle will be extracted as part of a 7.2 s SPS slow-extraction cycle with a 1.2 s flat-top, transferred via TT20 and a new beam line, and diluted onto the SHiP target with an rms beam size of at least 6 mm in both horizontal and vertical projections. For machine protection arguments, the proton beam momentum will vary from 400 GeV/c by at least 5-10 GeV/c, with 390 GeV/c a likely choice. In this baseline scenario, the per-cycle intensity would offer a total of 4×1019 protons on target per year, while providing 4×1019 to the other North Area targets, thus meeting the required number of protons on target for SHiP of 2×1020 in 5 years.
The main challenges in meeting the integrated intensity requirements of SHiP lie in the beam extraction system of the SPS. The accelerated intensity of 4.0×1013 p/cycle is well within the reach of the SPS, which has previously accelerated up to 5.3×1013 p/cycle; however the slow-extraction of 4.0×1013 p/cycle is equal to the historical maximum extracted intensity per spill. When combined with a quicker spill and a factor two increase in the total number of protons extracted per year the challenges start to become evident. Clearly, with the use of conventional slow-extraction small losses are unavoidable on the wires of the electrostatic septum (ZS) that must necessarily intercept the beam. Increased activation of the extraction region will lead to challenges for the reliability of the system, with its maintenance, intervention and dose management becoming more important. The behaviour of the ZS under the pressures of an increased spill rate and total extracted beam intensity are still to be checked and understood in future machine development studies. The issues faced by the extraction system are outlined at length in this annex along with the mitigation techniques needed to realise the SHiP experiment at the SPS.
In subsequent sections, the design of the new beam line is outlined, including the new splitter/switch magnet that is required to operate both the existing North Area facility and SHiP in parallel, the dilution system required to dilute the beam power density impacting the SHiP target, the interlocking system, the beam instrumentation and the expected time structure of the spill.
2. Electrostatic extraction septa ZS performance limits The beam intensity needed for the SHiP cycles are 4×1013 p+ extracted at 400 GeV/c with a ≈1 second long flat-top, every 7.2 seconds, through the existing extraction channel in LSS2, to TT20 and the new section of SHiP beamline.
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The high extracted intensity per spill and the short spill length are both concerns for the performance of the electrostatic ZS septa, which are very special technology high-voltage systems used to split the beam with as few losses as possible. In the following sections the ZS septa design and operating conditions are described, together with the performance concerns. Data from comparable operational periods are presented to estimate the realistic operational performance limits, together with recommendations for improvements in instrumentation, controls and interlocking to minimise the potential impact on the ZS and the overall machine availability.
2.1 Slow extraction Slow extraction from the SPS in LSS2 is routinely operational and used for supplying beam to the North Area. The slow extraction is accomplished with a set of suitably located extraction sextupoles used to create a stable area in horizontal phase space. This initial phase space area is larger than the area occupied by the beam. A dedicated
servo-quadrupole consisting of 4 short QMS quadrupoles moves the tune towards QH = 26.666 shrinking the stable phase space area. The beam is debunched and the chromaticity set to a large negative value. For a given momentum and thus tune, protons with coordinates outside the stable area move away from the beam core along the outward going separatrices, and eventually cross the wires of the ZS septum, into its high field region. The ZS deflects the particles into the magnetic elements of the extraction channel consisting of thin MST and thick MSE septum magnets, which move the beam into TT20 proper. A servo quadrupole is used in combination with a beam current transformer in TT20 to modulate the rate at which the beam is extracted.
The high chromaticity means that the extraction is effectively made in a combination of momentum and betatron space, with highest momentum offset particles coming into resonance and being extracted first. There is therefore a momentum change through the spill, which via the dispersion in the transfer line will couple into position changes in time in the transverse plane.
2.2 ZS electrostatic septa The ZS septa were designed and built in the 1970s [1]. Each unit consists of two parallel electrodes of approximately 3 m in length. The circulating beam passes through the field-free region within the hollow anode, which is bounded toward the cathode by an array of this W / Re alloy wires, Figure 1, and when particles cross the wires they experience the high electric field between anode and cathode that deflects them across the thin magnetic septum downstream. Five such ZS units are needed to extract the beam at 400 GeV/c. The main parameters are given in Table 1. The design has a high complexity with the array of 2080 anode wires aligned precisely by the anode support, to within 20 µm straightness. The use of Invar for the anode support of the first 3 ZS anodes in the extraction channel minimises mechanical deformation with beam heating. Clearing electrodes with a few kV potential are needed inside the anode to sweep any ions produced from residual gas, which can cause sparking if allowed to drift into the high field gap.
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Figure 1. ZS electrostatic septum used for slow extraction from SPS
Clearly the electrostatic septum must be as thin as possible to minimise beam losses, and must contain as little material per unit length as possible, for the same reason. In addition it must be compatible with UHV and high voltage and must also withstand the intense heating by the beam. This determines the use of 60 µm diameter W76 / Re24 alloy wire for the septum anode plane for the first, most upstream, 2 ZS anodes.
Table 1. Parameters of electrostatic septa ZS
Parameter Value Electrode length [mm] 2997 Cathode material Anodised Al Applied voltage [kV] 220 Inter-electrode gap [mm] 20 Operating field [MV/m] 11 Sparks per year [per unit] <10,000 Decoupling resistance [M] 400 Anode support material Invar Anode wire material W / Re Anode wire diameter [µm] 60 Number of anode wires per unit 2080 Anode wire spacing [mm] 1.5
2.3 Potential ZS performance limitations at SHiP intensities The performance of the ZS with these very high extracted beam intensities in a short spill is likely to be a key factor in the overall SHiP performance. For very high extracted
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beam intensities, the ZS septa are liable to experience increased sparking, vacuum pressure rise, and eventually damage of the wires through beam heating. There are also secondary effects like high voltage feedthrough damage from beam losses.
2.3.1 Wire heating Tests and operational experience in the past have shown that the ZS anode wires can withstand slow extraction spills up to and above the SHiP value of 4×1013 p+. The half- integer extraction used to the West Area Neutrino Facility extracted a much higher instantaneous flux of protons, with 1.5×1013 p+ extracted in about 5 ms [2], which is around a factor 75 higher in p+/s. Similarly, slow third integer extractions have been made for operation to the North Area with 4×1013 p+ extracted in 10 seconds. Studies for worst-case impact of a fast-extracted LHC beam were also made in the past [4], which indicated that temperatures of around 2300°C would be reached by the direct impact of an LHC type beam, with zero divergence and 1.2×1013 protons impacting the 11 wire. For SHiP, about 4×10 protons are expected to impact the wire per spill, which even without any heat loss mechanism (dominated by radiation), the wires would reach ‘only’ about 800°C, which is below the operationally assumed limit of 1000°C and well below the 3100°C melting point of the material. Tests made in the SPS with ZS wires have confirmed these simulations [5], with a measurement of 3.4×1012 protons at 450 GeV/c impacting a 60 µm wire before it broke through melting. This is almost an order of magnitude above the number of protons expected to impact the ZS wires per extraction during SHiP operation. In the past, damage to the ZS wires has occurred when operational errors have led to the circulating beam core impacting the wires [9], and this must be prevented by adequate interlocking – both with fast-response BLMs but also with settings and function tracking and locking capability.
2.3.2 Septum beam conditioning Operation with high extracted intensity will require a period of conditioning of the septa, with progressively increasing beam intensity. This is for vacuum and high voltage reasons, as the hot wires outgas significantly – high vacuum pressure can degrade the high voltage performance significantly, for instance through the production of ions which penetrate the anode wires and are accelerated onto the cathode, causing a spark. It is expected that the conditioning period with beam could take of the order of a week, before the full operational intensity is reached. Beam conditioning will need to be repeated after each venting of the ZS system.
2.3.3 High voltage feedthroughs The recurring damage to the main ZS HV feedthroughs encountered during WANF operation was due to ionisation and bubble formation in the dielectric liquid of the ZS feedthrough [6], shown together with the plug and cable in Figure 2, which resulted in discharges in the feedthrough and eventual punch-through of the structural and insulating alumina. Mitigation measures against this weakness have already been deployed on the operational ZS, notably with significant improvements in the hydraulic system used to circulate and regenerate the dielectric liquid. Since these measures were
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taken, the number of broken feedthroughs has dropped enormously, from a total of ~23 in the years 1983 and 1984 [7], to 0 since 2003.
2.3.4 Average beam power and anode heating The SHiP cycle of 4 ×1013 p+ extracted in 7.2 s represents a doubling of the extracted beam power compared to past operation at 4 ×1013 p+ extracted in 14.4 s. This will double the power deposited in the anodes of the septa, the first three of which are made of Invar with a low coefficient of thermal expansion. The effect on the alignment of the septa needs to be verified with beam, with the risk that extra heating can result in worse septum alignment and an increase in specific beam loss per proton.
The higher power may also result in a higher dynamic vacuum level which could result in more sparks, as a direct result of the higher pressure or as a result of more positive ions escaping into the high field gap. Again, studies with beam will be needed to determine whether these effects occur and whether they can be mitigated e.g. by modification of the ion trap voltage or with the extra pumping capacity for the ZS planned as part of the LIU project.
Figure 2. Alumina ZS HV feedthrough (top) and associated plug.
2.3.5 High spark rates and cathode damage The final concern is about excessive sparking of the high voltage with very high intensities, which results in a collapse of the field seen by the beam and eventual beam
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loss on the downstream ZS or MST. Very high spark rates can also irredeemably damage the cathode or even lead to damage of the feedthrough, and as such are protected against by detection systems and interlocking which cuts the high voltage and can as well dump the beam [8].
2.4 Improvements and testing Some sparking of the ZS during slow extraction is an inevitable feature of proton operation, however, and improvements to automatic surveillance, trending and the on- line analysis of operational extraction parameters like specific beam loss per proton and spill quality are all measures which will both minimise beam losses and activation, and reduce the spark rates and risk of equipment damage. A full analysis of requirements in terms of ZS protection interlocks and surveillance should be made at an early stage, which will allow time for development and deployment of such tools.
The instrumentation used for setting up of the slow extraction needs a serious review and upgrade, to allow more precise control of the process, faster setup and an easier optimisation.
These developments will need to be tested with beam, together with the SHiP cycle and the 1 s extraction spill. Machine Development tests with increasing intensity extracted over 1 s to the North Area on the SHiP cycle are planned at the end of the 2015 proton run to probe experimentally the limits, at least in terms of scaling of the behaviour, measurements of stability and of spill quality.
2.5 Conclusion on ZS performance limits The proposed intensities for SHiP appear to be within the acceptable operational envelope for the ZS septa, based on considerable previous operational experience and the total and peak proton intensities extracted. Nonetheless, given the high activation expected for the ZS and the serious consequences of faults in the event of damage, a serious effort needs to be made to improve interlocking, diagnostics, surveillance, trending and long-term control of the extraction quality. Such developments will also directly benefit the Fixed Target program through increased availability and reduced beam losses in the extraction region. It must be borne in mind, in case of a ZS failure, and taking into account the ALARA procedures and restrictions imposed by RP, that the cool down time (without beam towards North Area and SHiP) may be significantly longer than the repair itself.
3. Beam Losses During Extraction The annual extracted beam intensity of 4×1019 p.o.t. proposed for SHiP is approximately a factor two higher than the previous record achieved at SPS during the 5 year operational period of the West Area Neutrino Facility (WANF, 1994-1998) through LSS6. Operation of the existing system at higher intensities will inevitably lead to higher activation of the extraction region and its components, and will provide challenges for its operation and maintenance.
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In this section historical measurements of activation and dose are examined as a function of the number of extracted protons and the results are put into the context of SHiP by scaling to provide preliminary loss estimates. The activation and dose estimates provide the first data for assessing the impact of SHiP operation, which will be important for understanding system reliability and intervention planning.
Finally possible mitigation measures to reduce losses and activation are discussed and the necessary actions outlined.
3.1 Beam Loss Mechanism During Extraction During slow extraction protons with coordinates outside the stable area move away from the beam core along the outward going separatrices and eventually cross the wires of the ZS septum into its high field region. Unavoidable beam losses induced by protons intercepting the septum wires represent less than 1% of the extracted beam intensity for a well-established cycle.
3.2 Comparison with SPS Operation During WANF A total of 7.6×1019 protons were extracted at 446 to 450 GeV from the SPS through LSS6 during the 5-year operation of WANF between 1994 and 1998 [10]. Concurrently, a total of 2.5×1019 protons were also slow extracted to the North Area via LSS2. During this period the intensity of the SPS proton beam increased from 3.5 to 4.9×1013 protons per cycle shared with slow and fast-slow extraction to LSS2 and LSS6. The extraction mechanism for the neutrino program was a half-integer fast-slow extraction with a spill length of 6 ms and an intensity per spill of up to 1.8×1013 protons. The slow extracted spill length was 2.3 s shared between LSS2 and LSS6, with an intensity of up to 2×1013 protons per spill. The proton yields on the fixed targets (T1, T2, T4, T6 and T9) during WANF are collected in Table 2.
It is expected that loss estimates based on fast-slow extraction will be conservative in comparison to the slow extraction technique foreseen for SHiP. This is because the fast-slow extraction technique is intrinsically more lossy owing to the higher proton density at the septum wire. It is expected that the losses per proton for SHiP will be lower than those for WANF - the exact factor needs to be verified with beam tracking simulations. The extraction system that was in place in LSS6 during WANF is essentially the same as is presently installed in LSS2 to be used for extraction to SHiP in the North Area.
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Table 2: Extracted proton intensities [×1018 p.o.t.] during the operation of WANF.
Year T2 T4 T6 North Area T1 T9 West Area (slow) (slow) (slow) Total (slow) (fast-slow) Total (LSS2) (LSS6) 1994 0.8 0.8 2.5 4.1 0.8 8.3 9.1 1995 1.1 1.4 3.0 5.5 1.2 12.8 14.0 1996 1.4 1.4 3.3 6.1 1.5 14.6 16.1 1997 1.1 1.9 1.0 4.0 1.0 16.6 17.6 1998 1.3 2.9 0.5 4.7 1.2 18.2 19.4 Total 24.4 76.2
3.3 High-Level Dosimetry The dose levels measured during SPS operation are documented annually [11] with readings taken from dosimeters placed at regular intervals around the SPS and at key positions in the LSS regions. Further details on the exact position and procedure for the dose measurements can be found documented at length in the aforementioned reference. The data from a dosimeter placed on a cable tray approximately 1 m from the middle ZS tank was used to assess the linearity of the dose as a function of the number of extracted protons. The results are presented in Figure 3. The time over which the measurements were integrated varies from annual and biennial measurements, with one dose reported for the entire WANF period.
Caution must be taken when using the absolute dose measurements because during operation prompt losses can be highly directional and vary depending on the exact measurement position in the tunnel. Nevertheless, the results show a reasonable linear correlation as a function of extracted proton intensity. On comparison of the two datasets in LSS2 and LSS6 there is some evidence that slow extraction is indeed a cleaner extraction mechanism per proton than fast-slow extraction. Scaling the dose out to a total of 2×1020 p.o.t. an estimate of the total dose to cables close to the ZS is found at the level of ~0.4 MGy over 5 years of nominal SHiP operation. In the event of a non-optimized extraction one could expect larger dose rates.
An attempt was made to compare the high-level dosimetry data with more recent data but due to a re-cabling programme in the SPS since WANF and the movement of dosimeters it is difficult to make such a comparison. There are signs that the specific dose measured by a similar dosimeter close to the ZS is a factor of 4 larger in recent years. The reasons for this are not clear, and remain to be investigated.
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Figure 3 – Dose measurements made at cable tray approximately 1 m from the ZS in LSS2 and LSS6 during the WANF operational period of 1994 to 1998.
3.4 Activation Activation surveys are made systematically 30 hours after SPS operation is halted by passing a tractor fitted with a radiation counter around the ring at approximately 1 m from the beam line. The measurements were carefully documented in trimestral reports [12] and the data extracted for the analysis presented here. It is important to state that the 30-hour delay of the measurement is not necessarily linked to the time at which extraction ceased, especially in more recent surveys, where extraction through either LSS2 or LSS6 may have ceased many hours before the SPS itself. An example survey through the sixth sextant is shown plotted in Figure 4 where the characteristic activation spike at the ZS in LSS6 stands out. The peak value measured at the ZS was used to characterise the induced activation as a function of the total number of extracted protons. The peak activation as a function of proton number is shown in Figure 5 for both LSS2 and LSS6 during WANF, and for LSS2 in recent years.
The activation scales linearly with extracted proton intensity. There are obvious uncertainties in the measurements, including the difference in time between when extraction is stopped and SPS operation halts, and the build-up effect of long-lived isotopes after significantly long periods of high intensity operation. For example, the data point for the Fixed Target proton run in 2008 has been excluded from the data set as the second half of the year was heavily disrupted and as a consequence the extraction region had essentially many months of cool down before the survey measurement was made.
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Figure 4 – SPS activation survey measurement of the sixth sextant taken 30 hours after the 1998 physics programme.
Figure 5 – End of run peak activation at ZS as measured during the SPS activation surveys in LSS2 and LSS6 during WANF, and more recently in LSS2.
Based on the data from WANF one would estimate a peak in the activation measured approximately 1 m from the ZS after 30 hours (during the SPS survey) of approximately 12 mSv/hr for SHiP operation delivering 4×1019 in a year.
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3.5 Impact of Increased Activation The higher extracted beam intensity will increase the activation of the extraction region with the likely consequence of increased radiation damage of sensitive equipment and cables combined with increased cooling times needed to make interventions [13]. To help characterise the activation of the extraction region an empirical model developed during the WANF period [14-15] was revived to aid the understanding of the activation process. At this time in the mid-90s dedicated radiation monitoring equipment was installed to monitor the activation of the region after beam stoppages. The data presented below consists of a sum of counts on all radiation detectors placed in LSS6, totalling about 10 detectors. The model fits a sum of exponential functions with three
fitting parameters 푘푐푎푙, 푘1 and 푘2 starting each day with an amplitude proportional to
the number of protons 푁푝 extracted that day subscripted as day j:
푘 −푘1 ln ( 푗−1) 2 퐼푅(푡)푛 = 푘푐푎푙 ∑ {푁푝,푛+1−푗e } 푗=1…푛
The model (푘1 = 1.8 and 푘2 = 0.73) fits very well data taken at least 5 hours after beam stoppage, which avoids the fast lived activation products that are complicated to model. The potential of the model to predict activation is shown in Figure 6 by the quality of the fit to 3 years of activity measurements made during WANF.
The impact on access for intervention becomes immediately clear when scaling to SHiP intensities, as is done for the 1995 WANF run shown in Figure 7, after normalisation using the activation survey measurements. The model predicts that 10 mSv/hr would be measured at the ZS during the activation survey after 30 hours, which can be considered as rather conservative based on fast-slow extraction losses. For long-term high intensity operation the build-up of longer-lived isotopes must also be included in the model. This work could be extended using the PMI detectors installed in the SPS to monitor the cool down and aid dose planning for interventions.
3.6 Possible mitigation measures The most obvious mitigation is a reduction of the extracted beam intensity. A factor of two would give about the same activation as WANF operation in 1998. This would clearly double the number of days of operation needed for the facility to reach 2×1020 p.o.t.
Reduction of the loss per proton extracted is a more attractive option. From the activation and dosimetry data, there is a rather large dispersion in the beam loss per proton, which presumably comes from a combination of different setting up of the extraction, stability of the extraction and machine, and the beam quality. It is clearly highly important to understand the reasons for the variations and to formulate methodologies to keep the operation at the lower end of the range. To this end, MD studies and simulation efforts will be required, together with the development of more sophisticated surveillance and interlocking software and upgraded instrumentation,
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Page 16 of 43 including possibly online dosimetry. Other beam-physics related possibilities also exist – the use of bent crystals has long been proposed as a method to extract high energy protons [16] and could possibly lead to at least a reduction factor in the beam loss per proton on the ZS wires. Alternatively, non-linear manipulation of the transverse phase space particle density using higher-order magnetic elements could conceivably reduce the particle density at the ZS wires during the extraction [17]. All of these aspects will need to be explored, with MD time, simulation effort and theoretical studies.
Another possible mitigation is in the adaptation of the material used in the extraction region for the key machine devices. Here there are two aspects – one is to minimise the activation resulting from the primary proton impact, which relies on reducing the amount of material present and also in very careful choice of material. This is a topic that should be considered, with a possible optimisation of some key elements made based on the known activation and decay pathways [18]. The second aspect is in the equipment design – both for reliability and long MTBF, and also for redundancy to be able to plan exchange at the best moment, with the possibility rapid and remote exchange when faults do occur. A design review of the existing systems will be made to examine the possible gains to be made on these fronts.
Figure 6 – Fitting of the empirical model describing activation measured at least 5 hours after shutdown of the SPS during the WANF period.
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Figure 7 – Scaling of the induced radiation measured in LSS6 during the 1995 physics run to 4×1019 protons to compare the cool down with equivalent SHiP operation.
3.7 Conclusion on beam losses during extraction Dose and activation estimates for the nominal operation of SHiP at SPS were made based on historical data of past SPS performance. The upper limit for the dose at approximately 1 m from the ZS is estimated in the region of 0.4 MGy for the extraction of 2×1020 protons. The activation survey data predicts the peak activation measured during a survey made 30 hours after SPS operation is halted at 12 mSv/hr, at approximately 1 m from the ZS. Increased activation leads to longer cool down times that can be modelled empirically and used to plan interventions.
Possible mitigation measures are discussed, and a serious effort will be needed to investigate these and deploy the most effective for SHiP operation. It should however be noted that most of the failure scenarios will not affect the LHC beams significantly, as the LSS2 extraction channel is not used for LHC beam.
4. Beam Line Design The SHiP target location in the North Area allows the re-use of about 600 m of the present TT20 transfer line, which has sufficient aperture for the slow-extracted beam at 400 GeV/c. The installation of new laminated and bipolar splitters [19], replacing the existing MSSB2117 splitter magnets, will permit switching the beam into a new line symmetric to the T6 beam line but on the left of the T2 instead on the right, see Figure 8. The new splitter will switch the beam to the left on the SHiP cycle but maintain the existing functionality and split beams to the rest of the North Area for Fixed Target cycles. The new beam line is approximately 360 m in length and will transport and dilute
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[20] the slow extracted beam onto the SHiP target. In this section the design of the new beam line will be described.
Figure 8 – Layout of switch from TT20 to the new beam line towards the SHiP target.
4.1 Beam Line Design The new beam line, starting immediately downstream of the first splitter, will exploit 17 MBB-type dipole magnets, running at a conservative field of 1.73 T giving 8 mrad each, to increase as much as possible the distance between the new and existing beam lines. A maximum deflection angle to exit the TDC2 tunnel is beneficial to reduce the longitudinal extent of the civil engineering works in the crucial junction region. The MBBs downstream of the splitter are grouped into a single dipole as early as possible and four ‘standard’ half-cells of 4 dipoles each separated with a quadrupole in-between. The powering scheme for the TT20 line remains largely unchanged up to the switch element with cycle-to-cycle re-matching of the last 9 quadrupoles before the splitter and steering to allow the entire beam cross-section to pass through the dipole aperture with very low losses. A maximum of 6 corrector dipoles is assumed. The quadrupoles in TT20 are already laminated and suited to cycle-to-cycle switching. In addition, the new beam line will require 1 QSL and 4 QNL-type quadrupole magnets to control the vertical beam size through the dipole apertures, and provide flexibility and tunability of the beam spot size and dispersion at the target. The dilution magnets will be located after the last MBB magnet at 120 m from the target, which gives a large lever arm over which to deflect and dilute the beam on the target.
In nominal Fixed Target operation the vertical beam size is made very large in the
vertical plane (βy = 24000 m) in order to split the beam at the MSSB, whereas for the SHiP cycle the beam must be made small to fit entirely through the dipole aperture. The new optics from the extraction point in the SPS, through TT20 and up to the SHiP target is shown in Figure 9.
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Figure 9 – Optics from SPS extraction, TT20 and the new beam line to the SHiP target. The MSSB-S splitter magnets are shown in white. The dilution magnets will be placed immediately downstream of the last dipole magnet but are not shown.
The beam spot is shown with βx,y = 3000 m but can be varied in both planes to match the SPS emittance to the target, if required. A beam size at the target of σx,y = 6 mm has been assumed. The cycle-to-cycle variation of the TT20 quadrupole gradients to achieve a small beam with βx,y < 150 m through the splitter is shown in Figure 9. The gradients required in TT20 for this modification are smaller than presently applied, and all extra downstream quadrupoles are well within the maximum quadrupole strength of 80.8 T for QNL type magnets. The cycle-to-cycle powering of TT20 will be tested in a dedicated MD and the transmission through the splitter aperture verified.
Without suppression of the dispersion function it would grow as large as 40 m at the target, which has the potential to cause the beam to move during the spill as the tune in the SPS is varied and the momentum of the extracted beam changes. Although the power converters in the transfer lines of the North Area are scaled linearly to suppress this effect in normal operation, large dispersion at the target should be avoided to reduce beam position sensitivity on the extracted beam momentum. It is possible to suppress dispersion at the target with the 5 new quadrupoles, as shown in Figure 11. The numbers and types of magnets needed for the beam line are given in Table 3, along with the number of converters and the maximum required current.
The most critical aperture in the line is the vertical gap in the last MBB magnets. The ±3σ vertical beam envelope is shown in Figure 12 with a conservative normalised rms emittance value of 8 mm mrad. The aperture restriction will need careful attention, with error studies and measurements of the extracted vertical beam emittance for the SHiP cycle to be done. Indeed, if the power converters in the North Area beam lines can be reliably scaled as will be tested in future MDs, then the constraint on having zero dispersion at the target can be relaxed and the quadrupoles used to control further the beam size. The dilution kickers were added after this vertical aperture restriction to ensure the acceptance is maximised.
Table 3 – List of new magnets required for the beam line to SHiP.
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Function Magnet type Number of Number of Max I [A] magnets converters Switch MSSB-S 3 1 1000 Main bends MBB 17 1 1500 Main quads QNL 4 4 400 Main quad (slim) QSL 1 1 400 Corrector dipoles MDX 6 6 50 Sweep dipoles MPLH-type 2 2 400
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I 0 0 5 10 15 20 25 Quadrupole number
Figure 10 – Comparison of integrated quadrupole gradients (BdL) [T] in TT20 between nominal Fixed Target operation and SHiP, including the extra 5 quadrupoles in the new beam line towards the SHiP target.
Figure 11 – Dispersion function from SPS extraction, TT20 and the new beam line to the SHiP target.
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Figure 12 – Vertical beam size and aperture from the SPS extraction point to the SHiP target assuming a conservative rms emittance of 8 mm mrad.
4.2 Conclusion on beamline design The position of the SHiP facility and the geometry of the new beam line was fixed by modifying the first splitter magnet in TDC2 and adding 17 MBB-type dipole magnets to deflect away from the TT20 beam line. The TT20 line is reused with modifications made to the powering of the 9 quadrupoles directly upstream of the splitter for the SHiP cycle. There is ample space for the installation of dilution kickers after the last active beam line element before the target. The vertical aperture in the MBBs is critical and will need to be carefully followed up.
5. Beam instrumentation for SHiP extraction and beamline With the high intensities needed for SHiP excellent setting up and control of the extraction and beam transfer will be essential to minimise activation and also risk of damage to equipment. The quality of the setting up and of the subsequent monitoring and control will depend to a large extent on the beam instrumentation, which will also be used in some cases for interlocking and active surveillance of the extraction quality.
5.1 Existing instrumentation The existing instrumentation in the LSS2 extraction channel and TT20 [21,22] was developed in the 1970s to fulfil the difficult requirements of instrumenting the beam losses, position and profile in the highly activated and high prompt dose region of the slow extraction septa. The basic monitor technology has proven robust but there are several improvements which could help with reducing the setup time and also which could help to better extraction and spill quality, and to control beamloss.
5.1.1 Position and profile monitoring The slow extracted beam is de-bunched and has no RF structure, which makes position measurements with standard SPS BPM electronics impossible. The slow extracted beam position is therefore measured with Secondary Emission Monitors (SEMs) that are made
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1 mm thick Al or 20 m thick Ti foils. These have a conversion efficiency of ~ 4% electrons per proton. There are 5 basic SEM monitor types for position and profile monitoring:
BSG: SEM grid with typically 16 strips (of width 0.5-2.5 mm).
BSP: two foils (a split-foil monitor) to measure the position, by comparing Left/Right or Top/Bottom foil signals).
BSM: same as BSP, but on a stepping motor to move the foils.
BBS: a thin movable strip (1 mm) to scan across the beam, used to monitor extracted beam profiles.
BSI: a single foil to measure beam intensity.
In TT20 the steering is performed with BSPs and BSGs. Profiles are obtained with BSGs and BBSs in the extraction channel (and also at the targets).
There are also 4 beam screens (BTVs) in TT20 before the first splitter. BTV.2100 and BTV.2102 just after the extraction channel, BTV.2103 in front of the TT20 TED and BTV.2116 some 20 m upstream of the first splitter.
Figure 13. Location of Horizontal and Vertical extracted beam SEM monitors, and circulating beam SEM monitors in the three half-cells used for LSS2 extraction.
5.1.2 Beam intensity monitoring During proton extraction the SEM detector (BSI) measures the secondary emission signal from an Alumina foil of 1 mm thickness. This is located in TT20 and is used directly for the regulation of the slow extraction spill, as the output from this monitor is used in the feedback look to the servo quadrupole QMS116 quadrupole string [23]. This controls the rate at which the beam is extracted by acting on the horizontal tune, to provide a
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smooth and steady extraction rate. The data is digitized at 10 kHz, allowing observation and correction of harmonics up to about 5 kHz.
Another “fast spill” diagnostic system has been used in the past for diagnostic purposes [22], and is presently being upgraded with new technology. It will allow the user to monitor the intensity evolution within an SPS turn, i.e. 23 s, and turn-by-turn during a full proton or ion extraction. In the past this instrument received signals from a Photo-Multiplier observing a Quartz screen and sampled them every 100 ns. It was hence possible to observe the intensity evolution of the extracted beam with a resolution of 230 acquisitions per turn. The recorded turns can be consecutive to check the turn- by-turn stability or separate to check the evolution over the whole extraction. As for the Servo Spill SEM instrumentation, a Fast Fourier Transform facility is available to analyse the frequency structure of the spill up to 5 Mhz. The new system based on diamond BLMs should provide similar functionality.
5.1.3 Beam loss monitoring Beam losses are monitored with standard SPS type ionisation chambers. These give a loss reading at a 20 ms time sampling, and are usually displayed with the loss per beam cycle, readout at the end of the extraction. Figure 14 shows beam losses measured with ionization chambers in the LSS2 extraction channel for slow-extraction of 2.5 ×1013 p+. The front-end electronics of the computers controlling the monitors generate beam interlocks, with a single threshold per monitor for total losses through the cycle. To monitor the losses in the TT20 beamline there are a total of 9 standard BLMs on selected elements, for surveillance and interlocking.
Figure 14. Beam losses measured with ionization chambers in the LSS2 extraction channel for slow-extraction of 2.5 ×1013 p+. The red line represents in the interlock level, above which the beam is dumped.
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In the extraction channel there are 15 ‘extraction’ BLMs which instrument the ZS, the TPST, the MST, the MSE, the enlarged quadrupoles and the TCE shielding block. The first 16 monitors in the extraction channel are connected to the fast loss beam dump (BLD) system electronics, where the interlock is generated directly in hardware. This produces an interlock with a s response time if the thresholds are exceeded, to protect against the failures which can happen on the timescales of ms or faster [24].
5.2 Changes needed to the existing instrumentation Although the basic functionality of the existing instrumentation is adequate the systems are ageing technology, designed to norms that are now superseded in terms of handling and quick connection and disconnection in a radioactive environment, and sometimes with limited spares. Targeted improvements would address some of these issues, increasing the reliability and reducing the risk of failure. Operational efficiency and beam-loss management reasons would also favour extending the functionality somewhat. The following upgrades are suggested for TT20 instrumentation:
Installation of some detectors which can measure the position of the beam without 200MHz structure at key locations in the line, for initial steering during setting up, and stability and extraction trajectory monitoring;
Replacement of some of the existing split foils with SEM grids, again at least in a subset of key locations, depending on expected radiation dose and cabling;
Improvement of the BLM coverage, with the addition of monitors at more regular intervals along the line;
Upgrade of the BLM electronics to LHC standard, with integration and readout times of the order of 20 s. Here a clear synergy exists with the Consolidation project, where this work is currently requested for LS3;
Replacement of SEM devices in extraction septa with modernised devices. Here a clear synergy exists with LIU project where an upgrade of the ZS pumping modules housing the SEM devices is planned in LS2;
It is also suggested to replace as many BSP monitors as possible with BSGs to make steering of TT20 more deterministic, as the BSPs require a guess of the emittance/beam profile which is not very reliable. Cabling needs to be investigated.
5.3 New instrumentation needed for the new section of SHiP beamline The new section of SHiP beamline will need to be equipped with instrumentation for setting up and surveillance of the beam transfer. Position, loss and current monitoring are all required, and a method of characterising the swept beam on the target and also analysing the sweep after each shot is proposed. The main items and approximate numbers of individual devices are given in Table 4. Again, as for TT20 the positioning measurement needs to work with unbunched beam. The detailed specifications for each item remain to be developed – however, the functionality needs to be at least as good
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(in terms of precision, dynamic range, radiation resistance, lifetime) as the equivalent existing instruments.
Table 4. Number and types of instruments for new section of SHiP beamline.
Function # items Beam position monitors 7 BTV screen 1 Sweep monitoring screen 1 Beam loss monitors 12 Beam current measurement 1 Fast beam current measurement (ns resolution) 1
The fast beam current measurement will be used to make an online characterisation of the spill, which will be essential for the target interlocking and may also be needed for the experimental veto or off-line reconstruction. Detailed requirements must be developed for this functionality.
A large dimension (approximately 40 cm width/height active region) screen will be needed to characterise during setting up, and possibly continuously monitor, the beam sweep upstream of the target.
5.4 Conclusion on beam instrumentation The beam intensities and spill structure required for SHiP can be instrumented by the existing monitoring systems in the LSS2 extraction channel and TT20 beamline. However, a set of moderate improvements are proposed to improve the operability of the beamline, and to also allow effective interlocking of the extracted beam. For the new section of beamline, a set of new instruments will be required, most of which replicate the functionality of the existing devices.
6. Design and powering of new splitter magnets One of the machine-related challenges for the proposed location of the SHiP experiment is the 400 GeV/c switch out of TT20 to the new beamline, due to the high beam rigidity, absence of available drift space and necessity to retain compatibility with the present type of North Area Fixed Target operation. The proposed solution is to replace the three existing MSSB2117 splitter magnets with newly built MSSB-S splitters, which allow negative polarity powering on a cycle-to-cycle basis. This would provide the new switch functionality and retain the existing splitter mode for the North Area. In the following sections the main requirements and proposed technical solutions are described.
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6.1 Design requirements The three existing MSSB magnets 211713, 211723 and 211732 need to be replaced by similar MSSB-S magnets which allow enough aperture for the beam deflected in the opposite direction. The main requirements for the new magnets are:
Replicate existing splitter functionality for present NA beams;
Polarity reversal possible within about 2 seconds;
Adequate good-field region around both sides of field-free septum hole;
Same ∫B.dl and physical length as present MSSB.
The present MSSB design [1] is an in-vacuum Lambertson septum, with a vacuum separation to keep the coils and water connections in air, built with radiation robust materials and low-maintenance assembly. The magnets operate with 0.8 T in the gap,
and have a limit Bmax of 1.6 T in the steel at the point of the septum element. For the
North Area splitter design, the wedge angle of the septum is 36°, and since Bmax.sin
≈ Bgap, it would therefore be possible by running at higher current to increase the gap field to about 0.95 T without a major effect on the field quality – the alternative of using a higher saturation steel like FeCo would gain something, but would be much more expensive, mechanically tricky and lead to activation issues.
The gap is 75 mm high, which requires about 48 kA.turns to reach 0.8 T.
The maximum offset for the switched beam at the exit of the 3rd MSSB is around 90 mm. Allowing another 40 mm for the beam size and orbit, alignment tolerances, the good field region (and pole width) needs to be extended by 130 mm only, although an extra 150 mm would make the septum hole symmetric to the pole.
The requirements are summarised in Table 5.
Table 5. Summary of functional requirements for upgraded TT20 splitter magnets. Parameter Unit Value Comment Number of magnets 3 Plus spare(s) Physical yoke length mm 5.2 Integrated fieldI T.m 3.76 Gap field T 0.8 At 400 GeV Vertical aperture mm 75 For deflected beam Horizontal aperture mm +150 / -130 Presently +150 mm Switching time s mm2.0 From +ve to –ve polarity, at full field Flat-top length s 20 Need to be able to run in DC mode
6.2 Magnet coil design The present coil scheme of 48 turns and 1 kA can be retained for the MSSB-S. The coil technology is special, using compacted MgO powder around a central copper current carrying water-cooled tube, mechanically supported by an external grounded copper sheath. The MgO is evacuated to avoid moisture degradation – the maximum voltage to earth is 1 kV.
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6.3 Magnet yoke design The present MSSB are built with solid yokes, assembled from several precision machined pieces. Because of the need to switch the polarity between SHiP and normal NA cycles a laminated yoke is essential for the MSSB-S. A possible technology would be 1.5 mm punched laminations, blue-steamed for insulation and assembled with a stacking factor of ~98%. This technology is routinely used in the SPS for the extraction septa MSE/T that are also exposed to high radiation doses. The drive current (or the magnetic length, in case the power convertors are really limited to 1000 A) might need to be increased by 2% compared to the existing magnet to compensate for slight reduction in ∫B.dl.
The new MSSB-S magnet cross-section can be a simple variation of the present MSSB, with the good field region extended to the other side of the septum hole, Figure 15. The overall yoke width is likely to increase from 1042 mm to approximately 1170 mm, and the weight will increase from the present 24 tonnes to about 27 tonnes.
Figure 15. Cross-section of existing MSSB splitter (top) and new MSSB-S with a laminated yoke and extended horizontal gap to allow for the additional switch functionality.
Main MSSB-S magnet parameters are compared to the existing MSSB in Table 6. The inductance and resistance are scaled from the existing magnet, with the preliminary pole width and coil size.
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Table 6: Parameters of existing MSSB and new MSSB-S magnet.
Parameter MSSB New MSSB-S Magnetic length [m] 4.7 4.7 Gap field [T] 0.8 0.8 Stacking factor [%] 100 98 Coil turns 48 48 Current [A] 994 1014 Vertical gap [mm] 75 75 Pole width [mm] 400 530 Magnet inductance [H] 0.11 0.14 Coil resistance [m] 65 66 Number of magnets in series 3 3 Minimum rise-time [s] 10 (?) 2 Maximum voltage to ground (3 magnets in series) [V] ~250 400
6.4 Splitter powering For the powering of the new MSSB-S magnets, a variant of the Linac4 transfer line converters (APOLO family) can be used. These can be assembled in 4 modules to deliver the requested current/voltage, in order to allow all three magnets to be powered in series. If needed, the maximum voltage of around 400 V could be reduced by a factor of two with balancing the voltage in +/-, however this does not seem necessary to foresee at this stage as 400 V is well within the voltage limit of the MgO coil conductor.
6.5 Schedule and lead times The main technical issue is the design and construction of the new splitter/switch magnet, which will require a longer lead-time than a ‘normal’ design of warm magnet. An initial R&D phase will be needed to verify that the design can achieve the very tight mechanical tolerances needed in the septum region, critical for beam losses. This R&D should start in mid-2015 to be ready for the LS2 installation date, as the overall schedule for R&D, design, production and testing of these magnets is estimated at 48 months. It is essential to install the new splitters in LS2, as they are needed for normal North Area operation, and can only be installed after a long cooldown period to allow removal of the existing highly activated devices.
6.6 Conclusion on new splitter magnet and powering The construction of a new magnet MSSB-S in place of the existing splitters will allow the switching of the full 400 GeV/c beam to the SHiP beamline and target. For this mode of operation there should be no significant beam losses at the new magnet; however, for the present mode of operation where beam is split to the T6 target the losses and activation will continue to be high. The technical design of the magnet appears feasible,
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based on an extension of the present technology with punched laminations. The powering of the magnet can be accomplished with a variant of standard CERN power converters. The R&D for the magnet needs to start in mid-2015 to be ready for the planned installation in LS2.
7. Beam Dilution With the average beam power deposited on the target over the spill close to 2.5 MW the maximum beam energy density is crucial for the target design. To relax the demands on the target, a pair of orthogonal conventional magnets with a fast Lissajous powering function is foreseen to dilute the beam energy density during the spill by maximising the path length of the sweep on the target block.
7.1 Sweep profile over target A full optimisation of the sweep is required taking into account the possible magnet and powering characteristics, as well as the limitations of the target in terms of protons per mm2. Some idealised sweeps have been proposed for evaluation.
An idealised Archimedean spiral [29] has been investigated and used as baseline to develop target R&D [30], as shown in Figure 18: a constant transverse separation between spiral arms of 6 mm (1σ) including 5 spiral turns in 1000 ms, starting at a radius of 5 mm and finishing at 35 mm. The frequency of the oscillation is varied to maintain a constant sweep speed on the target, implying that the waveform powering the orthogonal dilution kickers must increase in frequency as the beam spirals in, or vice versa. In this case the sweep speed on the target is approximately 0.65 m/s.
Figure 18- Reference beam trajectory on SHiP target.
The variation in frequency and amplitude as a function of time during the spill is visualised in Figure 19, where the product of frequency and kick amplitude remains constant at a value of 0.7 Hz mrad.
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Figure 19- Horizontal and vertical beam positions on the target as a function of time, proportional to the current powering the dilution magnets.
7.2 Dilution magnets With a drift distance of ~120 m available to the target and a sweep radius tentatively fixed at 30 mm, a maximum deflection of ~0.25 mrad per plane is needed. The parameters demanded for the Archimedean sweep presented in Figure 18 are collected in Table 8.
Table 8 – Dilution system specification Parameter Value Number of magnets 2 (H and V) Dilution magnet to target distance [m] 120 Integrated field strength per magnet ∫ 퐵 푑퐿 [T m] 0.33 Maximum kick amplitude [mrad] 0.25 Frequency x kick [Hz mrad] (constant) 0.7 Maximum frequency (min. amplitude) [Hz] 18.0 Minimum frequency (max. amplitude) [Hz] 3.0 Length of sweep on target [m] 0.67
Possible magnet types could be similar to the MPLH (SPS extraction bumpers) that can ramp with a dI/dt of around 1300 A/s. With a current of ~80 A corresponding to 0.25 mrad, a maximum sweep frequency of approximately 3 Hz would be possible using the present type of magnet and power converter. Starting with larger amplitude and spiraling inwards would probably be easier for the dilution magnet powering. The monitoring and interlocking of the sweep currents will be very important for protecting the target.
7.3 Conclusion on dilution sweep The time scale of the sweep during the spill is relatively slow and the available drift space downstream of the final active element in the beam line before the target is
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sufficient such that conventional magnet technology can be used, which is already existing and in operation at SPS.
8. Interlocking The beam intensity needed for the SHiP cycles are 4×1013 p+ extracted at 400 GeV/c every 7.2 seconds, through LSS2, TT20 and the new section of SHiP beamline.
In addition to measures needed to protect against beam loss in LSS2 and the TT20 beamline with this high beam power, there is a new section of beamline to interlock, new switch-splitter elements between the TT20 and SHiP beamline, and a dilution sweep system that must operate correctly to prevent damage to the target. The SHiP beamline will therefore require a new beam-interlocking system, in addition to the normal equipment interlocks for the new magnets and power converters. In this section the requirements, concept and proposed inputs for this beam interlocking are described.
8.1 Hardware interlocking design requirements The hardware beam interlocking for SHiP must fulfil the following requirements:
Accept logical inputs (user inputs) from different equipment systems;
The system should be extendable in case new additional inputs arise;
High level of reliability, with redundant user inputs;
Dump SPS beam in case of fault condition, within a reaction time which should be less than a millisecond;
A subset of user inputs to be maskable, for setting-up with low intensity beam;
Masks must be automatically removed when intensity is above the setup limit;
An interlock condition for the SHiP beamline should prevent injection into the SPS for the SHiP cycle, but not for other cycles;
8.2 Hardware interlocking concept The interlocking can be based on the standard Beam Interlock Controllers (BICs) used elsewhere in the SPS [26]. Each controller accepts 14 redundant inputs, of which 7 are maskable with a ‘setup beam’ input. The output is a simple AND of all unmasked inputs. The BICs are connected to the SPS Beam Interlock System (BIS) by means of optical fibres, and also to the Safe Machine Parameters system that provides several flags such as the setup beam flag. The inputs surveilling the extraction, lines, target etc. will require dedicated BICs with the outputs connected as inputs to the master BIC. The master BIC will be connected to the ring BA2 BIC. Three separate BICs are needed: one “TT20 BIC” for the common elements like extraction channel and TT20 beamline, one “toSHiP BIC” which has all the elements needed for the SHiP section of the beamline, the splitter (with SHiP setting), the target and experiment, and one “toNA BIC” with the elements used for the North Area beamline, targets and splitter settings for the NA targets.
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Two new Safe Machine Parameter (SMP) Flags will be needed to differentiate between NA fixed target beam and beam to SHiP: stable 390 GeV and stable 400 GeV (ST_390 and ST_400, respectively). These flags should be generated if the energy corresponds to the given value for more than several 10s of ms. The exact value needs to be defined, after analysis factors such as the ramp rates and power converter settling times. The four logic equations for the master BIC are then:
NO_SLOW_EXTRACTION || SHiP || NA (1)
NO_SLOW_EXTRACTION = ! ST_390 && ! ST_400 (2)
SHiP = ST_390 && TT21 && toSHiP BIC (3)
NA = ST_400 && TT21 && toNA BIC (4)
Figure 16. Schematic of new interlocking for SHiP and NA. Four additional BICs are needed, of which one is a Master BIC connected to the existing SPS ring BIC in BA2.
The SPS SMP system supplies four flags to the extraction BICs:
2 x E_LHC (450GeV) = go to LSS4 and LSS6 extraction (for LHC)
1 x E_CNGS (400-430 GeV) = goes to LSS4 extraction (for AWAKE)
1 x E_HIRADMAT (440 GeV) = goes to LSS6 extraction (for HiRadMat)
Presently it is not possible to make more than four flags from the SPS SMP controller. In addition, an extension to the SMP concept is needed, in that the ST_390/400 flags need to be generated ONLY when the machine energy is stable at the specified energy, NOT when the magnets are ramping through the energy. This is needed to avoid generating a spurious beam dump e.g. when ramping the SPS to 450 GeV for LHC beam,
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when the interlock conditions for SHiP or NA will not in general be true. An upgrade of the SMP system will be needed, which will need to be planned well in advance as there is presently no more space in the CCR for an additional system.
Some items require more detailed study before the final implementation. The interlocking of the splitter-switch magnets must be made such that it is never possible to send the primary SHiP beam to any of the T2, T4 or T6 North Area targets. A detailed analysis of the reliability of the proposed concept and the specific interlocking for the splitter-switch magnets is needed to verify that the standard firmware based power converter solutions are adequate, or whether a fully hardware channel is also needed. To this end the splitter/switch elements will likely need a direct connection to the Master BIC. The sweep on the target is also critical and here it needs to be determined whether an addition system is needed to survey the magnet sweep currents, in addition to the regular power converter interlock functionality – this may be more complicated as the reference sis a dynamic function, rather than a static value. The use of the Setup Beam Flag with low intensity for extraction setup needs clarification, as the present limit is only 5 x1011 p+, and the SBF is generated by a special Beam Current Transformer 1 s before fast extraction and held for 3 s after a fast extraction. Finally, if an access beam stopper (TBSE) is needed in the beamline proper to the SHiP target then this will need to be an input to the hardware interlock.
8.3 Magnet current surveillance For the extraction septa and beamline magnets the surveillance of current functions needs to be possible for the power converters, as the values need to be surveyed throughout the flat-top rather than at a single point in time as is presently the case just before fast extraction. This functionality does not presently exist in the Front End Interlock (FEI) system in the power converter controls; for most converters the surveillance is against a single value, but for the dilution magnets a time varying function is needed. The planned converter controls upgrade to FGC3 could take this requirement into account – however, the details of the implementation for some of the North Area power converters remains to be checked (for the new converters such as the splitters and dilution sweep magnets there should be no issue in providing this functionality). The most general implementation would be a function through the cycle, with the thresholds very relaxed until the extraction plateau, Figure 17. The Master extraction BIC then combines the TT20, NA and SHiP beamline user permits as described abover and only generating a beam dump when extraction energy is set to SHiP/NA and an interlock condition from the SHiP/NA BICs is false.
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Figure 17. Schematic showing magnet current interlock function for extracted beam.
8.4 Fast Magnet Current Change Monitor Interlocks A subset of the main SHiP magnets will probably need to be equipped with special Fast Magnet Current Change Monitor (FMCM) interlock cards [27]. These monitor the magnet current on a single circuit at the power converter level, and can act very rapidly to generate an interlock; these are needed for circuits which are critical in the interlocking where the current can change too rapidly for the standard PLC based interlocking to react in time. Provisionally, pending detailed analysis, 5 circuits may need FMCMs: the MST, MSE, MSSB-S, TT20 MBE/B and the new main dipole string of the SHiP beamline. Deployment on the MSE and MST needs to be investigated in detail.
8.5 Hardware interlock user inputs The user inputs presently identified for SHiP are shown in Table 7. Some of the other required inputs are already covered in the existing SPS interlocking, such as losses in the extraction region. This list may be modified as a result of more detailed analysis. Many of the inputs are a logical “OR” sum from a group of similar equipment types, as is currently done in the SPS and other machines at CERN. A total of 16 user inputs are proposed, which will require two BICs for the facility, possibly more if more channels are identified, such as the experiment status, ventilation status, fire alarms etc. The signals can be organised into “extraction and TT20” and “new beamline and target”.
8.6 Software interlocks In addition to the relatively small number of hardware beam interlocks for the facility, a larger number of software interlocks will be needed. These will be deployed within the existing highly reliable Software Interlock System (SIS) [28]. This is already used widely in the SPS and LHC, and allows flexible configuration and more complicated interlock conditions to be programmed, at the expense of response time and configuration- dependant software implementation.
Table 7: User inputs for TT20/SHiP beamline hardware interlocking.
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User Input Maskable Target status no Access system no Dilution sweep magnet current no Splitter-switch magnet current no SHiP beamline TBSE no LSS2 extraction septa current/voltage no Extracted spill maximum current no FMCM (x5) yes Transfer line beamloss yes Beam position yes Beam screen yes TT20/SHiP beamline power converters / current yes SIS extraction, beamline and target yes
8.7 Conclusion on interlocking Interlocking of the SHiP extraction, beamline and target facility will mainly rely on existing BIC and SIS solutions, and should be a feasible as an extension of the present interlocking concepts and technology, although a careful functional analysis of the interlocking needs to be made to determine the details of the implementation. A need for four additional BICs has been identified, with a simple topology, and an extension of the present SMP concept is needed with the provision of at two more energy flags for SHiP, which need to be true only when the machine energy is stable. Two key specific user systems (splitters and dilution magnets) may require somewhat more sophisticated or secure surveillance systems.
A change to the surveillance of function-based interlocks for at least a subset of the standard power converters seems mandatory, for the converters to be able to check the current against a reference function; it is possible that this may be accommodated in upcoming planned controls renovations if the requirements are clearly defined. The fact that the North Area convertors and controls are very old technology may complicate this in some cases. Overall the addition of the SHiP facility should pose no major feasibility issues concerning the beam and equipment interlocking, although a lot of details remain to be finalised.
9. Spill structure and control For SHiP the slow extraction spill quality is important for several reasons. The experiment is sensitive to combinatorial background, and large spikes in the extracted proton rate have an impact on the sensitivity. In addition the target is designed for a certain maximum transverse proton density, which could be exceeded if the spill shape departs too far from the ideal trapezoid.
The SPS slow extraction spill is controlled by the servo-spill system [31], a closed loop feedback measuring the current using the BSI SEM monitor in TT20 and acting on
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four dedicated QMS quadrupoles located in LSS1 to stabilize the extracted beam intensity. The harmonics of 50 Hz cannot be corrected by this system and are compensated using a feed-forward system.
9.1 Slow extraction servo spill The intensity signal from the beam extracted to TT20 is compared to a reference values and used to feedback on the spill intensity by adjusting the machine tune with the QMS quadrupoles. The block diagram of the feedback loop is shown in Figure 20. The total tune trim is typically 0.03. The loop gain of the servo-spill system is low, and it is not capable of correcting the residual 50 Hz (and harmonics) tune ripple that is present on the beam. The correction of these harmonics is therefore based on a feed-forward mechanism [32]. A 50 Hz modulation, with a determined phase relative to the mains (defined in PCR) and defined amplitude is added to the servo-spill quadrupole current.
Figure 20. Block-diagram of the servo feedback system controlling the spill signal (t). The fictive signal produced by the PD-controller is the time derivative of the power supply reference input signal rPS(t) and is proportional to the tune change dQ/dt driving the extraction process.
The setting of the feed-forward signal are adjusted manually and as long as the ripple is stable in amplitude and phase, it is possible to perform a good correction of the 50 Hz harmonics. This adjustment needs to be made rather regularly for best spill quality, with significant drifts seen over periods of a few days.
9.1.1 Effective spill duration For the short extraction duration required for SHiP the beginning of the spill, within the first 150 ms, will be characterised by an overshoot in the spill rate, with the presence of large fluctuations. The method of classifying these fluctuations has been developed for experiments sensitive to the variations in the spill intensity [35], for a nominal spill duration . The beam intensity fluctuations about the average 〈퐼〉 are measured by the square variance 〈휂2〉 which is also the integral of the power spectrum (A.C. power) in the frequency domain, normalised to the square amplitude of the constant term (D.C.
power), and the effective spill duration 휏푒푓푓 is defined as:
휏푒푓푓 퐷.퐶. 푝표푤푒푟 1 ≡ = 휏 푇표푡푎푙 푝표푤푒푟 1+〈휂2〉
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where the total power is the sum of the A.C. and D.C. power. For the NA48 data taking, the spill length was 2.38 s, while the effective spill length was 1.7 s [35].
9.1.2 Low frequency harmonic content of spill from mains ripple The typical harmonic content of the current in the SPS main magnets is shown in Fig. 2, measured for the main SPS focusing QF quadrupoles. The ripple is typically 2 ×10-6 at 50 Hz, reducing below 1 ×10-6 up to 500 Hz.
For an ideal spill, with rectangular temporal profile, the rate of extracted particles dN/dt is constant and equal to the total number of protons divided by the spill length. This rate is controlled by the rate of tune change 푄̇ . In the presence of tune ripple of amplitude δ at a frequency f, the rate dN/dt will be modulated as:
푑푁 ∝ 푄 + 2푛푓훿 coṡ (2푛푓푡) 푑푡
The modulation amplitude of the spill at the frequency f is therefore:
2휋푓훿 퐴 = 푚 푄̇
For SHiP extraction, the total tune change will be about 0.03 in one second, i.e. 푄̇ ≈ 0.03. For the 50 Hz line the amplitude modulation is then expected to be only a few %, even without the feedforward correction. The amplitude of the higher harmonic lines is smaller – taking a pessimistic value of 1 ×10-6 at 500 Hz, the uncorrected amplitude modulation at this frequency will be about 10%, which experience has shown can be reduced by the feedforward to a few %, even for spills which are 5-10 times longer and correspondingly more sensitive.
Figure 21. Measured harmonic content in main SPS focussing quadrupole current.
9.1.3 Medium frequency variations The fixed-target beam spectrum in the SPS has a pronounced structure at the revolution frequency of 43 kHz and its second harmonic of 86 kHz, due to the filling of the SPS from the PS, where the 2.1 s PS single turn is injected into the SPS in 5 turns, leading to a pattern of two trains of 10.5s of beam with two gaps of 1 s. The time needed for
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the beam to completely debunch to wash out this structure is much longer than the ~1 s time available for the extraction.
9.1.4 Residual 200 MHz beam structure The main SPS accelerating RF system imposes a 200 MHz structure on the proton beam. When the RF is switched off just prior to extraction the protons start to debunch, due to the large (artificially increased) momentum spread. The particles with negative momentum offset move forward in phase while those with positive offset move backwards. As measured by a pickup in the SPS ring, after some 10 ms the debunching is complete, as the particles with negative offset in one bunch overlap fully with the positive offset particles from adjacent bunches. However, as the slow extraction effectively selects a narrow band of momentum (via the large chromaticity), the 200 MHz structure is still present in the extracted beam for several 100 ms, until the debunching and phase space mixing is complete. This is illustrated in Figures 22 and 24. This structure may be important to understand for the SHiP experiment, and will also vary through the spill.
Figure 23. Measurement by NA48 [35] of 200 MHz content of SPS extraction spill at the start (100-150 ms) and end (2200-2250 ms) of the 2.38 s extraction. The debunching of the initial 200 MHz structure is replaced by a much smaller 100 MHz modulation, which at that time was considered to be impedance driven.
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Figure 24. Measurement by NA48 [35] of 100 and 200 MHz content of SPS extraction spill, as a function of time along the spill. For the 1 second long SHiP spill, there will be a large 200 MHz content over the first 200-300 ms, as the beam debunches fully.
9.2 Conclusion on spill structure The time structure of the slow extracted spill exhibits variations from low frequencies up to 200 MHz. The different sources of the fluctuations are understood and can in the case of low frequency mains harmonics be corrected for. However, the effective spill length and the time-varying 200 MHz structure must be taken into account by the design of the SHiP experiment.
10. Machine Development Studies Beam transfer from SPS to the SHiP target will demand a new cycle with a faster slow extracted spill of just 1 second at a nominal intensity of 4.0×1013 protons. This pushes the operation of the extraction hardware, namely the electrostatic septa (ZS), into a new regime of operation by moving beyond past experience. Indeed, faster extraction rates have been achieved with half-integer fast-slow extraction but at a lower intensity per spill. In addition, the SHiP goal of 4.0×1019 protons on target per year will approximately double the previous SPS record for slow-extracted p.o.t.
A new 7.2 s SPS SHiP cycle will need developing that gives a stable extraction during the shorter flat-top. The optics of TT20 transferring the beam from the SPS to the North Area will need adapting for the SHiP cycle by powering the existing quadrupoles at different gradients to permit the entire beam envelope to pass through the dipole gap of the splitter. This will need to be done on a cycle-to-cycle basis to keep compatibility with the present North Area experimental facility.
A series of machine development (MD) sessions are planned to investigate and understand the relevant issues that have been identified throughout this report.
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10.1 Foreseen program of studies The list of MD studies to be carried in the context of SHiP is shown below:
Deployment of a new SHiP SPS cycle: Flat-top of 1.2 s (1 s spill length) and a total length of 7.2s. Essentially, the existing FT cycle will need scaling during the flat-top to drive the tune across the resonance quicker.
Extraction loss characterisation and optimisation: An opportunity to benchmark beam dynamics simulation tools and use them to understand the behaviour of the machine as a function of different parameters with the objective to optimise the system. Of particular interest will be to reduce the proton density of the beam at the septa wires by manipulating the bump and extraction sextupole strengths. In adjusting the spiral step the aperture limitations of the SPS during slow extraction will be probed as well as the alignment of the beam and septum.
Investigation of ZS performance as a function of extracted intensity: With protons impinging the septum wires at a higher rate one would expect an increased rate of heating, deterioration of the vacuum in the region of the ZS and consequently an increased rate of sparking and breakdown of the high- voltage on the ZS. It is critical to understand the limits of the ZS in the SHiP cycle as a function of the number of extracted protons.
Development of new TT20 optics for SHiP: The TT20 line will be used to transport the beam to the new splitter and beam line during the SHiP cycle. In order to maintain compatibility with North Area operation the optics will need to change on a cycle-to-cycle basis such that the beam can be split vertically for the North Area programme or squeezed through the dipole aperture of the splitter for SHiP. The pulsing of the line at different currents on a cycle-to-cycle basis in TT20 can be tested even without the new beam line and with the existing splitter to test steering and transmission.
Characterisation of spill structure: Controlling the intensity of the spill, especially during the start and end of the spill, will be critical and need to be optimised to keep the variations in the proton intensity at the experiment as small as possible. The level of stability achievable will be important input for the development of the SHiP detector. During the start of the spill the extracted beam retains some memory of its bunched nature before the rf is turned off and it is left to de-bunch. Measurements of the frequency spectrum of beam are foreseen over a wide bandwidth with specialised instrumentation.
10.2 Conclusion on machine development studies A series of machine development studies are being planned to test the critical issues that have been identified for the SPS and its slow extraction system. The results of these investigations will provide important information for the SHiP project by providing concrete operational limits and possibly highlighting mitigation techniques.
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11. Conclusions and R&D activities The documents present the conceptual design of the SHiP primary beamline, including the major feasibility aspects of new equipment subsystems, as well as the modifications needed to the existing beam transfer systems and TT20 beamline. It also examines the issues of beamloss in the extraction channel and the performance limitations of the electrostatic septa. The expected harmonic content of the spill is quantified as input to the target and experimental design.
The study shows that operation of the slow extraction and the beam transfer with SHiP parameters are feasible provided that increased beam loss control and operational surveillance are implemented, with improvements to some key systems highlighted. The activation in the extraction area will be highly dependent on the quality of the extraction spill, and automatic setup, optimisation and monitoring methods will be needed, complimented by improvements to instrumentation. Possible beam-physics methods to reduce losses also need to be actively pursued, since even a moderate gain can be very beneficial.
The modification to existing hardware and the new hardware systems required are technically feasible: the systems which need specific development are the new splitter magnet, the dilution sweep system and the beam interlocking. Of these, it is most urgent to start R&D work on the splitter magnet design and key technologies.
12. References
[1] Y.Baconnier, K.Bätzner, R.Dubois, High voltage aspects of the electrostatic septa for the CERN-SPS, CERN-SPS-ABT-78-13, 1978
[2] M.Gyr, E.Vossenberg, Half-integer fast resonant extraction with quasi rectangular spill, Proc. 3rd European Particle Accelerator Conference, Berlin, Germany, 24 - 28 Mar 1992, pp.1501-1503, 1992.
[3] https://ab-dep-op-sps.web.cern.ch/ab-dep-op-sps/SPSss.html
[4] B.Goddard, P.Knaus, Beam Loss Damage in a Wire Septum, CERN-SL-2000-035- BT, 2000
[5] G.Ferioli, B.Goddard, P.Knaus, J.Koopman, Energy Deposition in a Septum Wire, SL-Note-2001-029-MD, 2001.
[6] A.Prost, Adaptation des fiches HT des Septa électrostatiques du SPS pour les Septa du PS en vue d’utiliser le câble EPR, CERN TE-Note-2009-006, 2009.
[7] R.Keizer, KH.Kissler, R.Oberli, Improvement of the extraction channels of the CERN-SPS accelerator, CERN-SPS-87-12-ABT
[8] R.A.Barlow, B.Balhan, J.Borburgh, E.Carlier, C.Chanavat, T.Fowler, B.Pinget, A new spark detection system for the electrostatic septa of the SPS North (experimental) Area, CERN-ACC-2013-0238, 2014.
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[9] J. Wenninger, SPS Machine Protection Tests and Incidents in 2007, CERN-AB- Note-2008-003 OP
[10] K.Cornelis et al., Acceleration of High Intensity Proton Beams, Proceedings of 1999 Particle Accelerator Conference, New York, 1999.
[11] M. Tavlet et al., High-Level Dosimetry Results for the CERN High-Energy Accelerators: 1993 (CERN-TIS-CFM/94-11), 1994 (CERN-TIS-95-12), 1995 (TIS- CFF/96-09), 1996 (CERN-TIS-TE/97-22), 1997 (CERN-TIS-TE/98-08), 1998 (CERN-TIS-99-009-TE) and 1999 (CERN-TIS-2000-006-TE).
[12] Rapport Trimestriel Section SL: RSR-TRIM/SL/94-01,02,03, RSR-TRIM/SL/95- 01,02,03, RSR-TRIM/SL/96-01,02,03, RSR-TRIM/SL/97-01,02,03, RSR- TRIM/SL/98-01,02,03, RSR-TRIM/SL/99-01,02,03, CERN, 1994 - 1999.
[13] Electrostatic extraction septa ZS performance limits, this document.
[14] R.L. Keizer, High Intensity Running and Radiation Problems, SL-Note 95-14 (MS), CERN, January 1995.
[15] R.L. Keizer, High Intensity Running and Radiation Problems During the 1995 Physics Run, SL-Note 96-05 (MS), CERN, January 1996.
[16] W. Scandale for the UA9 Collaboration, Status of UA9, the Crystal Collimation Experiment in the SPS, Proceedings of the 2nd International Particle Accelerator Conference, San Sebastian, Spain, 4 - 9 September 2011, pp. TUOAA02.
[17] M. Giovannozzi for the PS Multi-Turn Extraction Study Group, Implementation Of The Proposed Multi-turn Extraction At The CERN Proton Synchrotron, CERN-AB- 2006-045, CERN, June 2006.
[18] ActiWiz, http://actiwiz.web.cern.ch
[19] Design and powering of new splitter magnets, this document.
[20] Beam Dilution, this document.
[21] cds.cern.ch/record/283839/files/sl-95-061.pdf
[22] G.Buur, G.Ferioli, J.J.Gras, R.Jung, CONTROL AND MONITORING OF THE SPS PROTON AND ION EXTRACTIONS, CERN SL/95-61 (BI)
[23] J.Camas, G.Ferioli, J.J.Gras, R.Jung, SCREENS VERSUS SEM GRIDS FOR SINGLE PASS MEASUREMENTS IN SPS, LEP AND LHC, CERN SL/95-62 (BI)
[24] J.Wenninger, SPS Machine Protection Tests and Incidents in 2007, CERN-AB- Note-2008-003 OP
[25] J.Wenninger, Introduction to Slow Extraction to the North Targets, jwenning.home.cern.ch/jwenning/documents/FTTrainingOP/Training-Slow- 2008.pp
[26] R.Giachino, B.Puccio, R. Schmidt, J.Wenninger, Architecture of the SPS beam and extraction interlock, CERN-AB-2003-010-OP, 2003.
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Page 43 of 43
[27] M.Werner, M.Zerlauth, A.Dinius, B.Puccio: Requirements for the Fast Manget Current Change Monitors (FMCM) in the LHC and SPS-LHC transfer lines, LHC- CIW-ES-0002, EDMS Doc Nr. 678140
[28] J. Wozniak et al., Software Interlock System, ICALEPCS’07, Knoxville, October 2007, WPPB03, p. 403.
[29] Archimedes of Syracuse, On Spirals, addressed to Dositheus of Pelusium, 225 BC.
[30] Design of the SHiP target and target complex, this document.
[31] M.Gyr, Proposal for a new Servo-Spill System : Power Requirements for different Configurations, CERN / SL 95-103 (BT).
[32] V.Rodel, La dynamique de l’extraction lente su Synchrotron a Protons de 400 GeV du CERN en vue d’un asservissement, These No 506 du Dept. de Mecanique de l’EPFL, 1983.
[33] jwenning.web.cern.ch/jwenning/documents/SPS/SlowExt/sps_spillharm.pdf
[34] http://sl-mgt-sps-swg.web.cern.ch/sl-mgt-sps-swg/SPSmin14.pdf
[35] G.Collazuol, Rate effects in the measurement of the direct CP violation with the NA48 experiment at CERN, Ph. D. thesis, Firenze, 2000.