614
ANTIPROTON ACCUMULATOR COMPLEX (AAC) PERFORMANCE
B. Autin, G. Carron, F. Caspers, V. Chohan, C.D. Johnson, E. Jonest,G. Le Dallic, S. Maury, C. Metzger, D. M6h1, Y. Orlov, F. Pedersen, A. Poncet, J.C. Schnuriger, T.R. Sherwood, C.S. Taylor, L. Thomdahl, S. van der Meer, and D.J. Williams CERN, PS Division, CH-1211 Geneva 23 idied the 2nd March 1990
Abstract Antiproton Production Antiprotons are produced in the target area, debunched and The production beam is focused on the target with 2 pulsed stochastically cooled in the Antiproton Collector (AC) and then quadrupoles. A high density target [11,12] made of iridium (8 transferred to the Antiproton Accumulator (AA) for final cooling ‘and 3 x 5.5 mm) embedded in graphite and enclosed in a sealed, water accumulation into a stack from which bunches are extracted and cooled, titanium container performs well. Despite the higher intensi- transferred IO the differeilt users. During Sp$S runs, the tics of the primary proton beam, no yield degradation due to target performance of the AAC is of crucial importance for the collider damage has been observed, although an irradiated target assembly luminosity. The stacking rate evolved from 1.2 X 1010jijh in early cut open 113,141showed that the iridium is damaged by the thermal 1988 to 5.X X 10’” ij/h in May 1989. A maximum stack intensity of shock, but sufficiently contained to maintain initial yield. 1.3 I x lO’* fj has been obtained. This is comparable to or exceeds Antiprotons emerging from the target are focused and matched into the ACOL project design performance. The Droblems encountered the injection transport line by a collector lens. and the co&&measut& ‘taken are presented. During periods of production for I-EAR only. the excellent AAC performance permits A lithium lens of 20 mm diameter, pulsed at 480 kA, was intemtittent 5 production; which results in low& operating c’ost and the principal collector lens used operationally and yieldecl62 X 10.’ a reduced power consumption F/p on the AC injection orbit after various optimizations. Introduction A 60 mm diameter parabolic aluminium horn operating at 400 kA peak has provided trouble free operation during several op- The ACOL project [1,2,3] design goal was a tenfold erational periods. It is simpler and cheaper to build and operate, but increacc of the antiproton accumulation rate from 6 X 109 p/h to at 400 k.4 its yield is about 10% lower than the 8 20 mm Li-lens. Lack of suitable test area outside the target area has until recently 6 :i 10 1’1i/h, while accumulating into stacks up to 101?h with prevented the exploring of high currents. acceptable transverse emittances. This performance was more or less obtained in May 1989, less than tw’o years after turn-on following the end of the ACOL project, Improvements were made to The above-rrlentioned yields agree with calculations [ 151 exqt for an unexplained factor of 1.5. These calculations a!so a!1fnc:ors which contribute to the stacking r;itr: indicated that an ever better yield could be obtained by using a l 26 GeV/c production bcarn intensity. 36 mm diameter Li-lens pulsed at 1.3 MA, thereby collecting G’s l AC injection yield. emerging at large angles. A collaboration with INP (Novosibirsk, l AC 5 debunching. USSR) was launched early in 1988, and in spring 1989 a 36 mm l AC stochastic cooling rate (p, H, V). diameter Li-lens (originally designed for 800 kA), a coaxial pulse l AA injection orbit precooling rate (p, V). transformer (designed for 1.5 MA), and an associated pulser was l Reliability. ready for test. A flange failure during testing at 1.1 MA forced us to The stochastic cooling rates influence both stacking effi- postpone beam tests until July 1989. These tests were encouraging ciencv and maximum repetition rate. In addition stack intensity with a 20% Z; yield improvement for the nominal production beam and a 40% improvement with lower intensity primary beam (with 1imit;;tionc due to coherent and incoherent instabilities caused b,y lower emittance). :~ccumul;tted ions were identified and cured. Intraheam scattering 15 also a lilnitinl: factor. During subsequent life test in the laboratory, the stainless 26 (;eV/c Proton Production Beam steel container failed after half a million pulses at 1.1 MA. New 34 mm diameter lenses 1161 with stronger containers are being Due to the circumference of the AC ring, the PS production made, and should be tested and ready for the SppS collider run this beam must be merged into one quarter of the PS circumference prior autumn to extraction. Since the end of the ACOL project, three different re-
Stochastic Cooling adding 2-4 GHz transverse cooling of the core, and, recently a proton stack of 1.67 X lo’* has been obtained with acceptable loss The novel 1-3 GHz AC stochastic cooling system [20,21] rate. Also the stack core momentum svstem (2-4 Gllz) has been in which moving pick-up and kicker electrodes accompany the beam improved by adding a l-2 GHz system. ’ as it shrinks, was very soon identified as a critical item in achieving design performance, even using a 4.8 s cycle instead of a 2.4 s cycle Stark Intensity as originally planned. In 1988 stack intensity was initially limited to about In spite of cold pick-up structures and preamplifiers, the 3X 10” 5 due to a coherent transverse ion-$ qundrupolar instability available powc* (c-10 kW) limits the gain to values below optimum [23,24]. This instability disappeared after improving the electrostatic during most of ttc cycle. Several improvements were introduced clearing and choosing a tune close to 2.25 in both planes. durinc 1988 and 1989: Nevertheless, residual ions caused high loss rates above l Ad 8ed cryogenic cooling of pick-up combiner bo,uds 6~ 101’~dueto excitation of high order non-linear resc)nar,res. This *Periodic filters for betatron systems to increase signal to noise was improved dramatically when the residual ion ncutralizatioll w;is ratio. further reduced by transverse shaking. The record stack intensity of *Two-stage momentum cooling filters. 1.3X 10’2 5 was obtained with less than 40% stacking efficiency *Dynamic phase correction as function of pick-up and kicker probably due to the limitation mentioned above in the core 4-X GIlz positions. system. After adding the l-2 GHz and 2-4 GHz systems recently *More band III power (2.4-3.0 GIIz). stacking efficiencies above 70 % has been obtained with more than l Better optimized pick-up and kicker movements versus time. 1012i in the stack. The first of these improvements was the most expensive Diagnostics and complex, but also the most effective. By lowering the tempem ture from 100 OK to 30 “K the thermal noise was reduced by 4 dB, These improvements would not be pcls5iblc M lrhutlr and acceptable transverse emittances and efficiency were obtained powerful diagnostic tools and controls software [2.5]: for cxumplc: after 2.4 s. But also the 4.X s cycle was improved (Table 11): *Transverse and longitudinal Schottky scans (tunes vs. freclucncy. emittances vs. frequency, emittances vs. time, etc.). Table II - AC stochastic cooling performance l Real time 5 efficiencies and momentum distribution by I-I-1 spectral analysis of Schottky signals [ 261. *Transverse and longitudinal coherent injection oscillations [27j for almost all injections (including correction matrices): p via loop to AA (L, H, V) - p via loop to AC (L H, V) - $ from target to AC (H. V) (I-csonant PU) (p-, e-) 6 from AC to AA (I,. H, V) (resonant PU) - p direct to AC (L, H, V) May 89 4R 92% 13n 70% - p direct to AA (L, H, V) *Transverse quadrupolz coherent injection oscillations [28] from Improvements wcrc‘ also needed for the AA precooling AC to AA, and from PS to AA (check and correct the mismatch) system (p, Vj: l Clearing current monitoring. l l Second band added : 1.h-2.4 GHz. (Initially only 0.X-l .6 Gf lzj. Software to localize acceptance limitations. *Lower noise predmplificrs. l Software to measure acceptances. *Damping of propagating ‘IX mades hq’ fcrritc nlateriel (cotlphng *Software to measure 5 emittances in AC and AA by sc~i:itill,ltors via longitudinal modes of stack) and scrapers. Nevertheless. the precooling and stack tail systems are not 4AC Pr~rformance sufficiently fast to digest the f; with adequate efficiency for the 2.4 s cycle, while the precooling and stack tail systems do not limit the After all these improvements the stacking rate’ at Inedium efficiency with a 4.X s cycle. stack intensities was increased by a f;lctor of 10 witlt respect to that of the old AA. As for the AC, the AA precooling gain is limited to below optimum by thermal noise and available power. The cheapest way to We show in ‘I‘ablc III the peak performance ant! the opera obtain sufficient gain and speed would be to add cryogenic cooling tional values, compared with the design values. The daily stacking of the AA precooling pick-ups. Even so, barely 10% could bc rate is an average during stacking periods, and takes into account the gained in overall daily production rate since the number of produc- fluctuations of PSR, IS and AAC machines. tion cycles per hour available from the PS using 2.4 s cycles only increase by a factor typically 1.5 to 1.7, and not 2, due to other Table III AA< I’crformance ussrs (LEAR, SPS, fixed target, East Hall, LEP). For this reason 1988 :91(9 (and others such as budget, manpower, future of SpFS Collider), - -._ the cryogenic pick-ups in AA were abandoned and therefore also OESlGY OP!zR*TIOb OPEA*rIOY , *Lxr 2.4 s operation. t -- I 0.10’~ l.JS”19” 1.15=10’~ t 4*11500/114 O‘,,SO,h, 4 S‘C’?SOib, The AA stack core 4-8 GHz transverse cooling [22] system 5 0’1.v 10IO vI0-L0.10’ 5.7.7’10’PI&v@ : X6 a 3’10’ initially suffered from difficulties in obtaining a good BTF (Beam I 0’10’ I.E.10 6 2.10 6 a.10 Transfer Function) due to hardware coupling and poor common 5 I.10 7 2’10’ 7.6.10’ 5.4’10 6 J’IO’ i o-lo? mode rejection, but after these problems were cured, equalizers were 10. a . made to improve phase and bandwidth. But even after improve- IO.I I . ments of the 2-4 GHz stack core momentum system, the stack mo- 5 J~IP'I4rYsl f SxlO~ 7 9'101 J a"to'i1av.J 6 PI01 6 r^xI@' mentuni width (tl.~e to intraheam scattering) at intensities above a 5 O"10' 4 a"101 7.0*10' 7 7.1OI few 10” particles is too wide to exploit the highest frequencies 7.5 JP 5 J 5 a 10 6 0 0 5 Ii I (above 6 GHz) of the transversesystem due to too high an q valur JJ I 4 s 16 l(Af/fMLzp/p)l. 1.10'2 O.OS~IO'~ 1 OJ.10'~ I 1’10’2 I-I . E-J , Z-J v This leads to heating of the low and high momentum edges so I 63 I II I OS I of the stack, and increased loss rate which eventually consumes a We also show in Fig. 1 the evolution of the AAC stacking large fraction of the stacking rate. For this reason, the transverse rate versus years. core bandwidth has been extended towards lower frequencies by 616
r111 C.D. Johnson et al., in Proceedings of the IEEE Part. Act. Conf., Washington , 1987, p. 1749. ( I* u CD. Johnson, CERN PS/87-95 (AA), 1987 > _...____. Y ...> //“’ [=I ‘1 [131 J. Cauwe , JRC, ISPRA. private communication / I ,,c 1 ’ 1141 T.W. Eaton, private communication.
z+I 1151 N. Walker “Theoretical Antiproton Yields for the AAC”, CERN PS/88-69 (AR), 1988. /j__ I I,,__ _/./A” L161 S. Maury, “Study of a 36 mm and 34 mm Lithium Lens”, CERN PS/AR/ME Note 89, 1990. @C i 186 mi Ie4 ,meJ 1171 B. Autin et al., “The CERN Antiproton Collector Ring”, in Proceedings of EPAC, Rome, 1988, Fig. 1 Stacking rate (10’” p/h) p. 308. Ll81 V. Chohan et al., IEEE Trans. on Nucl. Sci., Vol. Summary NS-32, no. 5, p. 2231, 1985. The good AAC performance and reliability enable one to [191 J. Boucheron et al., “A 1 MV 9.5 MHz RF System stack typically 9 X 10” $/every day. On several occasions, more for CERN Antiproton Collector”, this conference. than Iif2 5 were obtained in &e&on during the SpijS period. During the 2 last oeriods of 19X9. all the i’J produced were dedi- LZ B. Autin, “Fast Betarron Cooling in an Antiproton cated to LEAR. During runs for LEAR ihysAics a lower j flux is Accumulator”, CERN/PS/AA/82-20, 1982. needed.The excellent AAC performance permits intermittent p pro- duction. i.e. 5 X 10” 0 are accumulated in the AA, then the accumu- 13.Autin et al., in Procredinrs of the IEEE Par-i. lation is stopped, rhe*injection line power supply currents are re- Act. Conf.. Washington, 10X7, p, 1539. duced to 10% of their onerational values, the AC ring switched off for saving power, ana’ finally just the 5 transfers are opera. 1321 G. Hosser et al., in Proceetlin~> of EPAC, Rornc, tional.This ttwdc is called Economy Mode, but the 6 accumulation i> IYXX, p. 13’1. tested every clay during 15 minutes. [23] J. Carron et al.. “Observation of Transverse During the last run of 1989, AAC was in this mode for Quadrupole Mode Instabilities in Intense Cooled 77%’ of the time. This represents a saving of 4650 MWh. Antiproton Beams in the AA”, CERN/PSIX9-18 (AR), presented at the Part. Act. Conf., Chicago, References 1989.
[11 E.J.N. Wilson (Editor). “Design Study of an 1241 R. Alves-Fires et al., “On the Theory of Coherent Antiproton Collector for the Antiproton Accumulator Instabilities Due to Coupling Between a Dense (ACOL)“, CERN 83-10, lY83. Cooled Beam and Charged Particles from the Residual Gas”, CERN/PS/89- 14 (AR), presented at 121 E. Jones “The CERN PP Facility”, in Proceedings the Part. Act. Conf., Chicago, 1989. of EPAC, Rome, 1988, p. 215. 1251 V. Chohan, S. van der Meer, “Aspects of 131 B. Autin et al., “Performance of the CERN Automation and Applications in the CERN Antiproton Accumulator Complex”, in ProceedinPs Antiproton Source”, CERN/PS/89-57 (AR), pre- of EPAC, Rome, 1988, p. 392. sented at the Int. Conf. on Act. and Exp. Phys. Control Systems, Vancouver, 1989. L4l G. Nassibian and K. Schindl, IEEE Trans. on Nucl. Sci., Vol. NS-32. Ko. 5, p. 2760, 1985. Ml T. Eriksson, “Measuring of AC and AA machine efficiencies during t production using NORD 100, ISI R. Garoby, CERN PS/RF Note 83-15, 1983 GPlB interface, HP9845 desktop computer and HP3562 Dynamic signal analyzer” CERN/PS/OP IhI R. Garoby, IEEE Trans. on Nucl. Sci., Vol. NS- Note X9-10, 1989. 32, no. 5, p. 2332, 1985. 1271 V. Chohan, , “The CERN Antiproton Source: 171 B.J. Evans et al., in Proceedinzs of the IEEE Part. Controls Aspects of the Additional Collector Ring Act. Conf., Washington, 1987, p. 1925. and Fast Sampling Devices”, CERN/PS/89-29 (AR), presented at the Int. Conf. on Act. and Exp. Phys. [81 R. Cappi et al., “Upgrading the CERN PS Booster Control Systems, Vancouver, 1989. to 1 GeV for Improved Antiproton Production”,, CERN PS 89-26 (HI), presented at the IEEE Part. WI V. Chohan et al., “Measurement of Coherent Act. Conf., Chicago, 1989. Quadrupole Oscillations at Injection into the Antiproton Accumulator”. This conference. I91 D. Boussard, G. Lambert, IEEE Trans on Nucl. sci., Vol. NS-30, p. 2239, 1983. ~291 B. Autin. “Non-linear Betatron Oscillations”, in Proceedings of CAS, CERN 90-04, Uppsala, 1989, [lo] R. Garoby, private communication. p. 1.