Preparation of a Primary Beam for the CERN Fixed Target Physics ICIS ‘13 D. Küchler, M. O’Neil, R. Scrivens, J. Sta ord-Haworth, CERN, BE/ABP/HSL, 1211 Geneva 23, Switzerland R. W. Thomae, iThemba LABS, P.O. Box 722, Somerset West 7130, South Africa

Abstract SOURCE AND LINAC SOURCE AND LINAC OPEN ISSUES II PERFORMANCE PERFORMANCE II he fixed target experiment NA61 in the North Area n the bias disk metal flakes had been accumulated of the SPS is studying phase transitions in strongly fter the spectrometer in the Faraday cup FC2 which could be identified as tantalum, the material T he operation of the source was quite simple compared O interacting matter. Up to now they used the primary currents in the order 120-140 eµA were measured. the bias disk is made of. The amount of sputtered material to the usual operation. The source was fed from A beams available from the CERN accelerator complex T The transformer in front of the RFQ showed 95-115 eµA. after only 10 weeks is of concern because the set-up of an argon bottle with a feedback-controlled needle valve. (protons and lead ions) or fragmented beams created In the Faraday cup after the RFQ 70-90 eµA and at the the accelerator chain and the experiment itself will take As feedback signal the pressure downstream of the valve from the primary lead ion beam. end of the linac in the transformer TRA15 55-65 eµA were around 8 months, so it is foreseen to change the plasma was used. This smooths out pressure fluctuations inside measured. It is clearly visible that all along the linac there chamber during this period as preventive maintenance. o explore a wider range of energies and densities the source. No additional support gas was used. a request was made to provide primary argon and are high beam losses but already in the part between the T he commissioning of the source took only around a xenon beams. spectrometer and the RFQ entrance a lot of beam is lost. Tweek. In the lead case four to six weeks are common. his poster describes the results of the setting up and When the source tripped or had to be stopped the 10 week test run of the Ar11+ beam from the 14.5 GHz T performance after the restart was reproducible. The 11+ 10+ Ar Ar ECR ion the source and the linear accelerator (Linac3) at source had to be retuned roughly 1-2 times per day. 150 CERN. or the measurement of the beam intensity two Faraday Ar9+ cups (one after the spectrometer, FC2, and one after F 8+ the RFQ, FC3) and two beam transformers (one in front 100 Ar

of the RFQ, TRA05, and one at the end of the linac, TRA15) Ar12+ 13+ Introduction were used. FC2 current/eµA Ar 50 Ar7+ Ar14+ Ar6+ A61[1] is a fixed target experiment in the North area Nof the Super (SPS). NA61 studies 0 the production in hadron-nucleus and nucleus- 30 32 34 36 38 40 42 44 46 48 50 52 54 nucleus collisions. The aim of this experiment is to study Electrical connection for the intermediate electrode BHZ current/A phase transitions in strongly interacting matter (quark gluon plasma) and the onset of deconfinement and to he microwave power during this test was in the order take reference measurements for the hadron production. T400-500 W and the time averaged drain current from the source was approximately 0.8-1.0 mA (with 50% duty cycle). he beam was less stable from pulse to pulse and also Twithin the pulses when compared to lead operation. or operation the shielding of the connection wire to There were periods with variations from pulse to pulse Fthe intermediate electrode of the source extraction higher than 20% of the full intensity. Within the pulse system will have to be improved, after the kapton sometimes a ripple in the range of tens of kHz was present. insulation layer was melted due to impact by the beam. In most of the cases the stability could be regained by ome issues concern the beam diagnostics. It was retuning the source. But the reasons for the instabilities Sfound that profile harps in the Low Energy Beam are not yet understood. Transport (LEBT) were charging up and steering the beam. During the shutdown they will be inspected and debugged. The Faraday cups need improved shielding to avoid the significant negative offset on the measured current, which makes the detection of low intensity beams impossible. OPEN ISSUES uring the test it was also found that the ion getter Dpumps in the LEBT were suffering from the argon gas load. While the pressure stayed quite stable the he test revealed a series of issues that have to be Time development of the different argon charge stages current of the pumps was rising more than an order of solved before the proper run can take place. T magnitude during the period of the test. To avoid this nside the stainless steel plasma chamber, some grooves problem an additional pumping group with a turbo Iwere found along the plasma loss lines. In the extracted pump will be installed and used as replacement of the beam different charge states of iron could be identified. ion getter pumps during the argon run. he linac accelerates the argon ions to 4.2 MeV per Tnucleon, which is above the neutron production threshold and to radiation levels of approximately 40-50 µSv/h at a distance of 40 cm away from the beam chambers when all the beam is lost (with 200 µs pulses n the last years protons and lead ions as primary beams, spaced by 1.2 seconds). Addition protection measures and light ions from fragmented beams were delivered I will be put into place for operation. to the experiment. It is planned to deliver primary argon and xenon beams from 2015 onward to be able to explore a wider range of energies and densities in the experiment. The accelerator chain will be set up with the argon beam in the second half of 2014. n the beginning of 2013 a 10 week test run was done Iat the linear accelerator Linac3 to find and optimize Conclusions the settings for the source and the linac, to measure the beam parameters (intensity, stability) and to study the he GTS-LHC ion source and Linac3 are capable to long term behavior of source and linac. Tdeliver an argon beam that is roughly ten times the particle current compared to the lead operation. The he GTS-LHC ion source [2,3], running at 14.5 GHz, setting up of the accelerator chain in 2014 will show if was set-up to provide an Ar11+ beam. The source was T this is sufficient for the experiment. running in the afterglow mode with a microwave heating pulse of 50 ms and a repetition rate of 10 Hz. The beam 100 ufficient information to run source and linac could was extracted with an extraction voltage of 9.6 kV to 11+ 10+ Sbe accumulated and no showstoppers were found. Ar Ar 9+ match the injection energy of 2.5 keV/u into the RFQ. Ar he critical operation issues could be identified and In the linac a pulse of 200 µs, cut out of the afterglow 80 Tfirst steps to mitigate them were already taken. pulse, was accelerated. At the end of the linac the beam reaches the final energy of 4.2 MeV/u. Ar13+ 60 Ar12+

40 References Fe16+

FC2 current/eµA 17+ [1] http://na61.web.cern.ch/na61/xc/index.html Fe Fe15+ Layout of Linac3 and 20 [2] C.E. Hill, D. Küchler, C. Mastrostefano, M. O‘Neil, R. Scrivens et al., Experience with the GTS-LHC ion source, positions of the intensity LHC Project Workshop - Chamonix XV, (2006) 240–242. measurement 0 [3] L. Dumas, C.E. Hill, D. Hitz, D. Küchler, C. Mastrostefano, 34 36 38 40 42 M. O‘Neil, et al., Operation of the GTS-LHC Source for the BHZ current/A Hadron Injector at CERN, LHC Project Report 985, (2007).

Contact information

Dr. Detlef Küchler CERN BE Department CH-1211 Geneva 23 Switzerland detlef.kuchler@.ch