results of the argon beam test at linac3 d. küchler be/abp/hsl including feedback from r. scrivens...
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![Page 1: Results of the argon beam test at Linac3 D. Küchler BE/ABP/HSL Including feedback from R. Scrivens and M. Bodendorfer](https://reader037.vdocument.in/reader037/viewer/2022110321/56649f535503460f94c784e7/html5/thumbnails/1.jpg)
Results of the argon beam test at Linac3
D. KüchlerBE/ABP/HSL
Including feedback from R. Scrivens and M. Bodendorfer
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Objectives
• NA61 requires a primary argon beam in 2015(the setup of the accelerator chain will be done in 2014)
• Find and optimize settings for source and linac• Measure beam parameters
(intensity, stability, emittance)• Study long term behavior of source and linac
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RESULTS
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Source behavior
• Easy to run with argon (gas bottle)• Performance well reproducible after stop• Short commissioning period
(one week should be sufficient)• Does not need tuning very often
(1-2 times per day)
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Intensity (Ar11+)
• 70-90 eµA out of the RFQ (FC3)• 55-65 eµA at TRA25 (end of the linac)
Lost beam intensity data in Timber due to misunderstanding and misconfiguration.
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Stability
• Overall beam stability OK, but it seems it is less stable compared to the lead beam
• Often quite some variations within the pulse
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Emittance
• Quadrupole scan in the ITF line (after the tanks)
• Limited explanatory power due to beam structure (not round nor Gaussian)
• Beam seems to fill the complete machine acceptance Courtesy of M. Bodendorfer
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OPEN ISSUES
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Plasma chamber
• Strong sputtering inside the plasma chamber• Metal flakes on the bias electrode• Grooves along the plasma loss lines
(several tenth of mm deep)• Iron in the extracted ion spectrum
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Intermediate electrode
• New design was working properly for the lead run
• During the argon test the wire was heated by the ion beam and the capton insulation was burned away -> short circuit
• By retuning the source most of the intensity could be regained but the stability suffered
• New design for the routing of the wire needed
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Beam diagnostic
• Beam steering due to charge up of the SEM grids
• Strong negative peaks in Faraday cup measurements do not allow to measure precisely beam impurities and lead to some uncertainty on the actual beam intensity
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Vacuum - Source
• Vacuum leak in the extraction tank in the last week
• Probably a broken welding due to beam losses
• The tank has been there for 20 years, that’s why it is difficult to say if it is related to the argon beam
• Spray sealed to finish experiment
Beam direction
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Vacuum - linac
• Ion pumps in LEBT and RFQ suffered due to the gas load
• Pressure was roughly stable, but the current in the pumps was rising
• Not all of them have recovered after the run
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Radiation
• For argon ions hitting iron the Coulomb barrier is of the order of 3.2 MeV/u
• For a full beam loss at the final energy of 4.2 MeV/u roughly 20µSv/h were measured (90cm away from the beam line)
• The calculated values for the loss point are three times higher
• Assumption: at 40cm from the beam line one can expect a neutron dose rate of 40-50µSv/h (to be scaled with beam intensity and repetition rate)
• Material at the end of the linac can now be also activated!
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SUMMARY
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Conclusions
• Linac3 can deliver an argon ion beam with roughly 10 times the particle current compared to lead
• The operation of source and linac is simpler compared to lead, no down time due to oven refills
• Before the run some modifications are needed
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To do I
• The plasma chamber has now to be considered as a consumable– After only 8 weeks with plasma clear damages visible– Setting up + run will be around 8 months– One should foresee at least 2 chambers (15kCHF each)
for the argon run and a scheduled down time of several days to replace it
– The present chamber has to be replaced as well (is a repair possible and will it be cheaper?)
– Similar considerations have to be applied for the xenon run
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To Do II
• Extraction tank will be replaced by a new, redesigned one, special protection for the intermediate electrode will be build in
• Spectrometer chamber not yet checked, to be done soon (damages?)
• Additional pumping group will be installed in the LEBT near to the source
• Ion pumps may be partially switched of during the run to protect them
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To Do III
• Evaluation of the radiation situation (input from LEIR needed: intensity, pulse length, rep-rate)
• Definition of limited stay areas needed• An improvement of the beam diagnostics in
the linac is necessary