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AccComplexCap-WG meeting
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This meeting is devoted to the ions, like the other few meetings of this WG in 2022. During a previous discussion it was defined that NA60+ will only require Pb ions like the ones that are currently produced and used in the CERN injector complex. For NA61, however, different types of ions are required covering He, P, O and Ar. In today's meeting Detlef will show the challenges to produce different types of ions and which resources are required to enable studies and easier operation in the future with different ion species.
Ion source development (D. Küchler)
- The current source was installed in 2005 and is an ECR type source with 14.5 GHz microwave heating (up to 2 kW power), which for heavy elements is operated in afterglow mode.
- Material can be injected through two gas lines (used for gases, liquids with high vapour pressure and metal ions from volatile compounds) or through two micro-ovens that can reach 1000 deg (for solids)
- The A/Q (mass over charge state) of the ions extracted towards the RFQ is constrained by the available voltage for matching as well as the linac requirement of A/Q<8
- As there is no separate source test stand (only and oven test stand), all studies involving exploring other ion species or performance improvement must be done on the operational source. This means that time for studies must be allocated outside the operational time, guaranteeing a minimal impact on the source performance.
- Another problem is that there is no beam diagnostics directly after the source and in general possibilities for beam diagnostics are limited even more downstream in the LEBT.
- For the moment there's only experience at the source with Pb, O, Ar and Xe. In was also produced but prior to 2005 with the previous source.
- To check different elements several aspects need to be considered
- For some elements isotopically enriched material is needed. However, not all isotopes are easily available and the cost could be important.
- Then to assess feasibility, but also stability and long-term operation, depending on the material, the development can take several weeks or months.
- Some materials may require additional safety procedures (e.g. calcium).
- Without tests, there cannot be any valid prediction of intensities or dominant charge states possible.
- With a test stand, development could be carried out also in parallel to normal operation and there are many advantages
- Study the material to be used (pure element, compound), which needs probably several iterations
- Study which support gas to be used, which also needs probably several iterations
- Study material consumption, which needs several weeks or up to months to get proper information
- Study charge state distribution, intensity of the main charge state and the emittance of the beam
- Study long term stability of the source, which normally takes several weeks, for oven operation even months
- Study the reliability of the source (plasma chamber, electrodes, insulators), which needs at least 2 months to see also minor effects on the source components
- Another problem is also the lack of diagnostics in the low energy part of Linac3.
- It was also discussed that the test stand could also be a second source attached to Linac3 (like at GSI, where they have three sources attached to Unilac, among which they can switch), so that the missing diagnostics could be installed as a measurement line with a switching magnet after the current source and then do studies in parallel to operation, as source pulses are currently only used one out of two (source operating at 10 Hz, LEIR injections at 5 Hz).
- The cost would be very roughly 1.5 MCHF source + 1.5 MCHF diagnostic line = 3 MCHF. Most of the body of the source can be assembled from existing spare parts, but this would only entail a saving of few hundreds of kCHF.
- If we should envisage staging the project, one could start from the low-energy diagnostic line, which is currently studied in the framework of the OXY4LHC project and for which a summary report is expected by the end of 2022. However, a decision would need to be taken very quickly to allow installation during LS3 and permit its use still during LS3 for source development before the return to operation.
- In terms of manpower, technical and scientific manpower will be needed for installation, commissioning and operation of the test stand (several man years). To be considered that further manpower is anyway needed as at the moment Detlef is running all source related activities (operation, development), but in the future we need to extend this expertise to avoid having one single point of failure.
- Marek says that among the species required for NA61, one could indeed consider Al or Mg instead of P. Detlef says that after careful check Al would not be ideal due to issues with hot chemistry with filament, so we should consider Mg.
- Marek said that He could be replaced by Li or Be (B starts to be to heavy and close to O). He seemed to cause intolerable neutron production in LEIR assuming intensities close to the current EARLY Pb beam. Detlef rules out Be, which is toxic and has a very high melting point, while Li has been already tried and it also makes hot chemistry, and besides, being light ions, one has to pay attention to the neutron generation which might require further shielding in Linac3.
- Heiko also added that the charge state ratios that can be accepted by LEIR need to be checked.
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