Minutes of the SPL working group

meeting no. 86

date: 4. July 2008

present: G. Bellodi (AB/BI), A. Bertarelli (TS/MME), P. Bourquin (TS/MME), S. Calatroni (TS/MME), C. Carli (AB/ABP), F. Caspers (AB/RF), E. Ciapala (AB/RF), C. De Almeida Martins (AB/PO), R. Garoby (AB/BI), F. Gerigk (AB/RF), D. Kuchler (AB/ABP), J. Lettry (AB/ABP), A. Lombardi (AB/ABP), E. Mauro (SC/RF), D. Missiaen (TS/SU), V. Parma (AT/MCS), M. Pasini (AB/RF), M. Poehler (TS/CE), S. Ramberger (AB/RF), M. Schuh (AB/RF), R. Scrivens (AB/ABP), R. Wegner (AB/RF)

agenda

1. Status of the SPL study (Roland Garoby)
2. Summary of the SPL review meeting (Frank Gerigk)
3. H^- ion source devlopment within SLHC-PP (Richard Scrivens)
4. A fast chopping system for high intensity linac beams (Fritz Caspers)
5. next meeting
6. linked documents in EDMS

1. Status of the SPL study (Roland Garoby)

R. Garoby reported on the developments of the SPL study since the last SPL meeting. He recalled the approval of Linac4, which is the first step of the LHC injector upgrade. Linac4 is now a funded CERN project and is foreseen to deliver beam in 2013.

The SPL itself receives support from the EU within 2 frameworks, which are both part of FP7: i) CNI-PP for SLHC: 9 man years and ~1 MCHF contribute to the R&D effort for an SPL H^- source and a low-level RF system (see talk below). This is augmented by 5 man years from CERN. This funding covers the period from 2008 to 2011. ii) Eu-CARD integrated activity consists of a collection of proposals, which was submitted in February 2008. Originally the proposed funding amounted to 45 M¤, then it became clear that there would be only 15 M¤, which was recently cut down to 10 M¤ even though EuCARD received high marks from the reviewers. It is highly likely that the cuts will remove the proposed SC RF test infrastructure, which includes an upgrade of the CERN installations in SM18. However, it is promised that this part of the proposal will be treated with high priority in the FP8 funding round, which starts in 2010. It is still assumed that the production of SC cavity prototypes at Saclay remains in the proposal together with some studies on Higher Order Modes (HOMs).

The question of "in-kind" contributions from France towards white-paper projects was recently settled. They include a number of items for the design and construction of an SPL-type cryo-module, which were negotiated by V. Parma in talks with CEA (see slide #5). Further possible external contributions could come from collaborations with ESS (negotations have started, 4 scientists will start this year at CERN to be trained on RF, beam dynamics, and target issues), SNS (MoU) and ProjectX (under negotiation), as well as with the UK (ASTEC, Cockroft Institute). There are further possibilities under US-LAUC (successor of LARP) and with Canada (TRIUMF).

R. Garoby clarified the goals of the SPL study for the coming years, which are: i) report on the frequency, temperature review in 2008, ii) design of components (mainly source and RF) in 2009, iii) construction of prototypes and a technical design report in 2010, and iv) report on source and low-level RF developments, cryo-module & SC cavity tests and SPL cost estimate in 2011.

The total available funding until 2011 has increased to almost 3 MCHF.

Technical progress has been made in the placement of a EURISOL facility on the CERN site and on the review/consolidation of the SPL parameters (see next talk). The overall planning for the SPL foresees beam commissioning (of the LP-SPL) in 2016. R. Garoby showed the expected evolution of the integrated luminosity in the LHC, when SPL and PS2 are commissioned as proposed.

2. Summary of the SPL review meeting (Frank Gerigk)

F. Gerigk summarised the results of the recent internal SPL review, which was organised to assess if we can profit from the ILC technology when going to 1408 MHz instead of using 704 MHz for the SC cavities. For this purpose a comparison was made between three SPL scenarioes: i) the nominal 704 MHz architecture with 2 types of elliptical cavities (5-cell), ii) using 1408 MHz from 160 MeV onwards with 3 families of SC cavities (7-cell plus 2 x 9-cell, ~15% longer than i)), and iii) using 352 MHz spoke cavities up to 760 MeV and then continuing with 1408 MHz. The last scenario seems to have a good beam dynamics performance because the frequency jump is shifted to higher energies, but it involves the technology of 2 different types of SC cavities and it still has all the implications of the 1408 MHz technology. Beam dynamics in scenarios i) and ii) is comparable in the transverse plane but the 1408 MHz option shows almost twice the longitudinal rms emittance growth, indicating a sensitivity to longitudinal errors in the machine. This implies that the phase and amplitude control in Linac4 has to be much tighter for a 1408 MHz SC linac. Higher order modes and beam break up are much more dangerous for a higher number of cells and it was found that the limiting beam break-up current is between 8 and 128 times smaller for the 1408 MHz option than for 704 MHz. Assuming that the Q₀ for both frequencies is equal at 2K (which is probably optimistic for the 2K option) one finds that the power consumption and the cooling power of the cryogenics plant is between 25 and 50% higher for 704 MHz than for 1408 MHz. Regarding the RF hardware it was felt that going to 1408 MHz does not reduce the size of the RF installations. Due to limitations in average power density, it is unlikely that one can save on the number klystrons, neither can one use smaller circulators, etc. While for 704 MHz many of these components can be found on the market, for 1408 MHz off-the-shelf products are in most cases limited by their average power capabilities. After re-assessing the cryo-module design it was concluded that the SPL design will certainly incorporate many solutions from ILC, but that a new design will be necessary to cope with more than 10 times higher average power load and the SPL specific cavities, couplers, etc. From an overall optimisation of the installations it seems clear that the power consumption is lowest for both frequencies at 2 K (rather than at 4.5K).

As a result it was concluded that there we cannot really profit more from ILC technology, when going to 1408 MHz. The higher power consumption at 704 MHz is annoying (but needs verification), but 704 MHz offers much more safety against HOM related instabilities. Furthermore 704 MHz will open the option of collaborating with other high-power proton projects such as the ESS, which are counting on even higher currents than the SPL and which would certainly suffer from HOMs at higher frequencies.

3. H^- ion source devlopment within SLHC-PP (Richard Scrivens)

R. Scrivens reported on the activities for SLHC-PP (Super LHC Preparatory Phase), which are supported by Brussels within FP7. He is coordinating this working group, which includes R&D on the plasma generator for a SPL-type H^- source and the design of a low-level RF system, which could be used to stabilise the field in the SPL SC cavities. The low-level RF part will be reported in one of the next SPL meetings.

The SPL source will be based on todays approach for the Linac4 source, an RF volume source, which is being adopted from DESY to the needs of Linac4. Since R&D for the two other candidate sources (SNS: caesiated with internal RF antenna, RAL: Penning, caesiated) is still ongoing, it was decided to invest the CERN efforts into the DESY source, which is no longer under development by DESY. That way more options will be open to make the final choice for a suitable source. Furthermore the DESY source offers the potential of operating without Caesium and of having a very long life time. Due to the limited funding (no funds for high-voltage extraction) it will not be possible to extract beam after the 3 years of R&D, which are supported by Europe. However, we should be in a position to estimate how much more R&D is needed to decide which source type should be used for the SPL. Within the running time of the SLHC-PP, CERN will develop all the necessary tools and skills (diagnostics, simulations tools, training of a CERN source team), which are needed to pursue further H^- source work. Given appropriate funding the test stand can then be used for the final source development.

4. A fast chopping system for high intensity linac beams (Fritz Caspers)

F. Caspers reported on the latest results of the 3 MeV fast chopper, which is built for Linac4 but which is meant to already fulfil the specifications of the HP-SPL. The construction process of the chopper plates was described, and the latest measurements (April 2008) on transmission attenuation, step response, phase distortion, reflection, etc. were shown. One of the major construction changes since 2006 was the replacement of the aluminum support plates, onto which the ceramic substrate with the striplines are mounted. The aluminum changed its geometry when heated by means of internal stress release during warming up of the structure, which even led to the destruction of one ceramic plate. The aluminum plates were replaced by heat treated and copper (+gold) plated stainless steel plates. The remaining work includes final assembly and repetition of final vacuum and electrical tests and then the test with beam. The developments of the chopper amplifier will be reported in one of the next meetings.

5. next meeting: 10th September 2008, 9:00 in 6-2-004

6. Linked Documents in EDMS

Status of the SPL study (R. Garoby)
Summary of SPL review meeting (F. Gerigk)
Super LHC, Preparatory Phase, R&D on plasma generator (R. Scrivens)
A fast chopping system for high-intensity linac beams (F. Caspers)

-- FrankGerigk - 08 Jul 2008

• review-inverted.pdf: review-inverted.pdf