Minutes of the SPL working group

meeting no. 79

date: 10 May 2006

present: G. Bellodi, F. Caspers, C. De Almeida Martins, R. Garoby, F. Gerigk, K. Hanke, D. Kuchler, S. Lanzone, J.-B. Lallement, A. Lombardi, T. Meinschad, S. Maury, A. Millich, G. Olry (IN2P3), M. Paoluzzi, M. Pasini, C. Rossi, E. Sargsyan, J. Tuckmantel, M. Vretenar, R. Wegner


1. A 90 - 160 MeV SC spoke cavity linac for Linac4/SPL (Guillaume Olry, IN2P3)
2. Diagnostics in Linac4 (Klaus Hanke)
3. General remarks (Roland Garoby)
5. Tour de table
6. next meeting

1. A 90 - 160 MeV SC spoke cavity linac for Linac4/SPL (Guillaume Olry, IN2P3)

G. Olry presented (slides) a spoke cavity option for Linac4/SPL for the energy range between 90 and 160/180 MeV. The goal of this study was to keep the same length (28 m) as for the reference normal conducting SCL, and to see if a spoke cavity linac with realistic gradients and element lengths is feasible. The presented design features cryostats with two triple-spoke cavities per period. The focusing lattice is FDO featuring warm quadrupoles between the cryostats. The distances between the elements are chosen according to the practical experience with Spiral2. An accelerating gradient of 6 MV/m is assumed (defined as Eacc = ngaps x betadesign lambda / 2), corresponding to approximately 2/3 of the maximum gradients that were already achieved in tests of similar structures. At a frequency of 352.2 MHz, and assuming a constant geometrical beta of 0.49 for all cavities the spoke linac section has a length of 26 m. First tracking studies with TRACE_WIN indicate an rms emittance growth of 5-7%, which can probably be reduced with further optimisation. Also the RF design can be further optimised. G. Orly stressed that particular care was taken to design a realistic layout, which does not push the limits of the technology. The result is a linac design that can be built with reasonable R&D effort, though it has to be said that there are more uncertainties when compared to the normal conducting SCL solution. The advantages of the spoke solution are a much lower power consumption (~4.5 MW@352NOSPAMPLEASE.2 MHz instead of 12.5 MW@704NOSPAMPLEASE.4 MHz), which could be covered by existing LEP klystrons, and a more flexible RF phasing (e.g. one could hope to increase the gradient to 8 MV/m after some years of experience with Linac4. This would boost the energy up to 180 MeV, the injection energy for the first section of the SPL.). There are also possible synergies with an envisaged superconducting option for the ISOLDE post-accelerator.

2. Diagnostics in Linac4 (Klaus Hanke)

K. Hanke presented (slides) the status of the diagnostics set-up and commissioning plans for Linac4. The diagnostics requirements are split between the needs for commissioning and operation. So far a list of devices and possible locations has been identified for each section of Linac4, including chopper line and transfer line to the PS booster. The need for steerers has been acknowledged but they need to be tied in with beam dynamics simulations of correction schemes. The final number and position of steerers has to be chosen with respect to the location of beam position measurements and the phase advance between steerers and BPMs. A multi-purpose box, the Feschenko monitor, which promises to measure transverse/longitudinal emittance as well as the energy is under study by U. Raich. R. Garoby remarked that the diagnostics devices should also be dimensioned for SPL operation. He also mentioned that there is some interest by L. Kravchuk (INR Moscow) to collaborate on the Feschenko monitor.

3. General remarks (Roland Garoby)

On collaborations R. Garoby reported that there seems to be little hope for a successful collaboration with China. The idea was to outsource the construction of electromagnetic quadrupoles for Linac4 and the transfer line to Chinese institutes. The work with India on the construction of pulsed power supplies for the LEP klystrons is progressing well. Negotiations between CERN and Russia are ongoing, and could result in substantial orders for the Russian industry (accelerating structures for Linac4). It is likely that the Russian government will have to sponsor these contracts to ensure competitiveness with Western suppliers. For the upcoming European Framework Program 7 (FP7) CERN submits one bid containing four subjects: a) overall concept of SPL based proton drivers for neutrino applications, b) H- source development, c) accumulator and compressor rings for the SPL, and d) partial H- laser stripping as a means to share a high-power linac beam between different users. The details for this bid still have to worked upon to establish: the participating labs, work plans, people, money issues.

Tour de table

  • F. Gerigk: CDR2: the copy-editing of the report takes longer than expected due to staff shortages in the CERN editing office. CDR2 editing was outsources to someone, who can only work on week-ends. The editing should be finished by mid-May. On the bright side it seems that there are not many corrections to make which should speed up the remaining process. On the injection of Linac4 into the PS booster: Christian Carli and Brennan Goddard agreed to look at longitudinal and transverse painting issues, respectively. B. Goddard is counting on getting a fellow who will work with ACCSIM on transverse painting schemes. Serious results, however, can only be expected by autumn. C. Carli will start soon with the longitudinal capture process, probably using Long1D. The latest simulation results from S. Cousineau with Orbit suggest substantially more transverse emittance growth in the PSB than M. Martinis simulations with ACCSIM. It is likely that these differences stem from different conditions for the simulations and one now needs to look for possible explanations. Generally it seems that already the simulations with ACCSIM predict a worse behaviour than actually observed in the PSB (comparing actual operating conditions).
  • E. Sargsyan: reported that a technical note on a possible spoke cavity linac (to replace the SCL section of Linac4) is currently being prepared.
  • G. Bellodi: reported that the work on the Linac4 transfer line now converges toward the version that was presented in the last SPL meeting (slides). There are no major objections from civil engineering and she is now entering a 2nd iteration of the design, looking in more detail at multi-particle tracking.
  • R. Wegner: reported that he works on comparing different normal conducting structures for the energy range of 90 - 160 MeV for Linac4. This work follows the request of the HIPPI advisory committee to draw up a list of possible structures and to compare the advantages and disadvantages of each alternative. This work will also help to assess if there is a "cheap" NC option only to be used for Linac4. In case the SPL gets approved one would then replace this section with a high-duty cycle structure which is likely to be superconducting. The first structure under study was a 7-cell pi mode structure @ 352.2 MHz, similar to the LEP NC accelerating cavities. Stability calculations suggest that this is possible, however one would need 14 LEP klystrons to power the structure, which is not possible because only 7 are still available and the existing space is too small to accommodate such a large number of RF systems.
  • A. Lombardi: received the latest LEBT layout from the source team and is now preparing end-to-end simulations of Linac4 starting with the LEBT.
  • F. Caspers: remarked that there is a possibility to use the chopper as a longitudinal pick-up, an option that was briefly discussed in the recent HIPPI WP4 meeting at CERN. He also showed the hardware set-up used to measure the field-coverage-factor of the chopper plates (the effective voltage seen by the beam on axis with respect to the voltage applied to the chopper plates). Furthermore a prototype of the Kyocera meander line structure was also handed around for inspection.
  • C. Rossi: reported that there was a meeting in April on the integration of CERN and IPHI control systems for the CERN HIPPI tests at Saclay. One of the subjects still to be solved is the synchronisation of the chopper pulser with the beam and the IPHI electronics. IPHI RFQ: the 3d module is now complete and ready for alignment and RF tests at Mecachrome. The brazing test which is foreseen to study possible transverse displacements during the brazing, is promised to take place soon (S. Mathot). 3 MeV test stand: the planning for the electrical and water installations is progressing. It is not yet clear if one needs to consider a dedicated cooling station for the test stand (~100 kCHF) or if one can make use of the "South station".
  • M. Paoluzzi: received first measurements from the chopper pulser prototype which is under construction in Russia. The measurements show that they already achieved the nominal voltage (700 V) and the specs for the 10-90% rise and fall time. The 3-90% fall time is not yet within specifications but they have another two months before sending the device to CERN and it seems likely that all specs will be met by this time. Furthermore a pulse generator with high sampling rate was just received from Israel, which is meant to drive the Russian amplifier. Tests on this device will start soon.
  • M. Vretenar: reported on the successful conditioning of the buncher cavity "30" for the chopper line. The conditioning process was quick and straightforward up to pulses of 3 ms at 50 Hz with 20 kW input power. In the end, however, there was some damage due to the heating of the power coupling loop. A. Millich remarked that calculations showed the need for cooling at full duty cycle. However, to keep the construction simple, the cooling was not implemented to explore if the coupler can be used without cooling. Eric Page has returned from an extended sick-leave and has now time to proceed with the vacuum tests on buncher cavities, the CCDTL, and the chopper. It was already found that there is a leaking problem at the connection between the two CCDTL half tanks, which will need further investigation.
  • D. Kuchler: reported that the Memorandum of Understanding (MoU) for the collaboration between CERN and DESY is now at DESY awaiting their signature. As soon as the document is signed the technical annexes for the specific collaboration items can be prepared.

next meeting:

June, 14th, 9:00, 6-2-004

-- FrankGerigk -

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Topic revision: r1 - 2007-11-28 - FrankGerigk
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