Minutes PSB Upgrade WG Meeting 25th of April

Present: C. Maglioni, A. Sarrio Martinez, R. Garoby, M-E. Angoletta, A. Findlay, D. Hay, W. Bartmann, R. Froeschl, A. Newborough, A. Blas, M. Delonca, W. Weterings, M. Paoluzzi, J. Hansen, L. Sermeus, J-L. Sanchez Alvarez, K. Hanke, B. Mikulec, V. Raginel.

Agenda:

1. Approval of Minutes

The minutes of the last LIU-PSB WG meeting were approved.

2. Follow-up of Open Actions

• Define hardware for BT, BTP, BTM line: A review on this topic is to be scheduled before summer.
• Check whether the vacuum window at the exit of the beam pipe withstands the new beam parameters: to be followed up during the next LIU-PSB WG meetings.
• Evaluate INCONEL vacuum chambers in injection region: A dedicated meeting is tentatively scheduled for the 30th of May.

3. Communications

• IPAC13 papers: K. Hanke reminded to upload papers and posters on EDMS (here for papers, here for posters).
• On the 18th of April the review on the H-/H0 dumps was held; a dedicated meeting will be organized to summarize the feedback of the reviewers.
• Yesterday's Linac4 BCC meeting was dedicated to the PSB half-injection sector test in Linac4. It was endorsed to have two different tests, the first one with only the stripping foil unit (final location 'reserved' at the start of L4T, but still needs to be confirmed) and the second one with the stripping foil unit and two chicane magnets including the H0/H- dump and beam instrumentation) - it was proposed to install it at the location of the debuncher. There are still open points (specifications of the beam needed for tests, infrastructure needed, temporary dump, radiation), but no show stoppers were identified.
• For the HL-LHC + LIU planning workshop, K. Hanke said that scenarios need to be developed which take into account the access to the LBS/LBE lines via the PSB or the PS.

4. PSB with Linac4 - RF matching

A. Blas presented the RF matching scheme in the framework of the PSB with Linac4 PSB with Linac4 - RF matching. For the injection into the PSB, the chopper and PSB RF need to be “in-phase”, i.e. they will be both synchronized to a single external reference clock and the energy modulation needs to be in-phase with the different ring injections. As soon as the injection starts in one ring, the RF system will decouple itself from the injection reference and follow a frequency program corresponding to the B-field increase (accelerating bucket). The RF and injection reference clock has a predictable phase relation during the filling phase. The same reference clock will be used to trigger the chopper, the energy modulation and the distributor. The injection in the PSB is planned to be done with h1 (1 MHz) or for exotic schemes also with h2 (2 MHz). M. Paoluzzi said that it needs to be confirmed that the chopper can operate at 2 MHz.

The RING Blanking is a reaction to so-called “external conditions” treated by the MTG. After a response time taking up to two cycles, different actions can be triggered (switching to a spare cycle if compatible, 0-turn imposed by timing means, ...). Contrary to that the Ring Inhibit is a real time action aimed at both stopping the beam at the chopper level (3 MeV) and inhibiting its acceleration at the PSB LL-RF stage. During a ring inhibit all machine parameters remain identical; there is no timing change. Ring Blanking and Inhibit can be activated without perturbing the other rings.

The energy modulation function has been depicted with a ring-by-ring framing to allow the usage of ring-blanking. In order to avoid unacceptable energy transients at the PIMS stage when making a ring blanking, an approach would be to allow for up to 20 us (full sweep of the modulator) of no-beam time at the beginning of an injection, in order for the modulator to settle to any requested energy. This approach would require 60 more us in the distributor’s PFN (460 us in total for 100 us injection per ring) and, according to L. Sermeus, one should assume 600 us as limitation for the distributor. W. Weterings reminded that in case of a reduced Linac4 intensity, the injected pulses per ring will be 150 us long so that there will be no spare time for such a scheme. B. Mikulec said that with the PIMS pulsing with a period of 20 us C. Carli expected to get 10% gain in beam intensity, but now that it is foreseen to pulse with a longer period of 40 us due to power limitations it would be interesting to re-estimate the gain in beam intensity. It was added that the longitudinal painting will probably not be used during the first period of run, but rather as a second step.

The effect of a ring blanking on beam parameters was presented for the worst case in terms of longitudinal relative emittance growth (3 first rings (4, 3, 2) programmed with 100 turns and the last one (R1) with 1/20th of a turn - LHC high intensity single bunch). The beam will reach directly ring 1 at the beginning of the cycle, when the ramping field will have a value 3.6 Gauss lower than expected. The beam will have thus a – 80 keV energy error with respect to the RF bucket; this error would roughly double its emittance after filamentation, but this should never occur as the phase loop will enter into action after 1 us and damp the motion in the phase space with a time constant of 50 us (faster than the synchrotron motion ≈ few ms). The radial error due to the 3.6 Gauss is around 2.5 mm, but with the upgraded TFB system and its increased power (800 W per kicker plate instead of 100 W) it is likely that this radial error will not be a concern.

As the minimum Chopper beam-ON time is 15 ns, the minimum beam intensity is 6E9 ppb (linac beam = 65 ma or 4E8 p/ns) and as the maximum of ON-OFF periods of the Chopper during one revolution is 2, it is just enough for an injection on h2.

W. Weterings reminded that all the injection equipments have to be ready by end of 2015.

5. Tour de table

• B. Mikulec prewarned the WG members that she will soon need their input to prepare the commissioning planning.
• A. Sarrio Martinez said that 3 options were foreseen for the procurement of the copper for the PSB dump core. The more promising option seems to be a German supplier. EN/STI will probably go there to discuss the procurement conditions. K. Hanke said that the material should be delivered to CERN at the latest mid-July in order for the dump to be installed during LS1. A. Sarrio Martinez added that tests to pull out the dump will be conducted in the coming days and that a solution needs to be found to reduce the dose taken by staff due to radiation emitted by the vacuum window at the end of BTM (shielding the vacuum window, removing it temporally... ). A visit of the zone was scheduled for Thursday 25th afternoon with D.Hay, STI, RP and VSC.
• D. Hay said that very soon one needs the "eye scan" to access the PSB (end of May).

The next LIU-PSB meeting is tentatively planned for Thursday 16th of May at 10h30 in 864-1-C02.