Minutes of the joint meeting Booster Commissioning and PSB Beam Dynamics with Linac4 Working Groups held on 1st of October 2009

Present: A. Lombardi, C. Carli, W. Weterings, J. Tan, K. Hanke, B. Mikulec.

PSB Commissioning to ultimate performance with Linac4

After the first brainstorming discussion on PSB Commissioning to nominal performance with Linac4, the discussion was continued on the steps to take during commissioning to ultimate performance (see last two slides prepared by C. Carli).

The commissioning phase to ultimate performance is planned to start immediately after commissioning to nominal performance (about 3 months after PSB startup with Linac4 in 2014).

The first step will be to set up longitudinal painting:

  • Set up energy ramping
  • Set up chopping for longitudinal painting: pieces with different length have to be chopped out that would fall outside the PSB bucket. A. Lombardi proposed to evaluate the flexibility of the chopper already at the 3 MeV test stand in 2011 using different chopping schemes. For the commissioning stage of longitudinal painting, it has to be made sure that energy/time resolution of the LBS line will be adequate. It still needs to be decided what kind of application/system will control the chopper with longitudinal painting.
  • Use longitudinal painting first with injection on flat bottom

As a second step, intensity and/or brillance has to be increased by increasing the number of turns and energy modulation periods. Adjustment of the dynamic working point and other optimisations might be needed. Injection at a ramp should be attempted at this point. Loss control will be the key issue.

Transfer of high intensity beams to ISOLDE: once high intensity beams can be accelerated, the transfer to ISOLDE should not be a problem. What could nevertheless be an issue is the steering to ISOLDE. Currently the steering is often performed minimising the BLM values along the transfer line; PUs sometimes show erratic measurements as they are sensitive when hit by the beam (although there will be additional PUs installed in the ISOLDE transfer line, they will show the same problem). In such a case one could put more effort in increasing the brillance. ISOLDE interlocks are currently implemented such that they will cut the PSB RF in case of a wrong magnet setting or a magnet failure to protect the targets. The question was raised by C. Carli if it could be evaluated by how much the activation would increase due to the ISOLDE interlocks (large losses, but rarely occurring). Increased activation with the higher PSB injection energy might become an issue. For this case K. Hanke will try to find out if an internal dump could be installed in the PSB.

Assigned to Start date Description State Result
K.Hanke 2009-10-07 Evaluate the possibility to install an internal dump in the PSB. Not further pursued. edit

PSB to PS transfer: special longitudinal gymnastics in PSB and PS for 25 ns LHC beams; tailor emittances for high intensity beams to improve the injection into the PS and to minimise losses.

B. Mikulec asked if it was foreseen to use skew quadrupoles for emittance exchange at PSB injection. Skew quadrupoles are not anymore used at injection, but with the currently ongoing multipole renovation it would be feasible and easier to use them during standard operation. C. Carli noted that the schemes proposed for low intensity beams (http://cern.ch/carli/PSBwithLinac4/Meeting09_06_25/ProductionSchemes09_06_25.pdf) aim at injecting short pieces of the Linac4 beam, but with a sufficient number of turns to tailor both transverse emittances.

A. Lombardi asked if one should rather compromise on the energy modulation amplitude (PIMS cavities) or on the energy spread (debuncher) in case both could not be achieved at the same time. One issue is that the debuncher might not be able to follow fast enough the energy modulation (as the bunches will arrive at different times). There is an ongoing discussion how to optimise the position of the debuncher. C. Carli answered that he would not compromise on the energy modulation, but he would like to know by how much the energy spread would decrease. As an additional complication the increase in energy spread is proportional to the beam intensity due to uncompensated space charge. Another possibility would be to make the energy modulation slower. There are schemes for longitudinal painting also of LHC type beams with longer energy modulation period, but they rely on features that are under discussion like (i) a reduction of the Linac4 beam current for that machine cycle and/or injection only every second or third turn (with implications for the Linac4 low level RF system).

A. Lombardi stressed that she needed the minimum beam parameters required from Linac4 at the various PSB commissioning stages.

Assigned to Start date Description State Result
C.Carli 2009-10-07 Provide a list of minimum required Linac4 beam parameters for each PSB commissioning step.   edit
J. Tan added that it might become difficult for the PUs to make a correct measurement if the signal gets too small. He was asked to give an estimate of the minimum required signal at different energies.
Assigned to Start date Description State Result
J.Tan 2009-10-07 Provide an estimate for the minimum required signal for the PUs at different Linac4 energies.   edit

-- BettinaMikulec - 2009-10-07

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