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Minutes of #10 Remote E-Beam Meeting (draft)

The meeting was held on Zoom on 21/04/2021 - See indico

Participants

Agnieszka Borucka, Christian Carli, Roberto Corsini, Bruno Galante, Davide Gamba, Andrea Latina, Javier Resta Lopez, Gerard Tranquille, Volodymyr Rodin, Adriana Rossi, Richard Scrivens, Lars Joergensen, Bianca Veglia, Raymond Veness, Michail Zampetakis

Bunch compression studies for inner target collisions within ELENA ring (Volodymyr Rodin)

This studied was triggered by an idea suggested to make a Reaction Microscope in ELENA (see ADUC 20/11/2012 and M. McGovern 2009, Phys. Rev A), in particular to measure the differential cross section of antiproton impact ionization of atomic hydrogen and helium. For such an hypothetical experiment, high density gas would need to be injected in a dedicated experimental chamber installed in the ELENA, and this would interact with the circulating antiproton bunches.

Rough estimate of ideal conditions were studied with the help fo Geant4 simulation and gave target parameter of 10e14 atoms/cm^3 gas density and antiproton bunch lengths of the order of 5 ns rms, which is considerably lower than target parameter of ELENA design: 75 ns rms. This very small bunch length is mainly necessary to allow for a narrow trigger event to suppress background noise in the detector that would measure recoil ions and electrons from the pbar-gas interaction. For these parameters, simulations predict of the order of 5.5e3 events/seconds (linear extrapolation from N. Petridis et al. NIMA.2011.07.035)

Simulations with BMAD were shown in which the nominal ELENA bunch at 100 keV (4.5e6 particles (~0.7 pC), h=1) could ideally be compressed down to ~10 ns rms with a sudden increase of RF voltage to 100 V. In practice:

  • collective effects like space charge (using 3D PIC space charge tracking module in BMAD) increase the minimum achievable bunch length, and induce a considerable tune spread (verified that simulated tune spread agrees with theory).
  • by adding magnet errors up to 3rd order defined as Gaussian distribution with mean 1e-4 and 1e-4 standard deviation the tune spread further increases and coupling through space charge is observed.

Volodymyr investigated also the effect of IBS (Martini model) and e-cooling (Parkhomchuk model) using betacool. The results from betacool are compatible with what obtained in B-MAD. Additionally, he crosschecked the implementation of IBS between MAD-X, JSPEC and BETACOOL, discovering a possible factor 2 missing in the computation of the longitudinal decay time in MAD-X for coasting beam. This is being investigated by MAD-X team at CERN.

In order to mitigate the collective effects one idea would be to decrease the bunch intensity of about a factor 10, for example by using higher RF harmonics. From simulations, it was shown that it would be possible to obtain bunch lengths of the order of 5 ns rms using h=16 with 500 V or RF voltage, or even down to about 1.5 ns using rebunching from coasting beam. The possibility of implementing bunch splitting was also evaluated in simulations using PyHEADTAIL and ESME showing good agreement between the two codes.

As an outlook for future studies, Volodymyr is planning to:

  • implement IBS model in PyHEADTAIL
  • try implementing optics correction to compensate for magnets errors
  • refine the bunch splitting algorithm, eventually testing it in ELENA

Discussion

Adriana was wondering if this is an actual ELENA experiment. Christian commented that this was an early proposal, but the community behind this experiment did not pursue with this. Volodymyr also commented that despite the experiment might not take place, Carsten Welsch (Liverpool university) is also working on a design of a possible gas jet insertion for such an experiment. Davide commented that this development could be interesting for the gas curtain monitor that is being designed for the HL-LHC hollow electron lens.

Davide wondered how to profit as much as possible from all the nice benchmark work presented. Volodymyr said that he is also in contact with Adrian Oeftiger to follow up the implementation of space charge in PyHEADTAIL, and with Lajos Bojtar for the magnetic imperfections of ELENA. Michail commented that he is also interested in all those developments, as he is working on the interplay between synchrotron radiation and IBS and space charge. Andrea commented that RF-Track could also make this kind of simulations, and it would be very interesting to get IBS implemented in RF-Track as well.