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SUMMARY:Plasma-based techniques for intense particle beam characterization
  at the frontiers of performance
DTSTART:20180430T103000
DTEND:20180430T113000
DTSTAMP:20260408T105146Z
UID:8c7c7aa6e89c56c032a429914338d1107a412332b33bcac37c14f94f
CATEGORIES:Conferences - Seminars
DESCRIPTION:Roxana Tarkeshian\, University of Bern\nLight induced dynamics
  in materials are widely studied at modern light sources and offer the pot
 ential to engineer new materials\, or understand chemical reactions and bi
 ological processes. The photon beams used for such experiments are themsel
 ves routinely characterized by photo-ionization based methods combined wit
 h time resolved streaking techniques. Maximizing the photon beam brightnes
 s relies on optimizing the electron accelerator performance. A new concept
  for measuring the charge density of the particle beams will be presented 
 that relies on tunnel ionization of a neutral gas by the electron beam’s
  transverse space charge field. By measuring the plasma dynamics including
  the plasma density\, kinetic energy distribution and arrival time distrib
 ution of the expanding ion cloud\, the charge density of a micron-cubed el
 ectron beam can be inferred and optimized. However\, when using intense el
 ectron beams to ionize a gas\, very different physics is manifested compar
 ed to photo-ionization. This is due to the large unipolar fields of the ch
 arged particle beam that impart a significant momentum to the plasma elect
 rons. As they escape with high radial velocities\, they leave the ions uns
 hielded. This non-neutral plasma undergoes Coulomb explosion and the resul
 ting dynamics offers new avenues for direct electron beam characterization
 . Using both analytic theory and highly sophisticated particle-in-cell sim
 ulations (using VSim and WARP)\, case studies were analyzed for electron b
 eams in conventional and advanced accelerators\, for different experimenta
 l conditions\, such as initial neutral gas density\, gas mixtures and elec
 tron beam properties. Due to the exponential dependency of the tunnel-ioni
 zation probability on the electric field strength\, it is shown that the m
 ethod has the potential to measure electron beams of sub-femtosecond in du
 ration focused down to sub-micrometer sizes. As such it provides a powerfu
 l noninvasive\, single-shot diagnostic for micron-cube electron beams\, in
 strumental to operation of advanced particle accelerators. We also note th
 at for ultra-short intense unipolar electron beams ionization quenching ma
 y be observed\, providing access to fundamental quantum mechanical questio
 ns. The elaborate simulation results and experimental planning at plasma w
 akefield accelerator at Berkeley lab (BELLA center) as well as RF-driven a
 ccelerator (LCLS machine) at SLAC laboratory will be presented.  \n 
LOCATION:ppb 019
STATUS:CONFIRMED
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