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SUMMARY:Coherent effects in atomic K-shell ionization and characteristic X
 -ray emission by ultrashort high-energy electron bunches
DTSTART;VALUE=DATE-TIME:20260923T125000Z
DTEND;VALUE=DATE-TIME:20260923T131000Z
DTSTAMP;VALUE=DATE-TIME:20260914T032424Z
UID:indico-contribution-550@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Vsevolod Skorobohatov ()\nThe coherent effects prese
 nt in atomic K-shell ionization and the subsequent emission of characteris
 tic X-ray radiation (CXR) induced by ultrashort relativistic electron bunc
 hes are investigated [1]. The approach distinguishing close and distant co
 llisions was applied to calculate the K-shell ionization cross section. Th
 e cross section associated with close collisions is independent on the num
 ber of electrons in the bunch and can be calculated using the approximatio
 n of hard binary electron-electron collisions. Meanwhile\, the cross secti
 on associated with distant collisions is affected by coherent effects and 
 was of primary interest. It was calculated based on the Weizsäcker-Willia
 ms method of equivalent photons.\n    \nIt was shown that the interference
  between the proper electromagnetic fields of single electrons can lead to
  a significant coherent enhancement of the ionization cross section in thi
 n light-element targets\, particularly beryllium and carbon. In particular
 \, the case of a microbunched beam was investigated using a periodically m
 odulated distribution of the bunch number of particles in longitudinal dir
 ection. According to calculations made for parameters of bunches achievabl
 e at modern X-ray free electron lasers\, a strong resonant amplification o
 f the cross section occurs. This leads to an enhancement of the ionization
  cross section by several orders of magnitude for a wide range of microbun
 ching periods.\n\nMoreover\, the analysis was extended to targets of arbit
 rary thickness to study the evolution of the K-shell ionization cross sect
 ion caused by the medium polarization (density effect) along the beam prop
 agation path. It was found that the cross section decreases with increasin
 g the depth of the beam penetration into the target\, reaching a plateau w
 hen the penetration depth significantly exceeds the absorption length of a
  photon with an energy equal to the K-shell ionization threshold. Furtherm
 ore\, it was shown that the main contribution to the CXR photons emitted f
 rom the target comes from a thin near-surface layer\, whose thickness can 
 be much smaller than the CXR attenuation length\, unlike in the case of a 
 single electron interacting with the target. The reasons for this are disc
 ussed.\n\nThe obtained results and the considered coherent effects could b
 e applied to the development of new techniques for diagnostics of paramete
 rs of subfemtosecond electron bunches.\n\nhttps://indico.bitp.kiev.ua/even
 t/18/contributions/550/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/550/
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