EM-PIC simulations of e-beam interaction with field emitted ions from bremsstrahlung targets

Conference · Thu Aug 13 04:00:00 EDT 1998

OSTI ID:292200

We investigate electron beam defocusing caused by field emitted ions from the bremsstrahlung target of a radiography machine using fully electromagnetic particle-in-cell simulations. This possibly deleterious effect is relevant to both current radiography machines (FXR) and machines being built (DARHT-2) or planned (AHF). A simple theory of the acceleration of ions desorbed from the heated target, and subsequent beam defocusing due to partial charge neutralization is in reasonable agreement with the more detailed simulations. For parameters corresponding to FXR (I{sub b}=2.3 kA, {epsilon}{sub b}=16 MeV), simulations assuming space-charge-limited emission of protons predict prompt beam defocusing. Time integrated spot-size measurement, however, is dominated by early-time small spot brightness, and so is not a sensitive diagnostic. Comparisons are made to available FXR data. We also investigate use of a recessed target geometry to mitigate field emitted ion acceleration; only modest improvements are predicted.

• Research Organization: Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 292200
• Report Number(s): UCRL-JC--130469; CONF-980827--; ON: DE98058638; BR: DP0102052; CNN: W-7405-Eng-48
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
BREMSSTRAHLUNG
COMPUTERIZED SIMULATION
ELECTRON BEAMS
ELECTRON-ION COLLISIONS
FIELD EMISSION
SPACE CHARGE
TARGETS