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Coherent Structures and Chaos in Beam Plasmas
AUTHOR(S)Chiping Chen Approved for public release; distribution unlimited.
S. FUNDING NUMBERS
F49620-97-1-0325 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)Air
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ABSTRACT (Maximum 200 words)This report summarizes our research carried out under the auspices of the above referenced grants from May 1, 1997 to December 31, 1999. The goal of this research is to investigate coherent structures and chaos in beam plasmas in regimes relevant to the development of advanced microwave/millimeter wave sources. Preprints and reprings describing detailed findings in recent investigations are provided in a compendium of 1997-2000 reprints in refereed journals at the end of the report. This report summarizes our research carried out under the auspices of the above referenced grant from May 1, 1997 to December 31, 1999. The goal of this research is to investigate coherent structures and chaos in beam plasmas in regimes relevant to the development of advanced microwave/millimeter wave sources. Preprints and reprints describing detailed findings in recent investigations are provided in a compendium of 1997-2000 reprints in refereed journals at the end of this report. The following is a brief summary of our research accomplishments in selected areas.
Mechanisms of Chaotic Electron Motion and Beam Halo Formation [1-3]An important issue in the design of HPM tubes is how to prevent high-intensity relativistic electron beams from forming halos because they cause electron beam losses and subsequent plasma formation, rf pulse shortening and rf breakdown [4]. Under the auspices of this grant, investigations were conducted of mechanisms by which chaotic particle motion and halo formation occurs [1][2][3].In particular, it was found [5,6] that there are two important mechanisms for chaotic particle motion and halo formation in high-intensity electron beams in such systems as high power klystrons. One mechanism is due to a root-mean-square (rms) mismatch between the beam and externally applied focusing field [5], The rms mismatch is induced by the bunching of the electron beam by intense rf (radiation phis electrostatic wave) fields inside the device. Above a certain threshold, rms mismatched electron beams produce pronounced (sizable) halos asymptotically. For high-intensity electron beams, the threshold occurs at the relative envelope mismatch of 42%, as predicated analytically and confirmed by self-consistent simulations in earlier work [7], The other mechanism is due to the subtle effect of a mismatch in the particle phase-space distribution (e.g., a nonuniform charge density distribution) under the rms matching condition [6]. In HPM tubes...