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Title: Mitigating chromatic effects on the transverse focusing of intense charged particle beams for heavy ion fusion

Authors:
; ;
Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1152653
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment; Journal Volume: 733
Country of Publication:
United States
Language:
English

Citation Formats

James M.,Mitrani, Igor D.,Kaganovich, and Ronald C.,Davidson. Mitigating chromatic effects on the transverse focusing of intense charged particle beams for heavy ion fusion. United States: N. p., 2014. Web. doi:10.1016/j.nima.2013.05.093.
James M.,Mitrani, Igor D.,Kaganovich, & Ronald C.,Davidson. Mitigating chromatic effects on the transverse focusing of intense charged particle beams for heavy ion fusion. United States. doi:10.1016/j.nima.2013.05.093.
James M.,Mitrani, Igor D.,Kaganovich, and Ronald C.,Davidson. Wed . "Mitigating chromatic effects on the transverse focusing of intense charged particle beams for heavy ion fusion". United States. doi:10.1016/j.nima.2013.05.093.
@article{osti_1152653,
title = {Mitigating chromatic effects on the transverse focusing of intense charged particle beams for heavy ion fusion},
author = {James M.,Mitrani and Igor D.,Kaganovich and Ronald C.,Davidson},
abstractNote = {},
doi = {10.1016/j.nima.2013.05.093},
journal = {Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment},
number = ,
volume = 733,
place = {United States},
year = {Wed Jan 01 00:00:00 EST 2014},
month = {Wed Jan 01 00:00:00 EST 2014}
}
  • A fi nal focusing scheme designed to minimize chromatic effects is discussed. The Neutralized Drift Compression Experiment-II (NDCX-II) will apply a velocity tilt for longitudinal bunch compression, and a fi nal focusing solenoid (FFS) for transverse bunch compression. In the beam frame, neutralized drift compression causes a suffi ciently large spread in axial momentum, pz , resulting in chromatic effects to the fi nal focal spot during transverse bunch compression. Placing a weaker solenoid upstream of a stronger fi nal focusing solenoid (FFS) mitigates chromatic effects and improves transverse focusing by a factor of approximately 2-4 for appropriate NDCX-II parameters.
  • Recent heavy ion fusion target studies show that it is possible to achieve ignition with direct drive and energy gain larger than 100 at 1MJ. To realize these advanced, high-gain schemes based on direct drive, it is necessary to develop a reliable beam smoothing technique to mitigate instabilities and facilitate uniform deposition on the target. The dynamics of the beam centroid can be explored as a possible beam smoothing technique to achieve a uniform illumination over a suitably chosen region of the target. The basic idea of this technique is to induce an oscillatory motion of the centroid for eachmore » transverse slice of the beam in such a way that the centroids of different slices strike different locations on the target. The centroid dynamics is controlled by a set of biased electrical plates called 'wobblers'. Using a model based on moments of the Vlasov-Maxwell equations, we show that the wobbler deflection force acts only on the centroid motion, and that the envelope dynamics are independent of the wobbler fields. If the conducting wall is far away from the beam, then the envelope dynamics and centroid dynamics are completely decoupled. This is a preferred situation for the beam wobbling technique, because the wobbler system can be designed to generate the desired centroid motion on the target without considering its effects on the envelope and emittance. A conceptual design of the wobbler system for a heavy ion fusion driver is briefly summarized.« less
  • Test particle motion is analyzed analytically and numerically in the field configuration consisting of the equilibrium self-electric and self-magnetic fields of a well-matched, thin, continuous, intense charged-particle beam and an applied periodic focusing solenoidal magnetic field. The self fields are determined self-consistently, assuming the beam to have a uniform-density, rigid-rotor Vlasov equilibrium distribution. Using the Hamilton{endash}Jacobi method, the betatron oscillations of test particles in the average self fields and applied focusing field are analyzed, and the nonlinear resonances induced by periodic modulations in the self fields and applied field are determined. The Poincar{acute e} surface-of-section method is used to analyzemore » numerically the phase-space structure for test particle motion outside the outermost envelope of the beam over a wide range of system parameters. For vacuum phase advance {sigma}{sub v}=80{degree}, it is found that the phase-space structure is almost entirely regular at low beam intensity (phase advance {sigma}{approx_gt}70{degree}, say), whereas at moderate beam intensity (30{degree}{approx_lt}{sigma}{approx_lt}70{degree}), nonlinear resonances appear, the most pronounced of which is the third-order primary nonlinear resonance. As the beam intensity is further increased ({sigma}{approx_lt}30{degree}), the widths of the higher-order nonlinear resonances increase, and the chaotic region of phase space increases in size. Furthermore, the many chaotic layers associated with the separatrices of the primary and secondary nonlinear resonances are still divided by the remaining invariant Kolmogorov{endash}Arnold{endash}Moser surfaces, even at very high beam intensities. The implications of the rich nonlinear resonance structure and chaotic particle motion found in the present test-particle studies are discussed in the context of halo formation. {copyright} {ital 1999 American Institute of Physics.}« less