Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session GI01: Inertial Confinement Fusion I
9:30 AM–12:45 PM,
Tuesday, October 18, 2022
Room: Ballroom 100 A
Chair: Brian Spears, LLNL
Abstract: GI01.00004 : Theory and simulation of cross-beam energy transfer mitigation through increased laser bandwidth*
11:00 AM–11:30 AM
Presenter:
Alexander Seaton
(Los Alamos National Laboratory)
Authors:
Alexander Seaton
(Los Alamos National Laboratory)
Lin Yin
(Los Alamos Natl Lab)
Russell K Follett
(Laboratory for Laser Energetics - Rochester)
Ari Le
(Los Alamos National Laboratory)
Brian J Albright
(Los Alamos Natl Lab)
It is found that CBET is most effectively suppressed when laser bandwidth exceeds the ion- acoustic wave (IAW) frequency. Such bandwidths reduce the coupling efficiency of laser beams with IAWs and can allow reverse (from lower frequency to higher frequency beams) transfer to occur, which reduces the net energy transfer rapidly as bandwidth is increased. The CBET gain exponent in this regime scales with bandwidth (Δω) as Δω-3 for Gaussian or Lorentzian laser spectra. However, linear analysis also finds that the IAW energy density scales as Δω-1, implying that nonlinear effects may be more difficult to control than the CBET scaling would suggest. Indeed, ion-trapping-induced nonlinear effects, such as modification of the ion wave dispersion, the two-ion wave decay, and ion wave self-focusing, lead to significant departures from linear theory. These nonlinearities can be mitigated through the reduction of intensity spikes in the laser drive, for example via smoothing by spectral dispersion.
[1] A. G. Seaton et al., “Cross-beam energy transfer in direct-drive ICF. II. Theory and simulation of mitigation through increased laser bandwidth”, Physics of Plasmas, 29(4), 042707 (2022).
*This work was supported by LANL ICF Program. VPIC simulations were run on LANL Institutional Computing Clusters.
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