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Turnbull D, Katz J, Sherlock M, Divol L, Shaffer NR, Strozzi DJ, Colaïtis A, Edgell DH, Follett RK, McMillen KR, Michel P, Milder AL, Froula DH. Inverse Bremsstrahlung Absorption. PHYSICAL REVIEW LETTERS 2023; 130:145103. [PMID: 37084458 DOI: 10.1103/physrevlett.130.145103] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 03/20/2023] [Indexed: 05/03/2023]
Abstract
Inverse bremsstrahlung absorption was measured based on transmission through a finite-length plasma that was thoroughly characterized using spatially resolved Thomson scattering. Expected absorption was then calculated using the diagnosed plasma conditions while varying the absorption model components. To match data, it is necessary to account for (i) the Langdon effect; (ii) laser-frequency (rather than plasma-frequency) dependence in the Coulomb logarithm, as is typical of bremsstrahlung theories but not transport theories; and (iii) a correction due to ion screening. Radiation-hydrodynamic simulations of inertial confinement fusion implosions have to date used a Coulomb logarithm from the transport literature and no screening correction. We anticipate that updating the model for collisional absorption will substantially revise our understanding of laser-target coupling for such implosions.
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Affiliation(s)
- D Turnbull
- University of Rochester Laboratory for Laser Energetics, Rochester 14623, New York, USA
| | - J Katz
- University of Rochester Laboratory for Laser Energetics, Rochester 14623, New York, USA
| | - M Sherlock
- Lawrence Livermore National Laboratory, Livermore 94550, California, USA
| | - L Divol
- Lawrence Livermore National Laboratory, Livermore 94550, California, USA
| | - N R Shaffer
- University of Rochester Laboratory for Laser Energetics, Rochester 14623, New York, USA
| | - D J Strozzi
- Lawrence Livermore National Laboratory, Livermore 94550, California, USA
| | - A Colaïtis
- Centre Lasers Intenses et Applications, Talence 33400, France
| | - D H Edgell
- University of Rochester Laboratory for Laser Energetics, Rochester 14623, New York, USA
| | - R K Follett
- University of Rochester Laboratory for Laser Energetics, Rochester 14623, New York, USA
| | - K R McMillen
- University of Rochester Laboratory for Laser Energetics, Rochester 14623, New York, USA
| | - P Michel
- Lawrence Livermore National Laboratory, Livermore 94550, California, USA
| | - A L Milder
- University of Alberta, Edmonton, Alberta T6G 2R3, Canada
| | - D H Froula
- University of Rochester Laboratory for Laser Energetics, Rochester 14623, New York, USA
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Katz J, Turnbull D, Ivancic ST, Milder AL, Froula DH. Measurement of laser absorption in underdense plasmas using near-field imaging of the incident and transmitted beams. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2022; 93:123510. [PMID: 36586936 DOI: 10.1063/5.0100084] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Accepted: 11/23/2022] [Indexed: 06/17/2023]
Abstract
Measurements of laser absorption in high-temperature, underdense plasmas produced at the Omega Laser Facility are made using two near-field imaging detectors that diagnose the spatial profile and energy of the port P9 beam before and after it transmits through the plasma. The incident beam is sampled using a partial reflection from a full-aperture, (30 cm-diam) uncoated wedge pickoff located before the target chamber vacuum window and final focus lens assembly. A concave mirror reduces the reflected beam size, allowing it to be recorded directly using a charged-coupled device (CCD) camera. The P9 transmitted beam diagnostic (P9TBD) characterizes the transmitted light by terminating the expanded beam on a semi-transparent diffuser and imaging the illuminated surface using a lens and CCD camera. The P9TBD samples a numerical aperture twice as large as the input beam, allowing the energy of transmitted beams with moderate levels of beam spray to be measured accurately. Calibration shots with no plasma provide a path to infer absorption without absolute photometric calibration of either detector. The cross-calibration between the two detectors was measured to remain stable at ±200 ppm, enabling measurements of total beam absorption below 1% with ±0.07% error.
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Affiliation(s)
- J Katz
- Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299, USA
| | - D Turnbull
- Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299, USA
| | - S T Ivancic
- Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299, USA
| | - A L Milder
- Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299, USA
| | - D H Froula
- Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299, USA
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Turnbull D, Katz J, Hinkel DE, Michel P, Chapman T, Divol L, Kur E, MacLaren S, Milder AL, Rosen M, Shvydky A, Zimmerman GB, Froula DH. Beam Spray Thresholds in ICF-Relevant Plasmas. PHYSICAL REVIEW LETTERS 2022; 129:025001. [PMID: 35867466 DOI: 10.1103/physrevlett.129.025001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2022] [Accepted: 06/15/2022] [Indexed: 06/15/2023]
Abstract
Beam spray measurements suggest thresholds that are a factor of ≈2 to 15× less than expected based on the filamentation figure of merit often quoted in the literature. In this moderate-intensity regime, the relevant mechanism is forward stimulated Brillouin scattering. Both weak ion acoustic wave damping and thermal enhancement of ion acoustic waves contribute to the low thresholds. Forward stimulated Brillouin scattering imparts a redshift to the transmitted beam. Regarding the specific possibility of beam spray occurring outside the laser entrance holes of an indirectly driven hohlraum, this shift may be the most concerning feature owing to the high sensitivity of crossed-beam energy transfer to the interacting beam wavelengths in the subsequent overlap region.
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Affiliation(s)
- David Turnbull
- University of Rochester Laboratory for Laser Energetics, 250 E River Road, Rochester, New York 14623, USA
| | - Joseph Katz
- University of Rochester Laboratory for Laser Energetics, 250 E River Road, Rochester, New York 14623, USA
| | - Denise E Hinkel
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - Pierre Michel
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - Thomas Chapman
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - Laurent Divol
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - Eugene Kur
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - Steve MacLaren
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - Avram L Milder
- University of Rochester Laboratory for Laser Energetics, 250 E River Road, Rochester, New York 14623, USA
| | - Mordecai Rosen
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - Alex Shvydky
- University of Rochester Laboratory for Laser Energetics, 250 E River Road, Rochester, New York 14623, USA
| | - George B Zimmerman
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - Dustin H Froula
- University of Rochester Laboratory for Laser Energetics, 250 E River Road, Rochester, New York 14623, USA
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Milder AL, Katz J, Boni R, Palastro JP, Sherlock M, Rozmus W, Froula DH. Measurements of Non-Maxwellian Electron Distribution Functions and Their Effect on Laser Heating. PHYSICAL REVIEW LETTERS 2021; 127:015001. [PMID: 34270287 DOI: 10.1103/physrevlett.127.015001] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 02/15/2021] [Accepted: 05/21/2021] [Indexed: 06/13/2023]
Abstract
Electron velocity distribution functions driven by inverse bremsstrahlung heating are measured to be non-Maxwellian using a novel angularly resolved Thomson-scattering instrument and the corresponding reduction of electrons at slow velocities results in a ∼40% measured reduction in inverse bremsstrahlung absorption. The distribution functions are measured to be super-Gaussian in the bulk (v/v_{th}<3) and Maxwellian in the tail (v/v_{th}>3) when the laser heating rate dominates over the electron-electron thermalization rate. Simulations with the particle code quartz show the shape of the tail is dictated by the uniformity of the laser heating.
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Affiliation(s)
- A L Milder
- Department of Physics and Astronomy, University of Rochester, Rochester, New York 14623, USA
- Laboratory for Laser Energetics, 250 East River Road, Rochester, New York 14623, USA
| | - J Katz
- Laboratory for Laser Energetics, 250 East River Road, Rochester, New York 14623, USA
| | - R Boni
- Laboratory for Laser Energetics, 250 East River Road, Rochester, New York 14623, USA
| | - J P Palastro
- Laboratory for Laser Energetics, 250 East River Road, Rochester, New York 14623, USA
| | - M Sherlock
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
| | - W Rozmus
- Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
| | - D H Froula
- Department of Physics and Astronomy, University of Rochester, Rochester, New York 14623, USA
- Laboratory for Laser Energetics, 250 East River Road, Rochester, New York 14623, USA
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