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1.
Phys Rev Lett ; 132(6): 065102, 2024 Feb 09.
Artigo em Inglês | MEDLINE | ID: mdl-38394591

RESUMO

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

2.
Rev Sci Instrum ; 94(5)2023 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-37219386

RESUMO

Resonance absorption (RA) occurs when a p-polarized electromagnetic wave, obliquely incident on an inhomogeneous plasma, tunnels past its turning point and resonantly excites an electron plasma wave (EPW) at the critical density. This phenomenon is important, for instance, in the direct drive approach to inertial fusion energy and is a particular example of a wider phenomenon in plasma physics known as mode conversion, which is crucial for heating magnetic fusion devices, such as tokamaks, via RF heating. Direct measurement of these RA-generated EPW accelerated hot electrons, with energy in the range of a few tens to a few hundreds of keV, is a challenging task due to the relatively low deflecting magnetic fields needed. The solution described here is a magnetic electron spectrometer (MES) with a continually changing magnetic field, lower at the entrance of the MES and gradually increasing toward the end, that enables the measurement of a wide spectral range of electrons with energies between 50 and 460 keV. Electron spectra taken in a LaserNetUS RA experiment were acquired from plasmas generated by irradiating polymer targets with the combination of an ∼300 ps pulse followed by a series of ten high intensity 50-200 fs duration laser pulses from the ALEPH laser at Colorado State University. The high intensity beam is designed as spike trains of uneven duration and delay pulses in order to modify the RA phenomenon.

3.
Phys Rev Lett ; 129(7): 075001, 2022 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-36018710

RESUMO

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion.

4.
Phys Rev E ; 104(3-2): 035201, 2021 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-34654095

RESUMO

The shape of the anisotropic velocity distribution function, beyond the realm of strict Maxwellians can play a significant role in determining the evolution of the Weibel instability dictating the dynamics of self-generated magnetic fields. For non-Maxwellian distribution functions, we show that the direction of the maximum growth rate wave vector changes with shape. We investigate different laser-plasma interaction model distributions which show that their Weibel generated magnetic fields may require closer scrutiny beyond the second moment (temperature) anisotropy ratio characterization.

6.
Phys Rev E ; 93: 043209, 2016 04.
Artigo em Inglês | MEDLINE | ID: mdl-27176420

RESUMO

Backward stimulated Raman and Brillouin scattering (SRS and SBS) are experimentally investigated by using two successive 1-µm, 1.5-ps FWHM laser pulses. The collinear pulses, separated by 3 or 6 ps and of moderate laser intensities (∼2×10^{16}Wcm^{-2}), are fired into a preionized He plasma of density ∼2.5-6×10^{19}cm^{-3}. The electron plasma waves and ion acoustic waves, respectively driven by SRS and SBS, are analyzed through space- and time-resolved Thomson scattering. Depending on the laser and plasma parameters, we observe the effect of the first pulse on the time-resolved SRS and SBS signals of the second pulse. The measurements are found to qualitatively agree with the results of a large-scale particle-in-cell simulation.

7.
Phys Rev Lett ; 113(4): 045002, 2014 Jul 25.
Artigo em Inglês | MEDLINE | ID: mdl-25105625

RESUMO

Stimulated Raman scattering (SRS) in its strongly nonlinear, kinetic regime is controlled by a technique of deterministic, strong temporal modulation and spatial scrambling of laser speckle patterns, called spike trains of uneven duration and delay (STUD) pulses [B. Afeyan and S. Hüller (unpublished)]. Kinetic simulations show that the proper use of STUD pulses decreases SRS reflectivity by more than an order of magnitude over random-phase-plate or induced-spatial-incoherence beams of the same average intensity and comparable bandwidth.

8.
Phys Rev Lett ; 94(22): 225003, 2005 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-16090406

RESUMO

Nested tungsten wire arrays (20-mm on 12-mm diam.) are shown for the first time to operate in a current-transfer mode at 16-19 MA, even for azimuthal interwire gaps of 0.2 mm that are the smallest typically used for any array experiment. After current transfer, the inner wire array shows discrete wire ablation and implosion characteristics identical to that of a single array, such as axially nonuniform ablation, delayed acceleration, and trailing mass and current. The presence of trailing mass from the outer and the inner arrays may play a role in determining nested array performance.

9.
Phys Rev Lett ; 86(17): 3787-90, 2001 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-11329324

RESUMO

Several models have been proposed to explain the broad spectral features characteristic of omega(0)/2 emission observed in laser-produced plasmas. In this article, the electromagnetic decay instability is examined as an alternative explanation for this emission. It is shown that the electromagnetic decay instability is able to explain some of the spectral features observed from laser-produced plasmas. In addition, the electromagnetic decay instability is consistent with two other features observed in experiments: the efficient generation of electromagnetic energy and the discrepancy in the levels of emission between the omega(0)/2 emission and the 3omega(0)/2 emission.

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