Physics of Plasmas

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ISSN / EISSN : 1070-664X / 1089-7674
Published by: AIP Publishing (10.1063)
Total articles ≅ 25,024
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E. N. Loomis, H. F. Robey, , T. Morrow, D. S. Montgomery, D. C. Wilson, H. Xu, , , , et al.
Published: 1 June 2022
Physics of Plasmas, Volume 29; https://doi.org/10.1063/5.0081346

Abstract:
Implosions of Hohlraum-driven double shell targets as an alternative inertial confinement fusion concept are underway at the National Ignition Facility. The double shell system relies on a series of energy transfer processes starting from thermal x-ray absorption by the outer shell, followed by collisional transfer of kinetic energy to a heavy metal inner shell, and finally, conversion to the internal energy of the deuterium-tritium fuel. During each of these energy transfer stages, low-mode asymmetries can act to reduce the ideal transfer efficiency degrading double shell performance. Mechanisms, such as hard x-ray preheat from the Hohlraum, not only decrease the efficiency of kinetic energy transfer but may also be a source of low-mode asymmetry. In this article, we evaluate the shape transfer processes through the time of shell collision using two-dimensional integrated Hohlraum and capsule computations. We find that the dominant mode of the shape transfer is well described using a “radial impulse” model from the shape of the foam pressure reservoir. To evaluate the importance of preheat on inner shell shape, we also report on first measurements of Au L-shell preheat asymmetry in a double shell with a tungsten pusher. These measurements showed a 65% higher preheat velocity at the pole of the capsule relative to the equator. We also found that the experiments provided rigorous constraints by which to test the Hohlraum model settings that impact the amount and symmetry of Au L-shell preheat via the plasma conditions inside the outer cone Au bubble.
Sang-Min Byun, , Sang-Jun Lee, Min-Ki Jung, Kyoung-Jae Chung, , Deok-Kyu Kim, Sang June Hahn
Published: 1 June 2022
Physics of Plasmas, Volume 29; https://doi.org/10.1063/5.0076927

Abstract:
This paper investigates wire X-pinch (WXP) evolutions by the Eulerian resistive magneto-hydrodynamic code, STHENO, on 2D/3D geometry. A single-fluid two-temperature model is applied to pinch plasmas in local thermal equilibrium. The equation of state based on the Thomas–Fermi model is used to determine the ionization degree of the plasma. Electron internal energy is determined by the local density, temperature, and ionization potential with the average ion charge state. Lee–More–Desjarlais transport models are employed to obtain the thermal conductivities and resistivity for a non-ideal plasma. The radiation loss rate is calculated by the Bremsstrahlung and recombination emissivity within the ionization balance. The crossing point, which is the central part of the X-pinch, is assumed to be an axisymmetric configuration on a small computational domain in the RZ plane. The 2D simulation demonstrates that the micrometer size plasma column is elongated axially with the onset of the neck cascading structure. The radiation power is calculated and compared with the measured x-ray power from a modular X-pinch device (120-kA in 650-ns) at Seoul National University. The time evolution of the radiation power reproduces the trend of the measured x ray. 3D analyses are performed for the aluminum WXP configurations by varying wire numbers and cross-angles. The relation between the radiation performance and the numbers of wires reveals that the current density, rather than the line density, determines the central pinching condition. In addition, the multiple plasma instabilities (m = 0) near the central regions are found to degrade the radiation performance on the small cross-angle WXP.
K. L. Baker, O. Jones, C. Weber, D. Clark, P. K. Patel, C. A. Thomas, O. L. Landen, R. Nora, G. J. Anderson, , et al.
Published: 1 June 2022
Physics of Plasmas, Volume 29; https://doi.org/10.1063/5.0080732

Abstract:
A goal of the laser-based National Ignition Facility (NIF) is to increase the liberated fusion energy “yield” in inertial confinement fusion experiments well past the ignition threshold and the input laser energy. One method of increasing the yield, hydrodynamic scaling of current experiments, does not rely on improving compression or implosion velocity, but rather increases the scale of the implosion to increase hotspot areal density and confinement time. Indirect-drive ( Hohlraum driven) implosions carried out at two target sizes, 12.5% apart, have validated hydroscaling expectations. Moreover, extending comparisons to the best-performing implosions at five different capsule sizes shows that their performance also agrees well with hydroscaling expectations even though not direct hydroscales of one another. In the future, by switching to a reduced loss Hohlraum geometry, simulations indicate that we can drive 20% larger-scale implosions within the current power and energy limitations on the NIF. At the demonstrated compression and velocity of these smaller-scale implosions, these 1.2× hydroscaled implosions should put us well past the ignition threshold.
Zhiqiang Fan, Jun Sun, Yibing Cao, Ping Wu, Zhimin Song, Ruidong Hou, Yanchao Shi, Shuang Li
Published: 1 June 2022
Physics of Plasmas, Volume 29; https://doi.org/10.1063/5.0093129

Abstract:
An oversized Ku-band Cerenkov oscillator with pure TM01 mode output is proposed. By utilizing a separated slow-wave structure (SSWS), the resonant characteristic of the operating mode is preserved, whereas the resonant characteristics of the high order electromagnetic modes are destroyed. As a result, only the expected mode can be stimulated, and undesired beam–wave interactions are suppressed effectively. In terms of an oversized Cerenkov oscillator, the usage of SSWS shows great potential for obtaining pure operating mode output. By utilizing particle-in-cell simulation, microwaves with an output power of 4.5 GW and frequency of 14.1 GHz are obtained, when the beam voltage is 0.9 MeV, and the beam current is 12.9 kA. The percentage of the operating mode is up to 99.5% and exceeds 99% in a wide range of the beam voltage.
Published: 1 June 2022
Physics of Plasmas, Volume 29; https://doi.org/10.1063/5.0086700

Abstract:
We study theoretically and numerically the Raman backscattering process of a laser beam carrying an orbital angular momentum. By expanding the electromagnetic and electrostatic waves over the Laguerre–Gauss modes, we retrieve the strong dependence of the growth rate on the radial overlap of these functions. The presence of an orbital angular momentum in the laser beam results in a mitigation of the Raman backscattering by 30%. This is confirmed with three-dimensional particle-in-cell simulations. Both the theoretical description and numerical analysis show that the scattered electromagnetic wave is generated with an azimuthal order equal to the laser beam's.
, Maria C. Garcia
Published: 1 June 2022
Physics of Plasmas, Volume 29; https://doi.org/10.1063/5.0083766

Abstract:
Nonthermal atmospheric pressure plasmas transform input electrical energy efficiently into reactive species, charged particles, and photons. This “activated gas” is being investigated as solutions for a range of environmental and health problems facing society today. In this Perspective, we take a cursory look at a few of these societal problems and the reflected role that plasmas may play in charting the pathway to a solution buoyed by supporting research. Here, we survey the plasma-based opportunities in the removal of trace contaminants in water supporting methodologies such as water reuse, which addresses scarcity and pollution, the opportunity posed by plasmas-based chemical depolymerization for plastics recycling, and the application of plasmas for food security, which includes sterilization of foodstuffs and the improvement of crop yield. Finally, we also included a short review on how plasmas may help control disease spread. In each case, the scope of the problem is presented along with the potential plasma-based solution.
Ayesha Nanda,
Published: 1 June 2022
Physics of Plasmas, Volume 29; https://doi.org/10.1063/5.0088478

Abstract:
A generalization of electrical conductivity in a plasma confined in a dipole magnetic field, in the presence of temperature anisotropy is presented. The anisotropy governed by the magnetic field distribution is found to be significant in the strong field region, and has a considerable effect on Pedersen and longitudinal conductivity of electrons over Hall conductivity, whereas the effect of temperature anisotropy on Hall conductivity can be observed in the case of ions. The work reveals new features in the conductivity tensor arising due to the temperature anisotropy and bidirectional nature of the dipole field, by incorporating all possible particle drifts, which would be helpful to enhance the understanding of electrical conduction in both laboratory and space dipole plasmas.
, , , B. Chapman-Oplopoiou, M. Curie, M. Halfmoon, , M. Kotschenreuther, , , et al.
Published: 1 June 2022
Physics of Plasmas, Volume 29; https://doi.org/10.1063/5.0087403

Abstract:
This paper reports on the development of reduced models for electron temperature gradient (ETG) driven transport in the pedestal. Model development is enabled by a set of 61 nonlinear gyrokinetic simulations with input parameters taken from pedestals in a broad range of experimental scenarios. The simulation data have been consolidated in a new database for gyrokinetic simulation data, the multiscale gyrokinetic database (MGKDB), facilitating the analysis. The modeling approach may be considered a generalization of the standard quasilinear mixing length procedure. The parameter η, the ratio of the density to temperature gradient scale length, emerges as the key parameter for formulating an effective saturation rule. With a single order-unity fitting coefficient, the model achieves an error of 15%. A similar model for ETG particle flux is also described. We also present simple algebraic expressions for the transport informed by an algorithm for symbolic regression.
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