Pub Date : 2024-03-07DOI: 10.1017/s0022377824000266
Kazunori Takahashi
Influence of the local-ionization-induced neutral depletion on the thrust imparted by the magnetic nozzle plasma thruster is discussed by simply considering reduction of the neutral density due to the ionization in the thruster model combining the global source model and the one-dimensional magnetic nozzle model. When increasing the rf power, it is shown that the increase rate of the plasma density is reduced, while the electron temperature continues to increase due to a decrease in the neutral density. Since the major components of the thrust are originated from the electron pressures in the source and in the magnetic nozzle, the increase in the electron temperature contributes to the increase in the thrust in addition to the gradual density increase by the rf power. The model qualitatively predicts the reduction of the thruster efficiency by the neutral depletion for the high-power condition, compared with the constant neutral density model.
{"title":"Modelling a thrust imparted by a highly ionized magnetic nozzle rf plasma thruster","authors":"Kazunori Takahashi","doi":"10.1017/s0022377824000266","DOIUrl":"https://doi.org/10.1017/s0022377824000266","url":null,"abstract":"<p>Influence of the local-ionization-induced neutral depletion on the thrust imparted by the magnetic nozzle plasma thruster is discussed by simply considering reduction of the neutral density due to the ionization in the thruster model combining the global source model and the one-dimensional magnetic nozzle model. When increasing the rf power, it is shown that the increase rate of the plasma density is reduced, while the electron temperature continues to increase due to a decrease in the neutral density. Since the major components of the thrust are originated from the electron pressures in the source and in the magnetic nozzle, the increase in the electron temperature contributes to the increase in the thrust in addition to the gradual density increase by the rf power. The model qualitatively predicts the reduction of the thruster efficiency by the neutral depletion for the high-power condition, compared with the constant neutral density model.</p>","PeriodicalId":16846,"journal":{"name":"Journal of Plasma Physics","volume":"142 1","pages":""},"PeriodicalIF":2.5,"publicationDate":"2024-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140055895","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-07DOI: 10.1017/s0022377824000217
Sergei R. Kamaletdinov, Ivan Y. Vasko, Anton V. Artemyev
<p>We present a theoretical analysis of electron pitch-angle scattering by ion-acoustic electrostatic fluctuations present in the Earth's bow shock and, presumably, collisionless shocks in general. We numerically simulate electron interaction with a single wave packet to demonstrate the scattering through phase bunching and phase trapping and quantify electron pitch-angle scattering in dependence on the wave amplitude and wave normal angle to the local magnetic field. The iterative mapping technique is used to model pitch-angle scattering of electrons by a large number of wave packets, which have been reported in the Earth's bow shock. Assuming that successive electron scatterings are not correlated, we revealed that the long-term dynamics of electrons is diffusive. The diffusion coefficient depends on the ratio <span><span><span data-mathjax-type="texmath"><span>$varPhi _0/W$</span></span><img data-mimesubtype="png" data-type="" src="https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline1.png"/></span></span> between the wave packet amplitude and electron energy, <span><span><span data-mathjax-type="texmath"><span>$Dpropto (varPhi _0/W)^{nu }$</span></span><img data-mimesubtype="png" data-type="" src="https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline2.png"/></span></span>. A quasi-linear scaling (<span><span><span data-mathjax-type="texmath"><span>$nu approx 2$</span></span><img data-mimesubtype="png" data-type="" src="https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline3.png"/></span></span>) is observed for sufficiently small wave amplitudes, <span><span><span data-mathjax-type="texmath"><span>$varPhi _0lesssim 10^{-3}W$</span></span><img data-mimesubtype="png" data-type="" src="https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline4.png"/></span></span>, while the diffusion is nonlinear (<span><span><span data-mathjax-type="texmath"><span>$1<nu <2$</span></span><img data-mimesubtype="png" data-type="" src="https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline5.png"/></span></span>) above this threshold. We show that pitch-angle diffusion of <span><span><span data-mathjax-type="texmath"><span>${lesssim }1$</span></span><img data-mimesubtype="png" data-type="" src="https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline6.png"/></span></span> keV electrons in the Earth's bow shock can be nonlinear. The corresponding diffusion coefficient scales with the intensity <span><span><span data-mathjax-type="texmath"><span>$E_{w}^{2}$<
{"title":"Nonlinear electron scattering by electrostatic waves in collisionless shocks","authors":"Sergei R. Kamaletdinov, Ivan Y. Vasko, Anton V. Artemyev","doi":"10.1017/s0022377824000217","DOIUrl":"https://doi.org/10.1017/s0022377824000217","url":null,"abstract":"<p>We present a theoretical analysis of electron pitch-angle scattering by ion-acoustic electrostatic fluctuations present in the Earth's bow shock and, presumably, collisionless shocks in general. We numerically simulate electron interaction with a single wave packet to demonstrate the scattering through phase bunching and phase trapping and quantify electron pitch-angle scattering in dependence on the wave amplitude and wave normal angle to the local magnetic field. The iterative mapping technique is used to model pitch-angle scattering of electrons by a large number of wave packets, which have been reported in the Earth's bow shock. Assuming that successive electron scatterings are not correlated, we revealed that the long-term dynamics of electrons is diffusive. The diffusion coefficient depends on the ratio <span><span><span data-mathjax-type=\"texmath\"><span>$varPhi _0/W$</span></span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline1.png\"/></span></span> between the wave packet amplitude and electron energy, <span><span><span data-mathjax-type=\"texmath\"><span>$Dpropto (varPhi _0/W)^{nu }$</span></span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline2.png\"/></span></span>. A quasi-linear scaling (<span><span><span data-mathjax-type=\"texmath\"><span>$nu approx 2$</span></span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline3.png\"/></span></span>) is observed for sufficiently small wave amplitudes, <span><span><span data-mathjax-type=\"texmath\"><span>$varPhi _0lesssim 10^{-3}W$</span></span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline4.png\"/></span></span>, while the diffusion is nonlinear (<span><span><span data-mathjax-type=\"texmath\"><span>$1<nu <2$</span></span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline5.png\"/></span></span>) above this threshold. We show that pitch-angle diffusion of <span><span><span data-mathjax-type=\"texmath\"><span>${lesssim }1$</span></span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240306134914101-0214:S0022377824000217:S0022377824000217_inline6.png\"/></span></span> keV electrons in the Earth's bow shock can be nonlinear. The corresponding diffusion coefficient scales with the intensity <span><span><span data-mathjax-type=\"texmath\"><span>$E_{w}^{2}$<","PeriodicalId":16846,"journal":{"name":"Journal of Plasma Physics","volume":"118 1","pages":""},"PeriodicalIF":2.5,"publicationDate":"2024-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140055974","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A modulational instability of nonlinearly interacting electron whistlers and magnetosonic perturbations is studied in the present paper. For typical parameters, there is no modulational instability. However, modulational instability appears in special cases. For example, when the whistler wavenumber is small enough, there is modulational instability. Its growth rate decreases as the angle between the external magnetic field and the perturbed wave's direction increases, while it increases as the whistler wavenumber increases. It is also found that there is no modulational instability when the whistler wavenumber is larger than a critical value ($k_0 > 0.05$), in which the perturbed wave frequency increases as the angle between the external magnetic field and the perturbed wave's direction increases when the angle between the external magnetic field and the perturbed wave's direction is large enough. Whereas, the perturbed wave frequency first increases as the whistler wavenumber increases, reaches a peak value and then decreases as whistler wavenumber increases.
{"title":"Modulational instability of the interacting electron whistlers and magnetosonic perturbations","authors":"Jiao-Jiao Cheng, Fang-Ping Wang, Zhong-Zheng Li, Wen-Shan Duan","doi":"10.1017/s002237782400014x","DOIUrl":"https://doi.org/10.1017/s002237782400014x","url":null,"abstract":"A modulational instability of nonlinearly interacting electron whistlers and magnetosonic perturbations is studied in the present paper. For typical parameters, there is no modulational instability. However, modulational instability appears in special cases. For example, when the whistler wavenumber is small enough, there is modulational instability. Its growth rate decreases as the angle between the external magnetic field and the perturbed wave's direction increases, while it increases as the whistler wavenumber increases. It is also found that there is no modulational instability when the whistler wavenumber is larger than a critical value (<jats:inline-formula> <jats:alternatives> <jats:tex-math>$k_0 > 0.05$</jats:tex-math> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S002237782400014X_inline1.png\" /> </jats:alternatives> </jats:inline-formula>), in which the perturbed wave frequency increases as the angle between the external magnetic field and the perturbed wave's direction increases when the angle between the external magnetic field and the perturbed wave's direction is large enough. Whereas, the perturbed wave frequency first increases as the whistler wavenumber increases, reaches a peak value and then decreases as whistler wavenumber increases.","PeriodicalId":16846,"journal":{"name":"Journal of Plasma Physics","volume":"1 1","pages":""},"PeriodicalIF":2.5,"publicationDate":"2024-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140006685","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-27DOI: 10.1017/s0022377824000229
Felipe A. Asenjo
It is known that a nonlinear Schrödinger equation describes the self-modulation of a large amplitude circularly polarized wave in relativistic electron–positron plasmas in the weakly and strongly magnetized limits. Here, we show that such an equation can be written as a modified second Painlevé equation, producing accelerated propagating wave solutions for those nonlinear plasmas. This solution even allows the plasma wave to reverse its direction of propagation. The acceleration parameter depends on the plasma magnetization. This accelerating solution is different to the usual soliton solution propagating at constant speed.
{"title":"Accelerating self-modulated nonlinear waves in weakly and strongly magnetized relativistic plasmas","authors":"Felipe A. Asenjo","doi":"10.1017/s0022377824000229","DOIUrl":"https://doi.org/10.1017/s0022377824000229","url":null,"abstract":"It is known that a nonlinear Schrödinger equation describes the self-modulation of a large amplitude circularly polarized wave in relativistic electron–positron plasmas in the weakly and strongly magnetized limits. Here, we show that such an equation can be written as a modified second Painlevé equation, producing accelerated propagating wave solutions for those nonlinear plasmas. This solution even allows the plasma wave to reverse its direction of propagation. The acceleration parameter depends on the plasma magnetization. This accelerating solution is different to the usual soliton solution propagating at constant speed.","PeriodicalId":16846,"journal":{"name":"Journal of Plasma Physics","volume":"14 1","pages":""},"PeriodicalIF":2.5,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140006793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-27DOI: 10.1017/s0022377824000151
Daniel W. Dudt, Alan G. Goodman, Rory Conlin, Dario Panici, Egemen Kolemen
Omnigenity is a desirable property of toroidal magnetic fields that ensures confinement of trapped particles. Confining charged particles is a basic requirement for any fusion power plant design, but it can be difficult to satisfy with the non-axisymmetric magnetic fields used by the stellarator approach. Every ideal magnetohydrodynamic equilibrium previously found to approximate omnigenity has been either axisymmetric, quasi-symmetric or has poloidally closed contours of magnetic field strength $B$. However, general omnigenous equilibria are a much larger design space than these subsets. A new model is presented and employed in the DESC stellarator optimization suite to represent and discover the full parameter space of omnigenous equilibria. Although exact omnigenity aside from quasi-symmetry is impossible, these results reveal that excellent particle confinement can be achieved in practice. Examples far from quasi-symmetry with poloidally, helically and toroidally closed $B$ contours are attained with DESC and shown to have low neoclassical collisional transport and fast particle losses.
{"title":"Magnetic fields with general omnigenity","authors":"Daniel W. Dudt, Alan G. Goodman, Rory Conlin, Dario Panici, Egemen Kolemen","doi":"10.1017/s0022377824000151","DOIUrl":"https://doi.org/10.1017/s0022377824000151","url":null,"abstract":"Omnigenity is a desirable property of toroidal magnetic fields that ensures confinement of trapped particles. Confining charged particles is a basic requirement for any fusion power plant design, but it can be difficult to satisfy with the non-axisymmetric magnetic fields used by the stellarator approach. Every ideal magnetohydrodynamic equilibrium previously found to approximate omnigenity has been either axisymmetric, quasi-symmetric or has poloidally closed contours of magnetic field strength <jats:inline-formula> <jats:alternatives> <jats:tex-math>$B$</jats:tex-math> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022377824000151_inline1.png\" /> </jats:alternatives> </jats:inline-formula>. However, general omnigenous equilibria are a much larger design space than these subsets. A new model is presented and employed in the DESC stellarator optimization suite to represent and discover the full parameter space of omnigenous equilibria. Although exact omnigenity aside from quasi-symmetry is impossible, these results reveal that excellent particle confinement can be achieved in practice. Examples far from quasi-symmetry with poloidally, helically and toroidally closed <jats:inline-formula> <jats:alternatives> <jats:tex-math>$B$</jats:tex-math> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022377824000151_inline2.png\" /> </jats:alternatives> </jats:inline-formula> contours are attained with DESC and shown to have low neoclassical collisional transport and fast particle losses.","PeriodicalId":16846,"journal":{"name":"Journal of Plasma Physics","volume":"28 1","pages":""},"PeriodicalIF":2.5,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140006799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-26DOI: 10.1017/s0022377824000023
A.V. Tykhyy, Ya.I. Kolesnichenko
Recently, stochastic motion of 3.5-MeV alpha particles with orbits that vary between locally trapped and locally passing states (transitioning particles) in a Helias reactor was observed numerically. This validated the theoretical predictions that (i) the stochastic diffusion represents a mechanism of considerable delayed loss of fast ions in quasi-isodynamic stellarators and (ii) it is possible to prevent the escape of particles to the wall by closing the separatrix between the locally trapped and passing states. It was concluded that, in principle, the separatrix could be made closed, resulting in a reduction of fast ion losses, by compensating for the effect of the helical component of the magnetic field $(1, 1)$ with an enhanced ‘anti-helical’ harmonic $(1, -1)$; the enlargement of this harmonic was proposed previously for other reasons. This possibility is explored in this work. Equations of previous relevant works were generalised to include the $(1, -1)$ harmonic. Calculations were carried out for several magnitudes of the ratio of anti-helical to helical magnetic field harmonics. Positive effects were found already at the smallest anti-helical harmonic considered: when the latter ratio is 0.25, transitioning particles with the smallest and intermediate pitch parameters are confined and, moreover, their fraction decreased. When the ratio is 0.85, almost all transitioning particles are confined and their fraction is minimal; well-confined localised orbits dominate at the smallest pitch parameters.
{"title":"Confinement of transitioning particles in bi-helical Wendelstein-type configurations","authors":"A.V. Tykhyy, Ya.I. Kolesnichenko","doi":"10.1017/s0022377824000023","DOIUrl":"https://doi.org/10.1017/s0022377824000023","url":null,"abstract":"<p>Recently, stochastic motion of 3.5-MeV alpha particles with orbits that vary between locally trapped and locally passing states (transitioning particles) in a Helias reactor was observed numerically. This validated the theoretical predictions that (i) the stochastic diffusion represents a mechanism of considerable delayed loss of fast ions in quasi-isodynamic stellarators and (ii) it is possible to prevent the escape of particles to the wall by closing the separatrix between the locally trapped and passing states. It was concluded that, in principle, the separatrix could be made closed, resulting in a reduction of fast ion losses, by compensating for the effect of the helical component of the magnetic field <span><span><span data-mathjax-type=\"texmath\"><span>$(1, 1)$</span></span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240223170730571-0694:S0022377824000023:S0022377824000023_inline1.png\"/></span></span> with an enhanced ‘anti-helical’ harmonic <span><span><span data-mathjax-type=\"texmath\"><span>$(1, -1)$</span></span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240223170730571-0694:S0022377824000023:S0022377824000023_inline2.png\"/></span></span>; the enlargement of this harmonic was proposed previously for other reasons. This possibility is explored in this work. Equations of previous relevant works were generalised to include the <span><span><span data-mathjax-type=\"texmath\"><span>$(1, -1)$</span></span><img data-mimesubtype=\"png\" data-type=\"\" src=\"https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20240223170730571-0694:S0022377824000023:S0022377824000023_inline3.png\"/></span></span> harmonic. Calculations were carried out for several magnitudes of the ratio of anti-helical to helical magnetic field harmonics. Positive effects were found already at the smallest anti-helical harmonic considered: when the latter ratio is 0.25, transitioning particles with the smallest and intermediate pitch parameters are confined and, moreover, their fraction decreased. When the ratio is 0.85, almost all transitioning particles are confined and their fraction is minimal; well-confined localised orbits dominate at the smallest pitch parameters.</p>","PeriodicalId":16846,"journal":{"name":"Journal of Plasma Physics","volume":"27 1","pages":""},"PeriodicalIF":2.5,"publicationDate":"2024-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139967515","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
BOUT++ turbulence simulations were performed to investigate the impact of turbulence spreading on the edge localized mode (ELM) size and divertor heat flux width <jats:inline-formula> <jats:alternatives> <jats:tex-math>$({lambda _q})$</jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022377824000199_inline1.png" /> </jats:alternatives> </jats:inline-formula> broadening in small ELM regimes. This study is motivated by EAST experiments. BOUT++ linear simulations of a pedestal radial electric field (<jats:italic>E<jats:sub>r</jats:sub></jats:italic>) scan show that the dominant toroidal number mode (<jats:italic>n</jats:italic>) shifts from high-<jats:italic>n</jats:italic> to low-<jats:italic>n</jats:italic>, with a narrow mode spectrum, and the maximum linear growth rate increases as the pedestal <jats:italic>E<jats:sub>r</jats:sub></jats:italic> well deepens. The nonlinear simulations show that as the net <jats:italic>E</jats:italic> × <jats:italic>B</jats:italic> pedestal flow increases, the pressure fluctuation level and its inward penetration beyond the top of the pedestal both increase. This leads to a transition from small ELMs to large ELMs. Both inward and outward turbulence spreading are sensitive to the scrape-off-layer (SOL) plasma profiles. The inward turbulence spreading increases for the steep SOL profiles, leading to increasing pedestal energy loss in the small ELM regime. The SOL width <jats:inline-formula> <jats:alternatives> <jats:tex-math>$({lambda _q})$</jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022377824000199_inline2.png" /> </jats:alternatives> </jats:inline-formula> is significantly broadened progressing from the ELM-free to small ELM regime, due to the onset of strong radial turbulent transport. The extent of the SOL width <jats:inline-formula> <jats:alternatives> <jats:tex-math>$({lambda _q})$</jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022377824000199_inline3.png" /> </jats:alternatives> </jats:inline-formula> broadening depends strongly on outward turbulence spreading. The fluctuation energy intensity flux <jats:inline-formula> <jats:alternatives> <jats:tex-math>${varGamma _varepsilon }$</jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022377824000199_inline4.png" /> </jats:alternatives> </jats:inline-formula> at the separatrix can be enhanced by increasing either pedestal <jats:italic>E<jats:sub>r</jats:sub></jats:italic> flow shear or local SOL pressure gradient. The <jats:inline-formula> <jats:alternatives> <jats:tex-math>${lambda _q}$</jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0022377824000199_inline5.png" /> </jats:alternatives> </jats:inline-formula> is broadened as the fluctuation ene
进行了BOUT++湍流模拟，以研究湍流扩散对边缘局部模式（ELM）尺寸和小ELM状态下分流器热通量宽度$({lambda _q})$拓宽的影响。这项研究的动机来自 EAST 实验。基座径向电场（Er）扫描的BOUT++线性模拟表明，主要环形数模（n）从高n转变为低n，模谱较窄，最大线性增长率随着基座Er井的加深而增加。非线性模拟显示，随着 E × B 基座净流的增加，压力波动水平及其向基座顶部以外的内穿透力都会增加。这导致小 ELM 向大 ELM 过渡。向内和向外的湍流扩散对刮离层（SOL）等离子体剖面都很敏感。陡峭的 SOL 剖面会增加向内的湍流扩散，从而导致小 ELM 状态下基座能量损失的增加。SOL 宽度 $({lambda _q})$在从无 ELM 到小 ELM 状态的过程中明显变宽，这是由于开始出现强径向湍流输运。SOL宽度$({lambda _q})$的扩大程度在很大程度上取决于向外的湍流扩散。在分离矩阵处的波动能量强度通量${varGamma _varepsilon }$可以通过增加基底二流剪切力或局部SOL压力梯度来增强。随着最后一个近通量面（LCFS）上波动能量强度通量 ${varGamma _varepsilon }$ 的增加，${lambda _q}$ 的范围也会扩大。局部 SOL E × B 流切变将抑制湍流向外扩展以及相关的热通量宽度扩大。在 H 模式下运行小 ELM 有可能解决两个关键问题：减小 ELM 尺寸和拓宽 SOL 宽度。
{"title":"Turbulence spreading effects on the ELM size and SOL width","authors":"Nami Li, X.Q. Xu, P.H. Diamond, Y.F. Wang, X. Lin, N. Yan, G.S. Xu","doi":"10.1017/s0022377824000199","DOIUrl":"https://doi.org/10.1017/s0022377824000199","url":null,"abstract":"BOUT++ turbulence simulations were performed to investigate the impact of turbulence spreading on the edge localized mode (ELM) size and divertor heat flux width <jats:inline-formula> <jats:alternatives> <jats:tex-math>$({lambda _q})$</jats:tex-math> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022377824000199_inline1.png\" /> </jats:alternatives> </jats:inline-formula> broadening in small ELM regimes. This study is motivated by EAST experiments. BOUT++ linear simulations of a pedestal radial electric field (<jats:italic>E<jats:sub>r</jats:sub></jats:italic>) scan show that the dominant toroidal number mode (<jats:italic>n</jats:italic>) shifts from high-<jats:italic>n</jats:italic> to low-<jats:italic>n</jats:italic>, with a narrow mode spectrum, and the maximum linear growth rate increases as the pedestal <jats:italic>E<jats:sub>r</jats:sub></jats:italic> well deepens. The nonlinear simulations show that as the net <jats:italic>E</jats:italic> × <jats:italic>B</jats:italic> pedestal flow increases, the pressure fluctuation level and its inward penetration beyond the top of the pedestal both increase. This leads to a transition from small ELMs to large ELMs. Both inward and outward turbulence spreading are sensitive to the scrape-off-layer (SOL) plasma profiles. The inward turbulence spreading increases for the steep SOL profiles, leading to increasing pedestal energy loss in the small ELM regime. The SOL width <jats:inline-formula> <jats:alternatives> <jats:tex-math>$({lambda _q})$</jats:tex-math> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022377824000199_inline2.png\" /> </jats:alternatives> </jats:inline-formula> is significantly broadened progressing from the ELM-free to small ELM regime, due to the onset of strong radial turbulent transport. The extent of the SOL width <jats:inline-formula> <jats:alternatives> <jats:tex-math>$({lambda _q})$</jats:tex-math> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022377824000199_inline3.png\" /> </jats:alternatives> </jats:inline-formula> broadening depends strongly on outward turbulence spreading. The fluctuation energy intensity flux <jats:inline-formula> <jats:alternatives> <jats:tex-math>${varGamma _varepsilon }$</jats:tex-math> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022377824000199_inline4.png\" /> </jats:alternatives> </jats:inline-formula> at the separatrix can be enhanced by increasing either pedestal <jats:italic>E<jats:sub>r</jats:sub></jats:italic> flow shear or local SOL pressure gradient. The <jats:inline-formula> <jats:alternatives> <jats:tex-math>${lambda _q}$</jats:tex-math> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022377824000199_inline5.png\" /> </jats:alternatives> </jats:inline-formula> is broadened as the fluctuation ene","PeriodicalId":16846,"journal":{"name":"Journal of Plasma Physics","volume":"1 1","pages":""},"PeriodicalIF":2.5,"publicationDate":"2024-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139955888","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-21DOI: 10.1017/s0022377823001411
S.M. Brask, S. Marholm, W.J. Miloch, R. Marchand
We investigate the effects of different guard geometries on the currents to needle-type Langmuir probes. The results are based on particle-in-cell numerical simulations. We show that if the guard length is less than 6–8 Debye lengths there can be a significant effect on the currents to the probe. A guard radius should not be larger than the Debye length, otherwise it can also significantly affect the currents. However, since guard radii are often close to the probe radius, the second condition is usually satisfied.
{"title":"Effects of guard and boom on needle Langmuir probes studied with particle-in-cell simulations","authors":"S.M. Brask, S. Marholm, W.J. Miloch, R. Marchand","doi":"10.1017/s0022377823001411","DOIUrl":"https://doi.org/10.1017/s0022377823001411","url":null,"abstract":"We investigate the effects of different guard geometries on the currents to needle-type Langmuir probes. The results are based on particle-in-cell numerical simulations. We show that if the guard length is less than 6–8 Debye lengths there can be a significant effect on the currents to the probe. A guard radius should not be larger than the Debye length, otherwise it can also significantly affect the currents. However, since guard radii are often close to the probe radius, the second condition is usually satisfied.","PeriodicalId":16846,"journal":{"name":"Journal of Plasma Physics","volume":"29 1","pages":""},"PeriodicalIF":2.5,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139921388","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-21DOI: 10.1017/s0022377824000011
A.A. Frolov
The theory of the terahertz (THz) waves emission from a near-critical plasma slab under the action of the focused p-polarized laser pulse is developed. The spectral, angular and energy characteristics of the THz signal are studied as functions of the focusing degree and the incidence angle of laser radiation, as well as the density and thickness of the plasma slab. It is shown that the extremely strong increase in the energy of the THz signal (up to millijoule level) and conversion rate (up to 10 %) occurs at the almost normal incidence of the ultra-short, tightly focused p-polarized laser pulse on the thin plasma slab with the near-critical density and rare electron collisions.
{"title":"Emission of terahertz pulses from near-critical plasma slab under action of p-polarized laser radiation","authors":"A.A. Frolov","doi":"10.1017/s0022377824000011","DOIUrl":"https://doi.org/10.1017/s0022377824000011","url":null,"abstract":"The theory of the terahertz (THz) waves emission from a near-critical plasma slab under the action of the focused <jats:italic>p</jats:italic>-polarized laser pulse is developed. The spectral, angular and energy characteristics of the THz signal are studied as functions of the focusing degree and the incidence angle of laser radiation, as well as the density and thickness of the plasma slab. It is shown that the extremely strong increase in the energy of the THz signal (up to millijoule level) and conversion rate (up to 10 %) occurs at the almost normal incidence of the ultra-short, tightly focused <jats:italic>p</jats:italic>-polarized laser pulse on the thin plasma slab with the near-critical density and rare electron collisions.","PeriodicalId":16846,"journal":{"name":"Journal of Plasma Physics","volume":"63 1 1","pages":""},"PeriodicalIF":2.5,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139921195","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-21DOI: 10.1017/s0022377824000138
C. Chen, K. M. Rabadanov, N. A. Ashurbekov, C. Yuan, A. M. Shakhrudinov
This study investigates the effect of a transverse magnetic field on high-voltage pulsed discharge in helium at a pressure of 30 Torr. A simple two-dimensional fluid model that describes the high-voltage pulsed discharge in helium in a transverse weak magnetic field (B = 0.4 T) is presented, which uses an empirical relation to account for the magnetic field. The results of using the empirical relation for the effective field agree well with the experimental results. The dynamics of discharge development in the presence of the magnetic field is also investigated. The magnetic field does not significantly affect the gas-discharge development dynamics in helium at a pressure of 30 Torr.
{"title":"Transverse magnetic field effects on the high-voltage pulsed discharge plasma in helium","authors":"C. Chen, K. M. Rabadanov, N. A. Ashurbekov, C. Yuan, A. M. Shakhrudinov","doi":"10.1017/s0022377824000138","DOIUrl":"https://doi.org/10.1017/s0022377824000138","url":null,"abstract":"This study investigates the effect of a transverse magnetic field on high-voltage pulsed discharge in helium at a pressure of 30 Torr. A simple two-dimensional fluid model that describes the high-voltage pulsed discharge in helium in a transverse weak magnetic field (<jats:italic>B</jats:italic> = 0.4 T) is presented, which uses an empirical relation to account for the magnetic field. The results of using the empirical relation for the effective field agree well with the experimental results. The dynamics of discharge development in the presence of the magnetic field is also investigated. The magnetic field does not significantly affect the gas-discharge development dynamics in helium at a pressure of 30 Torr.","PeriodicalId":16846,"journal":{"name":"Journal of Plasma Physics","volume":"40 1","pages":""},"PeriodicalIF":2.5,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139928179","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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