We investigate a model of turbulent magnetic reconnection introduced by Yokoi and collaborators (Phys. Rev. Lett. 110, 255001) and show that the classic two-dimensional, steady-state Sweet-Parker and Petschek reconnection solutions are supported. We present evidence that these are the only two steady-state reconnection solutions, and we determine the criterion for their selection. Sweet-Parker reconnection occurs when there is no growth in turbulent energy, whereas Petschek reconnection occurs when the current density in the reconnecting current sheet is able to surpass a critical value, allowing for the growth of turbulent energy that creates the diffusion region. Further, we show that the Petschek solutions are self-similar, depending on the value of the turbulent time scale. The self-consistent development of Petschek reconnection through turbulence, within the model, is an example of fast and steady magnetic reconnection without an explicit need for the collisionless terms in an extended Ohm's law.
{"title":"On turbulent magnetic reconnection: fast and slow mean steady-states","authors":"Sage Stanish, David MacTaggart","doi":"arxiv-2409.07346","DOIUrl":"https://doi.org/arxiv-2409.07346","url":null,"abstract":"We investigate a model of turbulent magnetic reconnection introduced by Yokoi\u0000and collaborators (Phys. Rev. Lett. 110, 255001) and show that the classic\u0000two-dimensional, steady-state Sweet-Parker and Petschek reconnection solutions\u0000are supported. We present evidence that these are the only two steady-state\u0000reconnection solutions, and we determine the criterion for their selection.\u0000Sweet-Parker reconnection occurs when there is no growth in turbulent energy,\u0000whereas Petschek reconnection occurs when the current density in the\u0000reconnecting current sheet is able to surpass a critical value, allowing for\u0000the growth of turbulent energy that creates the diffusion region. Further, we\u0000show that the Petschek solutions are self-similar, depending on the value of\u0000the turbulent time scale. The self-consistent development of Petschek\u0000reconnection through turbulence, within the model, is an example of fast and\u0000steady magnetic reconnection without an explicit need for the collisionless\u0000terms in an extended Ohm's law.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"24 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142196021","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Simulation results are presented to demonstrate electron temperature and electrical potential development in dilute and cold plasma development. The simulation method is a hybrid method which adopted fluid model for electrons due to their high mobility, while heavy ions and neutrals are modelled with the direct simulation Monte Carlo and Particle-In-Cell methods. The flows include steady, starting-up and shutting-down scenarios. The goal is to illustrate the exponential behaviors which were predicted in several recently developed formulas. Those formulas include many coefficients related with local properties, and they are difficult to determine. Hence, those trends can only efficiently demonstrate by numerical simulations which are more convenient than experimental measurements. The results confirm several facts. For steady plasma flows, the electron temperature and potential profiles are smooth, very likely, they can be approximated with exponential functions. For unsteady flows, the property developing trends in the shutting down or starting-up processes change monotonically. Further, at locations with large gradients, the property change trends are less ideal than those formulas. This is consistent with the assumptions with which those formulas were developed.
{"title":"Numerical Investigations on Dilute Cold Plasma Potential and Electron Temperature","authors":"Shiying Cai, Chunpei Cai, Zhen Zhang","doi":"arxiv-2409.06758","DOIUrl":"https://doi.org/arxiv-2409.06758","url":null,"abstract":"Simulation results are presented to demonstrate electron temperature and\u0000electrical potential development in dilute and cold plasma development. The\u0000simulation method is a hybrid method which adopted fluid model for electrons\u0000due to their high mobility, while heavy ions and neutrals are modelled with the\u0000direct simulation Monte Carlo and Particle-In-Cell methods. The flows include\u0000steady, starting-up and shutting-down scenarios. The goal is to illustrate the\u0000exponential behaviors which were predicted in several recently developed\u0000formulas. Those formulas include many coefficients related with local\u0000properties, and they are difficult to determine. Hence, those trends can only\u0000efficiently demonstrate by numerical simulations which are more convenient than\u0000experimental measurements. The results confirm several facts. For steady plasma\u0000flows, the electron temperature and potential profiles are smooth, very likely,\u0000they can be approximated with exponential functions. For unsteady flows, the\u0000property developing trends in the shutting down or starting-up processes change\u0000monotonically. Further, at locations with large gradients, the property change\u0000trends are less ideal than those formulas. This is consistent with the\u0000assumptions with which those formulas were developed.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"9 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142196024","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The mechanisms by which media inhomogeneity affects the three wave parametric instability (PI), including the wave number mismatch and the parameter gradients, are investigated using an approach based on the Wentzel-Kramers-Brillouin-Jeffreys (WKBJ) approximation. This approach transforms the coupling wave equations into an amplitude equation and iteratively solves its characteristic polynomials. By analyzing the solutions, we proposed that the wave number of the quasi-mode, a key term in the wave number mismatch of non-resonant type PI, should be a complex root of the quasi-mode's linear dispersion equation. Based on this, we derive a unified amplification factor formula that covers the resonant and non-resonant, the forward-scattered and backward-scattered types of PI. The impact of parameter gradients on the local spatial growth rate becomes significant when the inhomogeneity exceeds 10^{-3}. Considering parameter gradients extends our approach's validity to an inhomogeneity of about 10^{-2}. This approach holds promise for more specific PI modeling in the future.
采用基于文采尔-克拉默-布里渊-杰弗里斯（WKBJ）近似的方法，研究了介质不均匀性影响三波参数不稳定性（PI）的机制，包括波数失配和参数梯度。这种方法将耦合波方程转换为振幅方程，并对其特征多项式进行迭代求解。通过分析求解结果，我们提出了准模式的波数（非共振型 PI 波数失配的关键项）应为准模式线性色散方程的复根。在此基础上，我们推导出了一个统一的放大系数公式，它涵盖了共振型和非共振型、前向散射型和后向散射型 PI。当同质性超过 10^{-3} 时，参数梯度对局部空间增长率的影响就变得非常显著。考虑参数梯度可以将我们方法的有效性扩展到约 10^{-2} 的不均匀性。这种方法有望在未来用于更具体的 PI 建模。
{"title":"Theoretical Study of Inhomogeneity Effects on Three-Wave Parametric Instability: A WKBJ Approach","authors":"Taotao Zhou, Nong Xiang, Chunyun Gan, Tianyang Xia","doi":"arxiv-2409.06677","DOIUrl":"https://doi.org/arxiv-2409.06677","url":null,"abstract":"The mechanisms by which media inhomogeneity affects the three wave parametric\u0000instability (PI), including the wave number mismatch and the parameter\u0000gradients, are investigated using an approach based on the\u0000Wentzel-Kramers-Brillouin-Jeffreys (WKBJ) approximation. This approach\u0000transforms the coupling wave equations into an amplitude equation and\u0000iteratively solves its characteristic polynomials. By analyzing the solutions,\u0000we proposed that the wave number of the quasi-mode, a key term in the wave\u0000number mismatch of non-resonant type PI, should be a complex root of the\u0000quasi-mode's linear dispersion equation. Based on this, we derive a unified\u0000amplification factor formula that covers the resonant and non-resonant, the\u0000forward-scattered and backward-scattered types of PI. The impact of parameter\u0000gradients on the local spatial growth rate becomes significant when the\u0000inhomogeneity exceeds 10^{-3}. Considering parameter gradients extends our\u0000approach's validity to an inhomogeneity of about 10^{-2}. This approach holds\u0000promise for more specific PI modeling in the future.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"66 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142196027","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Guillaume Bouchard, Arnaud Beck, Francesco Massimo, Arnd Specka
The design of absorbing boundary conditions (ABC) in a numerical simulation is a challenging task. In the best cases, spurious reflections remain for some angles of incidence or at certain wave lengths. In the worst, ABC are not even possible for the set of equations and/or numerical schemes used in the simulation and reflections can not be avoided at all. Perflectly Matched Layer (PML) are layers of absorbing medium which can be added at the simulation edges in order to significantly damp both outgoing and reflected waves, thus effectively playing the role of an ABC. They are able to absorb waves and prevent reflections for all angles and frequencies at a modest computational cost. It increases the simulation accuracy and negates the need of oversizing the simulation usually imposed by ABC and leading to a waste of computational resources and power. PML for finite-difference time-domain (FDTD) schemes in Particle-In-cell (PIC) codes are presented for both Maxwell's equations and, for the first time, the envelope wave equation. Being of the second order, the latter requires significant evolutions with respect to the former. It applies in particular to simulations of lasers propagating in plasmas using the reduced Complex Envelope model. The implementation is done in the open source code Smilei for both Cartesian and azimuthal modes (AM) decomposition geometries.
{"title":"Perfectly Matched Layer implementation for E-H fields and Complex Wave Envelope propagation in the Smilei PIC code","authors":"Guillaume Bouchard, Arnaud Beck, Francesco Massimo, Arnd Specka","doi":"arxiv-2409.06287","DOIUrl":"https://doi.org/arxiv-2409.06287","url":null,"abstract":"The design of absorbing boundary conditions (ABC) in a numerical simulation\u0000is a challenging task. In the best cases, spurious reflections remain for some\u0000angles of incidence or at certain wave lengths. In the worst, ABC are not even\u0000possible for the set of equations and/or numerical schemes used in the\u0000simulation and reflections can not be avoided at all. Perflectly Matched Layer\u0000(PML) are layers of absorbing medium which can be added at the simulation edges\u0000in order to significantly damp both outgoing and reflected waves, thus\u0000effectively playing the role of an ABC. They are able to absorb waves and\u0000prevent reflections for all angles and frequencies at a modest computational\u0000cost. It increases the simulation accuracy and negates the need of oversizing\u0000the simulation usually imposed by ABC and leading to a waste of computational\u0000resources and power. PML for finite-difference time-domain (FDTD) schemes in\u0000Particle-In-cell (PIC) codes are presented for both Maxwell's equations and,\u0000for the first time, the envelope wave equation. Being of the second order, the\u0000latter requires significant evolutions with respect to the former. It applies\u0000in particular to simulations of lasers propagating in plasmas using the reduced\u0000Complex Envelope model. The implementation is done in the open source code\u0000Smilei for both Cartesian and azimuthal modes (AM) decomposition geometries.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"62 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142225105","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the solar atmosphere, flux ropes are subject to current driven instabilities that are crucial in driving plasma eruptions, ejections and heating. A typical ideal magnetohydrodynamics (MHD) instability developing in flux ropes is the helical kink, which twists the flux rope axis. The growth of this instability can trigger magnetic reconnection, which can explain the formation of chromospheric jets and spicules, but its development has never been investigated in a partially-ionised plasma (PIP). Here we study the kink instability in PIP to understand how it develops in the solar chromosphere, where it is affected by charge-neutral interactions. Partial ionisation speeds up the onset of the non-linear phase of the instability, as the plasma $beta$ of the isolated plasma is smaller than the total plasma $beta$ of the bulk. The distribution of the released magnetic energy changes in fully and partially-ionised plasmas, with a larger increase of internal energy associated to the PIP cases. The temperature in PIP increases faster also due to heating terms from the two-fluid dynamics. PIP effects trigger the kink instability on shorter time scales, which is reflected in a more explosive chromospheric flux rope dynamics. These results are crucial to understand the dynamics of small-scale chromospheric structures - mini-filament eruptions - that this far have been largely neglected but could significantly contribute to chromospheric heating and jet formation.
{"title":"Kink instability of flux ropes in partially-ionised plasmas","authors":"Giulia Murtas, Andrew Hillier, Ben Snow","doi":"arxiv-2409.06901","DOIUrl":"https://doi.org/arxiv-2409.06901","url":null,"abstract":"In the solar atmosphere, flux ropes are subject to current driven\u0000instabilities that are crucial in driving plasma eruptions, ejections and\u0000heating. A typical ideal magnetohydrodynamics (MHD) instability developing in\u0000flux ropes is the helical kink, which twists the flux rope axis. The growth of\u0000this instability can trigger magnetic reconnection, which can explain the\u0000formation of chromospheric jets and spicules, but its development has never\u0000been investigated in a partially-ionised plasma (PIP). Here we study the kink\u0000instability in PIP to understand how it develops in the solar chromosphere,\u0000where it is affected by charge-neutral interactions. Partial ionisation speeds\u0000up the onset of the non-linear phase of the instability, as the plasma $beta$\u0000of the isolated plasma is smaller than the total plasma $beta$ of the bulk.\u0000The distribution of the released magnetic energy changes in fully and\u0000partially-ionised plasmas, with a larger increase of internal energy associated\u0000to the PIP cases. The temperature in PIP increases faster also due to heating\u0000terms from the two-fluid dynamics. PIP effects trigger the kink instability on\u0000shorter time scales, which is reflected in a more explosive chromospheric flux\u0000rope dynamics. These results are crucial to understand the dynamics of\u0000small-scale chromospheric structures - mini-filament eruptions - that this far\u0000have been largely neglected but could significantly contribute to chromospheric\u0000heating and jet formation.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"179 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142196025","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We discuss conditions for the enhancement of fusion reactivities arising from different choices of energy distribution functions for the reactants. The key element for potential gains in fusion reactivity is identified in the functional dependence of the tunnellng coefficient upon the energy, ensuring the existence of a finite range of temperatures for which reactivity of fusion processes is boosted with respect to the Maxwellian case. This is shown, using a convenient parameterization of the tunneling coefficient dependence upon the energy, analytically in the simplified case of a bimodal Maxwell-Boltzmann distribution, and numerically for kappa-distributions. We then consider tunneling potentials progressively better approximating fusion processes, and evaluate in each case the average reactivity in the case of kappa-distributions.
{"title":"Enhancement of fusion reactivities using non-Maxwellian energy distributions","authors":"Ben I. Squarer, Carlo Presilla, Roberto Onofrio","doi":"arxiv-2409.05848","DOIUrl":"https://doi.org/arxiv-2409.05848","url":null,"abstract":"We discuss conditions for the enhancement of fusion reactivities arising from\u0000different choices of energy distribution functions for the reactants. The key\u0000element for potential gains in fusion reactivity is identified in the\u0000functional dependence of the tunnellng coefficient upon the energy, ensuring\u0000the existence of a finite range of temperatures for which reactivity of fusion\u0000processes is boosted with respect to the Maxwellian case. This is shown, using\u0000a convenient parameterization of the tunneling coefficient dependence upon the\u0000energy, analytically in the simplified case of a bimodal Maxwell-Boltzmann\u0000distribution, and numerically for kappa-distributions. We then consider\u0000tunneling potentials progressively better approximating fusion processes, and\u0000evaluate in each case the average reactivity in the case of\u0000kappa-distributions.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"69 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142195852","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Baillod, E. J. Paul, G. Rawlinson, M. Haque, S. W. Freiberger, S. Thapa
The Columbia Stellarator eXperiment (CSX), currently being designed at Columbia University, aims to test theoretical predictions related to QA plasma behavior, and to pioneer the construction of an optimized stellarator using three-dimensional, non-insulated high-temperature superconducting (NI-HTS) coils. The magnetic configuration is generated by a combination of two circular planar poloidal field (PF) coils and two 3D-shaped interlinked (IL) coils, with the possibility to add windowpane coils to enhance shaping and experimental flexibility. The PF coils and vacuum vessel are repurposed from the former Columbia Non-Neutral Torus (CNT) experiment, while the IL coils will be custom-wound in-house using NI-HTS tapes. To obtain a plasma shape that meets the physics objectives with a limited number of coils, novel single-stage optimization techniques are employed, optimizing both the plasma and coils concurrently, in particular targeting a tight aspect ratio QA plasma and minimized strain on the HTS tape. Despite the increased complexity due to the expanded degrees of freedom, these methods successfully identify optimized plasma geometries that can be realized by coils meeting engineering specifications. This paper discusses the derivation of the constraints and objectives specific to CSX, and describe how two recently developed single-stage optimization methodologies are applied to the design of CSX. A set of selected configurations for CSX is then described in detail.
{"title":"Integrating Novel Stellarator Single-Stage Optimization Algorithms to Design the Columbia Stellarator Experiment","authors":"A. Baillod, E. J. Paul, G. Rawlinson, M. Haque, S. W. Freiberger, S. Thapa","doi":"arxiv-2409.05261","DOIUrl":"https://doi.org/arxiv-2409.05261","url":null,"abstract":"The Columbia Stellarator eXperiment (CSX), currently being designed at\u0000Columbia University, aims to test theoretical predictions related to QA plasma\u0000behavior, and to pioneer the construction of an optimized stellarator using\u0000three-dimensional, non-insulated high-temperature superconducting (NI-HTS)\u0000coils. The magnetic configuration is generated by a combination of two circular\u0000planar poloidal field (PF) coils and two 3D-shaped interlinked (IL) coils, with\u0000the possibility to add windowpane coils to enhance shaping and experimental\u0000flexibility. The PF coils and vacuum vessel are repurposed from the former\u0000Columbia Non-Neutral Torus (CNT) experiment, while the IL coils will be\u0000custom-wound in-house using NI-HTS tapes. To obtain a plasma shape that meets\u0000the physics objectives with a limited number of coils, novel single-stage\u0000optimization techniques are employed, optimizing both the plasma and coils\u0000concurrently, in particular targeting a tight aspect ratio QA plasma and\u0000minimized strain on the HTS tape. Despite the increased complexity due to the\u0000expanded degrees of freedom, these methods successfully identify optimized\u0000plasma geometries that can be realized by coils meeting engineering\u0000specifications. This paper discusses the derivation of the constraints and\u0000objectives specific to CSX, and describe how two recently developed\u0000single-stage optimization methodologies are applied to the design of CSX. A set\u0000of selected configurations for CSX is then described in detail.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142196030","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jonathan Squire, Eliot Quataert, Philip F. Hopkins
We show that there exist two qualitatively different turbulent states of the zero-net-vertical-flux shearing box. The first, which has been studied in detail previously, is characterized by a weakly magnetized ($betasim50$) midplane with slow periodic reversals of the mean azimuthal field (dynamo cycles). The second (the "low-$beta$ state"), which is the main subject of this paper, is characterized by a strongly magnetized $betasim1$ midplane dominated by a coherent azimuthal field with much stronger turbulence and much larger accretion stress $alpha sim 1$. The low-$beta$ state is realized in simulations that begin with sufficiently strong azimuthal magnetic fields. The mean azimuthal field in the low-$beta$ state is quasi steady (no cycles) and is sustained by a dynamo mechanism that compensates for the continued loss of magnetic flux through the vertical boundaries; we attribute the dynamo to the combination of differential rotation and the Parker instability, although many of its details remain unclear. Vertical force balance in the low-$beta$ state is dominated by the mean magnetic pressure except at the midplane, where thermal pressure support is always important (this is true even when simulations are initialized at $betall1$, provided the thermal scale-height of the disk is well-resolved). The efficient angular momentum transport in the low-$beta$ state may resolve long-standing tension between predictions of magnetorotational turbulence (at high $beta$) and observations; likewise, the bifurcation in accretion states we find may be important for understanding the state transitions observed in dwarf novae, X-ray binaries, and changing-look AGN. We discuss directions for future work including the implications of our results for global accretion disk simulations.
{"title":"Rapid, strongly magnetized accretion in the zero-net-vertical-flux shearing box","authors":"Jonathan Squire, Eliot Quataert, Philip F. Hopkins","doi":"arxiv-2409.05467","DOIUrl":"https://doi.org/arxiv-2409.05467","url":null,"abstract":"We show that there exist two qualitatively different turbulent states of the\u0000zero-net-vertical-flux shearing box. The first, which has been studied in\u0000detail previously, is characterized by a weakly magnetized ($betasim50$)\u0000midplane with slow periodic reversals of the mean azimuthal field (dynamo\u0000cycles). The second (the \"low-$beta$ state\"), which is the main subject of\u0000this paper, is characterized by a strongly magnetized $betasim1$ midplane\u0000dominated by a coherent azimuthal field with much stronger turbulence and much\u0000larger accretion stress $alpha sim 1$. The low-$beta$ state is realized in\u0000simulations that begin with sufficiently strong azimuthal magnetic fields. The\u0000mean azimuthal field in the low-$beta$ state is quasi steady (no cycles) and\u0000is sustained by a dynamo mechanism that compensates for the continued loss of\u0000magnetic flux through the vertical boundaries; we attribute the dynamo to the\u0000combination of differential rotation and the Parker instability, although many\u0000of its details remain unclear. Vertical force balance in the low-$beta$ state\u0000is dominated by the mean magnetic pressure except at the midplane, where\u0000thermal pressure support is always important (this is true even when\u0000simulations are initialized at $betall1$, provided the thermal scale-height\u0000of the disk is well-resolved). The efficient angular momentum transport in the\u0000low-$beta$ state may resolve long-standing tension between predictions of\u0000magnetorotational turbulence (at high $beta$) and observations; likewise, the\u0000bifurcation in accretion states we find may be important for understanding the\u0000state transitions observed in dwarf novae, X-ray binaries, and changing-look\u0000AGN. We discuss directions for future work including the implications of our\u0000results for global accretion disk simulations.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142225086","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. López-Bruna, S. Denizeau, I. Predebon, A. La Rosa, C. Poggi, P. Agostinetti
SPIDER (Source for the Production of Ions of Deuterium Extracted from Rf plasma) is a full-scale prototype of the ITER NBI source. It is based on the concept of inductive coupling between radio-frequency current drive and plasma. Present three-dimensional (3D) electromagnetic calculations of stationary RF fields in SPIDER permit an evaluation of the power dissipation in its main constituents. Taking experimental plasma parameters as input, we concentrate on the power dissipation in the copper-made Faraday shield lateral wall (FSLW) of the source for discharges with and without a static magnetic filter field. In agreement with our previous results and a first comparison with calorimetry data from the FSLW cooling circuit, the FSLW cylinder alone absorbs around 50% of the available power for the studied plasma parameters. A hypothesized improvement of transport confinement may increase significantly the efficiency.
{"title":"Faraday shield dissipation in the drivers of SPIDER based on electromagnetic 3D calculations","authors":"D. López-Bruna, S. Denizeau, I. Predebon, A. La Rosa, C. Poggi, P. Agostinetti","doi":"arxiv-2409.05821","DOIUrl":"https://doi.org/arxiv-2409.05821","url":null,"abstract":"SPIDER (Source for the Production of Ions of Deuterium Extracted from Rf\u0000plasma) is a full-scale prototype of the ITER NBI source. It is based on the\u0000concept of inductive coupling between radio-frequency current drive and plasma.\u0000Present three-dimensional (3D) electromagnetic calculations of stationary RF\u0000fields in SPIDER permit an evaluation of the power dissipation in its main\u0000constituents. Taking experimental plasma parameters as input, we concentrate on\u0000the power dissipation in the copper-made Faraday shield lateral wall (FSLW) of\u0000the source for discharges with and without a static magnetic filter field. In\u0000agreement with our previous results and a first comparison with calorimetry\u0000data from the FSLW cooling circuit, the FSLW cylinder alone absorbs around 50%\u0000of the available power for the studied plasma parameters. A hypothesized\u0000improvement of transport confinement may increase significantly the efficiency.","PeriodicalId":501274,"journal":{"name":"arXiv - PHYS - Plasma Physics","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142196031","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Miguel Saavedra-Melo, Nelson Castro, Robert Marosi, Eva Rajo-Iglesias, Filippo Capolino
We explore the use of glide symmetry (GS) and electromagnetic bandgap (EBG) technology in a glide-symmetric double corrugated gap waveguide (GSDC-GW) slow wave structure (SWS) for traveling wave tube (TWT) applications. Notably, this GS structure provides the advantage of wide-band operation and the EBG eliminates the need for a conductive connection between the top and bottom waveguide plates. The TWT performance is evaluated via particle-in-cell simulations that reveal a 3-dB bandwidth of approximately 12 GHz spanning from 54.5 GHz to 66.3 GHz, accompanied by a maximum gain of 23 dB. Because of GS, the backward wave in the first spatial harmonic is not longitudinally polarized, leading to a low risk of backward wave oscillations in the TWT. This work places the GSDC-EBG structure within the arena of potential SWS topologies for TWTs operating under similar conditions.
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