The physics of spherical torus plasmas

Peng, Yueng Kay Martin

doi:10.1063/1.874048

Cited by 91 publications

(63 citation statements)

References 42 publications

(26 reference statements)

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“…The spherical tokamak (ST) concept [1] provides attractive features such as high toroidal beta and a high bootstrap-current fraction. However, the size of the centersolenoid coil must be reduced owing to the small space near the central axis.…”

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confidence: 99%

Separated Double-Current Layers in a High-Guide-Field Reconnection Experiment

Kondo

Inomoto

Xiaohong

et al. 2017

Plasma and Fusion Research

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Magnetic reconnection in the presence of a high-guide-field is utilized to heat the plasma in the merging startup of a spherical tokamak configuration. The reconnection current layer between two spherical tokamaks was gradually compressed, and a quasi-steady current-sheet thickness was obtained. During the compression phase, the current layer split transiently into two separated layers, which provided a flattened magnetic-field-region near the X-point. This modification may affect the electron-energization mechanism in the merging start-up of a spherical tokamak in a high-guide-field. The spherical tokamak (ST) concept [1] provides attractive features such as high toroidal beta and a high bootstrap-current fraction. However, the size of the centersolenoid coil must be reduced owing to the small space near the central axis. One center-solenoid-free start-up method is the merging formation that has been developed in the TS-3/4 [2], UTST [3], and START/MAST [4] devices. In the merging formation, two STs are inductively formed using poloidal-field coils and are then merged into one ST via magnetic reconnection [5] of the poloidal fields of the two initial STs. This rapidly converts magnetic energy to plasma kinetic/thermal energy.In the merging start-up of an ST, a strong toroidal magnetic field, which is perpendicular to the reconnecting magnetic field, acts as a "guide field," magnetizing the plasma particles even at the reconnection X-point and changing the global/microscopic behavior of reconnection [6]. A unique feature of guide-field-assisted reconnection is that electrons are effectively accelerated along the guide field via the reconnection electric field. The maximum energy attained by the electrons is affected both by the reconnection electric field and the ratio of the toroidal (guide) magnetic field to the poloidal (reconnection) magnetic field [7,8]. In this study, we investigate the detailed structure of the reconnection magnetic field around the Xpoint of a high-guide-field reconnection event in the UTST merging experiment. Figure 1 shows the magnetic flux surfaces observed at an early phase of an ST merging experiment via a 2D pickup-coil array whose locations are indicated by the small "x"s in the figure. The time evolutions of the reauthor's e-mail: kondo@ts.k.u-tokyo.ac.jp connected magnetic flux and of the reconnection electric field are shown in Figs. 2 (a) and (b). The plasma merging is completed within ∼60 µs because the poloidal magnetic flux contained in each of the initial STs is limited. The reconnection electric field reached ∼100 V/m in the middle of the merging period. This high electric field accelerates the electrons in the region wherein the poloidal magnetic field is much weaker than that of the toroidal magnetic field. The detailed structure of the reconnection magnetic field B r was measured via a 1D pickup-coil array at intervals of 1 cm, as shown by the small red circles in Fig. 1. The time evolution of the current-layer thickness obtained using the fitting of the Harris-type fu...

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confidence: 99%

Separated Double-Current Layers in a High-Guide-Field Reconnection Experiment

Kondo

Inomoto

Xiaohong

et al. 2017

Plasma and Fusion Research

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“…A broad range of encouraging advances have been made in the exploration of the Spherical Torus (ST), a very low aspect-ratio tokamak concept [1]. A schematic of the ST magnetic configuration is shown in Fig.…”

Section: Motivation and Mission Of Nstxmentioning

confidence: 99%

Overview of the initial NSTX experimental results

Ono¹,

Bell²,

Bell³

et al. 2001

Nucl. Fusion

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“…Spherical tokamaks (STs) have been found, both theoretically 1 and experimentally 2 , to be capable of confining plasmas at high beta, a quality attractive for prospective fusion reactor applications. NSTX 3 is an ST with typical parameters of R=0.86 m, a=0.68 m, κ=2, B T =0.3 T, I p =1 MA, n e0 =3x10 19 m -3 , and T e0 =1 keV.…”

Section: Introductionmentioning

confidence: 99%

Confinement of Neutral Beam Ions in the National Spherical Torus Experiment

Darrow¹,

Medley²,

Roquemore³

et al. 2001

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The loss of neutral beam ions to the wall has been measured in the National Spherical Torus Experiment (NSTX) by means of thermocouples, an infrared (IR) camera, and a Faraday cup probe. The losses tend to exhibit the expected dependences on plasma current, tangency radius of the injector, and plasma outer gap. However, the thermocouples and the Faraday cups indicate substantially different levels of loss and this difference has yet to be understood.

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The physics of spherical torus plasmas

Cited by 91 publications

References 42 publications

Separated Double-Current Layers in a High-Guide-Field Reconnection Experiment

Separated Double-Current Layers in a High-Guide-Field Reconnection Experiment

Overview of the initial NSTX experimental results

Confinement of Neutral Beam Ions in the National Spherical Torus Experiment

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