High-beta characteristics of first and second-stable spherical tokamaks in reconnection heating experiments of TS-3

Ono, Yasushi; Kimura, Toshiro; Kawamori, Eiichirou; Murata, Y.; Miyazaki, Satoru; Ueda, Yoshimichi; Inomoto, Michiaki; Balandin, A. L.; Katsurai, Makoto

doi:10.1088/0029-5515/43/8/321

Cited by 58 publications

(60 citation statements)

References 25 publications

(53 reference statements)

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“…1 and 2), there are a large number of significant ST results which are unique to STs, while at the same time reaffirming many common physics features with conventional tokamaks. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] As a member of the tokamak family, 19 ST research contributes to advancing conventional tokamaks such as ITER 20,21 by providing data that extends into a unique plasma and device parameter space. Since ITER represents a significant extrapolation from present day tokamaks, ST research provides a different set of tokamak-related data for the improvement of predictive capabilities by providing leverage over a wide range of parameter space.…”

Section: Introductionmentioning

confidence: 99%

Recent progress on spherical torus research

Ono

Kaita

2015

Physics of Plasmas

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The spherical torus or spherical tokamak (ST) is a member of the tokamak family with its aspect ratio (A = R0/a) reduced to A ∼ 1.5, well below the normal tokamak operating range of A ≥ 2.5. As the aspect ratio is reduced, the ideal tokamak beta β (radio of plasma to magnetic pressure) stability limit increases rapidly, approximately as β ∼ 1/A. The plasma current it can sustain for a given edge safety factor q-95 also increases rapidly. Because of the above, as well as the natural elongation κ, which makes its plasma shape appear spherical, the ST configuration can yield exceptionally high tokamak performance in a compact geometry. Due to its compactness and high performance, the ST configuration has various near term applications, including a compact fusion neutron source with low tritium consumption, in addition to its longer term goal of an attractive fusion energy power source. Since the start of the two mega-ampere class ST facilities in 2000, the National Spherical Torus Experiment in the United States and Mega Ampere Spherical Tokamak in UK, active ST research has been conducted worldwide. More than 16 ST research facilities operating during this period have achieved remarkable advances in all fusion science areas, involving fundamental fusion energy science as well as innovation. These results suggest exciting future prospects for ST research both near term and longer term. The present paper reviews the scientific progress made by the worldwide ST research community during this new mega-ampere-ST era.

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Section: Introductionmentioning

confidence: 99%

Recent progress on spherical torus research

Ono

Kaita

2015

Physics of Plasmas

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“…However, those heating characteristics of reconnection are still under serious discussion, indicating that direct evidence for the reconnection heating mechanisms should be provided by a proper laboratory experiment. Since 1986 the merging of two toroidal plasmas (flux tubes) has been studied in a number of experiments: TS-3 [6] [7], START [8], MRX [9], SSX [10], VTF [11], TS-4 [12], UTST [13] [14], and MAST [15]. For those laboratory experiments, evidence of plasma acceleration toward outflow direction were observed as split line-integrated distribution function in 0D [16], 1D and 2D bidirectional toroidal acceleration during counter helicity spheromak merging [17] [18], and in-plane Mach probe measurement around X point with and without guide field [19][20] [21].…”

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confidence: 99%

Electron and Ion Heating Characteristics during Magnetic Reconnection in the MAST Spherical Tokamak

Tanabe

Yamada²,

Watanabe

et al. 2015

Phys. Rev. Lett.

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Local electron and ion heating characteristics during merging reconnection startup on the MAST spherical tokamak have been revealed for the first time using a 130 channel YAG-TS system and a new 32 chord ion Doppler tomography diagnostic. 2D local profile measurement of Te, ne and Ti detect highly localized electron heating at the X point and bulk ion heating downstream. For the push merging experiment under high guide field condition, thick layer of closed flux surface formed by reconnected field sustains the heating profile for more than electron and ion energy relaxation time τ E ei ∼ 4 − 10ms, both heating profiles finally form triple peak structure at the X point and downstream. Toroidal guide field mostly contributes the formation of peaked electron heating profile at the X point. The localized heating increases with higher guide field, while bulk downstream ion heating is unaffected by the change in the guide field under MAST conditions (Bt > 3Brec).PACS numbers: 52.35. Vd, 52.55.Fa, 52.72.+v Magnetic reconnection is a fundamental process which converts the magnetic energy of reconnecting fields to kinetic and thermal energy of plasma through the breaking and topological rearrangement of magnetic field lines. Recent satellite observations of solar flares revealed several important signatures of reconnection heating. In the solar flares, hard X-ray spots appear at loop-tops of coronas together with another two foot-point spots on the photosphere. The loop-top hot spots are considered to be caused by fast shocks formed in the down-stream of reconnection outflow [3]. The two-dimensional (2D) measurements of the Hinode spectrometer documented a significant broadening of Ca line-width downstream of reconnection [4]. These phenomena strongly suggest direct ion heating by reconnection outflow. On the other hand, the V-shape high electron temperature region was found around X-line of reconnection as an possible evidence of slow shock structure [5]. However, those heating characteristics of reconnection are still under serious discussion, indicating that direct evidence for the reconnection heating mechanisms should be provided by a proper laboratory experiment. Since 1986 the merging of two toroidal plasmas (flux tubes) has been studied in a number of experiments: TS-3

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“…Presently, the high power heating of the magnetic reconnection is being used in TS-3 and the larger TS-4 device to study the high-β stability of spherical tori. In these experiments two spheromaks with opposite toroidal fields are merged to form an oblate FRC that is subsequently transformed into an spherical tokamak configuration by applying the external toroidal field [10].…”

Section: Spherical Tokamak Experiments Worldwidementioning

confidence: 99%