Reconnection heating experiments and simulations for torus plasma merging start-up

Y. Ono, S. Inoue, H. Tanabe, Chio-Zong Cheng, H. Hara, R. Horiuchi

Research output: Contribution to journalArticle

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Abstract

A series of merging experiments, TS-3 (TS-3U), TS-4, MAST and ST-40, made clear the promising characteristics of reconnection heating during merging formation of a high-beta spherical tokamak (ST), spheromak and field-reversed configuration (FRC). We developed the MW-class (<30 MW in TS-3U) ion heating using magnetic reconnection of torus plasma merging. Both the merging experiments and particle-in-cell (PIC) simulations (and also partly solar observation) agree on, (i) ion heating of the reconnection in its downstream, (ii) negative potential formation in the downstream for accelerating ions and (iii) low dependence of ion heating on the guide (toroidal) field B g. An important finding is that the reconnection heating energy depends on the reconnecting magnetic field B rec but has little dependence on B g in the tokamak operation region with the safety factor at the magnetic axis q 0 > 2. The plasmoid/current sheet ejection promotes ion heating in the high-q region, weakening the B g dependence of ion heating. Since the reconnection accelerated ions up to 70% of the Alfven speed of B rec, the ion temperature T i increment (and the reconnection heating energy) scales with B rec squared under the constant plasma density. This promising reconnection heating does not depend on plasma size, as long as the reconnection time is shorter than the plasma confinement time. This scaling law extended over 1.2 keV suggests that the merging start-up may realize the burning plasma temperature T i > 10 keV by increasing B rec. The merging/reconnection heating can explore a new direct route to burning plasma regimes without using any additional heating, such as neutral beam injection (NBI). This scaling leads us to new reconnection heating experiments for direct access to burning plasma regimes: ST-40 at Tokamak Energy and TS-3U at the University of Tokyo.

Original languageEnglish
Article number076025
JournalNuclear Fusion
Volume59
Issue number7
DOIs
Publication statusPublished - 2019 Jun 7

Fingerprint

heating
simulation
ions
plasma control
beam injection
plasma temperature
neutral beams
current sheets
ion temperature
ejection
scaling laws
plasma density
routes
scaling
energy
configurations

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics
  • Condensed Matter Physics

Cite this

Ono, Y. ; Inoue, S. ; Tanabe, H. ; Cheng, Chio-Zong ; Hara, H. ; Horiuchi, R. / Reconnection heating experiments and simulations for torus plasma merging start-up. In: Nuclear Fusion. 2019 ; Vol. 59, No. 7.
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Reconnection heating experiments and simulations for torus plasma merging start-up. / Ono, Y.; Inoue, S.; Tanabe, H.; Cheng, Chio-Zong; Hara, H.; Horiuchi, R.

In: Nuclear Fusion, Vol. 59, No. 7, 076025, 07.06.2019.

Research output: Contribution to journalArticle

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T1 - Reconnection heating experiments and simulations for torus plasma merging start-up

AU - Ono, Y.

AU - Inoue, S.

AU - Tanabe, H.

AU - Cheng, Chio-Zong

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AB - A series of merging experiments, TS-3 (TS-3U), TS-4, MAST and ST-40, made clear the promising characteristics of reconnection heating during merging formation of a high-beta spherical tokamak (ST), spheromak and field-reversed configuration (FRC). We developed the MW-class (<30 MW in TS-3U) ion heating using magnetic reconnection of torus plasma merging. Both the merging experiments and particle-in-cell (PIC) simulations (and also partly solar observation) agree on, (i) ion heating of the reconnection in its downstream, (ii) negative potential formation in the downstream for accelerating ions and (iii) low dependence of ion heating on the guide (toroidal) field B g. An important finding is that the reconnection heating energy depends on the reconnecting magnetic field B rec but has little dependence on B g in the tokamak operation region with the safety factor at the magnetic axis q 0 > 2. The plasmoid/current sheet ejection promotes ion heating in the high-q region, weakening the B g dependence of ion heating. Since the reconnection accelerated ions up to 70% of the Alfven speed of B rec, the ion temperature T i increment (and the reconnection heating energy) scales with B rec squared under the constant plasma density. This promising reconnection heating does not depend on plasma size, as long as the reconnection time is shorter than the plasma confinement time. This scaling law extended over 1.2 keV suggests that the merging start-up may realize the burning plasma temperature T i > 10 keV by increasing B rec. The merging/reconnection heating can explore a new direct route to burning plasma regimes without using any additional heating, such as neutral beam injection (NBI). This scaling leads us to new reconnection heating experiments for direct access to burning plasma regimes: ST-40 at Tokamak Energy and TS-3U at the University of Tokyo.

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