Title: Design Considerations for the Implementation of a High-Field-Side Transient CHI System on QUEST

Abstract

Transient coaxial helicity injection (T-CHI), a method first developed on the small helicity injected torus (HIT-II) experiment and then validated on the much larger National Spherical Torus Experiment (NSTX) device, is a method to initiate an inductive-like tokamak plasma discharge without reliance on the central solenoid. A CHI discharge is initiated by driving current along magnetic flux that connects the inner and outer divertor plates on one end of the tokamak. To permit this, on both HIT-II and NSTX, toroidal ceramic insulators were used to electrically separate the inner and outer vessel components. The use of such large toroidal vacuum insulators may not be easy to implement in reactors. To address this issue, the Q-shu University experiments with steady-state spherical tokamak (ST) (QUEST) is developing a reactor-relevant CHI configuration in which one of the divertor plates is electrically insulated from the rest of the vessel. The first application of T-CHI on QUEST biased the CHI electrode to the outer vessel. While the CHI discharges could be easily generated, it was found that as the discharge filled the vessel, the separation distance between the injector magnetic flux footprints widened, a condition that is not favorable for the generation of closed fluxmore » surfaces. Biasing the electrode to the inner wall is a configuration similar to that used on NSTX and HIT-II, but initial testing in this configuration has proved to be challenging. The design described here overcomes the present limitation by locating the CHI electrode much closer to the CHI injector flux coil and using an NSTX-like gas injection manifold to enable high-field-side T-CHI startup on QUEST. Finally, the concepts described in this article should also benefit the future implementation of T-CHI systems in other tokamaks and spherical tokamaks.« less

Authors:

Raman, R.  ^[1];

• Search DOE PAGES for author "Raman, R."
• Search DOE PAGES for ORCID "0000-0002-2027-3271"

Kuroda, K.  ^[2];

• Search DOE PAGES for author "Kuroda, K."
• Search DOE PAGES for ORCID "0000-0003-2451-4893"

Hanada, K. ^[2]; Ono, M.  ^[3];

• Search DOE PAGES for author "Ono, M."
• Search DOE PAGES for ORCID "0000-0001-9849-9417"

Hasegawa, M. ^[2]; Onchi, T. ^[2]; Ikezoe, R. ^[2]; Idei, H.  ^[2];

• Search DOE PAGES for author "Idei, H."
• Search DOE PAGES for ORCID "0000-0001-6282-4521"

Ido, T. ^[2]; Rogers, J. A. ^[1]

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+ Show Author Affiliations

1. Univ. of Washington, Seattle, WA (United States)
2. Kyushu Univ., Kasuga (Japan)
3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

Publication Date:

Thu Aug 11 00:00:00 EDT 2022

Research Org.:

Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Org.:

USDOE; Japan Society for the Promotion of Science (JSPS); Kyushu University; National Institute for Fusion Science (NIFS)

OSTI Identifier:

1887998

Grant/Contract Number:  

SC0019415; AC02-09CH11466

Resource Type:

Accepted Manuscript

Journal Name:

IEEE Transactions on Plasma Science

Additional Journal Information:

Journal Volume: 50; Journal Issue: 11; Journal ID: ISSN 0093-3813

Publisher:

IEEE

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; electrodes; plasmas; tokamak devices; insulators; electric discharges; toroidal magnetic fields; magnetic separation; coaxial helicity injection (CHI); helicity; noninductive; spherical tokamak (ST); startup