Title: Non-inductively driven tokamak plasmas at near-unity β_t in the Pegasus toroidal experiment

Abstract

A major goal of the spherical tokamak (ST) research program is accessing a state of low internal inductance ${\ell }_i$, high elongation $\kappa$ , and high toroidal and normalized beta ( ${\beta }_t$ and ${\beta }_N$ ) without solenoidal current drive. Local helicity injection (LHI) in the Pegasus ST [Garstka et al., Nucl. Fusion 46, S603 (2006)] provides non-solenoidally driven plasmas that exhibit these characteristics. LHI utilizes compact, edge-localized current sources for plasma startup and sustainment. It results in hollow current density profiles with low ${\ell }_i$. The low aspect ratio ( $R_0/a~1.2$) of Pegasus allows access to high κ and high normalized plasma currents $I_N=I_p/a{B}_T>14$). Magnetic reconnection during LHI provides auxiliary ion heating. Together, these features provide access to very high ${\beta }_t$ plasmas. Equilibrium analyses indicate that ${\beta }_t$ up to ~100% is achieved. Finally, these high ${\beta }_t$ discharges disrupt at the ideal no-wall β limit at ${\beta }_N~7.$

Authors:

Reusch, Joshua A.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-8424-9422"

Bodner, Grant M.  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-2497-9172"

Bongard, Michael W.  ^[1];

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Burke, Marcus G.  ^[1];

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Fonck, Raymond J.  ^[1];

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Pachicano, Jessica L.  ^[1];

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Perry, Justin M.  ^[1];

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Pierren, Christopher  ^[1];

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Rhodes, Alexander T.  ^[1];

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Richner, Nathan J.  ^[1];

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Rodriguez Sanchez, Cuauhtemoc  ^[1];

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Schlossberg, David J.  ^[2];

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Weberski, Justin D.  ^[1]

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• Search DOE PAGES for ORCID "0000-0002-5626-7914"

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+ Show Author Affiliations

1. Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Publication Date:

Wed Mar 14 00:00:00 EDT 2018

Research Org.:

Univ. of Wisconsin, Madison, WI (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES)

OSTI Identifier:

1433090

Grant/Contract Number:  

FG02-96ER54375; SC0006928

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 25; Journal Issue: 5; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; tokamaks; spherical tokamaks; helicity injection; equilibrium reconstruction; beta limit; magnetic reconnection