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Title: Plasma density injection and flow during coaxial helicity injection in a tokamak

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  1. Woodruff Scientific Inc., 3900 Paseo Del Sol, Santa Fe, New Mexico 87507, USA
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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 2; Related Information: CHORUS Timestamp: 2018-02-15 03:05:02; Journal ID: ISSN 1070-664X
American Institute of Physics
Country of Publication:
United States

Citation Formats

Hooper, E. B. Plasma density injection and flow during coaxial helicity injection in a tokamak. United States: N. p., 2018. Web. doi:10.1063/1.5018196.
Hooper, E. B. Plasma density injection and flow during coaxial helicity injection in a tokamak. United States. doi:10.1063/1.5018196.
Hooper, E. B. 2018. "Plasma density injection and flow during coaxial helicity injection in a tokamak". United States. doi:10.1063/1.5018196.
title = {Plasma density injection and flow during coaxial helicity injection in a tokamak},
author = {Hooper, E. B.},
abstractNote = {},
doi = {10.1063/1.5018196},
journal = {Physics of Plasmas},
number = 2,
volume = 25,
place = {United States},
year = 2018,
month = 2

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.5018196

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  • The electron temperature and density profiles of plasmas in the Helicity Injected Torus [HIT-II: T. R. Jarboe et al., Phys. Plasmas 5, 1807 (1998)] experiment are measured by multipoint Thomson scattering (MPTS). The HIT-II device is a small low-aspect-ratio tokamak (major radius 0.3 m, minor radius 0.2 m, toroidal field of up to 0.5 T), capable of inductive ohmic (OH) current drive, Coaxial Helicity Injection (CHI) current drive, or combinations of both. The temperature and density characteristics have been characterized by a ruby laser MPTS diagnostic at up to six locations within the plasma for a single diagnostic time permore » discharge. Observed hollow temperature profiles of CHI discharges are inconsistent with open flux only predictions for CHI and indicate a closed flux region during CHI current drive.« less
  • Coaxial helicity injection is used to produce low-aspect-ratio tokamaks with toroidal currents reaching 150 kA (highest value yet attained by helicity injection current drive) and sustained over 100 kA for many resistive diffusion times, without a current drive transformer. Current drive power efficiency, assuming no anomalous helicity dissipation, is 40% that of Ohmic. These tokamaks have a rotating [ital n]=1 toroidal distortion, with poloidal distortions only on the outer bad-curvature region. Equilibrium reconstruction suggests these plasmas have up to 112 kA of closed-field toroidal current, an aspect ratio [ital A]=1.69, a tokamak [ital q] profile, and a hollow toroidal currentmore » profile.« less
  • Low-aspect-ratio tokamaks with toroidal currents, {ital I}{sub {ital p}}, up to 250 kA are formed and sustained in the Helicity Injected Tokamak experiment [Nelson {ital et} {ital al}., Phys. Rev. Lett. {bold 72}, 3666 (1994)] using coaxial helicity injection. These plasmas are produced without use of a current drive transformer. Average toroidal currents are sustained at high values, {l_angle}{ital I}{sub {ital p}}{r_angle}=225 kA for 2 ms, where electron thermal energies are measured up to 80 eV with spectroscopy data suggesting burnthrough to the higher ionization states of oxygen. Currents can also be sustained for longer periods at lower values, {l_angle}{italmore » I}{sub {ital p}}{r_angle}=138 kA for 7 ms. These tokamaks are characterized by a rotating, {ital n}=1 distortion, with poloidal distortions approximately following the field line pitch, which only occur on the outer bad-curvature region. Equilibrium reconstructions show these plasmas have a tokamak {ital q} profile ({ital q}{sub 0}=5 -- 8, {ital q}{sub 95}=10 -- 12, {ital q}{sub cyl}{congruent}3.6), with a hollow toroidal current profile and up to 170 kA of closed field toroidal current in a low-aspect-ratio, {ital A}=1.68 configuration.« less
  • Coaxial helicity injection is used to form and sustain low aspect ratio tokamaks at currents of up to 250 kA in the Helicity Injected Tokamak experiment. Plasma currents can be sustained at an average of 225 kA for 2 ms, with on axis electron thermal energies up to 80 eV, or for longer times, 140 kA average for 7 ms, many resistive diffusion times. Spectroscopic measurements of the higher current discharges suggest burn-through of oxygen impurities. These plasmas have a rotating n = 1 distortion, appearing only on the outer, bad-curvature region. Equilibria reconstruction , fitting to experimental data, showsmore » tokamak q profiles achieved with hollow plasma current profiles. 11 refs., 4 figs., 1 tab.« less
  • A method of coaxial helicity injection has successfully produced a closed flux current without the use of the central solenoid in the NSTX device, on a size scale closer to a spherical torus reactor, for a proof-of-principle demonstration of this concept. For the first time, a remarkable 60 times current multiplication factor was achieved. Grad-Shafranov plasma equilibrium reconstructions are used to verify the existence of closed flux current. In some discharges the generated current persists for a surprisingly long time ~400 ms.