Formation of a 100-kA Tokamak Discharge in the Princeton Large Torus by Lower Hybrid Waves

Jobes, F. C.; Stevens, J.; Bell, R. E.; Bernabei, S.; Cavallo, A.; Chu, T. K.; Cohen, Samuel A.; Denne, B.; Efthimion, P. C.; Hinnov, E.; Hooke, W. M.; Hosea, J. C.; Mazzucato, E.; McWilliams, R.; Motley, R. W.; Suckewer, S.; Taylor, G.; Timberlake, J.; Goeler, S. von; Wilson, Robert R.

doi:10.1103/physrevlett.52.1005

Cited by 107 publications

(64 citation statements)

References 8 publications

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“…In general, increases in plasma density and total particle number may result from three possible causes: (1) increased ionization of hydrogen, (2) increased ionization of impurities, and (3) improved particle confinement.…”

Section: Density and Ionization Behaviormentioning

confidence: 99%

Particle confinement and the anomalous Doppler instability during combined inductive and lower-hybrid current drive

Luckhardt¹,

Chen²,

Mayberry³

et al. 1986

The Physics of Fluids

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Increases in average density have been observed during lower-hybrid current drive experiments (LHCD) on the Versator II tokamak, and on other LHCD experiments where inductive-ohmic and lower-hybrid current drive are combined. In the present experiments it is found that this density increase is the result of an improvement in global particle confinement time, rp, in comparison to purely ohmic discharges with similar plasma parameters.Furthermore, it is found that the improved confinement occurs only when the anomalous doppler relaxation instability of the anisotropic high energy electron tail is stabilized during LHCD. tPermanent address:

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Section: Density and Ionization Behaviormentioning

confidence: 99%

Particle confinement and the anomalous Doppler instability during combined inductive and lower-hybrid current drive

Luckhardt¹,

Chen²,

Mayberry³

et al. 1986

The Physics of Fluids

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“…Eventually, a pure rf mode of operation appears feasible. 4 The low-density limit in the PLT experiments is believed to be a consequence of the relatively low frequency (/ = 0.8 GHz) used. In other experiments current drive has been demonstrated by injecting rf power during full Ohmic heating (OH) operation.…”

mentioning

confidence: 99%

Observation of Lower-Hybrid Current Drive at High Densities in the AlcatorCTokamak

et al. 1984

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A quasi-steady-state lower-hybrid current-drive operation is demonstrated in the Alcator C tokamak at densities up to n e -1 x 10 14 cm" 3 . The current-drive efficiency is measured experimentally over a wide range of densities and magnetic fields. The radial distribution of high-energy x rays indicates that the current-carrying electrons peak near the plasma axis. PACS numbers 52.40.Db, Generation of toroidal currents in tokamaks by injection of traveling lower-hybrid waves is currently of great interest in magnetically confined plasma-fusion research. 1 This interest arises from the possibility of steady-state tokamak operation which would make the tokamak concept a more attractive reactor candidate. 2 To present date, efficient "quasi-steady-state" operation has been demonstrated only at relatively low electron densities, namely at n e < 8x 10 12 cm" 3 in the PLT tokamak. 3 This mode of tokamak operation is achieved by terminating the inductive current sources (Ohmic power) as the rf power is injected. Eventually, a pure rf mode of operation appears feasible. 4The low-density limit in the PLT experiments is believed to be a consequence of the relatively low frequency (/ = 0.8 GHz) used. In other experiments current drive has been demonstrated by injecting rf power during full Ohmic heating (OH) operation. 5 " 8 In these experiments significant dc electric fields often exist during rf injection Avhich may modify the rf current drive figure of merit J/Pj. 1 In particular, the question of the influence of electron tails generated by the OH electric fields which existed before, or during rf injection, arises. Due to the relatively low frequencies (/=^1.3-GHz) even such "OH-assisted" experiments were carried out mostly at low densities (n e <2 xl0 13 cm-3 ).In this Letter we present experimental measurements of the efficiency of lower-hybrid current drive at reactor-relevant densities, namely at 10 13 <. /Hem" 3 ) < 10 14 . The experiments were carried out on the Alcator C tokamak (major radius R =64 cm, minor radius a = 16.5 cm) where the high rf frequency (/ = 4.6 GHz) and high rf powers (P < 1.1 MW) used allowed us to demonstrate rf current-drive operation at high densities. 9 The lower-hybrid waves were launched by two 4x4 wave-guide arrays located 180° relative to each other around the torus. For the current-drive experiments described in this paper the phases of adjacent waveguides in each row were set at 90°. The Brambilla rf power spectrum under such conditions is concentrated between N u = c/cn/co = 1 and 2.5 in the OH electron-drift direction, with approximately 30% of the power being in the opposite (negative) direction. 10 The negative portion of the spectrum is concentrated at relatively high values of N\\ (N n ~~ 6) and is expected to be absorbed by, and heat, the bulk plasma.In the present experiments the primary winding of the Ohmic heating transformer was opencircuited before application of the rf power. After the OH primary is opened the plasma current decays inductively with a typical time scale ...

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“…Lower Hybrid Current Drive (LHCD) start-up to 100 kA was demonstrated on PLT 40 and ECRH was used to provide start-up to low current levels on DII-D 41 , TS2 42 and LATE 43 . For the ST, however, Electron-Bernstein Wave (EBW) seems most promising 44 .…”

Section: Start-up Using Rf Wavesmentioning

confidence: 99%

The Physics of Tokamak Start-up

Mueller¹

2012

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Tokamak start-up on present-day devices usually relies on inductively induced voltage from a central solenoid. In some cases inductive startup is assisted with auxiliary power from electron cyclotron radio frequency heating.ITER, the National Spherical Torus eXperiment Upgrade and JT60, now under construction, will make use of the understanding gained from present-day devices to ensure successful start-up. Design of a spherical tokamak (ST) with DT capability for nuclear component testing would require an alternative to a central solenoid because the small central column in an ST has insufficient space to provide shielding for the insulators in the solenoid. Alternative start-up techniques such as induction using outer poloidal field coils, electron Bernstein wave start-up, coaxial helicity injection and point source helicity injection have been used with success, but require demonstration of scaling to higher plasma current.

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Formation of a 100-kA Tokamak Discharge in the Princeton Large Torus by Lower Hybrid Waves

Cited by 107 publications

References 8 publications

Particle confinement and the anomalous Doppler instability during combined inductive and lower-hybrid current drive

Particle confinement and the anomalous Doppler instability during combined inductive and lower-hybrid current drive

Observation of Lower-Hybrid Current Drive at High Densities in the AlcatorCTokamak

The Physics of Tokamak Start-up

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