Stabilization of sawteeth by lower hybrid waves in the Alcator C tokamak

Knowlton, S.; Porkoláb, M.; Takase, Y.

doi:10.1088/0029-5515/28/1/008

Cited by 20 publications

(8 citation statements)

References 16 publications

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“…A different way of stabilizing sawteeth is by modifying the q profile locally around the q = 1 surface with localized electron cyclotron heating, as was demonstrated experimentally in the WT-3 tokamak [52]. Another way of stabilizing sawteeth was demonstrated in the Alcator C-Mod tokamak [53] where off-axis currents were driven by lower hybrid waves so that q 0 was raised to above 1.…”

Section: Sawtooth Stabilization With N-nbimentioning

confidence: 99%

Fast particle experiments in JT-60U

et al. 2000

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Results of fast particle experiments in JT-60U are presented. The fast particles were created with ICRF heating and negative ion based neutral beam injection (N-NBI) heating. With both heating systems Alfvén eigenmodes (AEs) were excited. The AEs that were excited with ICRF during sawtooth stabilization experiments are used to extract information about the magnetic safety profile in the plasma centre. These measurements are compared with motional Stark effect measurements and with sawtooth models. The first results on the radial mode structure of TAEs as measured with an X mode reflectometer system are also given. When the N-NBI beam was injected into a sawtoothing plasma, a significant increase in sawtooth period was observed. A survey is given of the bursting, chirping and stationary frequency modes that have been found in the Alfvén range of frequencies when N-NBI was injected. Most, but not all, of these modes scale with the Alfvén velocity. One group of modes that starts in the continuum and chirps up to the toroidicity induced Alfvén eigenmode (TAE) gap in typically 200 ms can be identified as resonant TAEs, whereas another group of modes appears as short bursts (up to 20 ms) in the Alfvén continuum.

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Section: Sawtooth Stabilization With N-nbimentioning

confidence: 99%

Fast particle experiments in JT-60U

et al. 2000

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“…An RF current of 2 MA was driven by LH waves in JT-60 [1][2][3] and a long non-inductive tokamak discharge of more than three minutes duration has been achieved by LHCD in the TRIAM-1M tokamak [4]. The effectiveness of LHCD in tokamak discharges was also demonstrated by many machines in aspects such as current ramp-up [5,6], sawtooth stabilization [7][8][9][10], current profile control [2,11], increase in confinement time [1][2][3]10], etc.…”

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confidence: 99%

Lower hybrid current drive efficiency in the JT-60 tokamak

et al. 1989

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Lower hybrid current drive (LHCD) experiments on JT-60 have been carried out in parameter n̄;e = (0.6−1.6)×1019 m−3, Ip = 0.5−1.5 MA, BT = 2.7−4.5 T, PLH < 2.5 MW, f = 1.75 and 2.0 GHz, with and without NB heating (PNB < 6 MW), limiter and lower side single null divertor configurations, and narrow and wide spectra. The current drive efficiency increases with the volume averaged electron temperature ⟨Te⟩ and with decreasing Zeff and a high efficiency of ηCD ≡ n̄eRPIRF/PLH ≤ 2.65 × 1019 m−2·A·W−1 was achieved by LHCD alone. The experimental data set has shown that the current drive efficiency is consistent with the scaling of ηCD ∼ 12 ⟨Te⟩/(5+Zeff)×l019 m−2·A·W−1. Low N1 waves with a narrow spectrum have a higher current drive efficiency than higher N1 waves with a wide spectrum insofar as launched waves satisfy the accessibility

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“…Finally, we discuss the problem of applying LHCD in NB heated plasmas. Stabilization of sawteeth by LHCD has been reported from many machines [20][21][22][23]; this procedure is an attractive way of achieving high temperatures and good confinement in the central plasma region. In JT-60 [1,3,4] and ASDEX [23] it has been demonstrated that a combination of LHCD and NB heating improves the energy confinement of beam heated plasmas.…”

Section: Discussionmentioning

confidence: 99%

Simultaneous heating by high power lower hybrid waves and neutral beams in the JT-60 tokamak

et al. 1989

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By injection of high power lower hybrid (LH) waves of up to 6.0 MW into neutral beam heated (20 MW) plasmas in the medium electron density regime (n̄e ≤ 3.5 × 1019 m-3) the plasma energy content is increased at the same incremental energy confinement time as it is increased with neutral beam heating alone. When LH heating is used in addition to thermal electron and ion heating, the beam ions are accelerated to energies considerably higher than the beam injection energy. In contrast to LH injection into ohmically heated plasmas in the same density regime, where substantial high energy electron production is observed, there are much less high energy electrons in the case of combined heating. The heating efficiency of LH waves during combined heating tends to decrease as the electron density is increased. Ray tracing analysis suggests that the accessibility condition prevents effective heating in a high density plasma. Calculation of wave damping, taking into account the beam component of the ion velocity distribution function, indicates that the waves are absorbed by beam ions before they are absorbed by electrons.

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Stabilization of sawteeth by lower hybrid waves in the Alcator C tokamak

Cited by 20 publications

References 16 publications

Fast particle experiments in JT-60U

Fast particle experiments in JT-60U

Lower hybrid current drive efficiency in the JT-60 tokamak

Simultaneous heating by high power lower hybrid waves and neutral beams in the JT-60 tokamak

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