Electron cyclotron heating of stellarator plasma with ordinary and extraordinary modes in JIPP T-II

Ohkubo, Κ.; Kawahata, K.; Noda, N.; Ogawa, I.; Kako, E.; Tanahashi, S.; Matsuura, K.; Fujita, J.; Cho, T.; Terumichi, Y.; Tanaka, Shigetoshi

doi:10.1088/0029-5515/22/8/009

Cited by 16 publications

(11 citation statements)

References 14 publications

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“…7(f).) 6), ( 7) and ( 9 Eqs (6) and (9). The calculation is initiated by giving initial conditions of 6 X , B and Wj, and a AW is given when the ECH condition is satisfied during the bounce motion, accompanied by a change of 0.…”

Section: Heating Process Of the Hot Electronsmentioning

confidence: 99%

“…Research related to electron cyclotron heating (ECH) has recently been intensified for several types of plasma confinement devices because of the development of a high power microwave source (gyrotron) [1][2][3][4][5][6][7][8]. Plasmas produced by injecting microwaves near the electron cyclotron resonance (ECR, a?…”

Section: Introductionmentioning

confidence: 99%

“…Plasmas produced by injecting microwaves near the electron cyclotron resonance (ECR, a? = fi e ) have been utilized in stellarators [6,7] and for preionization of discharges in tokamaks [8,9]. High energy (hot) electrons produced by ECH play an important role in maintaining MHD stability in bumpy tori [10] and as resonant particles for radiofrequency (RF) current startup without Ohmic heating [11][12][13] as well as for ECH current drive [14] in tokamaks.…”

Section: Introductionmentioning

confidence: 99%

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Observation of hot electrons produced by second harmonic electron cyclotron heating in the axisymmetric tandem mirror GAMMA 10

et al. 1987

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Microwave power, P ECH < 140 kW, has been injected at 28 GHz into the axisymmetric plug/barrier cell in the axisymmetrized tandem mirror GAMMA 10. As observed by soft X-ray measurements, the microwaves generate a hot (50-60 keV) electron population, radially peaked on the magnetic axis, which results in the formation of a thermal barrier. The production mechanism of these hot electrons is found to be second harmonic electron cyclotron heating (ECH), corrected for the effects of the relativistic mass variation and the Doppler shift. This mechanism also explains the first experimental observation of a saturation of the single-component hot electron temperature T eh as being caused by the finite width of the incident microwave lobe. The dependence of the plasma parameters on the filling gas pressure, the plasma density and the ECH power is studied. It is found that the heating process can be interpreted as a competition between electron acceleration by the incident wave, electron deceleration by collisions, and the mirror trapping efficiency of the source electrons for hot electrons. The axial profile of the soft X-rays is investigated in relation to the mechanism of the second harmonic ECH. The heating process is discussed in terms of the electron pitch angle and the magnetic field intensity.

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Section: Heating Process Of the Hot Electronsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Observation of hot electrons produced by second harmonic electron cyclotron heating in the axisymmetric tandem mirror GAMMA 10

et al. 1987

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“…The development of non-inductive current drive is one of the key issues in the investigation of tokamaks and, so far, only the lower hybrid slow wave current drive (LHSWCD) has been found to achieve it [1][2][3][4][5][6][7][8][9]. However, its prospects are bleak because of its density limit, and various alternative candidates for noninductive current drive have been proposed and discussed in the design work for the DEMO reactor [10].…”

Section: Introductionmentioning

confidence: 99%

ICRF current drive experiment on JIPP T-IIU

et al. 1986

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In the JIPP T-IIU tokamak an experiment to demonstrate the feasibility of fast wave current drive using five loop antennas has been successfully carried out with a relatively high density plasma (ωpe2/ωce2∼5). The RF frequency is 40 MHz and the toroidal field is 2 kG, which corresponds to ω = 13ωcH. The experiment is conducted in the density range n̄e ∼ 2 × 1018 m−3 where only the fast wave can propagate, eliminating the possibility of slow wave current drive. This density is two orders of magnitude higher than the density limit predicted for slow wave current drive. The dependence of the drive efficiency on the relative phase difference Δφ is clearly observed with a maximum of about Δφ = π/4. The plasma current was limited by MHD instability which begins to occur around qa = 10.

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“…First, a cold and lowdensity target plasma is produced by the electron cyclotron wave of an ordinary mode (/=35.5 GHz) which is injected from the low-field side. 9 The electron cyclotron-resonance layer (ECR layer) is located at R =0.91 m where the toroidal field B t is L27 T. The initial filling-gas pressure P is 5x 10" 5 Torr for hydrogen. The electron temperature and density of the ECR plasma are about 20 eV and 2x 10 12 cm" 3 , which are measured by a movable floating double probe.…”

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confidence: 99%

Startup and Quasistationary Drive of Plasma Current by Lower Hybrid Waves in a Tokamak

et al. 1984

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A plasma current is initiated and raised to a quasistationary level of about 20 kA by injection of the lower hybrid wave into a cold and low-density plasma produced by electron cyclotron resonance. The plasma current rises more slowly than the experimentally obtained L p /Rp magnetic diffusion time of the bulk plasma. The current rise time is inversely proportional to the bulk electron density, and agrees well with the collision time of the currentcarrying high-energy electrons with the bulk plasma.PACS numbers: 52.40.Db, 52.55.Gb A plasma current generated by an Ohmic heating electric field is maintained by injecting lower hybrid waves (LHW) in many tokamaks. 1 "" 6 These experimental results demonstrate the possibility of a steady-state operation in a future large tokamak.The startup of plasma current by a noninductive method is attractive for the further saving of the volt-seconds of the Ohmic heating transformer.Recently, experiments on current-startup by LHW have been tried in a target plasma produced by LHW alone 7 or by electron cyclotron resonance (ECR). 8 In the WT-2 tokamak, the plasma current increases linearly in time. However, the quasisteady state is not attained since the pulse duration of LHW is relatively short. The realization of the quasisteady state in the plasma current initiated by rf is necessary to clarify the mechanisms of the startup and quasistationary drive and to establish the startup scenario in a future large tokamak.In this Letter, we report on the startup and quasistationary drive of the plasma current by LHW in which the pulse width (=170 ms) is much longer than the experimentally obtained L p /R p time, where L p and R p are the total inductance and resistance of the bulk plasma. The experiments are carried out on the Japanese Institute of Plasma Physics T-IIU tokamak (major radius R 0 = 0.93 m and minor radius a L = 0.25 m). First, a cold and lowdensity target plasma is produced by the electron cyclotron wave of an ordinary mode (/=35.5 GHz) which is injected from the low-field side. 9 The electron cyclotron-resonance layer (ECR layer) is located at R =0.91 m where the toroidal field B t is L27 T. The initial filling-gas pressure P is 5x 10" 5 Torr for hydrogen. The electron temperature and density of the ECR plasma are about 20 eV and 2x 10 12 cm" 3 , which are measured by a movable floating double probe. Next, the LHW is injected into the ECR plasma via the launcher of a pair of C-shaped waveguides. 4 The calculated spectrum of the power emitted from the waveguides has a wide spread of parallel refractive index (n\\) from 4 to 1.4, which corresponds to a critical value of the accessibility condition for n e = 2x 10 12 cm -3 . In the current startup by rf alone, it is particularly essential to control the vertical field carefully. A quasistationary vertical field of about 10 G is always applied at the beginning of the LHW pulse to bring the Larmor radius of a high-energy electron beam inside the vacuum vessel, 10 where the stray field is estimated at below 2 G under this exper...

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Electron cyclotron heating of stellarator plasma with ordinary and extraordinary modes in JIPP T-II

Cited by 16 publications

References 14 publications

Observation of hot electrons produced by second harmonic electron cyclotron heating in the axisymmetric tandem mirror GAMMA 10

Observation of hot electrons produced by second harmonic electron cyclotron heating in the axisymmetric tandem mirror GAMMA 10

ICRF current drive experiment on JIPP T-IIU

Startup and Quasistationary Drive of Plasma Current by Lower Hybrid Waves in a Tokamak

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