Complete stabilization of a tearing mode in steady state high-β<sub>p</sub>H-mode discharges by the first harmonic electron cyclotron heating/current drive on JT-60U

Isayama, A.; Kamada, Y.; Ide, S.; Hamamatsu, K.; Oikawa, T.; Suzuki, Takahiro; Neyatani, Y.; Ozeki, T.; Ikeda, Y.; Kajiwara, K.

doi:10.1088/0741-3335/42/12/102

Cited by 169 publications

(132 citation statements)

References 14 publications

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“…An advanced plasma control system allows integrated control of these elements. Neoclassical tearing modes ͑NTMs͒ are avoided through current profile control, although active feedback stabilization using localized ECCD [10][11][12][13] has also been demonstrated.…”

Section: Introductionmentioning

confidence: 99%

Progress toward fully noninductive, high beta conditions in DIII-D

et al. 2006

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The DIII-D Advanced Tokamak ͑AT͒ program in the DIII-D tokamak ͓J. L. Luxon, Plasma Physics and Controlled Fusion Research, 1986, Vol. I ͑International Atomic Energy Agency, Vienna, 1987͒, p. 159͔ is aimed at developing a scientific basis for steady-state, high-performance operation in future devices. This requires simultaneously achieving 100% noninductive operation with high self-driven bootstrap current fraction and toroidal beta. Recent progress in this area includes demonstration of 100% noninductive conditions with toroidal beta, ␤ T = 3.6%, normalized beta, ␤ N = 3.5, and confinement factor, H 89 = 2.4 with the plasma current driven completely by bootstrap, neutral beam current drive, and electron cyclotron current drive ͑ECCD͒. The equilibrium reconstructions indicate that the noninductive current profile is well aligned, with little inductively driven current remaining anywhere in the plasma. The current balance calculation improved with beam ion redistribution that was supported by recent fast ion diagnostic measurements. The duration of this state is limited by pressure profile evolution, leading to magnetohydrodynamic ͑MHD͒ instabilities after about 1 s or half of a current relaxation time ͑ CR ͒. Stationary conditions are maintained in similar discharges ͑ϳ90% noninductive͒, limited only by the 2 s duration ͑1 CR ͒ of the present ECCD systems. By discussing parametric scans in a global parameter and profile databases, the need for low density and high beta are identified to achieve full noninductive operation and good current drive alignment. These experiments achieve the necessary fusion performance and bootstrap fraction to extrapolate to the fusion gain, Q = 5 steady-state scenario in the International Thermonuclear Experimental Reactor ͑ITER͒ ͓R. Aymar et al., Fusion Energy Conference on Controlled Fusion and Plasma Physics, Sorrento, Italy ͑International Atomic Energy Agency, Vienna, 1987͒, paper IAEA-CN-77/OV-1͔. The modeling tools that have been successfully employed to both plan and interpret the experiment are used to plan future DIII-D experiments with higher power and longer pulse ECCD and fast wave and co-and counterneutral beam injection in a pumped double-null configuration. The models predict our ability to control the current and pressure profiles to reach full noninductivity with increased beta, bootstrap fraction, and duration. The same modeling tools are applied to ITER, predicting favorable prospects for the success of the ITER steady-state scenario.

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Section: Introductionmentioning

confidence: 99%

Progress toward fully noninductive, high beta conditions in DIII-D

et al. 2006

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“…Moreover, we find that an adjacent resonant mode previously expected to compete with and adversely affect the principal operating mode does not in fact jeopardize but rather helps this mode as a result of nonlinear effects. The result improves the outlook for using these devices for heating and instability control in future experimental fusion reactors, such as ITER [14][15][16][17][18][19] .…”

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confidence: 85%

Achievement of robust high-efficiency 1 MW oscillation in the hard-self-excitation region by a 170 GHz continuous-wave gyrotron

et al. 2007

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Gyrotrons are a high-power source of coherent microwave radiation 1 . Their oscillation mechanism is a cyclotron-resonance maser effect, in which a fraction of the rotational kinetic energy of a mildly relativistic magnetized electron beam is converted into electromagnetic energy. The most active area of gyrotron development is their potential use for heating magnetically confined fusion plasmas to the point of thermonuclear ignition. A major obstacle to this endeavour is that during high-power millimetre-wave operation 2-9 competing modes and mode shifts seriously degrade a gyrotron's stability and efficiency 10-13 . Here, we show that these problems can be overcome by active control of the electron-beam parameters during the oscillation. In doing so, we successfully demonstrate the robust steady-state operation of a 170 GHz gyrotron producing a continuous 1 MW output power with an unprecedented efficiency of over 55% in a hard-selfexcitation region. Moreover, we find that an adjacent resonant mode previously expected to compete with and adversely affect the principal operating mode does not in fact jeopardize but rather helps this mode as a result of nonlinear effects. The result improves the outlook for using these devices for heating and instability control in future experimental fusion reactors, such as ITER [14][15][16][17][18][19] .A basic configuration of the high-power gyrotron oscillator used in the experiment 7 is shown in Supplementary Information, Figs S1,S2. The nominal operation mode is TE 31,8 , in a cylindrical open resonator, whose radius is 17.9 mm. An annular electron beam of 9.13 mm in radius is injected into the resonator along the axial magnetic field to excite TE 31,8 . The oscillation millimetre-wave power P osci is converted to a gaussian-like beam using a quasi-optical launcher 20,21 attached to the resonator, and transmitted through an edge-cooled diamond window as P out . Here, P out ∼ 0.92P osci due to the ohmic loss and the diffraction loss P loss . The collector of the gyrotron is earthed. By applying a positive voltage V d.c. to the resonator section against the collector, the energy recovery of the spent electron beam is available to enhance the overall efficiency 22 .After a demonstration of 1 h oscillation at P out = 0.6 MW with fixed parameters, the operation parameters are actively controlled with a slow timescale to investigate the oscillation characteristics in the continuous-wave state. Figure 1a shows the dependence of the output power on the magnetic field in the resonator, B c . Here, V b ∼ −72.5 kV and V d.c. ∼ 25.5 kV. After the electron-beam I b had stabilized at ∼30 A completely, which takes ∼1 min, the B c scan started from 6.72 T. The frequency is ∼170 GHz. The power increases as the B c decreases, that is, the cyclotron resonance mismatch factor Δ = (1 − (f ce /γf )) increases. Here, f and f ce are oscillation and non-relativistic cyclotron frequencies, respectively, and γ is a relativistic factor of the initial electrons. The maximum power of 0.8 MW is obtained...

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“…By the time of the previous review [5], the suppression of (m=3,n=2) NTMs had been demonstrated in several tokamaks [24], [25], [26] and [27] and first experiments on partial (2,1) suppression had been carried out. Also, first attempts at feedback control of the deposition had been made.…”

Section: Application Of Ecrh and Eccd For Optimization Of Plasma Stabmentioning

confidence: 99%

Recent Experimental Progress in Electron Cyclotron Resonance Heating and Electron Cyclotron Current Drive in Magnetically Confined Fusion Plasmas

Zohm

2007

Fusion Science and Technology

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A review of recent experimental results in the area of ECRH and ECCD is given. Special emphasis is put on the recent developments of new schemes in which EC waves can heat and drive current in magnetically confined fusion plasmas. These comprise scenarios to overcome the density cutoff experienced in application of the classical O1 and X2 scheme as well as to increase the current drive efficiency of EC waves while maintaining their good localization. In particular, we discuss recent experimental progress in tokamaks, stellarators and spherical tori in the areas of the O2, X3 and EBW schemes (mostly OXB scheme) as well as experiments in which the combination of ECCD with Lower Hybrid Current Drive (LHCD) leads to a synergetic increase of the ECCD efficiency. A particular application of ECCD that has recently received a lot of attention and is therefore reviewed in this paper is the suppression of Neoclassical Tearing Modes (NTMs) by ECCD. We show that the theoretically predicted requirements for ECCD in terms of deposition (maximising the ECCD driven current density) and injection in phase with the O-point of the magnetic island associated with the NTM (which is needed when the island width falls below the deposition width) have been verified experimentally. Also, many of the elements needed for constructing a reliable, feedback controlled NTM suppression system for ITER based on ECCD have now been demonstrated experimentally and the next step, which is their integration into a reliable scheme, is well within reach.

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Complete stabilization of a tearing mode in steady state high-β_pH-mode discharges by the first harmonic electron cyclotron heating/current drive on JT-60U

Cited by 169 publications

References 14 publications

Progress toward fully noninductive, high beta conditions in DIII-D

Progress toward fully noninductive, high beta conditions in DIII-D

Achievement of robust high-efficiency 1 MW oscillation in the hard-self-excitation region by a 170 GHz continuous-wave gyrotron

Recent Experimental Progress in Electron Cyclotron Resonance Heating and Electron Cyclotron Current Drive in Magnetically Confined Fusion Plasmas

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Complete stabilization of a tearing mode in steady state high-βpH-mode discharges by the first harmonic electron cyclotron heating/current drive on JT-60U

Cited by 169 publications

References 14 publications

Progress toward fully noninductive, high beta conditions in DIII-D

Progress toward fully noninductive, high beta conditions in DIII-D

Achievement of robust high-efficiency 1 MW oscillation in the hard-self-excitation region by a 170 GHz continuous-wave gyrotron

Recent Experimental Progress in Electron Cyclotron Resonance Heating and Electron Cyclotron Current Drive in Magnetically Confined Fusion Plasmas

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Complete stabilization of a tearing mode in steady state high-β_pH-mode discharges by the first harmonic electron cyclotron heating/current drive on JT-60U