Efficient lower hybrid current drive using a multijunction launcher on JT-60

Ikeda, Yoshitaka; Imai, T.; Ushigusa, K.; Seki, M.; Konishi, Kuniaki; Naito, O.; Honda, M.; Kiyono, K.; Maebara, S.; Nagashima, Takashi; Sawahata, M.; Suganuma, K.; Suzuki, Norio; Uehara, K.; Yokokura, K.; Team, Jt

doi:10.1088/0029-5515/29/10/016

Cited by 26 publications

(8 citation statements)

References 25 publications

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“…The following constraint is needed to get the driven current to 70% of the total plasma current: e 05 ft, = 1.07 (5) Equations ( 4) and ( 5) are based on the Hinton-Hazeltine theory, which is valid only for extremely slender and pure electron-ion plasmas. The parameter dependence is significantly different from that calculated with the finite aspect ratio from the Hirshman-Sigmar theory [24].…”

Section: Bootstrap Currentmentioning

confidence: 99%

“…Current drive by lower hybrid waves has been studied extensively after the outstanding results of Fisch [4] became generally known. The current drive efficiency in JT-60 has been improved [5], but the lower hybrid wave is thought to be applicable only for peripheral current drive in a high temperature reactor because of poor wave penetration into the plasma core [6]. Recent observations of the bootstrap current in TFTR [7] have stimulated renewed interest in a stationary tokamak based on the bootstrap current.…”

Section: Introductionmentioning

confidence: 99%

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Steady state tokamak reactor based on the bootstrap current

1990

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A concept of a steady state tokamak fusion reactor based on the bootstrap current is presented. Operation at high poloidal beta (βp ≥ 2.0) and high q (4–5) with a relatively small limit on ∈βp (< 0.5) makes it possible to drive a bootstrap current constituting up to 70% of the total plasma current without exceeding the Troyon beta limit. The rest of the plasma current can be driven by the high energy neutral beam with an energy multiplication factor Q of 30. Energy confinement scaling laws predict that the reactor condition is attainable by increasing the major radius up to 9 m in such a high βp and high q plasma at a relatively low plasma current (12 MA) with a confinement enhancement factor of 2 compared with the L-mode scaling. This reactor has a reasonable size (Vp = 1500 m3) and fusion output power (2.5 GW) and is consistent with present knowledge regarding tokamak plasma physics, namely the Troyon limit, the energy confinement scalings, the bootstrap current and the current drive efficiency (neutral beam current drive with a total power of 70 MW and a beam energy of 1 MeV) with good prospects for the formation of a cold and dense divertor plasma.

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Section: Bootstrap Currentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Steady state tokamak reactor based on the bootstrap current

1990

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“…Here we ignore terms of order r/R., so that there is no distinction made between p and r. Since n is conserved and the initial edge value of m is taken to be zero, one finds that k 11 , ; n/R, and m -(kI 1 p, whose precise calculation depends on the details of the ray trajectory. However, because the power spectrum of the source, S(n 1 ), is narrow compared to the spectrum which is found inside the plasma from the ray tracing, we may take (nI 10 ) to be a constant. The prediction of (47) is shown in Figure 3 …”

Section: (Ukl -W)a(k X)mentioning

confidence: 99%

Fast electron transport in lower-hybrid current drive

Küpfer

Bers

1991

Physics of Fluids B: Plasma Physics

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The quasilinear Fokker–Planck formulation is generalized for lower-hybrid current drive to include the wave-induced radial transport of fast electrons. Toroidal ray tracing shows that the wave fields in the plasma develop a large poloidal component associated with the upshift in k∥ and the filling of the ‘‘spectral gap.’’ These fields lead to an enhanced radial E×B drift of resonant electrons. Two types of radial flows are obtained: an outward convective flow driven by the asymmetry in the poloidal wave spectrum, and a diffusive flow proportional to the width of the poloidal spectrum. Numerical results relevant to Alcator C [Phys. Rev. Lett. 53, 450 (1984)] and JT-60 [Nucl. Fusion 29, 1815 (1989)] are presented; they show that the radial convection velocity has a broad maximum of nearly 1 m/sec and is independent of the amplitude of fields. In both cases, the radial diffusion is found to be highly localized near the magnetic axis. For JT-60, the peak of the diffusion profile can be quite large, nearly 1 m2/sec.

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“…A double stub matching network with electronically controlled tuning stubs is under development for the lower hybrid current drive (LHCD) system on Alcator C-Mod [3,4]. The multijunction concept employed in many LHCD experiments [5,6,7,8,9] reduces reflected power passively through destructive interference of the reflected waves, but at the cost of n || spectrum control. The peak n || of a multijunction antenna is adjustable over a small range (n ||,peak = n ||,0 ± δn || where δn || ∼ 0.1 for ITER and δn || ∼ 0.3 for Tore Supra), but is not capable of larger changes in n || or use in reverse current operation.…”

Section: Introductionmentioning

confidence: 99%

Analysis of double stub tuner control stability in a phased array antenna with strong cross-coupling

Wallace

Hillairet

Koert

et al. 2014

Fusion Engineering and Design

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Active stub tuning with a fast ferrite tuner (FFT) has greatly increased the effectiveness of fusion ion cyclotron range of frequency (ICRF) systems (50-100 MHz) by allowing for the antenna system to respond dynamically to changes in the plasma load impedance such as during the L-H transition or edge localized modes (ELMs). A high power waveguide double-stub tuner is under development for use with the Alcator C-Mod lower hybrid current drive (LHCD) system at 4.6 GHz. The amplitude and relative phase shift between adjacent columns of an LHCD antenna are critical for control of the launched n || spectrum. Adding a double-stub tuning network will perturb the phase and amplitude of the forward wave particularly if the unmatched reflection coefficient is high. This effect can be compensated by adjusting the phase of the low power microwave drive for each klystron amplifier. Crosscoupling of the reflected power between columns of the launcher must also be considered. The problem is simulated by cascading a scattering matrix for the plasma provided by a linear coupling model with the measured launcher scattering matrix and that of the FFTs. The solution is advanced in an iterative manner similar to the time-dependent behavior of the real system. System performance is presented under a range of edge density conditions from under-dense to over-dense and a range of launched n || . Simulations predict power reflection coefficients (Γ 2 ) of less than 1% with no contamination of the n || spectrum. Instability of the FFT tuning network can be problematic for certain plasma conditions and relative phasings, but reducing the control gain of the FFT network stabilizes the system.

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Efficient lower hybrid current drive using a multijunction launcher on JT-60

Cited by 26 publications

References 25 publications

Steady state tokamak reactor based on the bootstrap current

Steady state tokamak reactor based on the bootstrap current

Fast electron transport in lower-hybrid current drive

Analysis of double stub tuner control stability in a phased array antenna with strong cross-coupling

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