Recharging of the ohmic-heating transformer by means of lower-hybrid current drive in the ASDEX tokamak

Leuterer, F.; Eckhartt, D.; Söldner, F. X.; Becker, G.; Bernhardi, K.; Brambilla, M.; Brinkschulte, H.; Derfler, H.; Ditte, U.; Eberhagen, A.; Fussman, G.; Gehre, O.; Gernhardt, J.; Gierke, G. von; Glock, E.; Gruber, O.; Haas, G.; Hesse, Michael; Janeschitz, G.; Karger, F.; Keilhacker, M.; Kissel, S.; Klüber, O.; Kornherr, M.; Lisitano, G.; Magne, R.; Mayer, H. M.; McCormick, K.; Meisel, D.; Mertens, V.; Müller, E.; Münich, M.; Mürmann, H.; Poschenrieder, W.; Rapp, H.; Ryter, F.; Schmitter, K.H.; Schneider, F.; Siller, G.; Smeulders, P.; Steuer, K.-H.; Vien, T.; Wagner, F.; Woyna, F. v.; Zouhar, Martin

doi:10.1103/physrevlett.55.75

Cited by 59 publications

(23 citation statements)

References 9 publications

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“…With several power levels, Eqs. (2) or (3) can be used to determine g 0 and g 1 simultaneously, by means of a simple two parameter least squares fit, even if in the absence of data at À DV V OH ¼ 1. For the three configurations, in which central electron temperature is about 1 keV and effective nuclear charge number (Z eff ) is about 3, the experimental dependence of the relative drop of loop voltage (DV=V OH ) on the normalized LHW power (P LH =I p n e R 0 ) are plotted in Fig.…”

Section: B Lhcd Efficiency Experiments and Analysismentioning

confidence: 99%

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Investigation of lower hybrid wave coupling and current drive experiments at different configurations in experimental advanced superconducting tokamak

Ding

Qin

et al. 2011

Physics of Plasmas

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Using a 2 MW 2.45 GHz lower hybrid wave (LHW) system installed in experimental advanced superconducting tokamak, we have systematically carried out LHW-plasma coupling and lower hybrid current drive experiments in both divertor (double null and lower single null) and limiter plasma configuration with plasma current (I p ) $ 250 kA and central line averaged density (n e ) $ 1.0-1.3 Â 10 19 m À3 recently. Results show that the reflection coefficient (RC) first is flat up to some distance between plasma and LHW grill, and then increases with the distance. Studies indicate that with the same plasma parameters, the best coupling is obtained in the limiter case (with plasma leaning on the inner wall), followed by the lower single null, and the one with the worst coupling is the double null configuration, explained by different magnetic connection length. The RCs in the different poloidal rows show that they have different coupling characteristics, possibly due to local magnetic connection length. Current drive efficiency has been investigated by a least squares fit with N peak == ¼ 2:1, where N peak == is the peak value of parallel refractive index of the launched wave. Results show that there is no obvious difference in the current drive efficiency between double null and lower single null cases, whereas the efficiency is somewhat small in the limiter configuration. This is in agreement with the ray tracing=Fokker-Planck code simulation by LUKE=C3PO and can be interpreted by the power spectrum up-shift factor in different plasma configurations. A transformer recharge is realized with $0.8 MW LHW power and the energy conversion efficiency from LHW to poloidal field energy is about 2%.

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Section: B Lhcd Efficiency Experiments and Analysismentioning

confidence: 99%

“…Nuclear fusion experiments have made a rapid progress since 1980s in many tokamaks by using LHCD. [1][2][3][4][5][6][7][8] A 2 MW 2.45 GHz LHW system has been installed and run in the experimental advanced superconducting tokamak (EAST), in which LHW-plasma coupling and LHCD experiments have been performed systematically recently.…”

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confidence: 99%

Investigation of lower hybrid wave coupling and current drive experiments at different configurations in experimental advanced superconducting tokamak

Ding

Qin

et al. 2011

Physics of Plasmas

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“…Hot Conductivity Current Condensation and Destabilization: In the presence of rf current drive, the ohmic current can be written as J OH = J Sp + J H , where J Sp = σ Sp E is the ohmic (Spitzer) current in the absence of the rf, and J H = σ H E is due to the hot conductivity σ H , arising from electron velocity space distortions proportional to the rf power dissipated [62]. Although the hot conductivity current is relatively small for usual tokamak operation, it may play a critical role in the case of rf current overdrive, which occurs when the rf is utilized for start-up operation [63][64][65][66][67][68], or when it is oscillated to optimize the current drive efficiency [69,70]. The hot conductivity σ H has been theoretically predicted [62] and experimentally verified in detail [71].…”

Section: Pacs Numbersmentioning

confidence: 99%

Suppression of Tearing Modes by Radio Frequency Current Condensation

Reiman

Fisch

2018

Phys. Rev. Lett.

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Currents driven by rf (radio frequency) waves in the interior of magnetic islands can stabilize deleterious tearing modes in tokamaks. Present analyses of stabilization assume that the local electron acceleration is unaffected by the presence of the island. However, the power deposition and electron acceleration are sensitive to the perturbation of the temperature. The nonlinear feedback on the power deposition in the island increases the temperature perturbation, and can lead to a bifurcation of the solution to the steady-state heat diffusion equation. The combination of the nonlinearly enhanced temperature perturbation with the rf current drive sensitivity to the temperature leads to an rf current condensation effect, which can increase the efficiency of rf current drive stabilization and reduce its sensitivity to radial misalignment of the ray trajectories. The threshold for the effect is in a regime that has been encountered in experiments, and will likely be encountered in ITER. PACS numbers:Introduction: A study of the root causes of disruptions in the JET tokamak found that neoclassical tearing modes (NTMs) were the single most common cause [1,2]. Theoretical calculations in the early 1980's showed the feasibility of using rf current drive to stabilize tearing modes [3,4]. The recognition in the late 1990's that bootstrap currents were driving NTMs in hot, collisionless tokamak plasmas [5][6][7][8], led to a resurgence of theoretical work in this area [9][10][11][12][13], to experimental demonstrations of stabilization [14][15][16][17][18][19][20], and to continuing intensive attention [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. A variety of rf waves are used to drive current [41], but, for stabilizing the NTM, the most studied methods are electron cyclotron current drive (ECCD) [42] and lower hybrid current drive (LHCD) [43]. ITER is designed with an NTM ECCD stabilization capability, with continued effort to model and improve this capability [25,29,30,44]. We identify here an rf current condensation effect, previously overlooked, which can significantly facilitate island stabilization.Calculations of rf stabilization of magnetic islands assume, at present, that the local acceleration of electrons is unaffected by the presence of the island. However, the local deposition is sensitive to small changes in the temperature, and these changes can be significantly affected by the presence of an island. The effect on the local deposition becomes significant when the fractional temperature perturbation exceeds about 5% for electron cyclotron waves and 2.5% for lower hybrid waves. Temperature perturbations as high as 20% have been measured in islands in rf stabilization experiments [45].In the conventional picture of rf current drive stabilization of a rotating island, a geometric effect associated with the equilibration of the rf driven current density within the flux surfaces of the island leads to a higher current density near the center of the island than near its peripher...

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“…These experiments confirm the general tendencies of transformer recharging experiments reported previously. [27][28][29][30] In the experiments, the plasma current was ramped up from I 0 ¼ 194 kA when 900 kW LH power injected, with which 240 kA current can be fully driven. Namely, the degree of current overdrive here is not high.…”

Section: Introductionmentioning

confidence: 99%

Current ramp-up with lower hybrid current drive in EAST

Ding¹,

Li²,

Fisch³

et al. 2012

Physics of Plasmas

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More economical fusion reactors might be enabled through the cyclic operation of lower hybrid current drive. The first stage of cyclic operation would be to ramp up the plasma current with lower hybrid waves alone in low-density plasma. Such a current ramp-up was carried out successfully on the EAST tokamak. The plasma current was ramped up with a time-averaged rate of 18 kA/s with lower hybrid (LH) power. The average conversion efficiency P el /P LH was about 3%. Over a transient phase, faster ramp-up was obtained. These experiments feature a separate measurement of the L/R time at the time of current ramp up. V C 2012 American Institute of Physics. [http://dx.

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Recharging of the ohmic-heating transformer by means of lower-hybrid current drive in the ASDEX tokamak

Cited by 59 publications

References 9 publications

Investigation of lower hybrid wave coupling and current drive experiments at different configurations in experimental advanced superconducting tokamak

Investigation of lower hybrid wave coupling and current drive experiments at different configurations in experimental advanced superconducting tokamak

Suppression of Tearing Modes by Radio Frequency Current Condensation

Current ramp-up with lower hybrid current drive in EAST

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