Non-Inductive Current Drive

Westerhof, E.

doi:10.13182/fst12-a13518

Cited by 3 publications

(3 citation statements)

References 57 publications

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“…Exceeding the bifurcation threshold gives a hysteresis effect, with the island suppressed to widths below what would otherwise be achievable. Suggestively, the experiment observed suppression to widths well below the calculated widths of the deposition profiles, where the geometric stabilizing effect is predicted to be much reduced [61].…”

Section: Pacs Numbersmentioning

confidence: 84%

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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Section: Pacs Numbersmentioning

confidence: 84%

Suppression of Tearing Modes by Radio Frequency Current Condensation

Reiman

Fisch

2018

Phys. Rev. Lett.

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“…The non-inductive current drive is the most important consideration for long-pulse reactors. Currently, the experiments with LHCD, ECRH and NBI have generated a certain database, showing efficiency γ CD up to 0.35 MA•m −2 •MW −1 [58][59][60][61]. However, for reactor level plasmas, the LHCD may not be suitable due to high densities and temperature and may drive current only in the outer region.…”

Section: Physics Considerations For the Staged Approachmentioning

confidence: 99%

A staged approach to Indian DEMO

Deshpande,

Maya

2023

Nucl. Fusion

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We present a revised strategy for Indian DEMO in the context of new technologies and concepts in fusion research. The central idea behind the new strategy is that the power plant is a reactor-park consisting of multiple, preferably compact, reactors with moderate fusion power ($\sim$ 1000 MW) with 35~\% to 50 \% availability for each. The DEMO is a single net electricity producing unit that becomes the basis for replication into multiple units on a commercial scale. One of the key enablers for the revised strategy is the emergence of high-temperature superconductors for high field magnets. For a steady-state burn we show that there exists an optimum regimeof plasma β and confinement where the fusion gain is maximum. Thus, we adopt a strategy with moderate confinement regimes and plasma $\beta$. This makes current drive a necessity for the reactors. Based on these considerations a four-stage approach to DEMO is proposed. It is argued that an electricity producing pilot plant with fusion power of 200 MW - 300 MW is needed before the DEMO to establish the power performance, tritium breeding and its re-use over sufficiently long pulses. An integrated test facility must precede the pilot to test and qualify the technologies for the pilot stage. The revised approach takes into account realistic assumptions on power balance, current drive efficiency and magnet lifetime-dose; factors that pose constraints in identifying potential reactor configurations. Parameter choices for possible options for the integrated test facility (Fusion Engineering Science and Test - FEST), pilot plant and DEMO are presented that can be used to initiate conceptual designs and directed R\&D.

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“…More recent reviews have focused on the electron cyclotron current drive effect [4] or the lower hybrid current drive effect [5]. There have also been a number of tutorial reviews or didactic reviews [6][7][8][9], including reviews of unsolved issues [10]. The underlying physical processes rely importantly on the wave-particle resonance, which was the subject of a recent tutorial paper as well [11].…”

Section: Past: the Current Drive Effectmentioning

confidence: 99%

Pushing Particles with Waves: Current Drive and <i>α</i>-Channeling

Fisch

2016

Plasma and Fusion Research

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It can be advantageous to push particles with waves in tokamaks or other magnetic confinement devices, relying on wave-particle resonances to accomplish specific goals. Waves that damp on electrons or ions in toroidal fusion devises can drive currents if the waves are launched with toroidal asymmetry. Theses currents are important for tokamaks, since they operate in the absence of an electric field with curl, enabling steady state operation. The lower hybrid wave and the electron cyclotron wave have been demonstrated to drive significant currents. Noninductive current also stabilizes deleterious tearing modes. Waves can also be used to broker the energy transfer between energetic alpha particles and the background plasma. Alpha particles born through fusion reactions in a tokamak reactor tend to slow down on electrons, but that could take up to hundreds of milliseconds. Before that happens, the energy in these alpha particles can destabilize on collisionless timescales toroidal Alfven modes and other waves, in a way deleterious to energy confinement. However, it has been speculated that this energy might be instead be channeled instead into useful energy, that heats fuel ions or drives current. An important question is the extent to which these effects can be accomplished together.

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Non-Inductive Current Drive

Abstract: ABSTRACT

Cited by 3 publications

References 57 publications

Suppression of Tearing Modes by Radio Frequency Current Condensation

Suppression of Tearing Modes by Radio Frequency Current Condensation

A staged approach to Indian DEMO

Pushing Particles with Waves: Current Drive and <i>α</i>-Channeling

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