Study of Electron Orbits for Formation of Toroidal Closed Flux Surface by ECH

Maekawa, Takashi; Yoshinaga, T.; Tanaka, Hitoshi; Uchida, Masaki; Watanabe, F.

doi:10.1088/1009-0630/13/3/13

Cited by 2 publications

(4 citation statements)

References 8 publications

(14 reference statements)

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“…In order to realize CFP orbits at an appropriate energy range in large devices B Z should be lowered substantially. This RB Z scaling was shown in a different way in a previous paper [29].…”

Section: The Case In a Large Tokamaksupporting

confidence: 48%

“…Effects from the equilibrium electrostatic electric field are neglected. By taking advantage of the merit that there are three constants of motion in the present case, the guiding-center orbits may be obtained as follows [29]. The constants are the angular momentum, magnitude of the velocity and the magnetic moment as follows,…”

Section: Cfp Orbits and Confinement Mappingmentioning

confidence: 99%

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Open field equilibrium current and cross-field passing electrons as an initiator of a closed flux surface in EC-heated toroidal plasmas

Maekawa¹,

Yoshinaga²,

Uchida³

et al. 2012

Nucl. Fusion

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A modeling for the non-inductive initiation of a closed flux surface observed in electron cyclotron (EC) heated toroidal plasmas is presented. First, a pressure driven equilibrium toroidal current develops under a weak external vertical field so as to counter balance the pressure-ballooning and current-hoop forces. When the self field from the current almost cancels out the external vertical field, a forward energetic part of electrons in the velocity space begin to make cross field passing (CFP) orbits. The CFP electrons are generated by the EC heating of bulk electrons and subsequent pitch angle scattering, which is analyzed using the Fokker Planck equation. They provide an additional current that closes the filed lines. The model is examined for experiments in the small low aspect ratio device of LATE and in the large conventional device of JT-60U with a search for appropriate modes of EC heating. Simultaneous coincidence of the model with these two experiments is obtained in terms of microwave power and driven current. The results predict that initiation of closed flux surface requires more and more EC power as the plasma major radius increases. Especially, careful injection of high N ∥ EC waves are needed for large devices, both for initiation of a closed flux surface and for subsequent enlargement of the flux surface by usual EC current drive (ECCD) onto the closed flux area.

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Section: The Case In a Large Tokamaksupporting

confidence: 48%

Section: Cfp Orbits and Confinement Mappingmentioning

confidence: 99%

Open field equilibrium current and cross-field passing electrons as an initiator of a closed flux surface in EC-heated toroidal plasmas

Maekawa¹,

Yoshinaga²,

Uchida³

et al. 2012

Nucl. Fusion

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“…Section 4.1 describes initiation of a plasma. Section 4.2 investigates appropriate location of R ECR and magnitude of B V for closing the field lines based on the close field passing (CFP) electron model [7,14] and another model for very strong B t case of ITER. Section 4.3 describes development toward the tokamak stage through transition stage, and finally 4.4 addresses power requirements.…”

Section: Ox Methodsmentioning

confidence: 99%

“…One candidate is the current carried by the CFP electrons [7,14]. Figure 16 shows the generation process of CFP electrons in the electron velocity space.…”

Section: Initiation Of a Closed Flux Surface With Appropriate Choice ...mentioning

confidence: 99%

Non-inductive build-up of a hot plasma by X-wave ECH/ECCD to remove initial high loop-voltage from start-up of fusion tokamaks

Maekawa¹,

Uchida²,

Tanaka³

2017

Nucl. Fusion

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The possibility of non-inductive build-up of a hot plasma by X-wave ECH/ECCD to remove initial high loop-voltage stage from start-up of fusion tokamaks is theoretically investigated, using ITER parameters. There are two injection methods for X-wave ECH/ECCD in ITER start-up plasmas. The first is oblique X-wave injection from the low-field side, referred to as the DX method. For the low density start-up plasma at n e ≈ 1.0 × 10 19 m −3 , the wave with ω/2π = 200 GHz and N ∼ 0.6 is damped away via cyclotron resonance absorption before encountering the cyclotron cutoff layer when the electron temperature is as high as T e > 170 eV. The wave power is deposited into the resonance electrons of which parallel velocity is as fast as v > 2 2T e /m, which enables an efficient ECCD. The second method is oblique O-wave injection from the low-field side, referred to as the OX method. The waves pass through the ECR layer with negligible power deposition when T e < 400 eV and are mode-converted into oblique X-waves upon reflection on the inboard wall. The X-waves propagate toward the ECR layer without cutoff, and are cyclotron-damped away even when the temperature is as low as T e ∼ 7 eV. The OX method is appropriate for the initial open field stage and transition stage of the discharge, while the DX method is appropriate for the final tokamak stage, where T e is high. Discussions are given on the choice of appropriate B V and location of ECR layer for initiation of closed flux surfaces. Nine model plasmas from an initial open field plasma to a final hot tokamak plasma, consisting of a series of snapshots of a build-up discharge, are generated using an equilibrium theory, enabling estimation of required RF power to drive the current. These investigations suggest that an injection power P rf ∼ 4 MW could build up a hot plasma with I p = 205 kA, n e0 = 1.2 × 10 19 m −3 , T e0 = 2 keV, a = 1 m and R 0 = 5.1 m.

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Study of Electron Orbits for Formation of Toroidal Closed Flux Surface by ECH

Cited by 2 publications

References 8 publications

Open field equilibrium current and cross-field passing electrons as an initiator of a closed flux surface in EC-heated toroidal plasmas

Open field equilibrium current and cross-field passing electrons as an initiator of a closed flux surface in EC-heated toroidal plasmas

Non-inductive build-up of a hot plasma by X-wave ECH/ECCD to remove initial high loop-voltage from start-up of fusion tokamaks

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