Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas

Abstract As a new spherical tokamak (ST) designed to simplify engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio (A) vacuum vessel (VV), encircling a central post assembly containing the toroidal field coil conductors. Multiple electron cyclotron resonance heating (ECRH) resonances are located within the VV to possibly improve current drive effectiveness. The energetic electrons are observed via hard X-ray detectors, carry the bulk of the plasma current ranging from 50kA to 150kA, which is maintained for more than 1s duration. It is observed that over one Ampere current can be maintained per Watt of ECRH power issued from the 28-GHz gyrotrons. The plasma current with high line-density (approaching 1019m-2) has been achieved for plasma currents as high as 76kA. An analysis was carried out combining reconstructed multi-fluid equilibrium, guiding-center orbits, and resonant heating mechanisms. It is verified that in EXL-50 a broadly distributed current of energetic electrons creates smaller closed magnetic-flux surfaces of low aspect ratio that in turn confine the thermal plasma electrons and ions and participate in maintaining the equilibrium force-balance.

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Investigations of microwave and THz radiation losses in CVD diamond and chemically modified diamond

MRS Proceedings ◽

10.1557/opl.2011.452 ◽

2011 ◽

Vol 1282 ◽

Cited By ~ 1

Author(s):

T. A. Scherer ◽

D. Strauss ◽

A. Meier ◽

Y.-L. Mathis ◽

V. Judin ◽

...

Keyword(s):

Electron Cyclotron Resonance ◽

Power Level ◽

Cvd Diamond ◽

Current Drive ◽

Electron Cyclotron Resonance Heating ◽

Thz Radiation ◽

Vacuum Vessel ◽

Tearing Modes ◽

Absorbed Power ◽

Tan Δ

ABSTRACTTo counteract plasma instabilities like Neoclassical Tearing Modes (NTM-modes) in nuclear fusion reactors (JET, ITER, DEMO) high power microwaves are used for the Electron Cyclotron Resonance Heating (ECRH) and for the plasma current drive (CD). The foreseen power level for ITER (Cadarache, France) is Ptot = 24 MW at f = 170 GHz. Each transmission line is designed for a maximum of 2 MW power. The vacuum and tritium barrier to the ITER vacuum vessel is realized by a CVD diamond disk window assembly. Diamond has an extremely high thermal conductivity of about k = 2100 W/Km and a very low loss tangent of tan δ < 10-5 for this frequency and shows therefore a very small microwave absorption. The normalized absorbed power A=Pabs/P0 can be calculated as A = (f/c) • π • (1+εr‘) • tan δ • t (with the rule of thumb estimate: (f/c)=0.5 mm-1; π • (1+εr‘) = 20; tan δ =10-5; A=10-4 • t [mm]); i.e. each t = 1 mm thickness of diamond absorbs Pabs = 100 W of Po = 1 MW microwave power transmitted through the CVD diamond window with an effective tanδ of 10-5.

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Observation of second harmonic electron cyclotron resonance heating and current-drive transition during non-inductive plasma start-up experiment in QUEST

Plasma Physics and Controlled Fusion ◽

10.1088/1361-6587/ac1838 ◽

2021 ◽

Author(s):

Shinichiro Kojima ◽

Kazuaki Hanada ◽

Hiroshi Idei ◽

Takumi Onchi ◽

Ryuya Ikezoe ◽

...

Keyword(s):

Cyclotron Resonance ◽

Electron Cyclotron Resonance ◽

Second Harmonic ◽

Electron Cyclotron ◽

Current Drive ◽

Electron Cyclotron Resonance Heating ◽

Start Up

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Structure and relative importance of ponderomotive forces and current drive generated by converted fast waves in pre-heated low aspect ratio tokamaks

Physics Letters A ◽

10.1016/s0375-9601(03)00459-6 ◽

2003 ◽

Vol 311 (2-3) ◽

pp. 221-241 ◽

Cited By ~ 1

Author(s):

S. Cuperman ◽

C. Bruma ◽

K. Komoshvili

Keyword(s):

Aspect Ratio ◽

Current Drive ◽

Relative Importance ◽

Low Aspect Ratio ◽

Ponderomotive Forces ◽

Fast Waves

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Low Aspect Ratio Tokamak Formation and Sustainment by Coaxial Helicity Injection Current Drive

Fusion Technology ◽

10.13182/fst95-a11947099 ◽

1995 ◽

Vol 27 (3T) ◽

pp. 333-336

Author(s):

B. A. Nelson ◽

T. R. Jarboe ◽

D. J. Orvis ◽

A. K. Martin ◽

J. Xie ◽

...

Keyword(s):

Aspect Ratio ◽

Current Drive ◽

Injection Current ◽

Helicity Injection ◽

Low Aspect Ratio ◽

Coaxial Helicity Injection

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Concurrent operation of 10 gyrotrons at W7-X experience and improvement opportunities

EPJ Web of Conferences ◽

10.1051/epjconf/201818701003 ◽

2018 ◽

Vol 187 ◽

pp. 01003 ◽

Cited By ~ 1

Author(s):

H. Braune ◽

K.J. Brunner ◽

H.P. Laqua ◽

S. Marsen ◽

D. Moseev ◽

...

Keyword(s):

Steady State ◽

Cyclotron Resonance ◽

Electron Cyclotron Resonance ◽

Heating System ◽

Current Drive ◽

Electron Cyclotron Resonance Heating ◽

Neutral Gas ◽

Steady State Operation ◽

Start Up ◽

Operation Phase

At the stellarator Wendelstein 7-X (W7-X) Electron Cyclotron Resonance Heating (ECRH) is the main heating system for steady-state operation and was the only available heating system during the operation phase OP1.2a in 2017. The ECRH, equipped with 10 operational 140 GHz gyrotrons [1], was used for different tasks at W7-X such as wall conditioning, controlled plasma start-up from the neutral gas up to steady state plasma control and different heating scenarios such as X2-mode and O2-mode heating as well as current drive (ECCD). The operational experiences and improvement opportunities of the ECRH plant will be discussed.

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