An effective heating method and experimental verification for a field-reversed configuration (FRC) plasma by applying the low-frequency magnetic pulse is presented. The low-frequency magnetic field is applied by an antenna that consists of two single-turn coils, and the frequency of the magnetic field is lower than the ion cyclotron frequency at the separatrix. An increase of the plasma energy and a fluctuation of the internal magnetic field are simultaneously observed. The comparison of the total temperature and the ion temperature shows that the increase of the plasma energy is mostly due to the ion heating. The fluctuation is directly observed by the internal magnetic probe arrays. The analysis of the phase velocity along the equilibrium magnetic field implies that the Alfven wave is excited and propagates.

Heating experiment of field-reversed configuration plasma by low-frequency magnetic pulse

Kinetic theory, including ion Larmor radius effects, is used to analyse the Alfven wave heating of cylindrical plasmas using axisymmetric waves excited by an antenna at frequencies up to the ion cyclotron frequency. At the Alfven resonance position, the compressional wave is mode converted to a quasi-electrostatic wave (QEW) which propagates towards the plasma centre or edge depending on whether the plasma is hot or warm. The energy absorbed by the plasma agrees with the MHD theory predictions provided the QEW is heavily damped before reaching the plasma centre or edge; if it is not, then QEW resonances may occur with a consequent increase in antenna resistance. The relation between ion cyclotron wave resonances and QEW resonances in a hot plasma is shown. The behaviour described above is demonstrated by numerical solution of the wave equations for small and large tokamak-like plasmas. WKB theory has been used to derive useful expressions which quantify the QEW behaviour.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022377800002816

Alfvdén wave heating of a cylindrical plasma using axisymmetric waves. Part 1. MHD theory

A multichannel radiation bolometer has been developed for the Tokamak Chauffage Alfven (TCA) tokamak. It has 16 equally spaced chords that view the plasma through a narrow horizontal slit. Almost an entire vertical plasma cross section can be observed. The bolometer operates on the basis of a semiconducting element which serves as a temperature‐dependent resistance. A new electronic circuit has been developed which takes advantage of the semiconductor characteristics of the detector by using feedback techniques. Measurements made with this instrument are discussed.

/pdf/multichannel-bolometer-for-radiation-measurements-on-the-tca-pvxnfmizyp.pdf

Multichannel bolometer for radiation measurements on the TCA tokamak

An experimental study of the direct excitation of the torsional Alfven wave in the scrape-off plasma by an antenna designed for Alfven wave heating experiments in the TORTUS Tokamak is described. The antenna incorporated a Faraday shield, and was printed in the plane perpendicular to the toroidal direction, in order to minimize such direct excitation. Wave magnetic field measurements nevertheless indicated strong direct torsional Alfven wave excitation by antenna elements perpendicular to the Tokamak magnetic field lines due to finite frequency effects. The torsional Alfven wave was measured to propagate essentially parallel to the magnetic field lines, except at frequencies close to the ion cyclotron frequency. The excitation efficiency was found to increase with frequency (up to the ion cyclotron frequency) and electron density. The relevance of these results to the Alfven wave heating scheme is discussed.

https://iopscience.iop.org/article/10.1088/0741-3335/31/1/003/pdf

Direct excitation of the torsional Alfvén wave in a Tokamak scrape-off plasma by a Faraday shielded antenna

A particle simulation study of shear Alfven wave resonance heating is presented. A particle simulation model has been developed for this application that incorporates Darwin’s formulation of the electromagnetic fields with a guiding center approximation for electron motion perpendicular to the ambient magnetic field. With this model, several cases of Alfven wave heating are examined in both uniform and nonuniform simulation systems in a two‐dimensional slab. When the antenna parameters match the shear Alfven resonance condition, the simulation plasmas in the homogeneous cases react strongly with the driven wave. For the inhomogeneous case studies, the kinetic Alfven wave develops in the vicinity of the shear Alfven resonance region. The electrons kinetically react with the wave through a collisionless process. The electron velocity distribution function flattens about the parallel phase velocity of the wave with accompanying changes in the spatial structure of the wave. The electron heating rate is in good agreement with the Landau damping model. A substantial electron current is also generated parallel to the applied magnetic field. The ions gain energy by oscillating in the wave electric fields.

Computer simulation of Alfvén wave heating

Alfven wave heating experiments have been carried out in the TCA Tokamak. RF power up to 75% of the value of the ohmic heating power has been delivered to the plasma. Increases in axial electron temperature of up to 80% ( Delta Te approximately 400 eV) and in axial ion temperature of up to 50% ( Delta Ti approximately 75 eV) have been measured. The RF pulse is accompanied by an increase in the radiated power loss, which becomes peaked on axis, and which is due to line emission by impurities predominantly iron.

/pdf/measurements-of-electron-and-ion-heating-by-alfven-waves-in-ez3dy39yr9.pdf

Measurements of electron and ion heating by Alfven waves in the TCA Tokamak

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Measurements of electron and ion heating by Alfven waves in the TCA Tokamak