Gyroresonant particle acceleration in a non-uniform magnetostatic field

Abstract

Particle motion in inhomogeneous magnetostatic and high-frequency fields at the gyroresonance is studied in the limit of a large number of particle revolutions in the resonance region. The role played by the magnetic mirror, Doppler and relativistic effects, wave attenuation and radiation pressure on particle acceleration is discussed. The time dependence of the orbital magnetic flux, the velocity along the magnetic lines of force and the width of the resonance region are calculated. An upper limit is found for the energy of the particle, when the effect of the magnetic field of the wave partially compensates for the change in mass with energy. The non-linear method we use is exact in the limit of many revolutions. It generalizes the results established by C.S. Roberts and S.J. Buchsbaum in a special case, to the more complex situation proposed by T. Consoli for injecting, accelerating and confining a hot plasma in a magnetic trap. A number of numerical examples are presented for various conditions. The energy transfer to the particles at the parametric resonances is also investigated. The space charge field which develops along the magnetic lines of force in a plasma accelerating structure is taken into account in the equations from the very beginning by assuming (Consoli) that the electron guiding centres move with the velocity of the ions.

Ponderomotive barrier as a Maxwell demon

“…(In this case, the quantityv equals the characteristic momentum a particle gains inside the resonance region [12]. )…”

“…The nonadiabatic dynamics of rf-driven particles in the cyclotron-resonance area has been studied in a number of works [2,5,[12][13][14][15][16][17][18][19], primarily inspired by interest in rf plasma confinement, yet the general analytical treatment, sufficient for studying the APCD effect, has not been fully put forth. For instance, weak heating was studied for particles quasi-adiabatically trapped by an rf field within a plasma [13][14][15] with little attention to those transmitting through rf plugs and leaving the operating volume of the fusion device.…”

“…The most general analytic model of transmitting particle dynamics was proposed in Ref. [12], where the major emphasis was made on particle acceleration from the resonance region. In other cases, effects caused by the inhomogeneity of the dc magnetic field were either studied heuristically [5], on the level of elementary estimates [2], or neglected completely [16,17].…”

Nonadiabatic ponderomotive potentials

“…For electrons and ions under rf drive near a cyclotron resonance in a magnetic field, this problem has been addressed previously in a number of works [2,8,[16][17][18][19][20][21][22][23][24][25][25][26][27]. None of those, however, has introduced a non-singular ponderomotive potential in a non-heuristic fashion, except for the essentially perturbative analysis proposed in Refs.…”

Experimental Characterization of an Overdense Plasma in a Compact Ion Source

“…In addition, the spectrum end point represents roughly the highest electron energy reached in the plasma. In the case of ECR heating, the maximum energy T max achievable by electrons can be calculated by means of Canobbio theory [16]:…”