Faraday–Fresnel rotation and splitting of orbital angular momentum carrying waves in a rotating plasma

Rotational Fresnel drag – or orbital Faraday rotation – in a rotating magnetised plasma is uncovered and studied analytically for Trivelpiece–Gould and whistler–helicon waves carrying orbital angular momentum (OAM). Plasma rotation is shown to introduce a non-zero phase shift between OAM-carrying eigenmodes with opposite helicities, similarly to the phase shift between spin angular momentum eigenmodes associated with the classical Faraday effect in a magnetised plasma at rest. By examining the dispersion relation for these two low-frequency modes in a Brillouin rotating plasma, this Faraday–Fresnel rotation effect is traced back to the combined effects of Doppler shift, centrifugal forces and Coriolis forces. In addition, the longitudinal group velocity in the presence of rotation is shown to depend both on rotation and azimuthal mode, therefore predicting the Faraday–Fresnel splitting of the envelope of a wave packet containing a superposition of OAM-carrying eigenmodes with opposite helicities.

Off-Axis Current Drive with Helicon Waves for CFETR

Off-axis current drive is necessary for Tokamak to maintain and regulate the current profile. Helicon wave is the high order harmonic fast wave and helicon wave current drive (HCD) is one of the key issues in the China Fusion Engineering Test Reactor (CFETR). The theory of HCD is briefly introduced and the simulation results are listed. Helicon waves can realize off-axis current drive under CFETR plasma parameters when the frequency is greater than 1 GHz and drive current is insensitive to the launched value of the parallel index of refraction n||, so wave accessibility issues can be reduced. Travelling Wave Antenna was analyzed by the commercial software package-CST. Near the resonant frequency of the antenna, the Voltage Standing Wave Ratio < 1.2 is obtained for the antenna in the bandwidth of 50 MHz, which means that the antenna does not require a matching system.

Influence of Nonuniform Magnetic Field on the Helicon Discharge Excited by Various Antennas

The influence of a nonuniform magnetic field, which increases with the distance from an inductive antenna, on a helicon discharge has been studied. The discharge was excited in the azimuthally symmetric mode of helicon waves, m = 0, making use of antennas of two different types. It is shown that if the discharge is produced by a loop antenna, which supplies the RF energy through the side boundary of plasma and perpendicularly to the external magnetic field, then the ionization is concentrated at the discharge periphery. Under those conditions, the imposing of a nonuniform magnetic field reduces the loss of ionizing electrons at the wall and enhances the plasma generation. If the discharge is excited with a planar antenna along the magnetic field, then the main ionization occurs in the inner plasma region around the axis. In this case, an increase in the plasma density, if any, may be a result of the plasma contraction in the magnetic field with force lines convergent to the axis.