Variational approach to radiofrequency waves in magnetic fusion devices

Abstract

Magnetic fusion plasmas feature two major classes of low frequency electromagnetic oscillations: waves in the ion cyclotron range of frequencies (ICRFs) constitute a well established method employed for plasma heating and current drive, whereas waves in the Alfvén range of frequencies naturally occur in the form of modes in close interaction with fast particles. The propagation of these waves is characterized by significant space-dispersion, making it necessary to incorporate non-local effects in the global kinetic full-wave codes which are often employed for their simulation. We present here a variational approach to this problem, which has the advantage of providing a common framework to the wave calculation and to the quasilinear response description. Two important points are discussed: firstly, we show that the irreversible part of the power transferred from the wave to the plasma particles is directly available and does not require an explicit evaluation of the kinetic flux; secondly, it is demonstrated that the symmetry of the obtained plasma functional ensures that these energy transfers are described in a consistent fashion, regardless of the level of approximation employed to evaluate the particle Hamiltonian. Finally, quasi-local, finite Larmor radius expressions are derived in the framework of this formalism and implemented in a new multi-dimensional full-wave code, named EVE, which is employed to analyse two ICRF heating scenarios for ITER.

Ion temperature profile stiffness: non-linear gyrokinetic simulations and comparison with experiment

“…This is due to the lower β and lower thermal and suprathermal pressure gradients in 73221 compared with 66404, reducing significantly the impact of the electromagnetic stabilisation. Furthermore, EVE [67] simulations of the ICRH power deposition profile show that the 73221 profile is significantly narrower than the 66404 case, suggesting that the 73221 suprathermal pressure profile may not overlap the experimentally relevant ρ = 0.33 location, in line with the separation of the two branches. However, EVE presently does not include finite orbit width effects.…”

Bulk ion heating with ICRF waves in tokamaks

“…Given that E crit = 600 keV for tritium in ITER D-T plasma at a nominal T e of 25 keV, this scheme is compatible with bulk ion heating. Furthermore, since the second harmonic ion cyclotron frequency of tritium coincides with the fundamental ion cyclotron frequency of 3 He, using small amounts of 3 He minority ions in the plasma provides a means to optimize the performance characteristics of the scenario. This may become relevant e.g.…”

A new ion cyclotron range of frequency scenario for bulk ion heating in deuterium-tritium plasmas: How to utilize intrinsic impurities in our favour

“…Since the results shown in Fig. 2 were computed with a 1D code, which neglects a number of effects intrinsic for the tokamak geometry such as a finite poloidal magnetic field, a more sophisticated modelling with the 2D full-wave codes TORIC [29,30] and EVE [31] was done to increase the degree of realism. Note that contrary to the 1D computations, in 2D modelling (since the tokamak vessel acts as a Faraday cage) all the RF power is eventually absorbed in the plasma, and the computed absorption coefficients reflect the relative strength of various damping mechanisms.…”