Analysis of ICRE (     _ci) plasma production in large scale tokamaks

Abstract

The authors study the possibility of target plasma radiofrequency (RF) production in the ion cyclotron range of frequencies (ICRF) (ω ⩽ ωci) in large scale tokamaks before the startup of an Ohmic discharge. A number of experimental and theoretical studies on dense plasma production in the ICRF in toroidal magnetic devices are reviewed. The criteria for optimal development of the RF discharge stages are analysed, i.e., for RF breakdown of the neutral fill gas in the vicinity of the antenna (non-wave stage, ne << na, where ne and na are the densities of electrons and atoms), and the wave stages of initial ionization (ne < na) and neutral gas burnout (ne approximately na) in the whole volume of the plasma torus. A number of requirements for the design of the antenna system are formulated for all stages of dense plasma ICRF production. A scenario for plasma ICRF production with slot type antennas in the ITER tokamak is proposed. Numerical simulations with a 0-D transport code show that in ITER a target plasma with an electron density of approximately=3*1012 cm-3 can be produced by coupling 3-6 MW of RF power to the plasma at a frequency of approximately=3 MHz. Such a level of RF power is sufficient not only for full ionization of the neutral gas but also for heating the produced plasma to electron temperatures of approximately 80 eV

0D model of magnetized hydrogen–helium wall conditioning plasmas

“…To describe numerically in a 0D approach the evolution of ICRF plasma parameters in tokamaks and stellarators, a set of transport equations [12,13,14,15] was adopted. The equations are derived from the standard continuity and heat balance equations given by Braginskii [16], where all particle species are assumed to have a Maxwellian energy distribution.…”

“…The four data sets can be approximately fitted with a same exponential decay length of λ d = 1.1 cm (dashed lines). For the typical modeled electron temperatures (T e ≈ 3 eV) the measured diffusion coefficient can be found from [36] The above charged particle loss mechanisms are summarized in the following general formula for the ion confinement time: (12) where λ p the mean free path of the ion, v Dz,p is the ' B × ∇B' drift velocity, v Dr,p is the radial outward ' E × B' drift velocity, v Bohm,p is the cross field diffusion velocity and v T,p the thermal velocity of the ions. Eq.…”

ICRF Wall Conditioning: Present Status and Developments for Future Superconducting Fusion Machines

“…The initiation of ICRF discharge in a toroidal magnetic field B results from the absorption of RF energy mainly by electrons [2,4,[21][22]. The RF z Ẽ -field (parallel to the B T B -field) is considered to be responsible for this process.…”

“…Plasma density build-up and its homogeneity: The plasma production process has been studied in present-day tokamaks and stellarators under various conditions [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][20][21][22][23]. The ICRF plasmas with typical density n e ≈3×10…”

“…An analysis of the parallel equation of motion for electrons in the presence of antenna-near locally generated z Ẽ -field revealed that the electrons perform complex motions: linear fast oscillations under the action of the Lorentz force and non-linear slow oscillations under the action of the RF ponderomotive force [21][22]. If the oscillation energy of the electrons exceeds the ionization potential for molecules (atoms), …”