Effect of ion orbit loss on distribution of particle, energy and momentum sources into the tokamak scrape-off layer

Abstract

The effect of ion orbit loss on the poloidal distribution of ions, energy and momentum from the plasma edge into the tokamak scrape-off layer (SOL) is analysed for a representative DIII-D (Luxon 2002 Nucl. Fusion 42 614) high-mode discharge. Ion orbit loss is found to produce a significant concentration of the fluxes of particle, energy and momentum into the outboard SOL. An intrinsic co-current rotation in the edge pedestal due to the preferential loss of counter-current ions is also found.

Co-current rotation of the bulk ions due to the ion orbit loss at the edge of a tokamak plasma

“…The ion orbit loss has long been thought to play an important role in generating the REF and the plasma rotation at the edge of a tokamak plasma [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30].…”

“…An initial Maxwellian distribution with the local ion temperature, , is assumed. The corresponding cumulative loss fractions are defined following Stacey's definitions [24,[28][29][30]: (1) The minimum loss energy of the counter-current passing ions is much larger than that of the counter-current trapped ions, as is shown in Figure 4(a)-(b). The minimum loss energy of the counter-current passing ions is smaller than that of the counter-current trapped ions in Refs.…”

Extensions of ion orbit loss theory

“…The most general is the loss of ions on passing or banana-trapped orbits that leave the plasma by drifting outward across the last closed flux surface (as developed, e.g., in Refs. 7 and 13-15 or [18][19][20][21][22]. Both thermalized plasma ions and energetic neutral beam ions (and fusion alpha particles) can be lost in this manner.…”

“…We have recently developed a model [18][19][20][21][22] for (i) the calculation of the radially cumulative fractions of ion particles F orb , momentum M orb , and energy E orb in a tokamak plasma flowing outward across an internal flux surface that are on drift orbits that would carry them immediately outward across the last closed flux surface (i.e., be ion orbit lost) and (ii) for the calculation of how these ion orbit losses reduce the corresponding radial particle C, momentum M, and energy Q fluxes that would be calculated in the absence of ion orbit loss from the respective radial particle (continuity), momentum and energy balance equationsĈ…”

“…(3) arises from taking into account the inward main ion particle fluxes from the SOL which are necessary to maintain charge neutrality in the presence of the beam and thermal plasma ion orbit losses. 19 Using these radial particle and heat fluxes evaluated with the experimental density and temperature, the experimental thermal diffusivities interpreted from the measured data can be calculated from the heat conduction relation …”