The effect of ion orbit loss and X-loss on the interpretation of ion energy and particle transport in the DIII-D edge plasma

Abstract

Calculation models are presented for treating ion orbit loss effects in interpretive fluid transport calculations for the tokamak edge pedestal. Both standard ion orbit loss of particles following trapped or passing orbits across the separatrix and the X-loss of particles that are poloidally trapped in a narrow null-B h region extending inward from the X-point, where they gradB and curvature drift outward, are considered. Calculations are presented for a representative DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] shot which indicate that ion orbit loss effects are significant and should be taken into account in calculations of present and future experiments.

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.…”

X-transport of ions in diverted tokamaks, with application to DIII-D

“…Three cases were considered: (1) the X-transport terms S X and q X were set to zero; (2) the X-transport terms S X and q X were evaluated as described in the previous section; and (3) the X-transport terms S X and q X were evaluated as described in the previous section, and "standard" ion orbit loss fractions F orb and E orb were calculated as described in Ref. 21 and used to further reduce the fluxes. These results are shown in Figs.…”

“…(6) and (7) for the ion particle and heat fluxes, and the E orb and F orb are ion orbit loss factors. 21 We have evaluated Eq. (12) using three different versions of the conductive heat flux q i and the experimental data for the two DIII-D shots.…”

“…It has recently been pointed out [14][15][16][17][18][19][20] that there is another "X-loss" type of ion-orbit-loss for particles which become poloidally trapped in the almost null poloidal field region near the X-point in diverted tokamaks and are carried outward across the separatrix by grad-B and curvature drift. A calculation model for taking these ion-orbit-loss effects into account within the context of a fluid calculation was recently developed and applied to edge pedestal analysis in DIII-D. 21 The idea of ion-orbit-loss, which is a rapid (compared to the transport time scale) transfer of ions from an inner flux surface outward across some bounding loss surface (e.g., the separatrix), suggests also the possibility of a rapid (relative to the transport time scale) outward transfer of ions (and their energy) from an inner to an outer flux surface, i.e., an "ionorbit-transport." Neoclassical "banana-plateau" transport theory is, in fact, based on the "standard" ion-orbit-loss theory but for confined ions whose orbits are interrupted by scattering.…”