Energetic particle physics issues for ITER

The paper summarizes the present understanding of the following energetic/alpha particle physics issues for the 21 MA, 20 TF coil ITER Interim Design configuration and operational scenarios: (a) toroidal field ripple effects on alpha particle confinement; (b) energetic particle interaction with low frequency MHD modes; (c) energetic particle excitation of toroidal Alfven eigenmodes; and (d) energetic particle transport due to MHD modes. TF ripple effects on alpha loss in ITER under a number of different operating conditions (L-mode, H-mode, and post-sawtooth) are found to be small, with a maximum loss of 1%. With careful plasma control in ITER reversed-shear operation, TF ripple induced alpha loss can be reduced to below the nominal ITER design limit of 5%. Fishbone modes are expected to be unstable for βα > 1%, and sawtooth stabilization is lost if the ideal kink growth rate exceeds 10% of the deeply trapped alpha precessional drift frequency evaluated at the q = 1 surface. However, it is expected that the fishbone modes will lead only to a local flattening of the alpha profile owing to small banana size. MHD modes observed during slow decrease of stored energy (as much as 20% in 50-100 msec) after fast partial electron temperature collapse (in about 100 μsec) in JT-60U reversed-shear experiments may be resonant type instabilities; they may have implications for the energetic particle confinement in ITER reversed-shear operation. From the results of various TAE stability code calculations, ITER equilibria appear to lie close to TAE linear stability thresholds. If TAEs are unstable in ITER, the stochastic diffusion is the main loss mechanism, which scales with (δBr/B)2, because of the relatively small alpha particle banana orbit size and TAEs saturate via the resonant wave-particle trapping process at very small amplitude. If a wide range of overlapping medium-to high-n TAEs do prove to be linearly unstable, then a global quasilinear, possibly bursty, flattening of the alpha profile, resulting from an explosive ''domino'' effect due to enhanced wave energy release, is possible. (author). 19 refs