Theory Weekly Highlights for January 2002

January 18 2002

In an earlier January highlight (see Highlight from January 04 2002), we reported on the renormalization of the 1996 GLF23 model to bring it into alignment with the best gyrokinetic simulations. This resulted in the ITG transport strength renormed by 0.27 and the ETG by 4.80. The statistical deviation from a 50 H-mode data base improved from 10% to 8.7%. Due a mistaken input file parameter, we erroneously reported that the ITER-FEAT Q increased by 50% compared to the projection from the 1996 model. We have corrected this input file error and now find that the improvement in the Q = 10 range is no more than 10-15%. Even though the renormalized model is less “stiff” than the 1996 model, it is still a stiff model, and in fact Q follows the “stiff” normalization, Q=Qnorm x F(Tped) quite accurately (Qnorm = κR (I/a)2 (n/nG)2/Paux). At (n/nG) = 0.85 and Paux = 40MW, Q=10 requires Tped = 4.5 keV according to the renormalized model.

January 11 2002

Recent results from Neutral Beam heated DIII-D, JET and JT-60U discharges, in which equilibria exhibited a “current hole”, have generated considerable attention; these discharges appear to have interesting confinement and stability properties. A new model has been developed, in which the current hole is supported by a flux of hot beam ions into the core, and which successfully describes the major features of the JT-60U equlibrium. The new model predicts that, given sufficient ion flux, this configuration could be maintained in steady state, which opens up the possibility of a steady state tokamak.

January 04 2002

The GLF23 transport model was renormalized using an H-mode database comprising nearly 50 discharges from the DIII-D, JET, and C-mod tokamaks. This was motivated by recent gyrokinetic simulations with adiabatic electrons indicating that the saturation levels for ITG transport are nearly a factor of four lower than the gyro-fluid results that were used to normalize the original GLF23 model and by work by Jenko, et al suggesting that ETG streamers can result in significantly larger electron heat fluxes compared with simple isomorphic estimates. Carrying out a 2 parameter search whereby the normalization factors for the ITG/TEM and ETG modes (unity in the original model) were varied independently, the minimum RMS error at zero offset was found in the incremental stored energy. The resulting normalization factors are 0.27 and 4.80 for the ITG and ETG modes, respectively. The renormalized GLF23 model is currently being applied to ITER-FEAT, FIRE, and IGNITOR. For ITER-FEAT, the predicted fusion gain Q increases by 50% compared with the original GLF23 simulations.

These highlights are reports of research work in progress and are accordingly subject to change or modification