CORE DENSITY PEAKING EXPERIMENTS IN JET, DIII-D AND C-MOD IN VARIOUS OPERATIONAL SCENARIOS - DRIVEN BY FUELING OR TRANSPORT?

Core density profile peaking and electron particle transport have been extensively studied by performing several dimensionally matched collisionality (?*) scans in various plasma operation scenarios on JET and on DIII-D and a 2-point ?*scan in I-mode on C-Mod. The experimental results from the various JET H-mode as well as the DIII-D H-mode scans show that density peaking increases with decreasing ?*. In JET, the NBI particle source is contributing 50-60% to the peaking in plasmas where Te/Ti~1 and at ?*=0.1-0.5 (averaged between r/a=0.3-0.8) independent of ?*. On DIII-D, the density peaking is solely a transport effect at low ?* while the NBI contributes to density peaking around 30-40% at higher ?*. The reason for JET and DIII-D being different with respect to NBI fueling versus inward pinch is under investigation. These dimensionally matched ?* scans give the best data for model validation. TGLF simulations are in excellent agreement with the experimental results with respect to the role of NBI versus inward pinch in JET and higher ?* discharges on DIII-D. GENE predicts larger role for the NBI fueling in JET than observed in experiment but is in good agreement within the DIII-D scan, justifying the use of these models/codes in predicting density peaking. In L-mode plasma conditions, the role of the NBI source is small, typically 10-20% and the electron particle transport coefficients are large. On C-Mod, the I-mode density peaking database indicated that in the I-mode plasmas, there is no ?* dependence in density peaking. This result indicates that particle transport characteristics are more analogous to those of L-mode than H-mode and similar to L-mode ones observed in JET and DIII-D.