RADIAL TRANSPORT EFFECTS ON ECCD IN THE TCV AND DIII-D TOKAMAKS AND ON OHMIC DISCHARGES IN THE MST RFP Page: 4 of 9
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RADIAL TRANSPORT EFFECTS ON ECCD IN THE TCV AND DIII-D
TOKAMAKS AND ON OHMIC DISCHARGES IN THE MST RFP
R.W. Harvey,1 O. Sauter,2 R. Prater,3 P. Nikkola,2 R. O'Connell,4 and C.B. Forest4
1CompX, P.O. Box 2672, Del Mar, California 92014-5672
2Ecole Polytechniuque Federale de Lausanne, CH-1015, Lausanne, Switzerland
3General Atomics, P.O. Box 85608, San Diego, California 92186-5608
4University of Wisconsin, Madison, Wisconsin 53706-1687
The comprehensive CQL3D Fokker-Planck/Quasilinear simulation code has been benchmarked
against experiment over a wide range of electron cyclotron conditions in the DIII-D tokamak (C.C.
Petty et al., 14th Topical Conf. on RF Power in Plasmas, 2002). The same code, in disagreement with
experiment, gives 560 kA of ECCD for a well documented, completely ECCD-driven, 100 kA TCV shot
[O. Sauter et al, PRL, 2000]. Recent work (R.W. Harvey et al, Phys. Rev. Lett., 2002) has resolved the
differences as due to radial transport at a level closely consistent with ITER scaling. Transport does not
substantially affect DIII-D ECCD, but at similar ECH power has an overwhelming effect on the much
smaller TCV. The transport is consistent with electrostatic-type diffusion (Dpp constant in velocity-
space) and not with a magnetic-type diffusion (Dpp cc lviil).
Fokker-Planck simulation of Ohmic reversed field pinch (RFP) discharges in the MST device
reveals transport velocity dependence stronger than Ivii will give agreement with current and soft
X-ray spectra in standard discharges, but in the higher confinement, current profile controlled PPCD
discharges, transport is again electrostatic-like. This is consistent with the object of PPCD, which is to
replace magnetic turbulence driven current with auxiliary CD to improve transport. The tokamak and
high-confinement RFP results mutually reinforce the constant-in-velocity-space "electrostatic-type
turbulence" conclusion. The steady-state energy and toroidal current are governed by the same radial
The role of radial transport on high energy electrons in tokamaks and reversed field
pinches (RFPs), particularly in regards to radiofrequency (rf) experiments, has been
examined by several authors [1-8, and references therein]. At high enough power, the plasma
temperature is high and the transport effects strong enough such that radial transport
dominates the collisional slowing down time of the fast electrons. Our calculations  show
that this is strongly the case for a representative full-toroidal-current-drive electron cyclotron
current drive (ECCD) experiment  in the TCV fusion energy tokamak. Although there is
little doubt as to whether plasma turbulence is responsible for the observed radial transport in
excess of collisional levels , questions remain on the extent electrostatic (ES) or magnetic
turbulence dominates  and also the degree of concurrence between tail electron transport
and bulk plasma transport. In tokamaks our work shows good agreement between experiment
and modeling based on radial diffusion due to ES turbulence at a level predicted by well-
known empirical modeling ; it shows poor agreement with the purely magnetic
In the MST reversed field pinch (RFP) device at UW, Madison, a similar result has been
found: In standard Ohmic MST discharges the transport appears to be due to magnetic-type
turbulence; however, when the plasma current driven by magnetic turbulence in the outer part
of the plasma is replaced by transiently driven Ohmic pulsed poloidal current (PPCD), the
transport improves and switches from magnetic-type to being dominated by electrostatic-
The primary results for DIII-D and TCV have been reported in Ref. 8. In this paper we
report on further aspects of the calculation, and outline some of the new, related results being
obtained in the MST device.
The calculations are performed with the comprehensive CQL3D Fokker-
Planck/Quasilinear (FP/QL) simulation code . The FP model includes two-dimensional in
momentum-space collisional diffusion, the full Stix  rf QL diffusion coefficient, a radial
diffusion Dpp and pinch term in non-circular flux-surface geometry, and is relativistic. The
pinch term is adjusted to maintain a target density profile. Steady-state, finite-difference
numerical solutions are obtained for the electron distribution fe(uo,00,p), evaluated at the
outer equatorial plane of the toroidal plasma, where uo =p/me is momentum-per-electron-rest-
GENERAL A TOMICS REPORT GA-A23978 1
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HARVEY, R.W.; SAUTER, O.; PRATER, R.; NIKKOLA, P.; O'CONNELL, R. & FOREST, C.B. RADIAL TRANSPORT EFFECTS ON ECCD IN THE TCV AND DIII-D TOKAMAKS AND ON OHMIC DISCHARGES IN THE MST RFP, article, July 1, 2002; United States. (digital.library.unt.edu/ark:/67531/metadc739022/m1/4/: accessed January 16, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.