Speaker
Dr
Lothar Schmitz
(University of California-Los Angeles)
Description
Quantitative proof is presented that the ion polarization current [1] dominates the evolution of the radial electric field E_r across the L-H transition, and needs to be properly taken into account in Ohm’s law. This is an important step towards developing a physics-based reduced L-H transition model, which in addition needs to include at a minimum the poloidal momentum balance, and evolution equations for the turbulence intensity and the pressure gradient [2]. The observed isotope dependence of the threshold power P_LH in ITER-similar H, He and D plasmas [3] can then be qualitatively understood: in D and He, where the Reynolds stress [2-4] dominates the neoclassical bulk viscosity and thermal ion orbit loss, P_LH is relatively low. In hydrogen plasmas, where the Reynolds stress is marginal and comparable to the neoclassical bulk viscosity and thermal orbit loss current, P_LH is much higher. The observed increased transition time to full turbulence suppression in hydrogen plasmas can also be quantitatively understood using this model.
Resonant magnetic perturbations (RMP) may have to be applied before the L-H transition in ITER to safely suppress the first ELM. In ITER-similar plasmas in DIII-D the increase of P_LH with n=3 RMP is most pronounced with ECH, with P_LH increasing with decreasing plasma collisionality [P_LH~(nu_star)^-0.3]. Two-fluid modeling with the M3D-C1 code [5] shows that the normalized L-mode radial density gradient a/L_n is toroidally modulated and periodically increased on the outboard midplane with applied RMP. Non-axisymmetric modifications with RMP include increased local long-wavelength turbulence (measured via BES) and reduction of the E_r well and ExB shear. We conjecture that the increase in threshold power with RMP results from locally enhanced instability drive (however without simultaneously increased Reynolds stress) and reduced ExB shear.
This work was supported by the US Department of Energy under DE-FG02-08ER54984, DE-FG02-08ER 54999, DE-AC05-00OR22725, and DE-FC02-04ER54698.
[1] K. Itoh, Plasma Phys. Control. Fusion 36 A307-A318 (1994).
[2] K. Miki, P.H. Diamond et al., Phys. Plasmas 19, 092306 (2012).
[3] Z.Yan et al. Nucl. Fusion, 57, 126015 (2017).
[4] L. Schmitz, Proc. 26th IAEA Fusion Energy Conf., Oct.17-22, 2016, Kyoto, Japan, paper EX-C P571.
[5] R.S. Wilcox et al. Nucl. Fusion 57 116003 (2017).
| Country or International Organization | United States of America |
|---|---|
| Paper Number | EX/4-2 |
Primary author
Dr
Lothar Schmitz
(University of California-Los Angeles)
Co-authors
Dr
Alessandro Marinoni
(PSFC, Massachusetts Institute of Technology, Cambridge, MA 02139, USA)
Dr
C. Craig Petty
(General Atomics)
Dr
Carlos Paz-Soldan
(General Atomics)
Dr
George R. McKee
(University of Wisconsin-Madison)
Dr
Lei Zeng
(University of California Los Angeles, PO Box 957099, Los Angeles, CA 90095-7099)
Matt Kriete
(University of Wisconsin-Madison, 1500 Engineering Dr., Madison, WI 53706, USA)
Dr
Punit Gohil
(General Atomics)
Robert Wilcox
(Oak Ridge National Laboratory)
Dr
Terry Rhodes
(UCLA)
Zheng Yan
(University of Wisconsin- Madison)
