Enhanced fusion performance due to plasma shape modification of simulated ITER discharges in DIII-D

Abstract

On the basis of several confinement scaling relations, the prediction has been made that tokamak performance, expressed as the volume averaged fusion triple product (nT) tau , should increase as the plasma is elongated by reducing the horizontal minor radius from the outer (low field) boundary with fixed heating power, safety factor and electron density. Experiments in DIII-D confirm this prediction, with performance enhancements of up to 40% observed as elongation is increased by 15%. It is recognized, of course, that such experiments do not constitute a simple test of elongation scaling, since the change to elongation was rather small, and other parameters, such as toroidal field, are allowed to change. Nevertheless, this `engineering test' of the effects of such small changes indicates possible advantages to the slightly modified shape. This enhancement appears most visibly as increased ion and electron temperatures. A surprising feature of the high elongation plasmas is the existence of a VH-mode-like `spin-up', where the high elongation plasmas tend to rotate with velocities as high as twice those in the low elongation plasmas. The resulting region of enhanced toroidal rotation gradient is associated with significant reductions in transport

Experimental and Theoretical Stability Limits of Highly Elongated Tokamak Plasmas

“…Similar disruption precursors have been seen in many tokamaks when operating near MHD stability limits [18][19][20][21][22]. Highly elongated plasmas, up to k 2.5, have also been obtained in the DIII-D tokamak [8,23], but the current limit was not tested at k 2.5.…”

Intercode comparison of gyrokinetic global electromagnetic modes

“…Eulerian vs. Lagrangian methods. All of the listed examples are inspired and based on the Cyclone Base Case 13,14 (CBC) which is a well established reference scenario in fluxtube studies. However, the individual benchmarks differ in details like assumptions regarding the specific shape of the temperature, density and safety factor profiles and the basic setups which consider decaying or gradient-driven turbulence or linear mode characterization.…”

A global collisionless PIC code in magnetic coordinates

“…[43], several fluid, gyrofluid and gyrokinetic codes are compared for the so called CYCLONE test case, which represents local parameters from an ITER-relevant DIII-D H-mode shot [42] i . The quasi-neutrality equation is solved with cubic B-splines on a N s = 128, N χ = 448, N ϕ = 320 grid and a field-aligned filter with ∆m = 5, is applied.…”