Thermal energy confinement scaling in PDX limiter discharges

Abstract

Experiments were performed on the PDX tokamak to study plasma heating and beta scaling with high-power, near-perpendicular neutral-beam injection. The data taken during these experiments were analysed, using a time-dependent data interpretation code (TRANSP), to study the transport and thermal confinement scaling over a wide range of plasma parameters. This study focuses on results from experiments with D° injection into H* plasmas using graphite rail limiters, a = 40-44 cm, R = 143 cm, I p = 200-480 kA, B T = 0.7-2.2 T, and, typically, n e = (2.5-4.2) X 10 13 cm" 3 . The results of this study indicate that for both Ohmic and neutral-beam-heated discharges the energy flow out of the plasma is dominated by anomalous electron losses which are attributed to electron thermal conduction. The ion conduction losses are not inconsistent with neoclassical theory; however, the total ion loss influences the power balance significantly only at high toroidal fields and high plasma currents. Therefore, except for these cases, the total thermal energy confinement time for the neutral-beam-heated discharges follows the scaling of electron energy confinement. While the confinement is found to have little dependence on toroidal field, it is a strong function of plasma current, increasing with increasing I p . In contrast, Ohmic confinement times are found to scale as n e q 1/2 . Because of the dominant effect of the electrons, the total confinement is found to depend heavily on the variation of the electron thermal diffusivity, Xe, in t n e outer region of the plasma (a/2 < r < 7a/8). The values of Xe m this region of the plasma show an approximately inverse dependence on the local value of the poloidal magnetic field.

Confinement and local transport in the National Spherical Torus Experiment (NSTX)

“…This behavior is very different from what was observed at higher aspect ratio, where it was the central T e that was most affected by variations in the toroidal field. 18 The ion temperature profiles, on the other hand, show less variation with B T . For all the discharges in this scan, the density profiles essentially overlaid each other.…”

LCS Users Manual

“…Note that Ary is the coordinate used by TSC to give the distance from the plasma center. PlFlg (6) A one-page plot showing the quasilinear smoothing function as a function of velocity. PlFlg (7) PlFlg (8) Setting either of these ags will prompt the production of a graph of the ray trajectories plotted on a v k versus grid;…”

“…PrFlg (6) Lists the quasiliner smoothing function versus velocity. PrFlg (9) A table of ray information (rates of power loss, etc.)…”

“…The LSC module can also be called by the TRANSP [4,5,6] code. TRANSP represents the plasma with a axisymmetric, xed-boundary model and focuses on calculation of plasma transport to determine transport coefcients from data on power inputs and parameters reached.…”

Confinement scaling and ignition in tokamaks

“…(4). Because our confinement model assumed very high thermal conductivity inside q = 1, it fails to account for the energy content associate!…”