Abstract
The scaling of particle confinement time with density is studied in detail First, we fit the poloidal Hα brightness distributions measured in a density scan series in the TEXT tokamak. Results of the fit suggest that there is not a monotonic decrease of the mean ionization radius with increase in density. While this detailed fitting procedure is an improvement over fitting global Hα data, it still requires the use of free parameters. We show that three-dimensional (3D) Monte Carlo calculations may be used to compute the expected Hα lineshape. As several experiments have recently reported measurement of this quantity, comparison of theoretical and measured values should allow improvement in confinement analysis. We have carried out experiments in the ORNL Plasma Materials Interaction Test Facility to measure the Hα lineshape in discharges with CH4 injection into pure D2 plasmas. We have observed the production of H0 by CH4 breakup in PMITF, and have measured the lineshape contribution due to dissociation products in a plasma environment. Finally, since many confinement studies are conducted in "carbonized" devices, we have studied the problem of determining the fueling profile in carbon-rich plasmas by calculating the H0 deposition due to CH4 breakup. We find that the penetration of H0 through the scrape-off layer by CH4 breakup should introduce a significant density scaling in the particle fueling source term.
| Original language | English |
|---|---|
| Pages (from-to) | 469-475 |
| Number of pages | 7 |
| Journal | Journal of Nuclear Materials |
| Volume | 162-164 |
| Issue number | C |
| DOIs | |
| State | Published - Apr 1 1989 |
Funding
The dependence of particle confinement time on plasma parameters (and its relation to energy confinement time) is one of the key diagnostic indicators for the validity of various theoretical models of turbulence-based transport. The experimental study of the dependence of rp on ii, has been conducted in a number of devices that range in size from small (Alcator-A, Mar-mar [l]), intermediate (TEXT, Rowan et al. [2]) to the large-scale (JET, Cordey et al. [3]; and JT-60, Yamada et al. [4]). The picture that has emerged is one of an increasing dependence of rr, on Ri, for low density, with a roll-over as density exceeds a critical value. Above EF, rp decreases with increasing density. The collective results from machines with small and large minor radii, and the density dependence, suggest that the neutral opacity is the determining factor in the fueling profile and that the inherent inefficiency of edge gas fueling, rather than fundamental plasma transport processes, causes the decline in global rp with increasing density * Research sponsored by the Office of Fusion Energy, US Department of Energy, under contract DE-AC05840R 21400 with Martin Marietta Energy Systems, Inc.
Keywords
- CH
- H-lineshape
- modelling