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Laser-produced plasma (LPP) devices have been modeled as the light source for extreme ultraviolet (EUV) lithography. A key challenge for LPP is achieving sufficient brightness to support the throughput requirements of high-volume manufacturing. An integrated model (HEIGHTS) was applied to simulate the environment of EUV sources and optimize their output. The model includes plasma evolution and magnetohydrodynamic processes in a two-temperature approximation, as well as photon radiation transport determined by the Monte Carlo method. It uses the total variation diminishing scheme for the description of magnetic compression and diffusion in a cylindrical 2-D geometry for the target. Generation of the internal magnetic field with nonparallel density and temperature gradients was also considered. Preliminary results from numerical simulation in hydrodynamics and line radiation output of xenon and tin plasmas are presented for planar and droplet targets. [ABSTRACT FROM AUTHOR]

The specific size and structure of the edge current profile has important effects on the magnetohydrodynamic stability and ultimate performance of many advanced tokamak (AT) operating modes. This is true for both bootstrap and externally driven currents that may be used to tailor the edge shear. Absent a direct local measurement of j(r), the best alternative is a determination of the poloidal field. Measurements of the precision (0.1°–0.01° in magnetic pitch angle and 1–10 ms) necessary to address issues of stability and control and provide constraints for EFIT are difficult to do in the region of interest (ρ=0.9–1.1). Using Zeeman polarization spectroscopy of the 2S–2P lithium resonance line emission from the DIII-D LIBEAM [D. M. Thomas, Rev. Sci. Instrum. 66, 806 (1995); D. M. Thomas, A. W. Hyatt, and M. P. Thomas, Rev. Sci. Instrum. 61, 340 (1990)] measurements of the various field components may be made to the necessary precision in exactly the region of interest to these studies. Because of the negligible Stark mixing of the relevant atomic levels, this method of determining j(r) is insensitive to the large local electric fields typically found in enhanced confinement (H mode) edges, and thus avoids an ambiguity common to motional Stark effect measurements of B. Key issues for utilizing this technique include good beam quality, an optimum viewing geometry, and a suitable optical prefilter to isolate the polarized emission line. A prospective diagnostic system for the DIII-D AT program will be described. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

One promising approach to maintaining stability of high beta tokamak plasmas is the use of a conducting wall near the plasma to stabilize low-n ideal magnetohydrodynamic instabilities. However, with a resistive wall, either plasma rotation or active feedback control is required to stabilize the more slowly growing resistive wall modes (RWMs). Previous experiments have demonstrated that plasmas with a nearby conducting wall can remain stable to the n=1 ideal external kink above the beta limit predicted with the wall at infinity. Recently, extension of the wall stabilized lifetime τL to more than 30 times the resistive wall time constant τw and detailed, reproducible observation of the n=1 RWM have been possible in DIII-D [Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159] plasmas above the no-wall beta limit. The DIII-D measurements confirm characteristics common to several RWM theories. The mode is destabilized as the plasma rotation at the q=3 surface decreases below a critical frequency of 1?7 kHz (˜1% of the toroidal Alfvén frequency). The measured mode growth times of 2?8 ms agree with measurements and numerical calculations of the dominant DIII-D vessel eigenmode time constant τw . From its onset, the RWM has little or no toroidalrotation (ωmode≤τw-1«ωplasma), and rapidly reduces the plasma rotation to zero. These slowly growing RWMs can in principle be destabilized using external coils controlled by a feedback loop. In this paper, the encouraging results from the first open loop experimental tests of active control of the RWM, conducted in DIII-D, are reported. [ABSTRACT FROM AUTHOR]