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Recent DIII?D experiments show that ideal kink-modes can be stabilized at high beta by a resistive wall, with sufficient plasma rotation. However, the resonant response to static magnetic field asymmetries by a marginally stable resistive wall mode can lead to strong damping of the rotation. Careful reduction of such asymmetries has allowed plasmas with beta well above the ideal MHD no-wall limit, and approaching the ideal-wall limit, to be sustained for durations exceeding 1?s. Feedback control can improve plasma stability by direct stabilization of the resistive wall mode or by reducing magnetic field asymmetry. Assisted by plasma rotation, direct feedback control of resistive wall modes with growth rates more than five times faster than the characteristic wall time has been observed. These results open a new regime of tokamak operation above the free-boundary stability limit, accessible by a combination of plasma rotation and feedback control.

The diagnostic instrumentation on TFTR (Tokamak Fusion Test Reactor) and the specific properties of each diagnostic, i.e., number of channels, time resolution, wavelength range, etc., are summarized in tables, grouped according to the plasma parameter measured. For comparison, the equivalent diagnostic capabilities of JET (Joint European Torus) and the Japanese large tokamak, JT-60, as of late 1987 are also listed in the tables. Extensive references are given to publications on each instrument.

In ST Tokamak discharges with hydrogen or helium as the working gas the measured plasma resistance is usually found to be slight but consistently larger (1.1-1.5 times) than the resistance calculated from measured electron temperature and ionic charge radial profiles. The discrepancy has been ascribed tentatively to undetected high-Z material (Mo or W) from the aperture limiter. Recent experiments with neon, with effective ionic charge Z=9-10 in the discharge, do show good agreement between measured and calculated resistance. In other respects the behaviour of the neon discharge differs only slightly and in the expected direction from hydrogen or helium discharges: larger power input, higher electron temperature, and higher radiation losses. Also, measurement of the intensities of the recently discovered resonance lines of Mo XIII and Mo XIV do indicate a molybdenum concentration in the discharges of the ST Tokamak that is adequate to account for the above mentioned discrepancies in the resistance of H and He plasmas.

A narrow line optically pumped D/sub 2/O laser operating at 385 ..mu..m has delivered more than 5 J in pulses longer than 3 ..mu..sec using a large aperture unstable resonator cavity design. Pulse levels which are > 1 J and 1 ..mu..sec are necessary for a single shot ion temperature measurement by Thomson scattering in large tokamaks. Experiments have, for the most part, been conducted at a 360 J, 5 ..mu..sec CO/sub 2/ laser pump level where high efficiency (approx. 2.5 J at 385 ..mu..m) has been obtained. These are the highest energies reported to date in the far infrared. In addition, the pulse length has been extended beyond the vibrational relaxation time.