This paper describes the design and operation of a 40 spatial channel Thomson scattering system that uses multiple 20-Hz Nd:YAG lasers to measure the electron temperature and density profiles periodically throughout an entire plasma discharge. As many as eight lasers may be fired alternately for an average measurement frequency of 160 Hz, or they may be fired in rapid succession (<10 kHz), producing a burst of pulses for measuring transient events. The high spatial resolution (1.3 cm) and wide dynamic range (10 eV–20 keV) enable this system to resolve large electron density and temperature gradients formed at the plasma edge and in the scrape-off layer during H-mode operation. These features provide a formidable tool for studying L–H transitions, edge localized modes (ELMs), beta limits, transport, and disruptions in an efficient manner suitable for large tokamak operation where shot-to-shot scans are impractical. The scattered light is dispersed by interference filter polychromators and detected by silicon avalanche photodiodes. Laser control and data acquisition are performed in real time by a VME-based microcomputer. Data analysis is performed by a MicroVAX 3400. Additional features of this system include real-time analysis capability, full statistical treatment of error bars based on the measured background light, and laser beam quality and alignment monitoring during plasma operation. Results of component testing, calibration, plasma operation, and error analysis are presented.

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The capability to inject deuterium pellets from the magnetic high field side ͑HFS͒ has been added to the DIII-D tokamak ͓J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 ͑1985͔͒. It is observed that pellets injected from the HFS lead to deeper mass deposition than identical pellets injected from the outside midplane, in spite of a factor of 4 lower pellet speed. HFS injected pellets have been used to generate peaked density profile plasmas ͓peaking factor (n e (0)/͗n e ͘) in excess of 3͔ that develop internal transport barriers when centrally heated with neutral beam injection. The transport barriers are formed in conditions where T e ϳT i and q(0) is above unity. The peaked density profiles, characteristic of the internal transport barrier, persist for several energy confinement times. The pellets are also used to investigate transport barrier physics and modify plasma edge conditions. Transitions from L-to H-mode have been triggered by pellets, effectively lowering the H-mode threshold power by 2.4 MW. Pellets injected into H-mode plasmas are found to trigger edge localized modes ͑ELMs͒. ELMs triggered from the low field side ͑LFS͒ outside midplane injected pellets are of significantly longer duration than from HFS injected pellets.

8 For the derivation of the power law it is assumed that the thickness of the thermal boundary layer is much larger than the gap depth in order to apply the Hele-Shaw cell concept even for the range of the boundary layer. This assumption is valid for moderately high Rayleigh numbers as observations by real-time interferometry have shown,, Measurements of the divertor-region plasma characteristics and argon exhaust efficiencies of the expanded-boundary divertor are reported. High plasma and neutral-hydrogen densities (~10 14 /cm" 3 ) are observed in the divertor region, and the exhaust efficiency for injected argon exceeds 95%. A simple model based on electron heat conduction parallel to the diverted field lines and frictional force due to proton-argon collisions in the divertor region accurately describes the experimental observations. PACS numbers: 52.25.Kn

The dependence of plasma energy confinement on minor radius, density and plasma current is described for Ohmically heated near-circular plasmas in Doublet III. A wide range of parameters is used for the study of scaling laws; the plasma minor radius defined by the flux surface in contact with limiter is varied by a factor of 2 (a = 44, 32 and 23 cm) , the line average plasma density, n̄e, is varied by a factor of 20 from 0.5 to 10 × 1013 cm−3 (n̄e R0/BT = 0.3 to 6 × 1014 cm−2·kG−1) and the plasma current, I, is varied by a factor of 6 from 120 to 718 kA. The range of the limiter safety factor, qL, is from 2 to 12. – For plasmas with a = 23 and 32 cm, the scaling law at low n̄e for the gross electron energy confinement time can be written as (s, cm) where qc = 2πa2BT/μ0IR0. For the 44-cm plasmas, is about 1.8 times less than predicted by this scaling, possibly owing to the change in limiter configuration and small plasma-wall separation and/or the aspect ratio change. At high n̄e, saturates and in many cases decreases with n̄e but increases with I in a classical-like manner. The dependence of on a is considerably weakened. The confinement behaviour can be explained by taking an ion thermal conductivity 2 to 7 times that given by Hinton-Hazeltine's neoclassical theory with a lumped-Zeff impurity model. Within this range the enhancement factor increases with a or a/R0. The electron thermal conductivity evaluated at half-temperature radius where most of the thermal insulation occurs sharply increases with average current density within that radius, but does not depend on a within the uncertainties of the measurements.