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Summary form only given. Transport of parallel momentum during reconnection events has been investigated in the Madison Symmetric Torus reversed field pinch (MST RFP). The events are characterized by a sudden increase of resistive tearing magnetic fluctuations and change in the plasma rotation. The parallel plasma velocity abruptly decreases in the core and speeds up in the edge which results in the flattening of the parallel momentum profile. The parallel velocity in the core is reconstructed from the poloidal velocity of bulk plasma measured with the Rutherford scattering diagnostic and the toroidal phase velocity of the core resonant resistive tearing modes measured with an edge array of magnetic pickup coils. The edge flow is measured by the Mach probe. The transport of parallel momentum can be understood within the framework of two-fluid turbulent relaxation theory and from detailed MHD calculations of fluctuation induced Maxwell and Reynolds stresses resulting from multiple tearing modes. Previous measurements show the Maxwell stress to be a factor of ten larger than either the inertial or the viscous terms in the momentum balance equation both in the edge and in the core. Recently, measurements of the Reynolds stress have been performed in the edge plasma of MST. The Reynolds stress is shown to balance the Maxwell stress and the difference of the two stresses is approximately equal to the rate of change of plasma momentum. Reduction of magnetic fluctuations, achieved by an inductive control of the plasma current profile, results in a significant decrease of the momentum transport in agreement with previously observed reduction of particle and energy transport. This was established by transiently applying an external torque to the plasma edge with biased electrodes. Application of the edge torque during improved confinement induces a fast edge rotation, but the change in the core rotation remains small, which is an indication of a reduced inward momentum transport.

Summary form only given, as follows. There is presently considerable worldwide interest in the study of high temperature plasmas. Much of this interest is driven by the goal of achieving controlled thermonuclear fusion, which involves the release of net nuclear energy from the fusion of light nuclei such as deuteneum and mtuim. In order to understand many of the issues and problems relating to the physics of magnetically confined plasmas, there is a need for accurate, high resolution and flexible diagnostic systems. The far-infrared spectral region (100-1OOO pm) is ideally suited to a number of fusion plasma diagnostic techniques such as collective Thomson scattering, multichannel interferometry and polarimetry. The only practical radiation source currently available is *e optically pumped far-infrared (FIR) laser. This paper describes the development of a high power, stable, twin frequency FIR laser for diagnosis of fusion plasmas. The use of buffer gases, temperature optimization and operation of the laser in both ring and linear cavities will be described. In addition, diagnostic measurements on the TEXT device will be presented to demonsuate the flexibility and importance of FIR diagnostics in the fusion program.

Summary form only given. Both the current density and electron current density are important parameters for fusion-oriented plasma research. In a reversed field pinch plasma, a far-infrared laser system is employed to measure both the Faraday rotation and electron density simultaneously with time response ~5 microseconds. This provides a single-shot capability for constraining magnetic equilibrium reconstructions and determining the current density distribution. Fast time response combined with low phase noise also enables us to directly measure magnetic, current density and electron density fluctuations. The two-fluid Hall effect is identified and found to be significant during magnetic reconnection events. A new diagnostic is being developed which detects the relativistic phase shift (Fizeau effect) of a laser beam propagating through a moving plasma thereby providing a measure of the electron current density. These diagnostic techniques have direct application to ITER.

A multichannel far-infrared (FIR) scattering system has been installed on the TEXT device utilizing both heterodyne and homodyne detection techniques. The system has allowed the power spectra of microturbulence to be measured on a single tokamak discharge. The results confirm many of the characteristics observed in a number of previous experiments [1,2,3]. However, significant new results are presented for a variety of plasma conditions, thereby expanding our knowledge of transport phenomena in fusion plasmas.

A multichannel, far-infrared (FIR) laser scattering system is used to study the temporal development of the power spectra of low frequency microturbulence in the TEXT tokamak. The single shot measurement capability has revealed significant modifications in the spectra during laser ablative injection of small quantities of scandium into the plasma. The present paper reports these observations in detail and discusses their relevance to transport phenomena in fusion plasmas.

Far infrared (FIR) and millimeter-wave source and receiver development has grown significantly in recent years. The existence of atmospheric windows around the millimeter wavelength has stimulated interest in areas such as communications and radar design. The advantages to be gained by the use of the FIR in fusion plasma diagnostics is already being realized and should prove increasingly important in the future.