Large Fusion Devices Research Articles

Proposal for a time-of-flight Thomson backscattering technique for large fusion devices

The application of 180° Thomson scattering using ultrashort laser pulses for measuring electron temperature and density profiles in large fusion devices is proposed. Spatial resolution along the laser beam is achieved by high-speed detection allowing time-of-flight measurements. This LIDAR (light detection and ranging) technique uses a minimum number of window ports and reduces the number of optical components in the vicinity of the discharge vessel. As an example, the performance of such a system for the JET tokamak geometry is discussed on the basis of available laser and detection technology.

User Perceptions of Large Versus Small Fusion Devices and Electric Power Research Institute-Funded Compact Reactor Studies

The rationale for Electric Power Research Institute interest in small fusion systems is discussed from two points of view: economic demonstration of the competitive features of fusion energy and end use application. The physics base is summarized for five fusion schemes, which might enhance the prospects for a small fusion reactor, and scaling laws, which connect small systems with high-power-density systems are derived.

Seals for large ports on the Tokamak Fusion Test Reactor

The Tokamak Fusion Test Reactor (TFTR) is a large fusion device being constructed at the Plasma Physics Laboratory of Princeton University. This unit is designed for bakeout at 250 °C, and for a base pressure of 10−8 Torr. The machine has a total of 57 large ports that are removable and are sealed with ‘‘Helicoflex’’ metallic gaskets. There are two seals on each port, a primary and a secondary, with flange bolts between seals. This arrangement balances the load on either side of the bolts, eliminating flange roll that could result from the high sealing forces. The dual seal arrangement also aids in leak detection and permits recovery from a failed primary seal by pumping between seals. All of the large ports have been leak-checked with a helium mass spectrometer leak detector, and all primary seals have been found to be leak tight.

Experimental results on boundary plasmas, resulting surface interactions and extrapolation to large fusion devices

Experimental results on boundary plasmas, impurity origins, and impurity transport in the boundary plasmas are summarized in relation to impurity control and wall erosion. Important parameters in the boundary plasma are surveyed in present-day tokamaks and the relation between the boundary plasma and the main plasma is induced. It is shown that the important parameters of the boundary plasma in a large device can be calculated from the assumed main plasma parameters. Impurity release from the first wall is governed mainly by the boundary plasma. Ion sputtering is shown to be the dominant process in the stable phase of a discharge. In addition to these processes, arcing, sputtering by charge-exchange neutrals etc., which may become serious in a large device, are considered. All released impurities do not flow into the main plasma, even without a divertor. Impurity contamination in the main plasma is governed by the impurity transport and atomic processes in the boundary plasma as well as by the transport in the main plasma and by the impurity production. Therefore, the study of impurity transport in the boundary layer is important and is summarized. It is shown that the impurity transport in the boundary layer is well simulated by Monte-Carlo calculation. Combining these results, impurity problems in a large device are discussed.

General atomic's superconducting high field test facility and initial performance

General Atomic has established a high field test facility whose primary mission is to investigate the J-B-T and stability performance margins of commercial NbTi superconductor in the 10 tesla, 4.2 K region. This work is part of the overall DOE/MFE/MAGNETIC SYSTEMS effort to provide an adequate technological base for construction of superconducting toroidal field coils for the next generation of large tokamak fusion devices. The principal components of the facility are the coil/cryostat assembly, the helium refrigerator-liquefier/compressor system, and the gaseous helium recovery and storage system. The epoxy impregnated, layer wound main background field coil generates 8 tesla within its 40 cm diameter bore. The insert background field coil was layer wound with cooling channels provided by "barber pole" mylar conductor insulation. Ten tesla is generated within its 22 cm bore. The initial performance of the facility will be discussed. Future testing calls for operating test coils with implanted heating elements to simulate mechanically induced perturbations. The normal zone growth and recovery behavior will be observed for various disturbance energies. This data will then be compared with results obtained from the transient recovery analysis developed at General Atomic.

Divertor experiments for controlling plasma-wall interactions

Divertor experiments in tokamak devices are summarized, and impurity control and the divertor in a large fusion device are discussed.

A Far Infrared Spectroscopic System Used in Fusion Plasma Diagnostics

A far infrared spectroscopic system, covering the wavelength region between 50 ?m and capable of variable spectral resolution between 100 and 1000, has been built. The spectroscopic system is described in some detail. It is comprised of a monochromator, which utilizes five different echelette gratings, each of which covers one octave, of a radiometric system for absolute power calibration, and of various cryogenic and room temperature detectors. The system works in two modes: a continuous mode using the absolute power calibration, the radiometer, and continuous standard radiation sources, and a pulsed mode without the radiometer for plasma radiation studies. In this manner the power spectrum of the observed pulsed plasma radiation is absolutely calibrated. A rather new method in monochromator design utilizing ray transfer matrix method and phase space diagrams is discussed, and various optical errors in the system are evaluated. The method of performing and the evaluation of radiation studies utilizing this system is presented. The system will be used in the very near future to measure the far infrared radiation from several of our fusion experiments: from Texas Tokamak, a large experimental fusion device; from a small, adiabatically heated, symmetric, hot electron stellarator; and from some other hot plasma devices. These experiments have strong magnetic fields, ranging between 30 to 5OkG. Moreover, high electron temperatures--between 1 to 20 keV--are expected, so that the synchrotron radiation in the far infrared will be appreciable. Synchrotron radiation from Tokamak as a function of the electron temperature and density is discussed.