T.J. Lutz

Thermal performance and flow instabilities in a multi-channel, helium-cooled, porous metal divertor module

Abstract Pressurized helium is under consideration for cooling Langmuir probes and plasma facing components of next generation fusion experiments. Helium is non-corrosive, does not activate, separated easily from tritium, vacuum compatible, and undergoes no phase transformations. Recently, the thermal performance of a bare-copper, dual-channel, helium-cooled, porous metal divertor mock-up, designed and fabricated by Thermacore Inc., was evaluated on Sandias 30 kW Electron Beam Test System equipped with a closed helium flow loop. The module uses short circumferential flow paths to minimize pressure drops and pumping requirements while achieving optimal thermal performance by providing a very large effective surface area. The module was tested under both uniform and non-uniform heat loads to assess the effects of mass flow instabilities. It survived a maximum absorbed heat flux of 29.5 MW/m 2 on a 2-cm 2 area. Results on the power sharing between the two channels is presented and compared with that of a previous design. These experimental results coupled with appropriate modeling provide insight on flow instabilities in multi-channel, helium-cooled heat exchangers.

The sandia ion beam — A high heat flux testing facility

The Sandia Ion Beam Test System is used to conduct high heat flux tests of full scale components for fusion experiments. Heat fluxes of more than 4 kW/cm2 have been achieved with a hydrogen ion beam. The ion beam 22 cm grid set provides an adjustable width Gaussian heat flux profile which can be focused to a full width at half maximum of 13 cm. Diagnostics include an imaging radiometer, two-color pyrometers, thermocouples, strain gauges, water calorimetry, as well as surface and metallographic analysis systems. A versatile sample cooling loop provides up to 32 l/s of water at pressures up to 6.9 MPa and temperatures up to 280 °C. The pH and oxygen content of the sample cooling water can also be controlled. A large target chamber allows targets of 1 m2 and can be separately vented for target exchange without reconditioning the ion beam grid set. An RF induction ion source allows precise beam power and perveance control for different target testing requirements. Computer control is employed through a CAMAC serial highway with a menu driven operator interface. High heat flux tests have been conducted for JET, DIII-D, and CIT. Results from these tests will be shown as examples of current high heat flux testing activities.

Measurements of lithium flow with an EM flow meter in LIMITS

A simple electromagnetic flow meter was constructed and used in the one-inch thick-walled 316 L stainless steel tubing (20.6 mm i.d.) of LIMITS, an experimental lithium flow loop at Sandia National Laboratories. (A parallel paper in this conference by Tanaka et al describes LIMITS.) The flow meter uses a pair of NdFeB permanent magnets (57.2 mmW /spl times/ 48.3 mmD /spl times/ 76.2 mmH) mounted on an iron yoke producing a field of about 0.5 Tesla. This paper describes the field measurements, calibration and use of the flow meter in experiments with flowing lithium. Initial calibration of the meter was done as lithium was moved using gas pressure from a transfer tank to the lithium furnace. In this calibration, we monitored the signal from the flow meter and the signal from a previously uncalibrated level meter in the lithium furnace. The reference for the calibration was the change in weight of the transfer tank, which we measured using a set of load cells under the sled supporting the tank. The flow meter signal ranged from 0 to about 6 mV for flow speeds of 0 to about 1 m/s. There was, as expected, some noise with the mV signal, but use of a running average essentially eliminated the noise. The signal was quite linear with flow as judged by the correspondence between the integrated flow signal and the weight of lithium transferred. We also have used the flow meter in lithium flow experiments in LIMITS and these data and the calibration procedure will be reported in the paper. Among the observed effects during the flow tests was a difficulty in interpreting the signal whenever vibration of stainless steel tubing occurred due to the (usually smooth running) pump or changes in the valve positions, for example, opening a valve with the pump running.

Phase Lag Infra-red Thermal Examination (PLITE); A New Non-destructive Test Process

The International Organization of ITER (International Thermonuclear Experimental Reactor) specifies a requirement of 3 mm in diameter for the largest permissible flaw in the joint of the beryllium (Be) armor tiles and the underlying heat sink made of a copper-chrome-zirconium (CuCrZr) alloy for the first wall (FW). We investigated the sensitivity of a new non-destructive process of detecting these flaws using a method in which we mapped the phase lag of the temperatures on the surface of a sample during thermal cycling with a sinusoidally varying water temperature. A method with hot-cold water test that we had pioneered during the 1990s for the development of a water-cooled mid-plane modular limiter for Tore Supra had worked well with the high conductivity armor made of pyrolytic graphite brazed to copper tubes. The paper describes the experimental system, test samples and some experimental results.