Jimmie M. McDonald

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.

Test results from a pumped single-phase porous metal heat exchanger

A pumped single-phase porous metal cooled microwave cavity design is being evaluated for use in a high-power gyrotron. A small-scale porous metal cooled test article was designed, built, and tested on a Phase I SBIR program. The program was funded by the United States Department of Energy. A copper/water porous metal heat exchanger test article was fabricated and was subsequently tested at absorbed heat fluxes up to 7.4 +/- 0.3 kW/cm2 before failure occurred. Multiple tests were successfully completed at heat fluxes of 4.0 to over 6.0 W/cm2 with no signs of failure. The test article design, coolant parameters, test methodology, and test results are presented. The results of this work show the potential of porous metal cooling to solve a number of high heat flux cooling problems; several such applications are described.

Investigation of cascade effect failure for tungsten armour

Abstract The glancing angle of incident power on the target of a tokamak divertor results in doubled and highly peaked heat flux onto adjacent downstream tile in the case of lost of tile event (LOTE). As a result downstream tile has higher probability to fail resulting in triple loads to the next downstream tile and so on (cascade effect). This paper devoted to analytical and experimental investigation of the cascade effect failure for the flat tile option of tungsten armoured plasma facing components. Armour geometry resistant to the cascade effect failure was selected on the base of thermal and stress analyses. Experimental investigation of the LOTE has been performed also. Small size W/Cu mock-up withstood not only LOTE simulation load, but also survived afterwards for 1500 cycles at 26–28 MW/m2 without damage in joint.

Recent results of high heat flux testing at the Plasma Materials Test Facility

High heat flux testing for the US fusion power program is the primary mission of the Plasma Materials Test Facility (PMTF) located at Sandia National Laboratory. This facility, an official Department of Energy User Facility, has been in operation for over 15 years and has provided much of the high heat flux data used in the design and evaluation of plasma facing components for many of the worlds magnetic fusion tokamak experiments. In addition to domestic tokamaks such as Tokamak Fusion Test Reactor at Princeton, the DIII-D tokamak at General Atomics, and Alcator C-Mod at MIT, components for international experiments like TEXTOR, Tore- Supra, and Jet also have been tested at the PMTF. High heat flux testing spans a wide spectrum including thermal shock tests on passively cooled materials, thermal response and thermal fatigue tests on actively cooled components, critical heat flux burnout testes, braze reliability tests, and safety related tests. The programs main focus now is on testing of beryllium and tungsten armor tiles bonded to divertor, limiter, and first wall components for the International Thermonuclear Experimental Reactor (ITER). The ITER project is a collaboration among the US, EU, RF, and Japanese fusion programs. This article provides a brief overview of the high heat flux testing capabilities at the PMTF, and describes some recent test results.

An Experimental Examination of the Loss-of-Flow Accident Phenomenon for Prototypical ITER Divertor Channels of Y = 0 and Y = 2

Abstract This paper discusses the thermal response of two prototypical International Thermonuclear Experimental Reactor (ITER) divertor channels during simulated loss-of-flow-accident (LOFA) experiments. The thermal response was characterized by the time-to-burnout (TBO), which is a figure of merit on the mockups’ survivability. Data from the LOFA experiments illustrate that (a) the pre-LOFA inlet velocity does not significantly influence the TBO, (b) the incident heat flux (IHF) does influence the TBO, and (c) a swirl tape insert significantly improves the TBO and promotes the initiation of natural circulation. This natural circulation enabled the mockup to absorb steady-state IHFs after the coolant circulation pump was disabled. Several methodologies for thermal-hydraulic modeling of the LOFA were attempted.

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.

A technique for efficient cleaning and conditioning of low‐ and medium‐energy accelerators *

A technique was developed to clean and condition low‐ and medium‐energy accelerators by alternating between a glow discharge with hydrogen gas and a glow discharge with oxygen gas. The technique was initiated on a 2.5‐MV Van deGraaff accelerator and has been used on both lower‐energy (down to 10‐keV) and higher‐energy (up to 10‐MV) accelerators with equal effectiveness. The conditioning time for attaining the nominal maximum voltage on the 2.5‐MV accelerator was reduced from about ten days using pumping and voltage conditioning to one day using the glow discharge technique. After a glow discharge conditioning sequence, the 2.5‐MV accelerator could be operated effectively at energies of ≤3.4 MV. In addition, the accelerator tube life was found to be significantly longer than expected. The technique is described, and safety considerations are discussed.

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.

Experimental time to burnout of a prototypical ITER divertor plate during a simulated loss of flow accident

Under the sponsorship of the Department of Energy, Office of Utility Technologies, the Energy Storage System Analysis and Development Department at Sandia National Laboratories (SNL) conducted a cost analysis of energy storage systems for electric utility applications. The scope of the study included the analysis of costs for existing and planned battery, SMES, and flywheel energy storage systems. The analysis also identified the potential for cost reduction of key components.