Plasma Materials Test Facility
The Plasma Materials Test Facility (PMTF) at Sandia National Laboratories is a DOE designated User and WFO Facility. This designation permits outside private companies and universities to either visit and use the facility when no DOE experiments are underway or contract Sandia directly through a Work for Others agreement to perform the testing.
During the past ten years, the PMTF performed 27 User Facility Agreements with private industry. High Heat Flux (HHF) testing was performed on ten helium-cooled heat exchangers for Creare, Thermacore, Ultramet and General Atomics, two water-cooled gyrotron cavities for Thermacore and Varian, a water-cooled vane tip for magnetrons and two water-cooled, cross-field microwave amplifiers for DoD applications developed by Jaycor and CPI, Inc. Liquid lithium-cooled refractory heatsinks fabricated by Plasma Processes, Inc. were also tested at the PMTF using a liquid metal cooling loop.
During the above testing, record heat fluxes were achieved on the gyrotron cavities of 140 MW/m 2 for the parallel channel device and 110 MW/m 2 for the porous metal device. A helium cooling technology milestone was achieved at the PMTF; a world, record heat flux was achieved on one of the porous metal, helium heat exchangers of 40 MW/m 2 . This type of testing would not be accessible to these companies anywhere in the U.S. except through Sandia. The PMTF has made significant contributions to the advancement of heat exchanger designs and the optimized cooling of high power devices used to ensure the security of the nation, as well as to advance fusion technology.
In addition to the UF/WFO agreements, work was also performed for other DOE labs, such as Lawrence Berkeley National Laboratory which used the PMTF to evaluate the thermal performance of an accelerator beam dump for ultimate use in neutron generation for cancer therapy. Other tests included a water-cooled, klystron source heat exchanger and a photon beam dump for use at the Stanford Linear Accelerator Center, a helium-cooled RF Faraday shield and EUV lithography electrodes both developed by Thermacore, Inc. and various x-ray tube anodes, windows and RF mirrors.
Plasma Materials Test Facility (PMTF)
The Plasma Materials Test Facility (PMTF) is operated for DOE by the Fusion Technology Department of Sandia National Laboratories. It contains a 1.2 MW, dual-source, CW electron beam system, the EB-1200, that is used for one-sided heating of test articles over areas as large as .7m x .4 m. The PMTF also has a 60 kW electron beam system for smaller targets, where targets can be connected to a closed-loop, 4 MPa, helium coolant system. Both electron beams share a high pressure, high temperature (7MPa, 280 °C) closed-loop water system for target cooling.
Sandia scientists and technical personnel at the PMTF can assist various customers by performing high-heat-flux testing and evaluation of fusion components, advanced heat exchangers, high-temperature materials, and advanced joining techniques. Our staff can also provide modeling of plasma/material interactions, particle transport in physical vapor deposition plumes and assist in the development of new PVD process control techniques.
Research is conducted in the following areas:
1. Modeling of plasma/material behavior and interaction. A fully equipped computer laboratory is housed at the PMTF for analytical and experimental support of high-heat flux experiments. Thermal hydraulic and thermal stress modeling and fluid flow analysis of experiments are routinely performed using the ABAQUS, PATRAN, CFD2000, CFDESIGN and FLUENT FEM/FVM codes. Custom software has been developed to model plasma evolution and disruptions, as well as runaway electron generation. An elaborate infrared analysis program known as SandIR was developed to obtain absolute temperature distributions on surfaces in real-time. The professional staff includes four Ph.D.s with over 60 person-years experience in HHF testing, thermal hydraulics, stress analysis, and component development.
2. Testing and evaluation under high heat flux conditions. Either the EB-1200 or the EBTS (two unique electron-beam systems available at PMTF) can be used to for testing a variety of materials and components under extremely severe surface heat loads. The 60 kW, Electron Beam Test System, which has many of the same diagnostics as the EB-1200, can also utilize helium and liquid metal coolants in the test article. Both e-beams can apply user-specified non-uniform heat load patterns through custom software written at Sandia. Examples of test articles include:
• Plasma facing components in fusion devices
• Microwave gyrotron cavities
• Particle and photon beam dumps
• High flux heat exchangers
• High-temperature materials
• Advanced bonding techniques (e.g., diffusion bonding, specialty brazing, explosion bonding)
3. Materials characterization. Materials characterization capabilities at the PMTF include a new high resolution, large area scanning electron microscope (SEM). The SEM has a resolution of 10 nm and is equipped with EDX and secondary electron analyses and backscattered electron imaging. Unique features of this SEM are its large vacuum chamber (~1 m dia.) and its large sample platen (25 cm x 25 cm in area).
4. Electron beam physical vapor deposition. The PMTF has unique capabilities for large-area electron beam physical vapor deposition of coatings and multi-layers. A wide variety of raster patterns can be edited by the operator in real time to provide a uniform temperature distribution across an ingot, even for non-normal beam incidence. The software also has the capability to perform programmed, high speed pattern switching. This allows the EB-1200 to process two or more ingots simultaneously with each beam resulting in larger deposition plumes. Such capability also and permits the heating of multiple ingots of dissimilar materials with widely different vapor pressures using the same electron beam source.
Electron Beam Test System
The Electron Beam Test System (EBTS), recently upgraded form 30 to 60 kW, is a multipurpose device for studying the surface modification, thermal response, and failure modes of high heat flux materials and components. Targets of all shapes varying in size up to 30 cm by 60 cm can be tested. A large variety of ports and vacuum feed-throughs are available for diagnostics and utility connections. The electron source is typically a tungsten or tantalum filament with maximum operating parameters of 20 kV and 60 kW. Magnetic lenses and deflection coils are used to focus, position, and raster the electron beam to cover a variety of sample surfaces with a finely tuned or defocused beam. Various scenarios can be simulated with the electron gun since it provides a variable directed heat source. 2 ms up to continuous pulse lengths over heated areas from 1 to 100 cm 2 are possible. The diagnostics of the facility are a TV monitoring system, an infrared camera and colorizing system, an array of optical and infrared pyrometers, a bank of imbedded thermocouples, strain gauges, a residual gas analyzer, and water calorimetry for actively cooled samples. Discharge and control of the electron beam gun as well as diagnostic control and data acquisition are carried out by a computerized data acquisition and control system. The post experimental analyses of high heat flux testing in the EBTS involve many in-house capabilities. Data analyses involve the processing of recorded data such as the extraction of temperature contours using IR camera records or the comparison of thermocouple records over a series of tests. Processed data such as temperature profiles, mechanical responses, and thermal hydraulic results are compared with predictions from analytical models. After samples are removed from the EBTS they are subjected to nondestructive and destructive analyses such as scanning electron microscope (SEM) surface studies and metallurgical cross sectioning for microstructural studies.
The digital electron beam rastering system software was upgraded to allow for high-speed pattern switching. Dwell times for each pattern can be as little as 2 ms. These short dwell times are required for thermal shock and disruption experiments. Also, non-uniform heating patterns are possible and selected areas within the overall pattern can receive no heating. The digital system is functionally identical to the EB-1200 system and is capable of controlling pattern size and shape, as well as generating very complex raster patterns at twice the rate of the EB-1200. Patterns such as sine-filled, sawtooth-filled or triangular-filled rectangles, ellipses or trapezoids can be generated as well as arcs and TV raster scans with flyback. Other patterns include spirals, figure eights and concentric circles of various density gradients. The system is very flexible, because new patterns can be programmed into the pattern library as required. In addition, the operator may set the density or dwell time of each of 40 sections of a pattern. Some can have a higher heat flux and others can be nulled out entirely. Several separate processing sequences each consisting of as many as 10 individual steps (patterns) can be input by the operator to meet the requirements of an experiment.
EB-1200 Facility
The Electron Beam-1200 kW System or EB-1200 is the largest steady-state high heat flux facility in the world fusion program, with 1.2 MW of beam power, can apply high heat fluxes to heated areas from 0.001 m 2 to 0.28 m 2 , and is also a beryllium compatible test system. The EB-1200 has two EH 600 S Von Ardenne electron guns each with a solid cathode, varioanode electron source, dual focusing and deflection coils. The beams can be rastered at 10 kHz. Even larger areas are possible at lower raster frequencies. The system is designed to study the thermal response of medium-sized, high heat flux components under energy depositions of the magnitude and duration expected in fusion devices, such as actively cooled beryllium clad first wall and tungsten-armored divertor components for the International Thermonuclear Experimental Reactor (ITER) Project and carbon-carbon clad plasma facing components for Japan 's Large Helical Device (LHD). EB-1200 testing of medium-scale, bare copper divertor prototypes to find critical heat flux or CHF limits for the ITER program was completed in 1998.
Two independent electron guns operating in a steady state mode provide a great deal of flexibility in the EB-1200. For instance, two adjacent targets can be tested at the same time provided that the required total power deposition on each target is below 600 kW. The beam raster patterns may be interlaced or even placed adjacent to one another to cover larger areas or test longer heated lengths. For example, heated lengths of 74 cm can be produced by using adjacent raster patterns. The EB-1200 can be used in a variety of high heat flux tests from 1200 kW/cm 2 deposited on a 1 cm 2 for 100 ms to less than 1 W/cm 2 deposited on a 2700 cm 2 area for times greater than 900 s. Although peak power densities greater than 100 kW/cm 2 over areas of approximately 12 cm 2 are possible, no existing beam dump can survive this heat load. Presently, the EB-1200 does not perform short duration pulse mode (<100 ms) shots.
The vacuum system consists of a large (~3 m 3 ) D-shaped target chamber, with over 50 ports viewing the target surface available for target diagnostics. The sources are mounted on side ports equipped with large isolation valves so sample changeout or filament replacement has minimal effect on the overall vacuum system. The system is pumped with two 3000 l/s commercially available cryopumps.
Diagnostics on the EB-1200 are similar to the EBTS. Four spot infrared pyrometers are used over their appropriate ranges to determine target surface temperatures. Two IR cameras are also available for surface temperature profiles. More than 48 channels of thermocouples are available for bulk temperature measurements under the heated area, as well as a variety of strain gauges. A residual gas analyzer is available to determine the species of outgassed constituents. A complete water calorimetry system is used to determine the actual power absorbed by actively cooled targets. In addition, three different length bore scopes are available along with a TV/video recording system to visually characterize the target during the experiments. LVDTs and strain gauges can be used to measure sample displacement and strain, respectively. A 0.3-m focal length spectrometer and a multitude of fiber optic cables that provide a variety of viewing angles are used for optical emission spectroscopy studies of high temperature chemical erosion mechanisms.
The EB-1200 is able to test the thermal response and critical heat flux limits of medium-sized divertor mock-ups (1 m x 1 m). It also can test up to four 25 cm x 1 m mock-ups with independent channels, simultaneously. The EB-1200 can perform critical heat flux tests up to 120 MW/m 2 over areas of 10 cm x 10 cm, normal divertor heat loads of 10 MW/m 2 over areas of 34 cm x 34 cm, or first wall heat loads of 1 MW/m 2 over 1 m x 1 m areas. Because of the large heated area, it is possible to study flow instabilities in parallel channels. The EB-1200 can be used to test medium-scale divertor mock-ups with multiple (5-10) parallel water-cooled channels in the subcooled flow-boiling regime where two-phase flow instabilities may exist at heat loads in the range of 10-100 MW/m 2 .
All of the tokamak-relevant conditions for measuring critical heat flux (CHF) can be achieved with the EB-1200. Critical heat flux correlations developed for uniform, circumferential heat loads are not applicable to one-sided heating. This area of thermal hydraulics requires extensive investigation. Although Araki, Celata and others have proposed correlations, none are widely accepted for design studies. Empirical correlations for heat transfer coefficients, pressure drop, and burnout limits due to one-sided heating for a variety of advanced heat sink designs such as hypervapotrons, inserts, fins, and internal porous coatings can be obtained on the EB-1200 for medium-sized divertor mock-ups, as well as on the EBTS for small-scale mock-ups.
The EB-1200 can also be used for fatigue testing of medium-scale components or testing of many small components at one time. The two electron guns can be used to fatigue test two medium-scale components side-by-side, if the required heat flux is below 8.7 MW/m 2 . As with thermal fatigue tests with the EBTS, cyclic pattern switching is also available on the EB-1200.
Another important feature of the EB-1200 is the digital raster control. Very complex heat flux patterns can be attained in the EB-1200 by utilizing its computer-controlled, digital sweep generator. In addition to controlling pattern size and position, raster patterns such as sine-filled, sawtooth-filled or triangular-filled rectangles, ellipses or trapezoids can be generated as well as arcs and TV raster scans with flyback. Other patterns include spirals and figure eights of various density gradients. New patterns can be programmed into the pattern library as required.
The raster controls also allow the operator to set the density or dwell time of each of 40 sections of a pattern. This allows some sections of the pattern to contain a higher heat flux than others. For example, tokamak divertor X-point sweeping can be simulated very easily in the EB-1200. Although the raster patterns are continuous, selected sections can be nulled out by setting their dwell time to zero. Therefore, two pseudo-circles at a separation distance of 1-3 cm can be rastered by nulling out the intersection point of a figure eight pattern, or rings can be rastered by nulling out the center portion of a spiral. With the two independent 600 kW electron beams on the EB-1200, different patterns can be juxtaposed to create intricate pattern shapes.
PMTF Flow Loop
The PMTF is a Defense Programs DOE Designated User Facility. This permits ease of access by both large and small businesses throughout the country who are engaged in HHF, heat exchanger and EB-PVD research and research areas such as thermal shock and thermal fatigue of materials, modeling and process control of large-area physical vapor deposition and thermal-hydraulics.
The PMTF flow loop provides high-quality, high pressure high-temperature (HPHT) water to high heat flux targets in the EBTS and EB-1200 vacuum chambers, and is used for infrared thermography in separate hot/cold transient tests that assess the quality of brazed joints. The flow loop gives the operator full control over pressure, temperature, flow, and water chemistry over a wide range of conditions. Control interfaces permit computer control of all flow loop parameters.
The most important part of the flow loop is a variable speed pump that permits flows from 50 to 500 gpm (3 to 30 liter/sec). The loop is pressurized to 1000 psi (6.9 MPa) using a nitrogen pressurizer. A positive displacement pump permits flow and pressure at the target to be varied independently and a surge tank damps pressure fluctuations in the system. The system has stainless steel piping designed to American National Standards Institute (ANSI) power plant standards and uses demineralized from a water treatment system. A 225 kW in-line electric water heater increases the high-temperature capability and stability of the flow loop while providing for fast heating of the loop water. High temperature water up to 280 °C can be delivered to the target inlet without reducing the operating pressure or the maximum flow capabilities of the system.
HeFL Helium Flow Loop
The EBTS is equipped with a closed helium coolant loop that can operate at a maximum pressure of 4.1 MPa and temperatures as high as 300 °C. Helium mass flow rates as high as 22.0 g/s have been achieved for sample pressure drops near 7 kPa (~1.0 psi) and total pressures of 4.0 MPa. The maximum pressure drop for a sample with steady flow in the present loop is 55 kPa (~8 psi) at 4.0 MPa. For some samples, use of a booster blower can produce higher mass flows and pressure drops across the samples as high as 186 kPa (27 psi).
LIMITS Liquid Metal Flow Loop
The EBTS also can be connected to a closed coolant loop designed to study flow of molten metals or molten salts in vacuum and has been used for a preliminary study of flowing liquid lithium surfaces inside of magnetic fusion reactors. The free surface of the flowing liquid can be heated by the EBTS, or the liquid metal can be used inside a tube or heatpipe assembly. The LIMITS system consists of a furnace that can reach 425 °C and has a high temperature impeller pump, a vacuum chamber where the flow is observed, and a transfer chamber for highly reactive molten metals such as lithium. Diagnostics include a magnetic flow meter, pressure transducers, level meter and thermocouples. Video cameras, a scanning infrared camera and multiple pyrometers are routinely used to measure surface temperatures.
Beryllium High Heat Flux Testing at the PMTF
Since the HPHT coolant loop at the PMTF can control inlet temperatures to the sample while maintaining high working pressures, it is an ideal choice for the fatigue testing of beryllium components. Inlet temperatures as high as 280 °C can be maintained easily. The entire PMTF is a Sandia/Department of Energy Environment, Safety and Health (ES&H) approved beryllium handling facility. The building is equipped with special ventilation ducts and a HEPA filter system, which permit high temperature water testing of beryllium-armored components in both the EBTS and EB-1200.
Our beryllium campaigns are currently aimed at applications for fusion energy in which power densities of 0.5 to 2.0 MW/m 2 over a 74 cm heated length, as are anticipated for ITER, can easily be applied for 10 2 cycles with 30 s durations. Using the HPHT loop, surface temperatures of beryllium between shots can be maintained above 150 °C, which is necessary to maintain beryllium above its ductile-to-brittle transition temperature.
The EB-1200 has been equipped with a portable negative pressure room at the door to the D-shaped vacuum chamber. This “gray” room is equipped with a HEPA filtration system and is maintained at a negative pressure anytime that beryllium is outside the vacuum chamber. The “gray” room prevents the potential spread of beryllium particulate into the EB-1200 high-bay and will be used as a staging area for all EB-1200 beryllium targets. All target instrumentation and coolant connections will be made in the room prior to installation into the EB-1200 vacuum chamber. The “gray” room is an ES&H requirement for safe beryllium handling during HHF testing of beryllium-armored mock-ups and beryllium-armored PFC prototypes.
A portable CO 2 pellet blast cleaning system, consisting of a pellet hopper, pellet delivery system, controls and blast gun, is now used for beryllium decontamination of the EBTS vacuum vessel and has shortened the beryllium clean-up procedure from three weeks to one week. The CO 2 cleaning system is supplied with compressed air at 150 psi and a dual-stage air dryer to remove moisture from the blast air. The chambers are maintained at a negative pressure for the duration of the cleaning and the CO 2 /debris exhaust passes through a Be-HEPA system. Glove box fixtures and custom blast nozzles were fabricated for both the EBTS and EB-1200. With the CO 2 system workers can perform efficient decontamination of the vacuum chambers, while they remain outside the chambers and, thus, reduce their risk of exposure to beryllium particulate.
PMTF Computer System
The PMTF Computer System is for theoretical modeling and analysis, experimental control and data acquisition and post-test data reduction and analysis. The system is a heterogeneous network with VMS and UNIX workstations, IBM and Macintosh PCs, data and file storage units and other peripherals are used for building models, graphically displaying theoretical analyses, design/drafting of mock-up units, and for control and data acquisition during testing on the EBTS and EB-1200 systems. Connections to international networks provide ease of electronic communications and file exchange.
The PMTF Data Acquisition and Control System, although connected to the facility computer network, operates independently. A star-hub configuration is used for both the EBTS and EB-1200 based upon CAMAC Ethernet crate controllers. PC-based Vsystem TM and Windows software packages increases flexibility to changes in experimental plans, provides a window based graphical user interface, and distributes control and data processes across multiple PC workstations, while preserving previous investments in CAMAC hardware and in-house software development.