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 m2 to 0.28 m2, 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 ITER Burning Plasma Experiment and carbon-carbon clad plasma facing components for Japan’s Large Helical Device (LHD). Scientists from around the world used the EB-1200 for testing of medium-scale, bare copper divertor prototypes and beryllium armored first wall hypervapotrons to find critical heat flux (CHF) limits and thermal fatigue limits necessary for the ITER program. 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/cm2 deposited on a 1 cm2 for 100 ms to less than 1 W/cm2 deposited on a 2700 cm2 area for times greater than 900 s. Although peak power densities greater than 100 kW/cm2 over areas of approximately 12 cm2 are possible, no existing beam dump can survive this heat load.
The Electron Beam-1200 kW System (EB-1200) is the largest steady-state high heat flux facility in the world fusion program, with 1.2 MW of beam power.
The vacuum system consists of a large (~3 m3
) 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/m2 over areas of 10 cm x 10 cm, normal divertor heat loads of 10 MW/m2 over areas of 34 cm x 34 cm, or first wall heat loads of 1 MW/m2 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/m2.
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. The validity of empirical correlations and of the physics models in modern computational fluid dynamics (CFD) codes for heat transfer coefficients, pressure drop, and burnout limits due to one-sided heating can be obtained on the EB-1200 for medium-sized divertor mock-ups, as well as on the EB-60 for small-scale mock-ups for a variety of advanced heat sink designs such as hypervapotrons, inserts, fins, and internal porous coatings.
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/m2. As with thermal fatigue tests with the EB-60, 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.