Life testing of the reflector assembly for CCR’s 1.5 MW CW RF load assembly was terminated on January 3rd after operating for more than 410,000 cycles. The assembly was still operating satisfactorily when the testing was stopped. This is more than twice the expected lifetime for a load in operation at a gyrotron facility. The assembly is being disassembled to determine areas where the design can be improved. These improvements will be implemented to further improve the reliability of the device. The previous post provides a video of the assembly operating in the testing structure.
Testing has begun on the RF reflector drive system for CCR’s new, 1.5 MW CW, RF load for gyrotrons. The new design eliminates rotating seals and bearings. The reflector is mounted to a hollow shaft passing through a stainless steel bellows that supports the reflector and provides water cooling. An external motor swings the reflector around the waveguide launcher that delivers RF power to the load. The reflector sweeps the RF power around the load interior, preventing excessive power densities and standing modes inside the structure.
The new design meets specifications for ITER, the international fusion reactor now under construction in France. Approximately 24 loads will be required for the initial phase.
The video below shows life testing of the the reflector support assembly. A dummy cone on the shaft duplicates the weight of the copper, water-cooled cone that will be used in the actual load.
CCR’s Periodic Permanent Magnet (PPM) focused klystron completed bakeout today. The tube is currently being prepared for high power testing at Communications & Power Industries, LLC. The klystron is being developed for a new generation of cancer therapy machines (CLINACs) produced by Varian Medical Systems, Inc. The PPM-focused klystron would replace traditional solenoid-focused klystrons, reducing the size and weight of the system.
The klystron is designed to produce 5.5 MW RF pulses at 2.856 GHz at approximately 50% efficiency. This development is funded by the U.S. Department of Energy through grant number DE-SC0007591.
A major milestone was achieved in fabrication of the diamond Brewster window when the brazed diamond disk assembly was successfully welded into the stainless steel support structure. This was the final assembly step potentially stressing the diamond.
The diamond Brewster window is designed to transmit up to 1.5 MW of RF power continuously from 100 – 140 GHz. The window will be mounted in 63.5 mm diameter HE11 waveguide and forwarded to General Atomic for testing in the ECH transmission line at DIII-D. It will be tested using 110 GHz gyrotrons at the maximum power and pulse width available.
The window is compatible with the Direct Coupler developed by CCR for extracting RF power from gyrotrons in HE11 waveguide. The Direct Coupler and Brewster window would allow development of broadband, high-power, long-pulse/CW gyrotrons for electron cyclotron heating, parasitic more suppression, and current drive in tokamaks.
This program is funded by U.S. Department of Energy Grant DE-SC0006212.
During the past several months, we’ve been extensively testing BOA beta version 6.3 and it is now ready for primetime. It uses the latest Simmetrix solid model and meshing libraries and the most recent DisLin plotting library for portability and implementation of UI interfaces. New features are listed below. More detailed information is available in the Release Notes at http://calcreek.com/products/software/.
New features in BOA v6.3 include:
• Option to use Inverse Cumulative Density Function technique for thermal effects in thermionic emission,
• More intuitive and simplified menu for beam optics display pane, especially for model background and symmetries,
• Models with built-in symmetries can now be specified.
• Both global and project level persistent preferences can be set via File, Options and View, User View Preferences, respectively,
• Parallel IO particle data are now available,
• Ability to plot images of power density from a 3D surface in either color or gray scale. Display power density on 3D surfaces in either color or gray scale,
• Plot emittances or brightnesses along a global or arbitrary axis.
• Injection of particles with arbitrary coordinates without specifying an injection plane in model. This is convenient for multipactoring ePIC simulations.
CCR’s Periodic Permanent Magnet (PPM) Focused klystron was sealed in on Friday and is now waiting for a bakeout oven. The tube is targeted for a new generation of cancer therapy devices. Elimination of solenoid focusing will allow a smaller package and downsizing of the medical equipment. The klystron is designed to produce 5.5 MW of pulsed RF power at 128 kV. A critical challenge was maintaining relatively high efficiency for a tube operating at high perveance. This klystron is a prototype and allows measurement of body current to determine beam transmission and includes tuners for several cavities. It will be tested at Communications & Power Industries, LLC, the industrial partner on this program. More information is available on the Research page .
This program is funded by U.S. Department of Energy Grant No. DE-SC0007591.
Accelerated life testing of test structures was started in September to evaluate corrosion mitigation coatings for copper cooling channels. This is similar to life tests performed a couple of years ago that were very successful. Those tests used ethylene glycol and water as the coolant fluid. To more closely duplicate the conditions on Navy ships (recall this is a Navy-funded program), the coolant mixture includes salts to mimic seawater contamination. We’re also bubbling air into the coolant reservoir to oxygenate the water. There are seven coated samples and one uncoated control sample in the experiment. It’s anticipated that the experiment will be terminate in early December and the test samples analyzed. This will provide useful information on the effectiveness of different materials with varying thickness. More information concerning this research is available on the Research page.
This program is funded by U.S. Navy contract N00014-14-P-1198.
CCR is nearing completion of its photocathode fabrication chamber. The main chamber was assembled and baked in March. The vacuum suitcase was assembled and is currently being baked. Figure 1 shows a photo of the chamber with the suitcase attached.
During the next couple of weeks we’ll be installing the support for the sputtering source and the internal support for the photocathode being processed. We also need to mount the laser and connect the picoammeter. We had a small setback when problems arose with our turbo pump. That’s now been replaced, and we’re moving forward again.
We’ll first fabricate cesium antimonide photocathodes. The antimony source will be installed in the next couple of weeks. We still need to assemble the first test photocathode with parts in stock. I’m hoping we can fabricate our first cathode by the end of November.
This program is funded by U.S. Department of Energy Grant No. DE-SC00009583.
The U.S. Navy funded the Phase I Option of CCR’s program to use innovative coatings to suppress arcing in electron guns and reduce or eliminate corrosion in RF systems deployed in the fleet. The corrosion occurs in copper coolant channels in RF sources and solenoids due to excess oxygen and salts in the coolant.
CCR is developing coatings to prevent coolant channel corrosion in collaboration with N.C. State University. This follows highly successful life test studies that demonstrated coolant channel lifetime could be increased more than 500% using a nanometer-scale coating of ceramic. The coating is applied by flowing a sequence of gases through the device’s cooling system. Figure 1 shows the setup to coat a TWT collector. It is anticipated the coating will be added prior to final device tests. The process would be applicable to any fluid cooled device where high quality coolant is not available.
The arcing issue arises in klystrons following weeks or months of stand-by operation. The sudden application of high voltage creates spurious electron emission from the focus electrode, immediately taking the system off-line.During the next few months, CCR and N.C. State University will test the process on the cooling circuit of a solenoid manufactured by Arnold Magnetic Technologies.
CCR is investigating coatings that preferentially react with oxygen. This program will determine if coatings of carbon, titanium carbide or tantalum carbide will absorb the oxygen and prevent barium oxide formation. High voltage tests are planned during the next few months using CCR’s cathode test chamber (Figure 2).