Diamond Brewster Window Nearing Completion

Brewster Window

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.

Beam Optics Analyzer Version 6.3 Released

BOA x-ray device image

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.

PPM-focused klystron ready for bakeout

PPM-Focused Klystron Seal-in
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.

Life testing initiated for corrosion mitigation coatings

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.

Life test setup

Photocathode Fabrication Coming On-Line

Photocathode fabrication chamber with vacuum suitcase
Figure 1. Photocathode fabrication chamber with vacuum suitcase

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.

Navy Funds Research to Mitigate Coolant Channel Corrosion and Gun Arcing

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.

TWT collector setup for application of protective coolant channel coating
Figure 1. TWT collector setup for application of protective coolant channel coating

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.

High Voltage Cathode Test Facility
Figure 2. High Voltage Cathode Test Facility

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).