Calabazas Creek Research, Inc. is involved in a variety of hardware development programs funded by the Department of Energy, the Department of Defense, the National Science Foundation and the National Aeronautics and Space Administration. The hardware development activity is focused on extending the state of the art in high power microwave generation, transmission, and efficiency. Programs include:

RF Sources

• Advanced Cathodes
• Micro-Fabricated RF circuits
  

High Energy Physics

• 10 MW, W-Band Gyroklystron for W-Band Accelerator Research
• 50 MW, X-band Multiple Beam Klystron
• High Power Microwave/Millimeter-wave Windows and Waveguide Components
• Low emittance accelerator electron gun
• 200 kW CW Multiple Beam Inductive Output Tube
• Annular Beam Klystron
• Doubly Convergent Multiple Beam Gun
• 200 MHz, 35 MW Multiple Beam Klystron

Fusion Related Technology

• Magnetron Injection Guns
• 2 MW CW Waterload for Gyrotrons
  

Defense, Space, and Homeland Security

• Active Denial Gyrotron
• Terahertz Backward Wave Oscillators
• W-band Traveling Wave Tubes
• Terahertz Traveling Wave Tube
• THz Gyrotron
  

Advanced Cathodes Creek Research, Inc. is developing advanced, high current density cathodes capable of lifetimes of hundreds of thousands of hours of operation. The approach is to combined a controlled porosity emitter with a reservoir of material designed to reduce the work function. CCR developed a technique for sintering small diameter tungsten wires to form a matrix of pores in a hexagonal pattern through the tungsten material. This material is sliced to form a cap over a reservoir of barium carbonate, calcium carbonate, and aluminum carbonate. The thickness of the cap can be selected to provide the diffusion rate of the barium compound required for the current density required. This optimizes the operation to achieve uniform electron emission with extremely long lifetime.

Figure 1. Face of tungsten emitter

Figure 2. Miram Plot

Figure 3. PWFD of CCR cathode with comparison to typical M-type cathode

Figure 1 shows a photograph of the sliced tungsten material with the uniform array of pores. Cathodes using this material are being fabricated and tested. Figures 2 and 3 show a typical Miram Curve and Practical Work Function Distrbution (PWFD) plot. The work function is as good as or better than that for “Best of Class” M-type cathodes. It also indicates that the work function is uni-function up to 60% of the space charge limited current. This performance has never been demonstrated in previous cathodes. Note also that the work function appears to improve with increasing current density.

Life testing is current in progress. The initial cathode has accumulated more than 5,000 hours of operation with the performance continuing to improve. As additional cathodes are built and tested, they are being installed in a Life Test Station. Efforts are in progress to determine the maximum current density capability. This requires redesign of the test device at support higher voltage operation. The heater stem is also being modified to allow higher temperature operation. A cathode is also being fabricated that will incorporate scandium in the reservoir mix. If scandium can be efficiently transported to the emission surface with the barium compound, this could significantly lower the work function and consequently the operating temperature.

[1]	R.L. Ives, L.R. Falce, S. Schwartzkopf, and R. Witherspoon, “Controlled Porosity Cathodes from Sintered Tungsten Wires, IEEE Trans. On Electron Devices, Vol. 52, No. 12, pp. 2800-2805 (December 2005).
[2]	Lawrence Ives, Lou Falce, George Collins, David Marsden, George Miram, Kim Gunther, Marc Curtis, Steve Schwarzkopf, Ron Witherspoon, “Performance of Tungsten Wire Cathodes,” 2009 IEEE Intern. Vacuum Electronics Conference, Rome, Italy, pp, 528-529, April 2009.

Micro-Fabricated RF circuits CCR has generated micro fabricated circuits using a number of techniques, including LIGA, deep reactive ion etching (DRIE), and micro electro discharge machining (EDM). Structures have been fabricated in silicon, copper, and chemically vapor deposited (CVD) diamond. These structures were developed for RF sources between 83 GHz and 700 GHz. 50 GHz BWO circuit fabricated using LIGa. The posts are 20 microns in diameter, 80 microns high, and separated by 30 microns. There are 1500 in the total structure. The material is copper.

Test W-Band meander Line circuit fabricated in CVD diamond Folded waveguide circuit fabricated using DRIE. The width of the channel is 320 microns. The material is silicon.

Section of 600-700 GHz step transition and mode converter. Fundamental waveguide 250x30 microns couples to a computer generated, non-linear mode converter, producing a TE01/TE02/ TE03 quasi-optical output mode. The structure is in copper. Section of BWO circuit fabricated by EDM in copper

R.L. Ives, "Microfabrication of high-frequency vacuum electron devices," IEEE Transactions on Plasma Science, Part 1, Vol. 32 Issue 3, pp. 1277-1291 (June 2004).

10 MW, W-Band Gyroklystron for W-Band Accelerator Research
Calabazas Creek Research, Inc., in association with the University of Maryland, developed a 10 MW gyroklystron at 91.392 GHz for W-Band accelerator research. The device is designed to produce 1 microsecond pulses at 120 Hz with an efficiency of approximately 40% and a gain of 55 dB. A magnetron injection gun produces a high-quality, 55 A beam at 500 kV that interacts with a six cavity, frequency doubling microwave circuit. A super conducting magnet produces a 28 kG magnetic field in the gun region with a separate coil for controlling the field in the gun region.

The input cavity and the first buncher cavity interact at the first harmonic in the TE011 mode; all other cavities interact near the second harmonic in the TE021 mode. The walls of the first five cavities are formed by abrupt radial transitions. Mode conversion in the three harmonic buncher cavities from the TE02 mode to the TE01 mode is minimized by adjusting the cavity length to provide destructive interference. Following extraction from the output cavity, the RF is converted to a mixed TE01/TE02 mode combination. This allows transmission across radial gaps in the collector and redirection using a right angle miter bend. The bend prevents secondary and reflected primary electrons from reaching the single disk, ceramic, output window.

Assembly of the gyroklystron was successfully completed in November 2002. It is available for testing of high-power components or systems. Interested parties should contact Dr. Lawrence Ives.

This program was funded by U.S. DOE Small Business Innovation Research Grant Number DE-FG03-99ER82754. Development was supported by U.S. Department of Energy Grant No. DE-FG03-99ER82754.

W. Lawson, R.L. Ives, M. Read, M. Mizuhara and J.M. Neilson, "18. “Design of a 10-MW, 91.4-GHz frequency-doubling gyroklystron for advanced accelerator applications,” IEEE Transactions on Plasma Science, Vol. 29 Issue 3, pp. 545-558 (Jun. 2001).

50 MW, X-band Multiple Beam Klystron CCR is developing a high efficiency, 50 MW, X-band, multiple beam klystron (MBK) that uses an eight-beam multiple beam gun. The beam voltage is 185 kV with a beam current of 59 A and a pulse length of 3 microseconds. The design includes electron gun, circuit, solenoid, collector, and input and output windows. The effort included development of computational design methodologies to support multiple beam operation and analyzing several circuit design configurations to determine those capable of providing the specified power and frequency with efficiency greater than 50%. Multiple beam klystrons provide higher efficiency and greater bandwidth than single beam devices. Such devices have a number of defense applications, including radar and electronic counter measures. They are also applicable for scientific, medical and industrial accelerators. Images to the left and right show a photograph following successful assembly and a sliced model to the tube. The tube is now under test at Brookhaven National Laboratories. This research is funded by U.S. Department of Energy Grant No.s DE-FG02-03ER83827 and DE-FG03-00ER82964.

High Power Microwave and Millimeter-wave Windows and Waveguide Components
CCR develops high power microwave windows and waveguide components for scientific, defense, and industrial applications. Waveguide components were developed for the Next Linear Collider at X-Band and for several accelerator systems at S-Band. Windows have been designed and fabricated at frequencies from 700 MHz to 700 GHz at power levels from milliwatts to Megawatts. CCR also designs and produces other components, including mode converters, waveguide bends, quasi-optical launchers, and vacuum pumpouts. The company has experience with several window materials, including high purity alumina, single crystal sapphire, silica, mica, and chemically vapor deposited diamond. CCR developed CASCADE for designing waveguide components and microwave windows and SURF3D/LOT for designing quasi-optical launchers and mirror systems.

This research supported by U.S. Department of Energy Grants DE-FG03-97ER82343, DE-FG03-00ER82965, DE-FG02-05ER84181, DE-FG03-99ER82754, DE-FG03-00ER82964, DE-FG03-02ER83378, DE-FG03-02ER83379, DE-FG02-05ER84181, DE-FG02-05ER84350, NASA contract NAS3-00079, and U.S. Air Force contract F29601-03-C-0049.

Low emittance accelerator electron gun CCR recently completed and delivered a low emittance, gridded electron gun system for an accelerator injector. The gun operated at 90 kV and generated 1 ns pulses in a 10 sec macropulse. Each micropulse delivered 1 A of beam current. CCR built and tested the electron gun system, which included the control electronics, heater power supply, grid pulser, grid bias supply, and interface circuitry. CCR did not provide the 90 kV power supply. The measured emittance was 2.5 mm-mrad, which exceeded the requirement of less than 10 mm-m-rad. The photograph at the left shows the electron gun sealed for shipping and the photograph to the right shows the major components in the high voltage floating deck. This interfaces to a console control deck using the orange fiber optic cables shown in the floating deck. M.E. Read, R.L. Ives, D. Marsden, and G. Collins, “Design and Test of a 90 kV, Low Emittance, Gridded Gun,” 2009 Vacuum Electronics Conference, Rome, Italy, pp. 181-182, April 2009.

200 kW CW, 350 MHz Multiple Beam Inductive Output Tube CCR is funded by the U.S. Department of Energy to develop a 350 MHz multiple beam inductive output tube (MBIOT) for accelerator applications. IOT typically operate with efficiencies approaching 70%, which make them ideal accelerator sources at moderate power levels. The power level is typically limited by the output power of the RF driver, since the IOT gain is typically limited to less than 24 dB. The multiple beam approach allows a significant reduction in the beam voltage. This facilitates use of production guns designed for lower power IOTs as well as a considerable cost saving for the power supply. The goal of the program is to achieve 200 kW CW with a gain of 30 dB using seven electron beams driving a single, fundamental mode output cavity. The operating voltage will be 30 kV. The computational design is nearing completion and parts fabrication is in progress. Testing is scheduled for spring 2010. This research is supported by U.S. Department of Energy Grant No. DE-FG02-07ER84876.

Annular Beam Kylstrons Calabazas Creek Research, Inc. has two research programs focusing on development of annular beam klystrons (ABKs). Annular beam klystrons posses many of the advantages of sheet beam klystrons without the expense and complication of 3D design and fabrication. One can think of ABKs as sheet beam klystrons rolled into a cylinder. The advantage is that cylindrically symmetric components are much easier and less expensive to design and fabricate. This can be a significant advantage for accelerator systems where hundreds of RF sources may be required. CCR began ABK research with a 200 MW development at L-Band. That program is nearing completion, and a photo of the klystron is shown at the right. This device is designed to operate at 500 kV and generate microsecond pulses of RF power. The U.S. Department of Energy recently awarded another program to CCR to develop a 10 MW, 1.3 GHz ABK. This device will be targeted for the International Linear Collider. It is anticipated that the klystron will operate around 120 kV.

Doubly Convergent Multiple Beam Gun
Calabazas Creek Research, Inc. is working with the Center for Research in Scientific Computation at North Carolina State University to develop doubly convergent multiple beam guns. Successful development would allow generation of high levels of RF power while still using fundamental mode circuits and low current density, long life cathodes. Multiple beam guns reduce the operating voltage over single beam guns while increasing bandwidth and efficiency. Doubly convergent guns result in beam compression toward the local axis of each cathode and compression of the ensemble of beams toward the device axis. Conservation of angular momentum, however, causes beams compressed toward the device axis to spiral about the axis. Fabrication of a klystron circuit with spiraling beams is currently impractical.

This research is applying modern computer optimization techniques to compensate for angular momentum effects and provide non-spiraling beams through the RF circuit. Results to date successfully derived a design meeting this goal for a very small beam shifted a few millimeters from the device axis. Figure 1 shows the effects of the compensation. The program is now focused on increasing the beam size and shifting the beams several centimeters from the axis. The goal is to develop a multiple beam electron gun for a 20 MW, L-Band klystron suitable for accelerator applications.

Figure 1. Plots of beam propagation without compensation (left) and after compensation (right).
The plots on the left show beam spiraling through the circuit region (40-80 mm), while the plots on the
right show propagation parallel to the device axis.

200 MHz, 35 MW Multiple Beam Klystron (MBK) Calabazas Creek Research will be funded by the U.S. Department of Energy to develop a 200 MHz, 35 MW, multiple beam klystron. The device will be targeted for acceleration and ionization of a muon collider, but there are several potential applications in this frequency range. An MBK uses multiple beams propagating in individual beam tunnels to reduce spaced charge and lower the accelerating voltage. This allows a major reduction in size while also improving efficiency and reducing the cost of the power supplies and support hardware and facilities. The research builds on previous design of a 5 MW MBK at this frequency. A solid model of that design is shown below. The image to the right shows a solid Model of 5 MW, 200 MHz multiple beam klystron.

Improved Magnetron Injection Guns
Large diameter magnetron injection guns are a key component in high power gyrotrons for fusion energy research and defense applications. Because these guns operate temperature limited, azimuthal emission uniformity is a significant problem. Guns with 6:1 variations in emission current have been measured and 1.5:1 and 2:1 are not uncommon. Emission non-uniformity can lead to reduced RF efficiency and excessive heating the collector.

CCR was funded to develop advanced guns with improved temperature and work function uniformity. A cathode – heater configuration was developed that utilized a free standing heater to allow adjustment of the temperature profile and elimination of a major failure component. Equipment was also developed to measure the work function and temperature uniformity of production guns.

This research was supported by DE-FG03-01ER83196 and DE-FG02-04ER83918.

2 MW CW Waterload for Gyrotrons

CCR is funded to develop a 2 MW CW waterload for high power gyrotrons used for electron cyclotron heating of tokamak plasmas. CCR currently produces a 1 MW CW waterload used in Europe , Japan, Korea, and the United States. These loads are crucial to development of high power gyrotrons. Gyrotrons generate Gaussian beams that are transmitted in overmoded waveguide or quasi-optically in mirror systems. The waterload must dissipate high levels of RF power without electrical arcs or thermal problems. CCR waterloads use a unique rotating reflector to distribute the RF power uniformly inside the load. RF loss material absorbs the power and converts it to heat, which is removed by water cooling. The goal is to distribute the power so that there are no regions subjected to damaging temperatures. Since the interior is highly overmoded, there is the potential in a static load to generate regions of constructive or destructive interference. This problem is addressed with the rotating reflector, which continuously changes the distribution of power in the load. The new program will refine the distribution of loss material in the waterload and incorporate a more effective technique for distributing the RF power. This will insure more uniform power distribution and eliminate leakage of RF power back through the input port. The new configuration will facilitate vacuum pumping and incorporate advanced optical diagnostics and protection devices. This research is funded by the U.S. Department of Energy.

Figure 1. MW CW Waterload for Gyrotrons

Active Denial Gyrotron
CCR is developing a 30 kW CW, 95 GHz gyrotron for the U.S. Department of Defense’s Active Denial System. The gyrotron will operate at the 3rd harmonic of the operating mode, reducing the magnetic field requirement and allowing use of a permanent magnet. All current active denial gyrotrons require a superconducting magnet. This significantly increases the turn on time required, as the superconducting magnet requires hours to achieve operating temperature. A permanent magnet gyrotron would require only minutes to turn on.

Since operation at the third harmonic is considerably less efficient than first harmonic operation, the gyrotron requires a 2-stage depressed collector to recover the lost efficiency. This reduces the input power requirement and power dissipation in the collector. The challenge was to incorporate the entire gyrotron within the permanent magnet. This requires the magnet to be assembled around the gyrotron. Design of the gyrotron is complete and testing is scheduled for fall 2009.

The magnet itself represented a significant technological challenge, due to the precise field profile required by the gyrotron. The magnet was designed and fabricated by Dexter Magnetic Technologies, Inc. A photograph of the magnet is shown at the right.

This program is funded by U.S. Air Force contract FA9451-07-C-0010 and U.S. Navy contract N00024-08-C-4112.

Jeffrey Neilson, Mike Read, Lawrence Ives, “Design of a Permanent Magnet Gyrotron for Active Denial Systems,” 2009 Intern. Vacuum Electronics Conference, Rome Italy, pp. 92-93, April 2009.

Terahertz Backward Wave Oscillators
CCR is developing the next generation of terahertz tunable Backward Wave Oscillators (BWOs). Successful development will result in devices that require significantly less input power, require less cooling, and have reduced weight and higher mode purity than sources now available. These will be the first BWOs with a depressed collector, spent-beam, energy recovery system, which will reduce the prime beam power requirement and allow air cooling instead of water cooling. The BWOs will include mode converters between the slow wave structure and the overmoded output to allow for single mode operation. Finally, advanced permanent magnet technology will reduce the magnet and system weight.

BWOs are presently used for ground based atmospheric sensing of trace chemicals, testing of solid state sensors, and basic spectroscopy research. CCR's innovative developments will allow these devices to be used for airborne or space atmospheric sensing missions, and will reduce the cost and complexity, making their unique tunability and output power capability more accessible to both private and government laboratories. A prototype 600-700 BWO is under construction and will be ready for testing in late 2003.

This research is funded by the National Aeronautics and Space Administration through SBIR Grant number NAS3-01014.

W-band Meander Line Traveling Wave Tubes
CCR and UW are also currently developing a W-band (82-85 GHz) TWT based on a planar, meander line circuit. The goal of this US Army supported program is to develop a device that clearly demonstrates micro-fabrication. The meander line circuit and coupler are shown below wherethe circuit transitions directly into WR-10 waveguide as an E-field probe to excite the waveguide.The circuit includes a metallized meander line trace on a dielectric substrate.

The meander line circuit offers excellent electrical performance in addition to the fabrication advantages associated with planar circuits.For the same operating specifications at 83.5 GHz, it offers one third the saturated length, and an RF efficiency 49% higher compared to the folded waveguide circuit. The prototype TWT will include a single section of circuit with about 15 dB of gain to demonstrate the concept.The TWT is presently being developed using the same electron gun, window, collector and focusing designs as the fwg TWT program described above.

Cut through view of back to back section of meander line circuit and couplers showing waveguide block, meander line circuit and E-field probes

The program is pursuing two different versions of the circuit- diamond and silicon substrates.The diamond circuit fabrication involves laser machining the meander line pattern directly into a block of CVD diamond.The silicon circuit fabrication involves using deep reactive etching ion (DRIE) to form the meander line pattern into silicon.Both are followed by selective metallization of the meander line trace.

Meander line TWT circuits before metallization. Laser cut diamond by Oxford Lasers, Inc. (left) and DRIE silicon by University of Wisconsin (right).

Meander line TWT circuit assembly

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