Calabazas Creek Research, Inc. | CCR Hardware Development Programs

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:

Industrial Applications

Gyrotron Annealing of Silicon Wafers: Ultra-short Term, High-temperature Processing

High Energy Physics

10 MW, W-Band Gyroklystron for W-Band Accelerator Research
100 MW Multiple Beam Gun for High Power RF Applications
50 MW, X-band Multiple Beam Klystron
13 kW CW Klystron for Jefferson Lab Superconducting Accelerator Upgrade
40 MW Sheet Beam Klystron
High Power Microwave/Millimeter-wave Windows and Waveguide Components
80 MW Gridded Sheet Beam Electron Gun

Fusion

Improved Magnetron Injection Guns
Multi-Stage Depressed Collectors for 1 MW CW Gyrotrons

Defense, Space, and Homeland Security

Terahertz Backward Wave Oscillators
Field Emission Array Electron Guns
W-band Traveling Wave Tubes

Gyrotron Annealing of Silicon Wafers: Ultra-short Term, High-temperature Processing
Virtually all advances in silicon (Si) electronics technology come from reductions in the size of the transistors on the chip being produced. Smaller transistors are faster and a greater number fit in a given surface area. Because the total cost of production remains unchanged, a greater number of faster, more powerful chips are produced at a lower per-chip cost. Building smaller features, however, requires elimination of interdiffusion between the various regions be eliminated, or at least minimized. This interdiffusion occurs when the chip is processed at high temperatures, i.e. 700C. Unfortunately, many of the chemical reactions needed to form the active regions of the transistor will not occur below 1200C.

To solve this challenging problem, CCR is using high-power microwave radiation, produced by gyrotrons operating at 110 GHz, to rapidly heat the Si chips to 1300C. CCR achieved ramp rates that exceed 250,000 C/sec, allowing the chips to reach the target temperature of 1300C in only a few milliseconds. Because the skin-depth of the radiation is about 0.1% of the sample thickness, and because the ramp rates are so rapid, most of the sample remains cool throughout the heating process. Consequently, the cool-down process is dominated by thermal conduction, which is much faster than any other cool-down mechanism available. CCR analysis shows that virtually no interdiffusion of the active regions occurs on these time scales, and that the chemical reactions are given adequate time and energy to move to completion. As a result, gyrotron annealing facilitates the production of superior transistors: smaller, faster, and cheaper.

This program is funded by the National Science Foundation Research Grant DMI-0319613.

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.

100 MW Multiple Beam Gun for High Power RF Applications
MBG Assembly The next generation of high energy accelerators will require RF sources producing output power levels in the range of 50-150 MW and frequencies of 10 GHz and higher. Typically these devices operate with a single electron beam where space charge forces and cathode emission density limitations force beam voltages above 300 kV. This increases demands on the power supply systems as well as electrical stresses on components. It also forces the voltage requirement above levels that can be provided by highly efficient switch mode power supplies.

One way to avoid high operating voltages is to use a klystron with a multiple beam gun to raise the effective perveance. In the multiple beam gun, the cathode emits a number of 'beamlets' that traverse the tube in separate beam tunnels. This reduces space charge forces that drive the voltage requirement. The perveance of each beamlet can be lower than would otherwise be necessary, leading to increased efficiency, greater bandwidth, and reduced size.

CCR is currently constructing a multiple beam gun consisting of eight cathodes producing more than 100 MW of beam power. A beam analyzer facility is also being constructed to map the transverse beam profile at various distances from the cathodes. This will provide details of the performance for feedback into the design codes to perfect the development capability.

This program is funded by U.S. Department of Energy Small Business Innovation Research Grant DE-FG03-00ER82964.

50 MW, X-band Multiple Beam Klystron
CCR is developing a high efficiency, 50 MW, X-band, multiple beam klystron (MBK) that uses the multiple beam gun under development and described above. 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 includes 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. The successful completion of this program will extend the technology of multiple beam klystrons substantially beyond present experimental results.

Scheme of 50MW, X-band Eight Beam Klystron

This research is funded by U.S. Department of Energy Grant No. DE-FG02-03ER83827.

13 kW CW Klystron for the Jefferson Laboratory Superconducting Accelerator Upgrade
CCR is developing a new klystron power source at 1497 MHz to drive accelerator superconducting cavities. The initial principal application will be the Thomas Jefferson National Accelerator Facility (TJNAF) upgrade. With a minor change in operating frequency, it will also be of potential use at other accelerators. Approximately 90 klystrons will be required for the TJNAF upgrade. These tubes could also serve as as drivers for free electron laser accelerators.

The klystrons require 13 kW CW at 1 dB below saturation, with the 1 dB being available for control of the output power. The required saturated power is thus 16.4 kW. The klystrons will operate at a variety of power levels depending on the parameters of each superconducting cavity and on the energy delivered to the electron beams. Because each superconducting cavity may require a different operating power level, the klystron electron gun will contain a perveance-determining electrode that will reduce the collector dissipation when operating at less than full power. Also, because the klystrons will be part of an energy feedback system, good stability is needed in the linear gain region of the klystron. The efficiency goal is 50%, significantly higher than the devices being used on the existing TJNAF accelerator.

CCR is currently fabricating two prototype klystrons. After testing they will be delivered to TJNAF for evaluation.

This research is funded by U.S. Department of Energy Grant No. DE-FG02-03ER83833.

40 MW Sheet Beam Klystron
CCR and the Stanford Linear Accelerator Center are designing an 11.424 GHz, 40 MW sheet beam klystron (SBK). This represents a novel source of microwave radiation for use in advanced accelerators. The design includes the ppm beam focusing system, RF cavities, input and output couplers, output window and spent beam collector.

The SBK uses a rectangular beam, rather than a conventional cylindrical beam. This allows a higher perveance (lower voltage, higher current) beam than is possible with conventional klystrons. In addition, the SBK incorporates a low voltage grid to control the current. The combination of these two features allows power supplies that are both more capable and less expensive than currently required.

Since microwave sources and their associated power supplies are a significant percentage of the cost of a large accelerator system, cost reduction in the RF source system will significantly reduce the total accelerator cost. Also, the reduced voltage provides RF sources with reduced size, increased efficiency, and larger bandwidth.

This sheet beam klystron is targeted for advanced accelerators and colliders for high-energy physics research. Accelerators are also used for diagnosing and treating cancer and other diseases.

This research is funded by U.S. Department of Energy Grant No. DE-FG02-03ER83617.

High Power Microwave and Millimeter-wave Windows and Waveguide Components
CCR developed high power microwave windows and waveguide components for high energy accelerator application. The research also applies to lower power devices. The program focused on devices for the Next Linear Collider (NLC), which requires waveguide components transmitting 600 MW of RF power and windows transmitting 75- 100 MW of power. The window research explored alternative window materials, including single crystal sapphire, high purity alumina, chemical vapor deposited diamond, and fused quartz and silica in an overmoded configuration.

Waveguide components included:

Ripple-wall and serpentine mode converters using standard modes in circular waveguide, and high power combiners
Overmoded waveguide bends using Gaussian, quasi-optical techniques
Components that transform and control the polarization of the mode for high power RF launchers and power extractors
TE01 windows for 100 MW Power transmission at X-Band

The program made extensive use of several advanced computational tools, including CCR's computer code Cascade and the finite element, thermomechanical programs Marc/Mentat and COSMOS.

This program was supported by U.S. Department of Energy SBIR Grant No. DE-FG03-97ER82343.

80 MW Gridded Sheet Beam Electron Gun
Sheet beam klystrons are currently being explored as high power RF sources for the next generation of high energy physics accelerators. RF circuits for these devices could be considerably less expensive than conventional circuits, and the sheet beam configuration facilitates reduction of the operating voltage. Reduced voltage can lead to dramatic cost savings in the power supply system for large accelerator systems. Unfortunately, design of sheet beam electron guns requires development of advanced 3D techniques for beam focusing and transport. Only recently have the computational tools become available to perform this development.

CCR is developing a gridded sheet beam electron gun applicable to a klystron producing approximately 40 MW of RF power at X-Band. Gridded operation will allow elimination of pulse compressors used to achieve the peak powers required for the accelerator cavities. This requires design of the gun structure to allow DC operation of the cathode by maintaining electric field gradients at acceptable levels. Detailed simulations are now in progress and a prototype should be ready for testing in 2004.

This program is funded by U.S. Department of Energy Grant DE-FG03-01ER83209.

Improved Magnetron Injection Guns
Large diameter magnetron injection guns typically exhibit azimuthal variations in current emission. CCR designed and built a test facility to study this problem and develop effective solutions. This Cathode Test Facility measures cathode emission as a function of position and verifies acceptable performance prior to installation into vacuum electron devices. CCR is investigating various heater configurations and factors influencing the work function to provide more uniform current emission.

CCR designed and is building a 500 kV electron gun using an improved cathode heater configuration with detailed attention to factors effecting the work function. This electron gun will be analyzed in the Cathode Test Facility and subsequently installed in a coaxial gyroklystron at the University of Maryland, if acceptable performance is demonstrated.

The technology developed in this program will be applicable for magnetron injection guns for gyroklystrons for driving advanced accelerators and colliders and radar. It will also be applicable for high power gyrotrons used for electron cyclotron heating of tokamak plasmas.

This program is funded by the DOE Research Grant DE-FG03-01ER83196.

Multi-Stage Depressed Collectors for 1 MW CW Gyrotrons
High power gyrotrons typically operate with circuit efficiencies of 30-35%. For tubes producing 1 MW of RF power, this means that approximately 2 MW of power remains in the spent beam entering the collector. CCR developed a multiple stage depressed collector to recover at least 65% of that power. This reduces the power that must be dissipated in the collector by approximately 1.2 MW and returns it to the electric power utility. This not only significantly reduces the gyrotron operating costs, but also reduces the cost of the collector cooling system.

Research focused on sorting the electron energy and guiding it to the appropriate collector surface for maximum energy recovery. The analysis included the effects of reflected primary electrons and low energy secondary electrons. CCR worked with the Institute for Plasma Research at the University of Maryland and Diversified Technologies, Inc. to develop the depressed collector, computer control software, and power supply system.

Funding for this program was provided by the U.S. Department of Energy SBIR Grant number DE-FG03-97ER82342.

This research was funded by U.S. Department of Energy Grant No. DE-FG03-02ER83377.

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.

Field Emission Array Electron Guns
Field emission array (FEA) cathodes offer unique properties for vacuum electron devices producing RF power. FEA cathodes are manufactured using lithographic techniques similar to semiconductor computer chips and are consequently inexpensive to produce in large quantities. The electrons are extracted from microscopic emitters using field emission, as opposed to thermionic emission in standard cathodes. This means no power is required to heat the emission surface, reducing cost and complexity. In addition, laboratory tests have demonstrated current emission densities of several hundred amps/cm^2, considerably higher than conventional cathodes.

Unfortunately, the configuration of FEA cathodes makes them vulnerable to destruction during high voltage arcs. Typical arcs lead to extremely high currents through the cathode that burn out the fragile elements of the emitter. This research program is focusing on developing electron gun designs and processing procedures that route the arc currents around the sensitive elements. An experimental vacuum device was constructed to explore and test these techniques and evaluate the effectiveness.

The goal of the program is to develop FEA cathodes sufficiently robust to operate in standard vacuum electron devices and withstand cathode-anode arcs commonly encountered during device conditioning. Specific objectives include:

Developing techniques to reduce emission nonuniformity to less than 20% across the array
Designing an FEA gun capable of absorbing 10 Joule arcs without permanent damage
Designing an FEA capable of operation in the presence of back streaming ions
Designing an FEA electron gun capable of generating a high quality electron beam suitable for a W-Band TWT operating at 13 kV, 26 mA, with current emission exceeding 50 A/cm2.

This research is funded by Air Force SBIR Grant No. F33615-03-M-1509.

W-band Traveling Wave Tubes
POC- Dr. Carol Kory (carol@calcreek.com)
CCR is developing miniaturized, efficient traveling wave tube (TWT) amplifiers incorporating micro-fabrication techniques. Two research programs are in progress to develop W-band TWTs. One uses a folded waveguide (fwg) slow-wave circuit, and the other uses a novel, planar meander line circuit.The overall objective of both projects is to integrate several TWT components into the fabrication procedure to avoid assembly and alignment procedures, which become increasingly difficult at higher frequencies.

Folded Waveguide TWT
CCR and the University of Wisconsin (UW) are currently developing a folded waveguide TWT under a US Air Force Contract.This program is tasked with developing a 10 W continuous wave (CW) TWT with 3 GHz bandwidth centered at 83.5 GHz for satellite and terrestrial communications High precision electro-discharge machining (EDM) has been used to fabricate the interaction circuit as shown below.

Zoomed in views of circuit including transition to WR-10 waveguide
The first prototype TWT will be tested using a single stage collector and solenoidal magnetic focusing.In addition, both electrical and mechanical designs for periodic permanent magnet (PPM) focusing are complete.

Meander Line TWT
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