David Marsden

650 GHz traveling wave tube amplifier

Calabazas Creek Research, Inc. (CCR) and the University of Wisconsin, Madison (UW) are developing a 650 GHz traveling wave tube amplifier (TWTA). Simulations predict 360 mW peak output power with a 2-10% duty cycle. This paper summarizes the design and fabrication of the TWT. Testing is expected in November, 2008.

Improved Magnetron Injection Guns for Gyrotrons

All efficient, vacuum, RF sources required a high quality electron beam for efficient interaction. Non uniform cathode emission occurs when either the temperature or the work function varies over the cathode surface. If the non-uniformity exceeds certain limits, the RF source cannot perform according the specifications. Magnetron injection guns for gyrotrons were built that separate the emission surface from the heater circuit, with both components being replaceable. Temperature variations over the surface are predicted to be less than 1 degree centigrade, and recent measurements indicated variations in work function are less than 6%. The MIG designs will be described and available test results will be presented. CCRs MIG test chamber was modified to improve measurements of surface emission and temperature.

Design and 3-D Simulations of a 10-kW/28-GHz Gyrotron With a Segmented Emitter Based on Controlled Porosity-Reservoir Cathodes

In this paper, the design of a 10-kW/28-GHz gyrotron is presented. The main characteristic of the new gyrotron is the emitter ring, which is assembled from twelve individually supplied emitters based on controlled-porosity reservoir (CPR) technology. The main goal is to evaluate the use of CPR emitters for gyrotron applications. In addition, the azimuthally segmented emitter ring could be used for the generation of controlled nonuniform electron beams. In this way, it is planned to experimentally study the effect of nonuniform emission on the gyrotron operation. In this context, the effect of nonuniform emission on the beam quality is numerically investigated using the 3-D, electrostatic, parallel-code Ariadne, while the effect of the degraded beam on mode coupling and stability of the wave-particle interaction in the cavity is numerically studied using the nonstationary, self-consistent multimode cavity code Euridice.

Advanced terahertz backward wave oscillators

Calabazas Creek Research, Inc. is funded by the National Aeronautics and Space Administration to develop efficient, light-weight, backward wave oscillators (BWOs) for applications from 300 GHz to more than I THz. These devices are needed as local oscillator (LO) sources in heterodyne receivers. BWOs have broad tunability (over 100 GHz) and high output power (/spl sim/1 mW); however, existing BWOs are heavy (over 20 kg), consume a lot of power (270 W), require water cooling, and have poor output mode purity. The technical objectives of the current program are as follows: utilize advanced manufacturing techniques to extend the operating range to frequencies exceeding 1 THz; incorporate a depressed collector to improve the efficiency and eliminate water cooling; improve the output coupling to increase coupling efficiency and mode purity; and reduce the magnet system size and weight. During the Phase I program, techniques were developed to couple the power from the slow wave circuit and transform the RF wave into a purely Gaussian output mode.

Confined flow multiple beam guns for high power RF applications

In this paper, confined flow multiple beam guns for high power RF applications is presented. Here, the challenge is to develop electron guns and the associated magnetic circuit to confine and compress the electron beams and transport them through the separate beam tunnels to the spent beam collector. A solid model of 185 kV multiple beam gun (MBG) for an X-band klystron is presented in this paper.

Design and fabrication of a 10 MW, L-band, Annular Beam Klystron

Design improvements and fabrication of a 10 MW, 1.3 GHz Annular Beam Klystron are described. The principal improvement is the electron gun. Utilization of a Controlled Porosity Reservoir (CPR) cathode allows the use of a zero-compression gun, resulting in improved beam quality and reductions in the gun and solenoid diameters.

Advances in beam optics analyzer

Beam Optics Analyzer (BOA) has the capability to design all components of an electron beam from its emitter, magnetic focusing system, to the resonant cavities and the collector. We will present the current status and advances toward the goal of making BOA a multiphysics modeling and simulation tool.

2 MW CW RF load for gyrotrons

Development is complete for a 2 MW CW, RF load for millimeter wave power transmitted in HE11 waveguide. A rotating launcher uniformly distributes the power over loss surfaces and minimizes returned power. Successful operation with a 1.5 MW long pulse gyrotron is described.

Compact 3MW, 60kV L-band multi-beam klystron

The research reported here was aimed at development of an L-band multi-beam klystron with parameters relevant for ILC. The chief distinction of this tube from MBKs already developed for ILC is its low operating voltage of 60 kV, a virtue that implies considerable technological simplifications in the accelerator complex. To demonstrate the concept underlying the tubes design, a six-beamlet quadrant (a 54□ high one-quarter portion of the full 1.3 GHz tube) was built and recently underwent initial tests, with main goals of demonstrating rated gun perveance, rated gain, and at least one-quarter-that is 2.5 MW-of the full rated power. These tests, with 10-15 μs RF pulses, produced output powers of up to 2.86 MW at an operating voltage of 60 kV with 56 dB gain and high efficiency, and showed acceptably small beam interception. Therefore, the klystron has already achieved more than its design output-power at 60 kV, albeit in short pulses. Our initial three-day conditioning campaign without RF drive (140 μs pulses at a 60 Hz repetition rate) was stopped at 53% of full rated duty because of time limits at the test-site; no signs appeared that would seem to prevent achieving full duty operation (i.e., 1.6 ms pulses at a 10 Hz repetition rate). This preliminary report presents raw data and a few straightforward conclusions, but does not postulate explanations for differences between the design and actual performance; for these additional tests are required and are currently planned to commence by the end of 2015 using facilities being installed in the Yale University Beam Physics Laboratory. Figure 1 shows a cut-away view of the tube, a photo of the tube itself, and a photo of it during installation in the test site at CPI. Details of the tube design have already been published elsewhere. Tube tests were performed with 10-15 μs RF-pulses centered within a wider gun pulse, as shown in Figs 2 and 3. The highest gun voltage was 66 kV. The perveance was found to be 5.5×10-6 A-V-3/2 for voltages between 40 and 66 kV-somewhat higher than the design value of 4.9 ×10-6 A-V-3/2. The body intercept as a percentage of beam-power, inferred from heat deposition on the klystron body, was found to be as low as 6.5 to 7% with RF applied, as shown in Fig 2 (right). This figure requires further analysis, to account for heat transfer between different portions of the tube and for ohmic losses in the RF structure. With an achieved power output at 60 kV as high as 2.86 MW, the klystron efficiency approached 59%, but with a body intercept current above 7%. With body intercept current below 7%, the observed efficiency at 60 kV was 55% (2.67 MW output). At present, the trade-off between intercepted current and efficiency is unclear, so further studies and conditioning are needed.

Fabrication and test of a 10 MW, L-band, annular beam klystron

Fabrication and testing of a 10 MW, 1.3 GHz annular beam klystron is reported.