Patrick Ferguson

MM‐Wave Source Development at Los Alamos

Summary form only given. A sheet-beam traveling-wave amplifier has been proposed as a high-power generator for RF from 95 to 300 GHz, using a microfabricated RF slow-wave structure. The planar geometry of microfabrication technologies matches well with the nearly planar geometry of a sheet beam, and the greater allowable beam current leads to high-peak power (up to 500 kW at 95 GHz), high-average power (up to 5 kW), and wide bandwidths (up to 10%). Simulations have indicated gains in excess of 1 dB/mm, with extraction efficiencies greater than 20%.

Large-signal klystron simulations using KLSC

We describe large-signal klystron simulations using the particle-in-cell code KLSC. This code uses the induced-current model to describe the steady-state cavity modulations and resulting RF fields, and advances the space-charge fields through Maxwells equations. In this paper, an eight-cavity, high-power S-band klystron simulation is used to highlight various aspects of this simulation technique. In particular, there are specific issues associated with modeling the input cavity, the gain circuit, and the large-signal circuit (including the output cavities), that have to be treated carefully.

Numerical determination of the matching conditions and drive characteristics for a klystron input cavity with beam

A numerical approach based on a cavity/drive circuit model and a numerical calculation of the beam impedance is outlined that self-consistently determines the modulation of a klystron input cavity for an arbitrary coupling of the rf source to the cavity and arbitrary cavity parameters. The model is fully defined by the cavity R/Q factor, resonant frequency, rf field distribution as determined by an rf cavity simulation, unloaded cavity Q, and externally-loaded Q without beam. We find an expression for the power required to maintain a desired steady-state input cavity modulation with beam for both the case when the coupling is perfectly matched to the rf drive, and also for the case of arbitrary coupling. In addition, we find expressions for the cavity detuning and externally-loaded Q that, if satisfied, lead to the optimum matching condition. This formalism is especially useful for high-power, relativistic klystrons, where the beam loading can be large and nonlinear. Examples are given for an X-band cavity. An extension of this approach to accelerator cavities is presented.

Accuracy of the equivalent circuit model using a fixed beam impedance for klystron gain cavities

Most small-signal calculations of the modulation in a klystrons gain cavity use an equivalent circuit which includes a fixed beam impedance. Comparing this calculation to the gain calculated self-consistently, we note there are appreciable errors in both the calculated amplitude and phase of the cavitys modulation. These errors may lead to large accumulated errors in determining either the tubes small-signal or large-signal gain. Both techniques are used in a comparison with an existing S-band klystron.

Design of a 10 MW,

The design of a 10 MW, 1.3-GHz annular beam klystron for accelerator applications has been analyzed in detail and optimized. Concerns about the diocotron instability were addressed by simulations, which showed the growth to be negligible. The calculated efficiency is 66%.

L

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.

-Band, Annular Beam Klystron

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.

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

The design of a 10 MW, 1.3 GHz Annular Beam Klystron for ILC has been analyzed in detail and optimized. Concerns about the diocotron instability were addressed by MAGIC simulations, which showed the growth to be negligible. Design improvements reduced the number of cavities to six and increased the efficiency to 66%. The magnetic field was reduced by 25%, decreasing the power required for the solenoid to less than 4% of the average power of the tube.

Advances in beam optics analyzer

Calabazas Creek Research Inc. (CCR) is developing an eight beam, 50 MW, multiple beam klystron (MBK) with 3.0 /spl mu/s pulse width and 120 Hz pulse repetition rate. Each circuit interacts with one 190kV and 66A beam and produces 6.25MW output power. We will employ an eight beam electron gun developed by CCR on a previous DOE SBIR grant. The MBK circuit is being fabricated and testing is scheduled for Fall 2005. The klystron design and available test data will be presented.

Optimized design of a 10 MW, L-band, Annular Beam Klystron

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