Michael Cusick

Demonstration of an S-band, 600-kW fundamental-mode multiple-beam klystron

We present initial experimental results from the successful operation of a 600-kW peak, fundamental-mode multiple-beam klystron (MBK). The eight-beam device operates at a cathode voltage of /spl sim/45 kV and a total beam current of /spl sim/32 A with an axial guiding magnetic field of 1.8-2.2 kG. In the absence of radio-frequency (RF) drive, the measured beam transmission is in excess of 99%; at a driven frequency of 3.25 GHz, the measured beam transmission at saturation is /spl ges/97%, where the four-cavity circuit generates a peak power of /spl sim/600 kW with an electronic efficiency of 40%. The measured beam transport and RF performance are in excellent agreement with predictions made by the three-dimensional gun/collector code, MICHELLE, and the large-signal klystron code, TESLA. The accuracy of the design codes enabled the achievement of a working device in a single hardware design pass.

Demonstration of a 100-kW Solenoidally Focused Sheet Electron Beam for Millimeter-Wave Amplifiers

The design and development of a high-perveance sheet electron beam is reported. A beamstick that employs a novel sheet beam gun together with a permanent magnet solenoid has been fabricated and tested up to 4.8 A at 22 kV. At the nominal operating point of 19.5 kV and 3.3 A, this beamstick has transported 98.5% of the emitted electron current through a 0.4 × 5 mm beam tunnel over a distance of 20 mm in a uniform 8.5-kG field. The beamstick collector has been depressed to -9 kV with very little effect on the beam transport. The performance very well agrees with simulations. This beamstick will be the basis for a high-power (~10-kW) W-band extended-interaction-klystron amplifier that is currently under development.

Electron gun design for fundamental mode S-band multiple-beam amplifiers

This paper describes the detailed design of an eight-beam electron gun for use in S-band multiple-beam amplifiers operating in the fundamental mode. The gun operating voltage is 45 kV with a total beam current of 32 A, evenly divided among the beamlets. Each individual beam has a perveance of 0.42 mpervs making a total beam perveance of 3.35 mpervs. The optimized electron gun is singly convergent using a four-fold symmetry with the four inner and four outer emitters interlaced 90/spl deg/ apart. The emitter current density has been kept below 10 A/cm/sup 2/ (space-charge limited). The cathode is magnetically shielded and the longitudinal magnetic field in the interaction region is in the range of 1.1-1.8 kG. The design of the magnetic focusing system minimizes beam corkscrewing as well as electron interception on the tunnel walls. Beam optics simulations of the gun indicate excellent beam transport characteristics with a final beam-to-tunnel radial fill factor of less than 0.45. The primary computational tools used in the design process were the three-dimensional gun code MICHELLE, and the magnetostatics code MAXWELL-3D.

X-Band Sheet Beam Klystron (XSBK)

The Sheet Beam Klystron (SBK) is characterized by a large drift tube, which allows the use of high beam current at a low voltage, resulting in low beam current density, high efficiency and the possibility of PPM focusing. CPI has designed, manufactured and is currently testing an X-Band SBK capable of 5 MW peak, 20 kW average output power This paper discusses the general design, manufacturing and performance to date of CPIs X-Band SBK.

Wide band Ka-band Coupled-Cavity Traveling Wave Tube (CCTWT) development

A series of Ka-band Coupled-Cavity Traveling-Wave Tubes (CCTWTs) has been successfully developed, built, and tested at Communications and Power Industries (CPI) in collaboration with the Naval Research Laboratory (NRL) and SAIC. These devices represent a significant advance in the state-of-the-art of millimeter-wave CCTWTs, exploring the limits of power, bandwidth, and stability. We discuss the design and successful demonstration of the series of CCTWTs, including the VTA-6430N1 prototype which achieved over 700-W (879-W maximum power) over a 5-GHz range in Ka-band.

3.4: Sheet beam stick for low-voltage W-band extended interaction klystron (EIK)

The stable transport of high-perveance, low-voltage sheet electron beams is a key requirement for the successful development of compact, high-power sheet beam amplifiers. We describe a beam stick to demonstrate the transport of such a beam (19.5 kV, 3.5 A) in a solenoidal magnetic field of about 8.5 kG. The beam stick consists of a novel sheet beam gun having single-plane convergence of a factor of ∼30, a permanent magnet solenoid, a 1.8-cm-long × 5 mm wide × 0.4 mm high beam tunnel, and an isolated collector. The engineering design was based closely upon MICHELLE and MAGIC-3D simulations of a W-band extended interaction klystron.

Operation of a 1.3 GHz, 10 MW multiple beam klystron

Summary form only given. Results are reported for a 1.3 GHz, 10 MW multiple beam klystron that is being developed for the TESLA linear accelerator facility. It features six off-axis electron beams which are contained in a common enclosure, common and higher-order-mode input and output cavities, conventional klystron intermediate cavities with external tuners, dual waveguide and window outputs and six isolated collectors for the measurement of intercepted beam current on each beam line. The design parameters for the device are 10 MW peak RF output power with 150 kW average power, 1.5 ms pulse length, 65% efficiency, 50 dB gain, 4 MHz 1 dB bandwidth, 114 kV beam voltage, 131 A total beam current (emitted by the six cathodes) and 2.0 A/cm/sup 2/ maximum cathode loading.

700 W Ka-band Coupled-Cavity Traveling Wave Tubes (CCTWT) for communication

A family of 700-W Ka-band Coupled-Cavity Traveling-Wave Tubes (CCTWTs) has been successfully developed, built, and tested at Communications and Power Industries (CPI). These CCTWTs are capable of up to 700-W Continuous Wave (CW) output power with 2.0 GHz of instantaneous bandwidth. They were built with the intended use for the commercial satellite and military communication market. We discuss the design and successful demonstration of the family of CCTWTs, including the VTA-6428S2B prototype which achieved over 700-W (783-W maximum output power) with an overall efficiency reaching as high as 52%.

Sheet beam for W-band extended interaction klystron (EIK)

Both the generation and the stable transport of high-perveance, relatively low-voltage sheet beams suitable for millimeter wave and submillimeter wave amplifiers are quite challenging. We have designed and fabricated a beam stick to validate our design1 of a 19.5 kV, 3.5 A sheet beam having a cross section of 0.3 × 4 mm, whose parameters were selected to drive a W-band extended interaction klystron (EIK). The electron gun uses a shielded cathode at an average loading of 8 A/cm2, with single-plane focusing to achieve a final beam density of∼275 A/cm2. The beam is transported through a 0.4 × 5 mm beam tunnel by a permanent magnet solenoid that produces a field of ∼8.5 kG over a distance of 1.8 cm, which is sufficient for a 3-cavity EIK interaction structure having a gain of ∼30 dB. A single-stage depressed collector collects the exiting beam.

Development of a 10 MW, L-band multiple beam klystron for TESLA

A high efficiency multiple beam klystron, designated the VKL-8301, is being developed for the DESY superconducting linear accelerator TESLA in Hamburg, Germany. The accelerator will require 572 klystrons each producing up to 10 MW of rf output power at 1300 MHz. A multiple beam klystron will be used due to its ability to produce large rf output powers using moderate electron beam energies.