Adam Balkcum

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.

Demonstration of a Multikilowatt, Solenoidally Focused Sheet Beam Amplifier at 94 GHz

A technological breakthrough is embodied in the successful demonstration of an extended interaction klystron (EIK) amplifier, which has produced over 7.5 kW of peak output power at W-band (94 GHz). An efficiency of ~17% has been achieved with a depressed collector. The EIK is driven by a 20-kV, 4-A sheet beam in a permanent magnet solenoid, with 99% beam current transmission from gun to collector. Key features that contribute to the success of this device are: tight beam focusing and correspondingly narrow beam tunnel, which are made possible by the solenoidal focusing and which provide high interaction impedance and high gain per unit length and the incorporation of design elements to stabilize the inherently over-moded circuit. Measured performance agrees well with 3-D particle-in-cell simulations.

Demonstration of a Wideband 10-kW Ka-Band Sheet Beam TWT Amplifier

A sheet-beam coupled-cavity traveling wave tube has produced over 10 kW of peak power at a center frequency of 34 GHz, with a 3-dB bandwidth of almost 5 GHz. The power of this amplifier is an order of magnitude higher than state-of-the-art conventional amplifiers of comparable frequency, bandwidth, and operating voltage (<;20 kV). This unprecedented performance is made possible by a unique, Naval Research Laboratory (NRL)-developed sheet electron beam along with a novel slow-wave interaction structure. High-current, low-voltage operation provides high gain per unit length and allows an interaction structure<;5-cm long to be used to achieve the desired gain of 15 dB at saturation. Measured performance agrees well with 3-D particle-in-cell simulations.

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.

Sheet beam extended interaction klystron (EIK) in W band

A W-band sheet-beam extended interaction klystron (EIK) has been fabricated and tested. The EIK integrates a 3-cavity circuit with our previously demonstrated 20-kV, 3.5-A beamstick. The EIK has produced a saturated peak output power of over 7.5 kW and a small-signal gain of almost 40 dB, in very good agreement with our simulations.

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.

High-Power High-Efficiency L-band Multiple-Beam Klystron Development at CPI

Communications and Power Industries, Inc., has designed and manufactured two versions of a 10-MW-peak high-efficiency multiple-beam klystron (MBK) operating at 1300 MHz. This type of klystron is favored for large particle accelerator projects such as the European X-ray Free-Electron Laser at the Deutsches Elektronen Synchrotron (DESY). Two klystrons have been made for DESY. The first-generation MBK was a vertically oriented prototype using a six-cavity design with higher order mode input and output cavities and conventional intermediate cavities. For cost and performance reasons, the second-generation MBK, designated VKL-8301B, utilized seven coaxial fundamental-mode cavities and is an “industrialized” horizontally oriented klystron. The klystron was designed and optimized using state-of-the-art multidimensional design codes to ensure that all performance requirements are exceeded. Agreement between the simulated and measured performances is good. The VKL-8301B prototype achieved a peak saturated RF output power of 10.4 MW and 67.8% efficiency. The data were measured at the full 1.5% duty and with 1.5-ms pulse width. The klystron satisfied all required operating conditions, including stable operation into an output mismatch of 1.2:1 voltage standing wave ratio at various phases. The prototype has been shipped to DESY and has been successfully tested by a customer.

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

Summary form only given, as follows. A high efficiency multiple beam klystron (MBK) is being developed for the superconducting linear accelerator TESLA. 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.

Development of a megawatt C-band klystron for radar

An air cooled, 1 MW klystron with an instantaneous bandwidth of 50 MHz centered about 5625 MHz has been developed for radar applications. Details of the design and test results are presented.