Aaron Jensen

A Self-Biasing Pulsed Depressed Collector

Depressed collectors have been utilized successfully for many years to improve the electrical efficiency of vacuum electron devices. Increasingly, pulsed, high-peak power accelerator applications are placing a premium on electrical efficiency. As RF systems are responsible for a large percentage of the overall energy usage at accelerator laboratories, methods to improve upon the state-of-the-art in pulsed high-power sources are desired. This paper presents a technique for self-biasing the stages in a multistage depressed collector. With this technique, the energy lost during the rise and fall times of the pulse can be recovered, separate power supplies are not needed, and existing modulators can be retrofitted. Calculations show that significant cost savings can be realized with the implementation of this device in high-power systems. In this paper, the technique is described along with experimental demonstration.

Pulsed depressed collector for high-efficiency RF systems

Many emerging applications for high power RF sources place a premium on electrical efficiency. For pulsed systems, much of the energy is lost in the rising and falling edges of the beam current. This paper presents the concept of a pulsed depressed collector and the resulting improvements in system efficiency.

S-band sheet beam klystron research and development at SLAC

Development of a 2.1 GHz, 200 kW CW sheet beam klystron (SBK) for the Navys free electron laser (FEL) is discussed. Design parameters and simulations of the klystron are presented. Calculations of transverse electric (TE) mode instability and mitigation are addressed.

Experimental demonstration of a 5th harmonic mm-wave frequency multiplying vacuum tube

We report the experimental demonstration of a 5th harmonic mm-wave frequency multiplying vacuum electronic device, which uses an over-moded spherical sector output cavity. In this device, a pencil electron beam is helically deflected in a transverse deflecting cavity before entering the output cavity. No magnetic field is required to focus or guide the beam. We built and tested a proof-of-principle device with an output frequency of 57.12 GHz. The measured peak power was 52.67 W at the 5th harmonic of the drive frequency. Power at the 4th, 6th, and 7th harmonics was 33.28 dB lower than that at the 5th harmonic.

Increasing Klystron Efficiency Using COM and BAC Tuning and Application to the 5045 Klystron

The Core Oscillation Method (COM) and Bunch-Align-Compress (BAC) cavity tuning schemes are discussed and applied to the re-design of the 5045 klystron towards achieving the highest efficiency micro-perveance 2.0 tube ever built.

Design and analysis of a radial X-band klystron

The radial klystron is a multi-dimensional rf source where the beam is generated by a cylindrical gun and it expands along the radial dimension. The space charge repulsion forces are balanced in the azimuthal direction. We present the design of a low-voltage klystron, showing the single cavity stability and high efficiency.

A modular 5 MW X-band multi-beam klystron

A novel modular combining scheme for multi-beam klystrons (MBK) is proposed and applied to the development of a 5 MW X-band MBK.

Klystron modulator system incorporating a pulsed depressed collector

Summary form only given. Applications utilizing high-power RF sources are increasingly placing a premium on electrical efficiency. In the case of particle accelerator laboratories, a large portion of the overall site electrical power is consumed by the RF systems. Therefore, new concepts for improving the efficiency of RF systems are desired. SLAC National Accelerator Laboratory has undertaken a multi-faceted approach for reducing laboratory energy demand. As part of this effort, a pulsed depressed collector is under development to significantly improve the efficiency of RF systems. This device recovers energy from the klystron collector and feeds it back to the modulator for use on subsequent pulses. While depressed collectors have been utilized extensively in CW TWTs, gyrotrons, and some klystrons, use in pulsed systems is not widespread. For pulsed systems, a significant amount of energy can be wasted in the rise and fall times, which places a constraint upon the modulators. The proposed pulsed depressed collector uses a novel feedforward, charge-mode energy recovery scheme. An advantage of this is that no external power supplies are necessary for biasing of collector electrodes. In addition, substantial modification of the modulator is not required; energy can be simply recovered to almost any useful point in the system. Also, the only fundamental modification of the klystron needed is the replacement of the existing collector with a modified collector. Results indicate that for one particular RF system, the efficiency can be improved from 37% to over 68%. Finally, use of this collector in new RF system designs may reduce the constraints on modulator rise and fall time, potentially simplifying and reducing the cost of such systems. This presentation will highlight aspects of a pulsed depressed collector design and focus on the power conversion chain from the collector back to the modulator. In particular, PIC simulations of the collector, SPICE models of the transformer and power converter, system layout diagrams, as well as several case studies will be presented.

Progress on design of radial klystrons

Vacuum electronic devices, such as rf sources for accelerator applications, must provide high rf power with high efficiency. To achieve these requirements, multi-beam klystron and sheet-beam klystron devices have been developed. Multi-beam klystrons, at high frequency employ separate output cavities; hence they have the disadvantage that combining externally all the rf pulses is challenging. Sheet-beam klystrons have problems with instabilities and with space charge forces that makes the beam not naturally confined. We are proposing an alternative approach that reduces space charge problems, by adopting geometries in which the space charge forces are naturally balanced. In this paper we will present the design and challenges of a radial klystron, composed by concentric pancake resonant cavities. In this case, space charge forces are naturally balanced in the azimuthal direction.

High-harmonic mm-Wave Frequency Multiplication using a Gyrocon-like Device

Traditional linear interaction RF sources, such as Klystrons and Traveling Wave Tubes, fail to produce significant power levels at millimeter wavelengths. This is because their critical dimensions are small compared to the wavelength, and the output power scales as the square of the wavelength. We present a vacuum tube technology, where the device size is inherently larger than the operating wavelength. We designed a low–voltage mm–wave source, with an output interaction circuit based on a spherical sector cavity. This device was configured as a phased-locked frequency multiplier. We report the design and cold test results of a proof-of-principle fifth harmonic frequency multiplier with an output frequency of 57.12GHz.