Andrew Haase

Industrialization effort of the SLAC XL5 klystron

The SLAC XL5 klystron, which produces 50 MW at 12 GHz, is being used in several high gradient accelerators and test stands. The design has been transferred to industry and is currently being modified for ease of assembly and for cost reduction. Two klystrons of the new design will be manufactured and fully characterized.

Prototyping high-gradient mm-wave accelerating structures

We present single-cell accelerating structures designed for high-gradient testing at 110 GHz. The purpose of this work is to study the basic physics of ultrahigh vacuum RF breakdown in high-gradient RF accelerators. The accelerating structures are π-mode standing-wave cavities fed with a TM 01 circular waveguide. The structures are fabricated using precision milling out of two metal blocks, and the blocks are joined with diffusion bonding and brazing. The impact of fabrication and joining techniques on the cell geometry and RF performance will be discussed. First prototypes had a measured Q 0 of 2800, approaching the theoretical design value of 3300. The geometry of these accelerating structures are as close as practical to singlecell standing-wave X-band accelerating structures more than 40 of which were tested at SLAC. This wealth of X-band data will serve as a baseline for these 110 GHz tests. Furthermore, the structures will be powered with short pulses from a MW gyrotron oscillator. RF power of 1 MW may allow an accelerating gradient of 400 MeV/m to be reached.

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.

R&D of a Super-compact SLED System at SLAC

We have successfully designed, fabricated, installed and tested a super compact X-Band SLED system at SLAC. It is composed of an elegant 3dB coupler / mode converter / polarizer and a single spherical energy storage cavity with high Q0 of 94000 and diameter less than 12 cm. The available RF peak power of 50 MW can be compressed to a peak average power of more than 200 MW in order to double the kick for the electron bunches in a RF transverse deflector system and greatly improve the measurement resolution of both the electron bunches and the Xray FEL pulses. High power operation has demonstrated the excellent performance of this RF compression system without RF breakdown, sign of pulse heating and RF radiation. The design physics and fabrication as well as the measurement results will be presented in detail. INTRODUCTION This diagnostics for X-ray temporal measurement based on the transverse deflectors, the magnetic spectrometer and the Ce:YAG screen located downstream of the FEL undulator has been intensively used at the LCLS operation [1]. Its layout is shown in Figure 1. Figure 1: Diagnostics layout of the X-ray temporal measurement at the LCLS. In order to improve temporal resolution, we have designed and fabricated a novel super compact SLED system to double the peak deflection. [2] This paper describes its principle, design and technical advances. DESIGN OF SUPER COMPACT SLED SYSTEM More than forty years ago, SLAC developed the SLED system to obtain high peak RF power in exchange for the RF pulse length reduction [3]. The key components of a SLED system include a 3dB coupler with two 90° apart power ports and two high Q energy storage cavities. The LCLS deflector is made of two traveling structures, Each one is a 1.0 m long, constant impedance structure with transverse impedance of 41.9 MΩ/m, filling time Tf=106 ns (group velocity of -3.165 % speed of light) and attenuation factor τ=0.62 Neper. If we assume the similar average RF power of 106 ns pulses for both the SLEDed pulse and non SLEDed flat pulses to feed a backward wave constant impedance deflector, the corresponding kick voltages are shown in Fig. 2. Figure 2: Kick voltage along the deflector structure. We need to optimize the SLED system by calculating its total gain for various coupling coefficients for the high Q0 cavity, its Q values and pulse length. Figure 3 shows that the highest gain of larger than factor of 2 can be obtained for Q0 ~9x10 and 1μs pulses if the over-coupling coefficient β is optimized to be 7-8 for 11424 MHz. Figure 3: SLED gain as function of pulse widths and Q0 values of energy storage cavity. Unified 3dB Coupler / Mode convertor / Polarizer Having all the basic functions of a 3dB coupler, a much more compact and elegant dual-mode circular polarizer was developed to transform the TE01 mode in a rectangular waveguide into two polarized TE11 modes in quadrature in a circular waveguide as shown in Fig. 4. Figure 4: Schematic view of the dual-mode polarizer. The input TE01 mode converts to both TE01 and TE02 modes in a widened rectangular waveguide region, and their magnetic field components will couple to two per___________________________________________ * Work supported by DOE contract DE-AC03-76SF00515. † Email address jywap@slac.stanford.edu Proceedings of IPAC2016, Busan, Korea MOOCA01 07 Accelerator Technology T06 Room Temperature RF ISBN 978-3-95450-147-2 39 C op yr ig ht

200 kW CW sheet beam klystron research and development

Development of a 200 kW CW sheet beam klystron for the Office of Naval Research. Specifications, beam stability, and cathode bell jar testing are discussed.