We present results on a new ferroelectric material based on bulk low‐loss BST (Barium‐Strontium Titanium oxides) compounds especially developed for accelerator applications We have demonstrated suitable nonlinear dielectric properties of this material that make it useful for switching and tuning RF accelerator components The material exhibits a dielectric constant of 400–500 and tunability factor of 12 The best sample of those studied demonstrated a loss factor <4×10−3 at 35 GHz Ferroelectric rings and substrates are key components required for electrically controlled switches and phase shifters for active pulse compressors for future linear colliders A thin ferroelectric layer incorporated into a dielectric loaded accelerating structure allows compensation of any frequency shift caused by ceramic waveguide machining tolerances and dielectric constant heterogeneity A tuning range of 11% has been demonstrated for an X‐Band (11–13 GHz) dielectric accelerating structure

New Low-Loss Ferroelectric Materials for Accelerator Applications

Recent charged-particle accelerator projects employ high power RF distribution systems to power superconducting radio frequency (SRF) accelerating cavities. Each cavity usually requires several hundred killowatts of pulsed power at relatively high duty cycle (roughly up to 10% in high-power proton linear accelerators) in low UHF bands for production of the particle beam. So far, one amplifier to one cavity configuration is common, since precise vector control of RF is done at the low power inputs of the amplifiers. If a fan-out configuration that feeds many cavities with a single very high-power amplifier klystron is realized, significant cost savings can be achieved in construction and installation. The fan-out configuration, however, requires independent control of RF amplitudes and phases to the cavities at high power level. A prototype high-power RF vector modulator for such applications has been built and tested. The vector modulator employs a quadrature hybrid and two fast ferrite phase shifters in square coaxial transverse electromagnetic (TEM) transmission lines. The square coaxial format can provide the power-handling capability and thermal stability. RF properties of the design and results of high power system testing of the design are presented.

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Development of Fast High-Power Rf Vector Modulator Employing Tem Ferrite Phase Shifters

A fast ferroelectric phase shifter controlled by an electric field bias is being investigated for high-power fast RF phase shifters to be used for vector modulation. Such a device could find applications in particle accelerators, allowing vector control of the RF power divided and delivered to accelerating cavities from a power amplifier. Bulk ferroelectric materials, particularly those based on barium-strontium titanate (BST) compounds, have shown promise in high-power applications because of their low loss tangent and high dielectric strength. Use of BST compounds is investigated in a coaxial phase shifter prototype for frequencies in the 400 MHz – 800 MHz range that could be adapted for future large-scale accelerator projects. Designs of subsystems such as the DC block and matching structure are discussed. Since BST is a nonlinear dielectric compound, preliminary study on the nonlinear propagation effects is also conducted through computer simulation.

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Investigation of using ferroelectric materials in high power fast rf phase shifters for rf vector modulation

Non-magnetic, pulse undulators are proposed for non-free-electron laser (FEL) applications. Both have a cm-sub-cm period and use a GW–sub-GW power level energy sources available within state-of-the-art technology. A two-beam undulator complements two-beam accelerator (TBA) scheme to generate polarized positrons using intense polarized gamma-photons radiated in a square waveguide powered by microwaves extractor-wakefield decelerator. Another concept revisits a bifilar pulse line carrying co-propagating non-sinusoidal wave driven by a high voltage, ns-pulse, commercial generator. It can be used as a short insertion device (ID) for synchrotron radiation facilities. Undulator factor approaching unity is achievable at substantial gap-to-period ratios exceeding 0.4 for both conceptual designs.

Two concepts of short-period, pulse helical undulators

High power vector modulators enable independent control of radio frequency (RF) power to each accelerating cavity, allowing a fan-out configuration to be used to power many cavities from a single high-power klystron. Previously, ferrite materials have been used in high-power phase shifters and vector modulators. It is shown that ferroelectric materials such as bariumstrontium titanate (BST) can also be used in such tunable structures. Since ferroelectrics are controlled by an electric, rather than a magnetic field, tuning can be faster than tuning a ferrite-loaded device. A BST-loaded coaxial structure is investigated theoretically and experimentally. The prototype is built using dielectric loaded TEM transmission line in order that no vacuum should be necessary. Good high voltage performance is critical since DC biasing voltages of up to 80 kV can be impressed on the BST sections for tuning. It can also be seen that matching structures around the BST can improve performance over a wider range of amplitudes and phases. BACKGROUND

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Investigation of Ferroelectrics for High-Power RF Phase Shifters in Accelerator Systems

A phase shifter to be the key element of an active high‐power switch is described. This phase shifter employs ultra‐fast, electrically‐controlled ferroelectric elements. This high‐power switch will allow one to build an active Delay Line Distribution System (DLDS), which would provide substantial reduction in the length of waveguide, compared to what would be required for the traditional passive DLDS design for NLC. The results of preliminary optimization of the phase shifter at the NLC frequency of 11.424 GHz are presented showing the feasibility of building the switch to control a power of 500 MW. Initial tests at a power of up to 50 MW are planned using the Omega‐P/NRL X‐band magnicon.

V. P. Yakovlev

Papers

Fast X-Band Phase Shifter