S. Kazakov

Ferroelectric Based Technologies for Accelerators

Ferroelectrics have unique intrinsic properties that make them extremely attractive for high‐energy accelerator applications. Low loss ferroelectric materials can be used as key elements in RF tuning and phase shifting components to provide fast, electronic control. These devices are under development for different accelerator applications for the X, Ka and L‐frequency bands. The exact design of these devices depends on the electrical parameters of the particular ferroelectric material to be used—its dielectric constant, loss tangent and tunability. BST based ferroelectric‐oxide compounds have been found to be suitable materials for a fast electrically‐controlled tuners. We present recent results on the development of BST based ferroelectric compositions synthesized for use in high power technology components. The BST(M) ferroelectrics have been tested using both transverse and parallel dc bias fields to control the permittivity. Fast switching of a newly developed material has been shown and the feasibil...

A New Design for A Super-Conducting Cavity Input Coupler

An attractive structure using capacitive coupling has been found for the input coupler for the 45 MV/m versions of the International Linear Collider (ILC) project. The coupler supports an electrical field gradient of ∼1 kV/m around the rf window ceramic with 500 kW through power, a VSWR of 1.1 and a frequency bandwidth of 460 MHz. No unwanted resonances were found in the rf window near the first and second harmonics of the operation frequency.

Progress towards a gap free dielectric-loaded accelerator

One of the major concerns in the development of dielectric-loaded accelerating (DLA) structures is the destructive breakdown at dielectric joints caused by a local electric field enhancement induced by the discontinuity of the dielectric constant at the surface of the joint gap. Our previous X-band traveling wave DLA structure design, for example, incorporated two separate impedance matching sections with at least two dielectric joints. In this paper, we present a new design to avoid this problem. This scheme is based on a coaxial type coupler which is able to implement mode conversion and impedance matching at the same time and therefore to eliminate joint gap induced breakdown. The new structure is under construction; bench test results will be presented.

Development of 26 GHz Dielectric‐Based Wakefield Power Extractor

High frequency, high power rf sources are needed for many applications in particle accelerators, communications, radar, etc. In this article we present a design of a 26 GHz high power rf source based on the extraction of wakefields from a relativistic electron beam. The extractor is designed to couple out rf power generated from a high charge electron bunch train traversing a dielectric loaded waveguide. Using a 20 nC bunch train (bunch length of 1.5 mm) at the Argonne Wakefield Accelerator (AWA) facility, we can obtain a steady 26 GHz output power of 148 MW. The extractor has been fabricated and bench tested, with the first high power beam experiments to be performed in the coming year.

The development of a superconducting traveling wave accelerating cavity with high gradient

The required accelerating gradient in the ILC project is over 30 MeV/m [1]. For current technology, the maximum accelerating gradient in superconducting (SC) structures is limited mainly by the value of the surface RF magnetic field. In order to increase the gradient, the RF magnetic field is distributed homogeneously over the cavity surface (low-loss structure), and coupling to the beam is improved by introducing aperture and cell shape (re-entrant structure). These features allow gradients in excess of 56 MeV/m to be obtained for a single-cell cavity. Further improvement of the coupling to the beam may be achieved by using a traveling wave (TW) SC structure with small phase advance per cell. Calculations show that an additional gradient increase by up to 46% is possible if a π/2 TW SC structure is used. However, a TW SC structure requires a SC feedback waveguide to return the few GW of circulating RF power from the structure output back to the structure input. We discuss variants of the superconducting traveling wave ring (STWR) with one and two feeding couplers.

Design of a 26 GHz Wakefield power extractor

High frequency, high output power, and high efficiency RF sources have compelling applications in accelerators for high energy physics. The 26 GHz RF power extractor proposed in this paper provides a practical approach for generating high power RF in this particular frequency range. The extractor is designed to couple out RF power generated from the high charge electron bunch train at the Argonne Wakefield Accelerator (AWA) facility traversing a dielectric loaded waveguide. Designs are presented including parameter optimization, electromagnetic modeling of structures and RF couplers, and analysis of beam dynamics.

Development of dielectric-based high gradient accelerating structures.

High gradient accelerating structures using dielectric‐lined circular waveguides have been developed for a number of years at Argonne National Laboratory. In this article, we first report the experimental results of high power rf testing on the quartz based Dielectric‐Loaded Accelerating (DLA) structure carried out on Feb. 2006 at the Naval Research Laboratory. The motivation for this experiment is to test the multipactor effect on different materials under high power and high vacuum condition. Up to 12 MW pulsed rf went through the tube without breakdown. Multipactor appeared during the experiment but with different features compared to other materials like alumina. Photomultiplier Tube (PMT) measurements were introduced into the experiment for the first time to observe the light emission time and intensity. In the second part of this paper, ways to achieve higher gradient for DLA structures are proposed: 1) smaller ID and longitudinal gap free DLA structures to reduce multipactor and obtain higher gradi...

CW ROOM TEMPERATURE RE-BUNCHER FOR THE PIP-II LINAC FRONT END

At Fermilab there is a plan for improvements to the Fermilab accelerator complex aimed at providing a beam power capability of at least 1 MW on target. The essential element of the plan (the Proton Improvement Plan II – PIP-II) is a new 800 MeV superconducting linac. The PIP-II linac consists of a room temperature front-end and a high energy part that uses five types of superconducting cavities to cover the entire velocity range required for beam acceleration. The room temperature front end is composed of an ion source, low energy beam transport line (LEBT), radio frequency quadrupole (RFQ), and medium energy beam transport line (MEBT). The paper summarises design of a re-buncher cavity used in the MEBT section.

Ferroelectric based technologies for high power RF and accelerator applications

We present recent results on development of BST based ferroelectric compositions synthesized for use in high power technology components for X-band and Ka-band RF systems and offer significant advantages for high power RF manipulation in the 300¿1000 MHz frequency range as well. These low loss ferroelectric materials can be used as key elements of both tuning and phase shifting components. Fast, electrically-controlled ferroelectric RF switches and phase shifters are under development for different accelerator applications in X, Ka and L - frequency bands either. The exact design of such a devise depends on the electrical parameters of particular ferroelectric material to be used, namely its dielectric constant, loss tangent and tunability. We have identified BST based ferroelectric-oxide compounds as suitable materials for a fast electrically-controlled 700 MHz, 50 kW tuner for Brookhaven National Lab and for high-power fast RF phase shifters to be used for SNS, Oakridge National Lab vector modulation applications. The bulk ferroelectric based phase shifter will allow coupling adjustment and control of the power consumption during the process of SC cavity filling, which is of great importance for the Intl. Linear Collider (ILC) program. New methods were developed in order to measure parameters of large ferroelectric components. The results of measurements are presented.

Performance of KEK-Toshiba PPM-Focused X band pulse klystrons

The R&D of PPM (periodic permanent magnet)-focused X-band (11.424GHz) pulse klystrons in Japan started in 1999, originally for Global Linear Collider (GLC) project. So far six prototype tubes (as named PPM1, ... PPM6) have been built. All these tubes were fabricated by Toshiba Electron Tubes and Devices Co. and tested at KEK. A new project named International Linear Collider started in 2004 and GLC project was terminated (and has been integrated into the worldwide research programs). The new collider is based on L-band (1.3GHz). Our recent X-band research interest lies in the development of a 50 MW-class tube which is stable enough, usable for various applications such as a compact linear accelerator. The research work in this paper includes the test of the rebuilt tubes as well as disassembling them after the test for further inspections.