Hitoshi Hayano

Design of Compact Monochromatic Tunable Hard X-Ray Source Based on X-band Linac

A compact tunable monochromatic (1 to 10 percent bandwidth rms) hard X-ray source based on laser-electron collisions for medicine is proposed. An X-band linac is introduced to realize a remarkably compact system. We have designed a compact monochromatic tunable hard X-ray source as a demonstration. An X-band (11.424 GHz) linac for the purpose is being manufactured. Numerical considerations using CAIN code and luminosity calculations have been performed to estimate the X-ray yield. An X-band thermionic-cathode RF gun and an RDS (round detuned structure) X-band accelerating structure are applied to generate a 50 MeV electron beam with 20 pC/micro-bunch, 1 µs macro-pulse. The total X-ray yield by laser-electron collision with the electron beam and Q-switch Nd:YAG laser with a pulse intensity of 2 J/10 ns is 107 photons/RF-pulse (108 photons/s in 10 pps). We will adapt the technique of laser pulse circulating to increase the X-ray yield up to 108 photons/pulse (109 photons/s). Twenty eight percent of the photons with an energy spread of 10% rms are expected to be available by collimating the scattering angles of X-ray photons.

Compact soft x-ray source using Thomson scattering

A compact soft x-ray source using Thomson scattering, enabled by the combination of a picosecond laser and an electron rf gun, was developed aiming at biological studies such as those using an x-ray microscope. The x-ray source included both a photoinjector system and a picosecond laser system with a tabletop size of 2×2m2. An infrared laser beam (λ0=1047nm) was obtained from an all-solid-state mode-locked Nd:YLF laser system and injected into the photocathode of an accelerator system. A 4.2MeV electron beam was generated from a laser-driven photocathode rf gun system. The residual laser beam was amplified up to about 4.2mJ/pulse using a flash-lamp-pumped laser amplifier. Upon collision of the electron beam with the amplified laser beam, 300eV soft x rays were generated by Thomson backscattering. The stable interaction between the two beams was achieved using the same seed laser pulse for irradiating the photocathode and the scattering process with laser photons.

Quench-Limited SRF Cavities: Failure at the Heat-Affected Zone

With the recent progress in surface cleaning, the performance of superconducting RF cavities is mostly limited by a quench. It is important to understand the nature of the quench origin. In a common SRF cavity design the RF magnetic field is concentrated near the equatorial weld of the cavity. This weld has long been the major suspect in forming a surface defect, either as an impurity or in an increased surface roughness, that eventually gives rise to a quench. We used surface mounted thermometers to obtain a temperature map of the cavity in the quench region. A high temperature, temporal, and spatial resolution of the thermometry system allows us to pinpoint the quench origin with an accuracy of a few millimeters. We found that the hot-spot precursor forms in the weld heat-affected area rather than in the melted zone. The high resolution optical inspection found surface defects in exactly the same locations as the temperature mapping system. We will describe the measurement techniques and discuss possible scenarios of formation of these defects.

Feasibility of optical diffraction radiation for a non-invasive low-emittance beam diagnostics

Abstract A “proof-of-principle” experiment on the optical diffraction radiation (ODR) as a single-pulse beam profile monitor is planned using an electron beam extracted from the KEK-ATF damping ring. The main goals of this experiment are the following: (i) To measure the yield and the angular distributions of the optical diffraction radiation from a large-size target at different wavelengths, impact parameters and beam characteristics for a comparison with analogous characteristics of optical transition radiation from a foil with identical optical parameters and for a verification of the model assumption (perfectly conducting semi-infinite target). (ii) To investigate the ODR angular distributions from a tilted target with a slit for observing the interference effects. (iii) To compare the results obtained by simulations based on classical approaches, taking into account the optical characteristics of the equipment and the beam parameters. (iv) To estimate the prospects of using ODR as a new non-invasive tool for ultrarelativistic beams. We estimated that the ODR photon yield in 10% bandwidth for 500 nm is about 106 photons/bunch with an impact parameter of 100 μm . This indicates that the ODR monitor is a promising candidate for single-pulse beam-profile measurements, and that it will be an extremely useful instrument for future linear colliders (JLC, NLC, TESLA and CLIC).

Present status and first results of the final focus beam line at the KEK Accelerator Test Facility

ATF2 is a final-focus test beam line which aims to focus the low emittance beam from the ATF damping ring to a vertical size of about 37 nm and to demonstrate nanometer level beam stability. Several advanced beam diagnostics and feedback tools are used. In December 2008, construction and installation were completed and beam commissioning started, supported by an international team of Asian, European, and U. S. scientists. The present status and first results are described.

Progress and Plans for RaD and the Conceptual Design of the ILC Main Linacs

The International Technology Recommendation Panel (ITRP) recommended a superconducting technology for the main linac design of the International Linear Collider (ILC). The basis for this design has been developed and tested at DESY, and R&D is progressing at many laboratories around the world including DESY, Orsay, KEK, FNAL, SLAC, Cornell, and JLAB. The parameters for the ILC Main Linac are discussed and described. The status and role of the different linac test facilities are discussed, and the critical items and R&D program to support a Baseline Configuration and a Conceptual Design are outlined.

Emittance measurement at KEK-ATF damping ring

In order to achieve an extremely low emittance down to /spl epsiv//sub y//spl sim/1/spl times/10/sup -11/ m-rad, the beam development has been continued at KEK-ATF for future linear collider. The emittance measurement in the damping ring is a key point to confirm the low emittance beam. The beam size measurement is done by SR interferometer using visible light (/spl sim/500 nm) at ATF damping ring. The measured beam sizes were already reached less than 14 /spl mu/m (vertical) acid 37 /spl mu/m (horizontal), respectively. The beta function was also measured by applying a perturbation on the quadrupole magnet. The dispersion function was measured by means of RF frequency modulation method. Combining these measured values, the emittance was measured as /spl epsiv//sub x/=1.8/spl times/10/sup -9/ m-rad, /spl epsiv//sub y/=6.1/spl times/10/sup -11/ m-rad. The measurement technologies are described.

Bunch Length Monitor Using Two-Frequency Analysis for RF Gun System

An rms (root mean square) bunch length monitor for a laser-driven photocathode rf gun system based on a two-frequency analysis technique has been developed. Typically, the photoelectron beam generated from the rf gun system has an energy of 3–5 MeV and an rms bunch length smaller than 20 ps down to 3–4 ps. This monitor is suitable for such electron beam measurement. The rms bunch length as a function of rf phase was experimentally measured using both the rms bunch length monitor and streak camera technique using a 50 MeV electron beam at the KEK accelerator test facility (KEK-ATF) injector section which has an rf gun system and a 3-m-long accelerator structure. A numerical simulation study was also performed using the PARMELA code. The availability of this monitor was clearly verified by comparing the results. Consequently, this monitor was installed in the rf gun system at Waseda University and the rms bunch length measurement for a 3.5 MeV electron beam was precisely performed using the monitor.

High gradient experiments by the ATF

A high gradient experiment using traveling wave structures at S-band frequencies is presented. The experiments have been carried out using the ATF (Accelerator Test Facility) phase-I linac. A 0.6-m-long constant-gradient traveling-type structure was utilized to generate the maximum accelerating gradient of 100 MeV/m at 200 MW of RF peak power. The dark current dependence on the structure length and the effect of a dustless and dielectricless structure are discussed. It is concluded that the clean structure of low-dust and low-dielectric material would be suitable for decreasing the dark current one order lower than the normal structure by a standard fabrication process.<<ETX>>

Intrabeam scattering analysis of measurements at KEK’s Accelerator Test Facility damping ring

We derive a simple relation for estimating the relative emittance growth in