Toshiyasu Higo

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.

Processing studies of X-band accelerator structures at the NLCTA

RF processing studies of 1.8-m X-band (11.4 GHz) traveling wave structures at the Next Linear Collider Test Accelerator (NLCTA) have revealed breakdown-related damage at gradients lower than expected from earlier tests with standing wave and shorter, lower group velocity traveling wave structures. To understand this difference, a series of structures with different group velocities and lengths are being processed. In parallel, efforts are being made to improve processing procedures and to reduce structure contaminants and absorbed gases. This paper presents results from these studies.

RF processing of X band accelerator structures at the NLCTA

During the initial phase of operation, the linacs of the Next Linear Collider (NLC) will contain roughly 5,000 X-Band accelerator structures that will accelerate beams of electrons and positrons to 250 GeV. These structures will nominally operate at an unloaded gradient of 72 MV/m. As part of the NLC R and D program, several prototype structures have been built and operated at the Next Linear Collider Test Accelerator (NLCTA) at SLAC. Here, the effect of high gradient operation on the structure performance has been studied. Significant progress was made during the past year after the NLCTA power sources were upgraded to reliably produce the required NLC power levels and beyond. This paper describes the structures, the processing methodology and the observed effects of high gradient operation.

High Gradient Study at KEK on X-Band Accelerator Structure for Linear Collider

This paper describes the high-field studies on accelerator structures conducted at the X-band Test Facility, XTF, which was commissioned at KEK in 2004. A 60cm-long structure built at KEK has been processed in 2004-2005, with an accumulated operation time with the RF turned on of ∼ 1000 hours. The RF breakdown rate of this structure at 65MV/m with 400nsec flat pulses was initially measured to be ∼ once per 0.2×106pulses, and decreased to ∼ once per 0.7×106pulses with the processing. This latter breakdown rate satisfies the stability requirement for use of such accelerator structures at the linear collider. The high-power performance of two more 60cm structures will be measured in 2005. These studies are expected to provide benchmark performance data of accelerator structures in both high-gradient and medium-gradient operations, such as those envisaged in applications to compact X-band accelerators.

Influence of fabrication errors on wake function suppression in NC X-band accelerating structures for linear colliders

Wake function suppression is effected by ensuring that the mode frequencies of an X-band normal conducting (NC) accelerating structure of multiple cells are detuned and moderately damped by waveguide manifolds attached to the outer wall of the accelerator. We report on the dilution in the wake function suppression that occurs due to errors resulting from the fabrication process. After diffusion bonding 206 cells a non-uniform expansion in the cell geometry forces a substantial shift in the frequencies of select cells. We remap all circuit parameters to these shifted cell frequencies to predict the wake function. Experiments performed on the SLC at the SLAC National Accelerator Laboratory indicate that the wake function is well predicted by the circuit model.

X-band accelerating structure for Japan Linear Collider

Candidates for the accelerating structure in realizing an operation in a multibunch mode in the Japan Linear Collider (JLC) are described. The external Q value of the TM110- pi mode in a damped structure with a slotted disk is very sensitive to the geometry. The damped structure with slots in the disk was found too sensitive to apply to the actual structure for the JLC. A damped structure of a crossed waveguide type was found to be a good candidate for the characteristics of the higher modes. A detuned structure with its frequency distributed similar to a truncated gaussian showed a good cancellation of a higher mode.<<ETX>>

Development of a Portable 950 keV X‐band Linac for NDT

We are developing a portable 950 keV X‐band (9.4 GHz) linac X‐ray source for on‐site nondestructive testing of erosion of metal pipes at a petrochemical complex. To develop it, we adopted a compact X‐band 9.4 GHz magnetron of 250 kW for RF generation device. The whole device, including power supply and cooling devices, were also downsized. The dose rate of X‐ray converted in a tungsten target is designed to be 0.2 Gy/min at 1‐m distance. We designed an accelerating tube that uses the π mode for the lower energy part and the π/2 mode cavity for the higher energy. We manufactured the accelerating tube and carried out beam acceleration tests, confirming that the electron beam was accelerated up to 950 keV.

High power tests of normal conducting single-cell structures

We report the results of the first high power tests of single-cell traveling-wave and standing-wave structures. These tests are part of an experimental and theoretical study of RF breakdown in normal conducting structures at 11.4 GHz. The goal of this study is to determine the gradient potential of normal-conducting RF-powered particle beam accelerators. The test setup consists of reusable mode converters and short test structures and is powered by SLACs XL-4 klystron. This setup was created for economical testing of different cell geometries, cell materials and preparation techniques with short turn-around time. The mode launchers and structures were manufactured at SLAC and KEK and tested in the SLAC klystron test lab.

Beam generation and acceleration experiments of X-band linac and monochromatic keV X-ray sorce of the University of Tokyo

In the Nuclear Professional School, the University of Tokyo (UTNS), we are constructing an X-band linear accelerator that consists of an X-band thermionic cathode RF gun and X-band accelerating structure. This system is considered for a compact inverse Compton scattering monochromatic X-ray source for the medical application. The injector of this system consists of the 3.5-cell coaxial RF feed coupler type X-band thermionic cathode RF gun and an alpha-magnet. The X-band accelerating structure is round detuned structure (RDS) type that developed for the future linear collider are fully adopted. So far, we have constructed the whole RF system and beam line for the X- band linac and achieved 2 MeV electron beam generation from the X-band thermionic cathode RF gun. In addition, we achieved 40 MW RF feeding to the accelerating structure. The laser system for the X-ray generation via Compton scattering was also constructed and evaluated its properties. In this paper, we will present the details of our system and progress of beam acceleration experiment and the performance of the laser system for the Compton scattering experiment.

Compact 950 keV X-band (9.4GHz) Linac X-ray Source for On-site Nondestructive Evaluation

We are developing a compact X-ray nondestructive evaluation (NDE) system using 9.4 GHz X-band linac with 250 kW magnetron. A conventional 1 MeV X-band machines use a large 1 MW magnetron system. We have chosen the 250 kW magnetron so that the RF heat loss is remarkably reduced. This design yields compactness and portable. This system consists of the X-band magnetron, modulator, thermionic 20 kV electron gun, X-band linac and metal target of X-ray generation. We aim that X-ray spot size is less than 1 mm. We designed the linac structure of the pi mode at low energy parts and the pi/2 mode at high energy parts by using updated commercial software. We finished to measure resonant frequency, and electromagnetic field on axis used by bead-pull method. These devices are to be applied to on-site NDE at petrochemical complex, nuclear- and thermal-power plants. We are also going to test the system at the Nuclear Professional School, the University of Tokyo this year. This paper presents the details of the system and experimental results.