Fumito Sakamoto

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.

Emittance and Energy Measurements of Low-Energy Electron Beam Using Optical Transition Radiation Techniques

Emittance and energy of an electron beam in the range of 8 to 22 MeV were measured via optical transition radiation (OTR) techniques. The beam divergence effect on observations of the far-field OTR image at low energies was studied by means of numerical analysis. The numerical analysis indicates that if the beam divergence is under 1.5 mrad, a simultaneous single-shot measurement of emittance and energy is possible. The results of the single-shot experiment agree with independent measurements conducted using the quadrupole scan method and an electron spectrometer. The experiments were performed with an S-band linac at the Nuclear Engineering Research Laboratory, The University of Tokyo (UTNL).

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.

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.

Experiment of X-ray source by 9.4 GHz x-band linac for nondestructive testing system

We are developing a compact X-ray source for nondestructive testing (NDT) system. We aim to develop a portable X-ray NDT system by 950 keV X-band linac to realize on-site inspection. We use a low power (250 kW) magnetron as RF source for compactness of whole system. By using low power magnetron, we can use small magnetron power supply and cooling system. Additionally, the system has X-band linac and it has small spot size of electron beam. Our final goal of X-ray spot size is less than lmm. We have designed the linac structure of the pi mode at low energy parts and the pi/2 mode at high energy parts by using calculation codes. It was finished to measure resonant frequency and electromagnetic field of the linac. And the result of measurement consists with calculation data. The components of this system was completed and installed in the Nuclear Professional School, the University of Tokyo. We are carrying out electron beam accelerate testing.

Two-colored Laser Circulation System for Monochromatic Tunable Hard X-ray Source

A two-colored laser pulse circulation system for a monochromatic tunable hard X-ray source via laser electron Compton scattering is investigated. The demonstration system of the X-ray source is under construction at the University of Tokyo. It consists of the X-band (11.424 GHz) electron linear accelerator and two Nd: YAG laser systems. The main advantage of this system is a monochromatic tunable hard X-ray. It is calculated that the X-ray intensity will be about 108 photons/s. In order to enhance the X-ray intensity for medical applications such as dual energy X-ray CT, a two-colored laser pulse circulation system has been designed. The laser pulse circulation experiment without an electron beam has been carried out by using a Nd: YAG laser fundamental wave (50 mJ) and a second harmonics wave (25 mJ). The result shows that the X-ray intensity can be enhanced by a factor of 10 times higher (i.e., up to 109 photons/s). This work is a part of the JST (Japan Science and Technology Agency) project. The entire X-ray source system is a part of a larger national project on the development of an advanced compact medical accelerator sponsored by the NIRS (National Institute for Radiological Science). The University of Tokyo and KEK are responsible for the X-ray source.

On‐site Real‐Time Inspection System for Pump‐impeller using X‐band Linac X‐ray Source

The methods of nondestructive testing (NDT) are generally ultrasonic, neutron, eddy‐current and X‐rays, NDT by using X‐rays, in particular, is the most useful inspection technique having high resolution. We can especially evaluate corroded pipes of petrochemical complex, nuclear and thermal‐power plants by the high energy X‐ray NDT system. We develop a portable X‐ray NDT system with X‐band linac and magnetron. This system can generate a 950 keV electron beam. We are able to get X‐ray images of samples with 1 mm spatial resolution. This system has application to real time impeller inspection because linac based X‐ray sources are able to generate pulsed X‐rays. So, we can inspect the rotating impeller if the X‐ray pulse rate is synchronized with the impeller rotation rate. This system has application in condition based maintenance (CBM) of nuclear plants, for example. However, 950 keV X‐ray source can only be used for thin tubes with 20 mm thickness. We have started design of a 3.95 MeV X‐band linac for bro...

MULTI-BEAM COMPTON SCATTERING MONOCHROMATIC TUNABLE HARD X-RAY SOURCE

Compton scattering hard X-ray source which consists of an X-band (11.424 GHz) electron linear accelerator and YAG laser is under construction at Nuclear Professional School, the University of Tokyo (UTNS). Monochromatic hard X-rays are required for variety of medical and biological applications. Our scheme of the hard X-ray source is to produce a monochromatic hard X-ray via collision between 35 MeV electron beam and 2.5 J/10 nsec Nd:YAG laser. In order to increase the efficiency of the X-ray yield, we adopt a laser pulse circulation system. In our case, the laser pulse circulation system can increase the X-ray intensity of up to 50 times. Main features of our scheme are to produce monochromatic tunable hard (10-40 keV) X-rays with the intensities of 108-109 photons/sec. In addition, X-ray energy can be changed with rapidly by 40 ms by introducing two different wavelength lasers (YAG fundamental (1064 nm), 2nd harmonic (532 nm)) and optical switch. This quick energy change is indispensable to living specimens and very difficult by a large SR light source and others. We designed a laser pulse circulation system to increase the X-ray yield 10 times higher (up to 108 photons/RF pulse, 109 photons/sec). It can be proved that the laser total increases 10 times higher by principle experiment with lower energy laser (25 mJ/pulse). Dual-energy X-ray CT and subtraction X-ray CT are available to determine 3D distribution of atomicc number density and electron density, and specified atomic distribution, respectively. Here, the construction status of the X-band beam line and the application plan of the hard X-ray will be reported.

MEDICAL APPLICATION OF MULTI-BEAM COMPTON SCATTERING MONOCHROMATIC TUNABLE HARD X-RAY SOURCE

Compton scattering hard X-ray source which consists of an X-band (11.424 GHz) electron linear accelerator and YAG laser is under construction at Nuclear Professional School, the University of Tokyo. Monochromatic hard X-rays are required for variety of medical and biological applications. Our scheme of the hard X-ray source is to produce a monochromatic hard X-ray via collision between 35 MeV electron beam and 2.5 J/10 nsec Nd:YAG laser. In order to increase the efficiency of the X-ray yield, we adopt a laser pulse circulation system. In our case, the laser pulse circulation system can increase the X-ray intensity of up to 10 times. Main features of our scheme are to produce monochromatic tunable hard (10-40 keV) X-rays with the intensities of 108-109 photons/sec. In addition, X-ray energy can be changed with rapidly by 40 ms by introducing two different wavelength lasers (YAG fundamental (1064 nm), 2nd harmonic (532 nm)) and optical switch. This quick energy change is indispensable to living specimens and very difficult by a large SR light source and others. Dual-energy X-ray CT and subtraction X-ray CT are available to determine 3D distribution of atomic number density and electron density, and specified atomic distribution, respectively. Here, the construction status of the X-band beam line and the application plan of the hard X-ray are described and discussed.

Laser pulse circulation system for compact monochromatic tunable hard X-ray source

We are construcing a laser electron Compton scattering monochromatic tunable hard X-ray source. It consists of the X-band (11.424 GHz) electron linear accelerator and Q-switch Nd:YAG laser. This work is a part of the JST (Japan Science and Technology Agency) project. The whole system is a part of the national project on the advanced compact medical accelerator development, hosted by NIRS (National Institute for Radiological Science). The University of Tokyo and KEK are working for the X-ray source. Main advantage of this X-ray source is monochromatic tunable hard X-rays (10-50keV) with the intensities of 108-109 photons/s. The table-top size X-ray source can generate dual energy monochromatic hard X-ray by turns and it takes about 40ms to chage the X-ray energy. It is calculated that the X-ray intensity is 107 photons/RF-pulse (108 photons/s in 10 pps) by the 35MeV electron and YAG laser (2J/pulse). The X-band beam line for the demonstration is under construction. We designed a laser pulse circulation system to increase the X-ray yield 10 times higer (up to 108 photons/RF-pulse, 109 photons/s). It can be proved that the laser total energy increases 10 times higher by the principle experiment with the lower energy laser (25mJ/pulse).