X-band thermionic cathode RF gun and multi-beam Compton scattering monochromatic tunable X-ray source

A Compton scattering X-ray source consisting of an X-band (11.424 GHz) electron linear accelerator (linac) and Q-switched Nd:YAG laser is currently under construction. Monochromatic hard X-rays are required for a variety of medical and biological applications. The new hard X-ray source produces monochromatic X-rays via collision between a 35-MeV multi-bunch (10(4) bunches in a I mu s RF pulse) electron beam and 1.4 J/10 ns (532 nm) Nd:YAG laser beam. The linac uses an X-band 3.5-cell thermionic cathode RF gun and an alpha magnet as an injector. The thermionic cathode RF gun is the first of its kind and can generate a high current (2 mu A) and a multi-bunch 2-MeV electron beam. To increase the efficiency of the X-ray yield, a laser pulse circulation system is adopted, that can increase the X-ray intensity by up to 50 times. This scheme can produce monochromatic tunable X-rays (10 similar to 40 keV) with intensities of 10(8) similar to 10(9) photons/sec. In addition, the X-ray energy can be changed rapidly over 40 ms by two different wavelength lasers (YAG fundamental (1064 nm), 2nd harmonic (532 nm)) and an optical switch. This quick energy change is very important for living specimens and is very difficult to achieve in light sources such as a large SR (Synchrotron Radiation) source. The system can be used for dual-energy X-ray CT and subtraction X-ray CT to determine the 3D distribution of the atomic number density and electron density, and specified atomic distribution, respectively. In this paper, we describe the details of the system, report on experiments on the X-band thermionic cathode RF gun, and discuss applications of monochromatic X-rays.