We have numerically studied on improvement of electron beam macro-pulse properties from thermionic RF gun [1,2]. Beam properties, such as energy spectrum, macro-pulse duration and emittance were measured with a 2 mm diameter slim thermionic dispenser cathode. Effect of the transverse magnetic field to reduce back-streaming electrons to these properties was studied experimentally. Comparison with measured and numerical results will be discussed. Effect of a non-flat RF input to compensate a decreasing beam energy during macropulse due to a back-bombardment effect will be also presented.

Users demands to a high power tunable IR laser are increasing in Japan in energy-related science, such as basic study of high-efficiency solar cells, generation of new energy source of alcohol and/or H₂ from polluted gas, and separation of DNA and/or RNA. To satisfy these demands, we decided to renew our FEL facility more user friendly and to operate more flexibly. Construction and fundamental studies on the KU-FEL have been carried out at a building of Institute of Chemical Research where few other accelerators are operating. Therefore, available machine time for our experiments is quite limited. We are now modifying the room by adding concrete walls of 2-m thickness and some space for users will be available. The present FEL system will be moved to the room A photocathode RF-gun system will be nearly added to the system and the present thermionic RF-gun will be used ternatively according to the demands of users. The photocathode material will be Cs₂Te. The room with the shielding will be completed in June, 2004, and we will moved the machine shortly. We hope to resume the operation of the linac in fall of 2004. The FEL is expected lasing in the next year.

An infrared FEL facility is under construction for advanced energy researches [1]. Electron beams of around 30 MeV have been obtained by an S-band 4.5-cell rf gun with a thermionic cathode, and a recently installed 3-m accelerating tube. A 180 degree arc consisting of three bending magnets have been also set up for bunch compression, and beam property measurements are under way. Transverse phase space distributions and resultant emittances have been obtained through the tomographic technique [2] by use of a quadrupole magnet, an alumina phosphor screen and a CCD camera. An OTR screen is being prepared for a higher spatial resolution as well as for longitudinal bunch shape measurements by use of a streak camera of 0.2 psec resolution. Comparison with the start-to-end simulation results [3] will be also presented.

An infrared FEL facility is under construction at Institute of Advanced Energy, Kyoto University[1]. The electron beam of 30 MeV has been successfully accelerated by the S-band linac consisted of thermionic RF-gun[2]. To reduce the back-bombardment effect in the 4.5-cell RF gun, several attempts have been done and the macro-pulse duration of 3 μs has been achieved[3]. However, there still needs several efforts to obtain enough macro-pulse duration[4]. Upgrade from the thermionic RF-gun to a photo-cathode RF-gun is a short-cut solution. So a design work for the system upgrade has been performed. The system will use not only a 1.5-cell photo-cathode RF-gun, but also use the existing thermionic RF-gun. A Gun-to-Linac beam transport system was designed for two different injectors. Numerical calculation of the beam property has been performed by PARMELA to compare the existing one. We will discuss on the expected FEL gain with the upgraded driver system.