Cavity optimization for compact accelerator-based free-electron maser
In previous works [1] we have successfully commissioned pre-bunched beam pumped free electron maser based on Stimulated Coherent Diffraction Radiation (SCDR) generated in an open resonator. An ultra-fast Schottky Barrier Diode (SBD) detector has enabled us to investigate the properties of the radiation in the range from 3 to 5 mm of wavelengths among broad frequencies stored in the cavity as well as the intrinsic properties of the cavity itself. We observed a turn-by-turn SCDR generated by a multibunch electron beam and directly measured the opened cavity quality factor of 11.4. In this report we represent the work directly related to optimization of both the maser system to achieve higher quality factor of the cavity essential to gain soft X-ray production via Thomson scattering in the next stage of the experiment and measurement system for better characterization of the maser light. One way of optimization is to minimize losses of energy due to transmission through resonator mirrors. For this purpose we have designed and constructed a test setup to investigate reflection and transmission properties of different mirror materials. Theoretical calculations have been performed using optical constants and theoretical models of electrical permittivity to compare with experimental results. In this report we summarize the experimental activity, represent new experimental results and represent steps undertaken to achieve the new resonator mirror design. For better understanding of the resonator performance a test of the SBD detector linearity is also demonstrated.
Upgrade of the accelerator for the laser undulator compact X-ray source (LUCX)
Abstract We have developed a compact X-ray source based on inverse Compton scattering of an electron beam and a laser pulse, which is stacked in an optical super-cavity, at the Laser Undulator Compact X-ray Source (LUCX) accelerator at KEK. The plan is to upgrade the accelerator and the super-cavity in order to increase the number of X-rays and to overcome the problems that have become clear in the experiments so far. A new RF gun with a high mode separation and a high Q value and a new klystron for the gun will be installed to provide good compensation with a high-intensity multi-bunch electron beam. A new optical super-cavity that consists of four mirrors is also being developed to increase the stacking power in the cavity and to reduce the laser size at the focal point. The final goal is to produce a long multi-bunch electron beam with 8000 bunches/train, 0.5 nC/bunch, and 5 MeV and to generate a soft X-ray with 6.5×107 photons/train after the upgrade. The upgrade plan is reported in this paper.
The comparison of characteristics of π− mesons produced in central Mg-Mg interactions with the quark gluon string model predictions

Abstract: A detailed study of pion production in central Mg-Mg collisions at a momentum of 4.3 GeV/c per incident nucleon was carried out with use of the setup GIBS. The average kinematical characteristics of pions (multiplicity n−, momentum P, transverse momentum PT, emission angle Θ, rapidity Y) and corresponding distributions have been obtained. The experimental results have been compared with the predictions of the Quark Gluon String Model (QGSM) and satisfactory agreement between the experimental data and the model has been found. The QGSM reproduces also the dependence of average PT on n−.
The temperatures of π− mesons have been estimated in the rapidity interval of 0.5 ≤ Y ≤ 2.1. A satisfactory fit for π− mesons has been achieved by using a form involving two temperatures T1 and T2. It is found that the QGSM underestimates T2 by (10−15)%.
The data have been analyzed using the transverse momentum technique. The observed dependence of the  on Y shows the S-shape behaviour. The slope at midrapidity F has been determined. The QGSM reproduces the  distribution satisfactorily, but underestimates the parameter F.