Hidenori Sagehashi

Advanced Neutron Reflectometer for Investigation on Dynamic/Static Structures of Soft-Interfaces in J-PARC

A novel neutron reflectometer with horizontal geometry will be established at BL16 in Materials and Life Science Experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC) as a successor of a reflectometer ARISA-II. ARISA-II corresponding to a single neutron beam downward at 2.22 deg has achieved off-specular and time-resolved reflectivity measurements. The novel reflectometer is designed so as to receive two tilted neutron beams (2.22 & 5.71 deg), which gives us an opportunity in investigation on a free liquid surface. The reflectometer can provide a micro-sized beam by slit collimation and obtain a fair reflectivity with small sample area. Also, T0 chopper and neutron focusing mirror are newly introduced. The T0 chopper can suppress the background due to fast neutrons. The focusing mirror produces further reduction of measurement time not only for specular reflection by focusing neutrons on a sample, but also grazing incidence small-angle neutron scattering (GISANS) measurements by focusing on a detector.

Development of a Physically Bent Cylindroid Mirror for Beam Focusing for a Pulsed Neutron Reflectometer

To gain in intensity and realize a grazing-incidence small-angle scattering (GISAS) measurement on a pulsed neutron reflectometer, we are now developing focusing devices using a cylindrically bent supermirror coated on a flat float glass substrate. They have been characterized at pulsed neutron sources, and we successfully focused neutron beam into about 1mm width in either vertical or horizontal direction using the bent mirror with the focal distance of about 4 m.

Measurement and Control of Beam Losses Under High Average-current Operation of the Compact ERL at KEK

The compact ERL (cERL) [1, 2] at KEK is a superconducting accelerator aimed at demonstrating ERL technologies for the future light source. In cERL, low-emittance and high-average-current electron beams of up to 10 mA will be recirculated in future. Toward this goal, we studied high-average-current operations where the beam losses should be controlled to very-small fractions. We have so far succeeded in recirculating beams of up to 0.9 mA with very-small beam losses. We report our accelerator tuning method for high-average-current operation, and present measured radiation data showing very-small beam losses. INTRODUCTION In cERL, production and transportation of lowemittance (< 1 mmmrad) and high-average-current ( 10 mA) electron beams are primarily important. In highintensity linacs such as cERL, reduction of beam loss is essential in order to reduce the risk of radiation hazard as well as to avoid damages in accelerator components. Till June of 2015, electron beam having an average current of 80 A was successfully transported to the beam dump in cERL. Due to careful accelerator tuning and the use of beam collimators, beam losses along a recirculation loop were reduced to small amounts. At this time, we conducted radiation measurements with several methods, and estimated amounts of beam losses [3]. Based on these data, we installed some additional radiation shields, and applied an increase in our authorized beam current, that is, from 100 A to 1 mA. This application was approved by the government in January, 2016. Until March of 2016, we established high averagecurrent operations of cERL up to a maximum beam current of 1 mA. Typical operational parameters are given in Table 1. We can choose one of two repetition rates of bunches, 1.3 GHz or 162.5 MHz, by selecting one of the laser oscillators of a photocathode DC gun. First, we tuned the machine at a higher bunch-repetition rate (1.3 GHz) with lower bunch charge (0.7 pC/bunch). After this Table 1: Typical Operational Parameters of cERL Beam energy 19.9 MeV Injection energy 2.9 MeV Bunch repetition rate (usual) (for laser-Compton scattering) 1.3 GHz

Operational Status of PF-Ring and PF-AR after the Earthquake

In 2011, two SR sources of KEK, PF-ring and PF-AR, needed to change the operation schedule because of the unprecedented earthquake on March 11. Though the injector linac and the storage rings suffered a serious damage, temporary recovery was accomplished quickly and the trial operation started in May. The regular user operation could be resumed in October 2011. In the restoration work after the earthquake, some old vacuum components were removed from PF-ring. This work fortunately brought an effect of settling the quadrupole-mode longitudinal instability. For the top-up injection of PF-ring, the pulsed sextupole magnet has been used instead of the conventional kicker magnets since 2011. The hybrid-fill mode in place of the single-bunch mode has become available. Recently, the 10-Hz orbit switching for the tandem circularly polarized undulators has been developed for the user operation.