Sakuo Matsui

Orbit Fluctuation of Electron Beam due to Vibration of Vacuum Chamber in Quadrupole Magnets

The fluctuation spectrum of the electron beam orbit in the SPring-8 storage ring had broad peaks at approximately 40 Hz vertically and from 80 to 100 Hz horizontally. Fourier analysis of orbit fluctuation identified these fluctuation sources not as magnet vibration but as chamber one due to the disturbance of the cooling water. When the chamber vibration was reduced by fixing the chamber rigidly, the orbit fluctuation was reduced in the same way. An eddy current induced in the vibrating thick chamber in quadrupole magnets produces a bending field, which kicks the electron beam. This field is equivalent to the vibration field of a quadrupole magnet with the same vibration amplitude. The calculated orbit fluctuation based on this model agrees with the measured one.

Commissioning Status of the Extreme-Ultraviolet FEL Facility at SACLA

To equip SACLA with wide ability to provide laser beams in EUV and soft X-ray regions to experimental users, we have constructed a new free electron laser facility for the SACLA beamline-1. Injector components, such as a thermionic electron gun, two buncher cavities, and their RF sources, were relocated from the SCSS test accelerator. At the downstream of a bunch compressor chicane, 3 C-band acceleration units were newly installed to effectively boost a beam energy up to 500 MeV. 3 invacuum undulators with a larger K-value of 2.1 were remodelled for increasing SASE intensity. Beam commissioning was started in autumn 2015. We carefully tuned an electron beam orbit and bunch compression processes to obtain 240 A at the peak along the injector and 2 bunch compressors. The bunch length was successfully compressed from 1 ns to 1 ps. After the tuning, the lasing of the EUV-FEL was realized. So far the FEL radiation with energy of about 25 J and a 30 nm wavelength driven by a 500 MeV electron beams was observed. In this summer, we will install additional 2 C-band accelerator units to raise the maximum beam energy to 750 MeV for providing a laser at 13 nm.

AC Sextupole Magnet for Cure of Transverse Instability in Synchrotron

An AC sextupole magnet system was developed and installed in the electron storage ring, NewSUBARU. This system is for a proof of principle experiment of a new suppression method of transverse beam instabilities. The magnet produces a modulation of the chromaticity with a synchrotron frequency, which creates a large tune spread and suppresses instabilities with Landau damping. The rating of the system is determined from the ring parameters and the yoke length is 150 mm, the bore radius is 80 mm, the maximum field is 36 T/m2 at 300 A and the operation frequency is 4-6 kHz. The coil conductor consists of an inner side half turn (closer to the magnet axis) and an outer side half turn for each pole. At the operation with peak current of 300 A, the power loss in the magnet was 900 W. The eddy current loss in the inner side coil conductor is the main part of this loss and is induced by the magnetic field excited by the outer coil current. It has no water-cooling system and the coil temperature was raised to higher than 70degC after 5 minutes operation and the interlock system is set to turn off the power at 80degC. However this is acceptable for the experiment in a short period. To drive the current of 300 A peak, an external capacitance is attached to the magnet, which forms the LC resonant circuit that is excited by a general-purpose AC power amplifier (DC-20 kHz, 170 V peak, 23 A peak). The Q-value of the circuit is 16.5 for 5 kHz. The resonant frequency is variable by remote switching of the several capacitances. With this magnet system, we successfully observed the suppression of beam instabilities.