Tatsuya Yamakawa

Transit times of pressure waves in an acoustic delay line

Abstract The transit times of the pressure waves of He, Ar, N 2 and air propagating in an acoustic delay line designed for practical use in a beam line of a synchrotron radiation source have been measured. It is found that the propagation velocity of a pressure wave increases with the increase in the starting pressure of the test gas in the reservoir and with the decrease in the pressure at the wave front. The speed of the pressure increase in the last segment of the acoustic delay line depends strongly on the kind of gas and on the size of the aperture in baffles installed in the acoustic delay line. A qualitative discussion of the propagation mechanism of the pressure wave is given.

Photon Tagging System at the INS Electron Synchrotron

A photon tagging system which determines the energy of each photon in the bremsstrahlung process is constructed, and is tested using an extracted electron beam from the 1.3 GeV electron synchrotron at the Institute for Nuclear Study, University of Tokyo. The system which consists of an analyzing magnet and twenty-five tagging counters detects the recoil electrons in the energy range from 100 MeV to 350 MeV. The energy of each tagged photon has been calibrated with a total absorption type lead glass Cerenkov counter. A good agreement within the error of ±10 MeV is obtained between the energy measured by the Cerenkov counter and the one calculated from the trajectory of the recoil electron. From the first experiment using this system, it is found that the intensity of the tagged photon beam is limited to 105 photons/s.

Observation of Undulator Radiation. : I. Operation Studies and Visual Observation

A 19-pole permanent magnet undulator has been tested by inserting it into a straight section from outside the vacuum chamber of the SOR-RING, a dedicated synchrotron radiation source operated between 0.2 and 0.38 GeV. It was confirmed that the undulator field did not seriously disturb stable operation by observing the shift of the closed orbit and the shift of the betatron numbers. Some results of visual observation of the radiation are presented. The polarization character was studied on the rainbow circle with a polarizer and some theoretical results by Kitamura were confirmed. It was found that the interfering synchrotron radiations along the straight section of the storage ring make a series of rainbows even without the undulator field.

The construction of the superconducting vertical wiggler and its operation in the photon factory

Abstract The superconducting vertical wiggler of the Photon Factory, KEK, was installed in the storage ring in October 1982. Its first operation with 2.5 GeV electron beam was successfully done in February 1983, the wiggler radiation was observed in the beamline through a Be window using a fluorescent screen as well as with a solid state detector, by changing the magnetic field strength of the wiggler. Since February 1984 it has been operated in the normal users time. The maximum magnetic field achieved after installation in the storage ring is 5.8 T. However, we have operated the wiggler magnet at 5.0 T in usual operation as to obtain long enough beam lifetimes for the users run. At this moment, we have achieved an average beam lifetime of 1500 min at a stored curret of 100 mA.

Design of a vertical wiggler with superconducting coils

Abstract A vertical wiggler has been designed, which will be installed in the 2.5 GeV electron storage ring under construction at KEK-PF. The wiggler magnet with superconducting coils produces magnetic fields of 6 T and wiggles electron beams in a vertical plane. Synchrotronn radiation generated by the wiggler has a critical wavelength of 0.5 A and has an electric field-vector in the vertical direction, which is very important for precise experiments in various fields of the material sciences. The wiggler consists of three pairs of superconducting coils, an iron magnetic shield, a beam pipe and a liquid helium cryogenic system and is contained in a vacuum vessel which can move up and down together with the wiggler. During the injection time, the vessel is pushed up, so that electron beams with a large spatial spread go through the lower part of the beam pipe, where the aperture of the beam pipe is large enough. After the beam size becomes small due to radiation damping, the vessel is pushed down so that the electron beams go through the narrow gap of the wiggler magnet. Using the iron magnetic shield with iron pole pieces, the ratio between the magnetic field in the gap and the maximum field on the superconductor coils is reduced to 1.1.

One-Third Resonance Extraction from INS AG Electron Synchrotron

Slow beam extraction from the INS-AG electron synchrotron was done by using a one-third resonance of the betatron oscillation. A current strip was used to change the number of the radial betatron oscillation per revolution from 2.25 to 7/3 and to enlarge the amplitude of the oscillation. The extracting beam orbit was analysed using an approximate Hamiltonian which has a separatrix represented by three straight lines and the result was in good agreement with that pursued by a computer. The properties of the extracted beam were as follows; The efficiency was 50% for electrons of 300 MeV up to 1 GeV. The maximum beam intensity was 4×1011 electrons per second. The maximum duty cycle was 3%. Phase volumes for the horizontal and the vertical motions were 10-3 rad cm and 0.75×10-3 rad cm, respectively. The beam transport system and the radiation shielding system are also described.

Beam Loading Effect on Capture Efficiency in Radio Frequency Acceleration in Electron Synchrotron

The effects of beam-loading on the RF field in the cavity and on the beam capture to the electron synchrotron from the injector linac have been studied experimentally and theoretically. In the present experiment, the amplitude and the phase of the RF field, which is a superposition of the external driving field and the beam-induced field, have been found to change during the transient period just after the injection from the linac. This phenomenon is striking, especially when the frequency of the external driving field is very different from the resonant frequency of the cavity. In this detuning of the cavity, a large capture efficiency of the injected beam from the linac has been observed. The mechanism of this has been elucidated by analyzing the effects of the beam-induced field in the cavity during the transient period.

Electron-Induced Cascade Shower in Lead Glass

In order to provide useful data for designing a lead glass Cherenkov counter, observations were made on the longitudinal distributions of cascade showers developed in the SF-2 lead glass at the energies of 450, 650 and 800 MeV. The results agreed well with the calculated values based on the approximation B.

Energy Indicator of the Electron Synchrotron

A new method is developed for the precision indicator of the electron synchrotron energy. The signal from a search coil placed inside the main magnet (∝dB/dt) is integrated by a 1 MHz Voltage-to-Frequency converter and its digital outputs are counted during the time interval between the zero field and the maximum field to give the precise value of B0 at the central orbit. After being calibrated with a standard pair spectroscopy, the device is capable of displaying the value of an endpoint energy of Bremsstrahlung beam itself with an accuracy of ±0.1 MeV for the energy range of 300~1200 MeV.

Electron Beam Extraction from INS AG Synchrotron. Part II. Experiment

The electron beam has been extracted from the INS 750 MeV AG synchrotron. A Piccioni scheme was applied and the extraction efficiency obtained was 10% at the electron energy of 540 MeV and 5% at 700 MeV. The behaviour of the beam inside and outside of the synchrotron was studied in comparison with the theoretical analysis. The pulse duration of the extracted beam could be extended to the order of 700 µs without any difficulty for the 21.5 cps operation of the synchrotron.