TRISTAN Accumulation Ring Research Articles

Beam instability due to higher-order modes of APS cavities in the Tristan accumulation ring

Shifts of resonant frequencies of the APS cavity were measured as a function of the tuner position and cavity temperature. From this measurement we found that cavity temperature warm-up plays an important part concerning coherent instability. There was evidence that the accumulation current was limited by resonance with higher-order modes. We could identify which cavity mode was responsible for the transverse coherent instability.

Hydrogen depth profile of Al-alloy vacuum chamber exposed to synchrotron radiation

The hydrogen depth profile was measured for an Al-alloy vacuum chamber of the TRISTAN accumulation ring, which had been exposed to synchrotron radiation over 6 y. By analysing the energy of hydrogen atoms elastically recoiled by a 52.28 MeV argon beam, a dense hydrogen concentration near the surface, whose number density is from 0.42 to 5.4 × 10 16 atoms cm −2, is observed. The surface irradiated directly with synchrotron radiation shows the least hydrogen content which is about 1 10 that of an unirradiated surface. The observed hydrogen concentration is the source of H 2 desorption during exposure to synchrotron irradiation. The most dense part of the observed hydrogen probably corresponds to a surface oxide layer of aluminium.

Construction of an in-vacuum type undulator for production of undulator x rays in the 5–25 keV region

A new 179-pole undulator with magnetic period of 4 cm for production of brilliant and quasimonochromatic hard x rays has been completed and installed in the TRISTAN Accumulation Ring (AR) in KEK, National Laboratory for High Energy Physics. The aperture of the undulator for the circulating electron can be flexibly changed to satisfy the operational requirements of AR, since the undulator magnets are encased in the vacuum chamber of the undulator. When it is operated at the magnet gap of 20 mm with 6.5-GeV operation of AR, intense 14.4-keV radiation for Mössbauer experiments is successfully obtained as the third harmonic of the undulator radiation.

Construction and performance of an x-ray undulator beamline at the TRISTAN Accumulation Ring

An in-vacuum type undulator and its beamline NE3 with a Si(111) double-crystal monochromator is under commissioning. Spectra of synchrotron radiation measured in the energy range of 5–25 keV from the undulator shows a very good agreement with theoretical calculation. Some experiments of resonant nuclear scattering using 57Fe have been carried out using the third harmonics of the spectra. It has been proved that the undulator x rays are quite suitable for experiments of very small scattering cross sections.

High time resolution x-ray measurements with an avalanche photodiode detector

An avalanche photodiode (APD) detector has been developed for x-ray timing measurements with a subnanosecond time resolution. The performance of the APD detector was investigated with synchrotron x-ray beams in multi- and single-bunch runs at the Photon Factory (PF) ring. A time resolution of 0.28 ns (FWHM) and a peak-to-background ratio of more than 107 were obtained from the main peak of 14.4-keV x rays in a single-bunch time spectrum. The intrinsic efficiency and the counting-rate capability were also measured. As an application with a high time resolution, time spectra of quantum beats in nuclear resonance of 57Fe were observed with the APD detector at the undulator beam line BL-NE3 of the TRISTAN accumulation ring; the first peak of the beats was completely separated from the prompt peak of the non-nuclear components with a good time resolution and the beat structure was sharply seen to the range of ≳100 ns later with a very low background.

Motions of trapped dust particles around the electron beam in the TRISTAN accumulation ring

High-energy bremsstrahlung synchronized with the electron beam in the TRISTAN accumulation ring was observed accompanied by a sudden decrease in the electron beam lifetime which occurred due to dust trapping in the electron beam. The bremsstrahlung observed with gamma-ray detectors was obviously different from that caused by interactions between residual gases and the electron beam. Other bremsstrahlung observations showed a trapped dust particle passing through the periphery of the electron beam in the bending magnetic field; the transit time through the periphery of the electron beam was 0.15 ms; the half period of the horizontal oscillation perpendicular to the orbit of the electron beam was about 200 ms and the period of the vertical oscillation was 1 s. Simultaneous observation at two adjacent gamma-ray detectors showed that a trapped dust particle in the bending magnetic field moved in a longitudinal direction at the average speed of about 0.191 m/s. These observations coincide with the results based on our newly developed theory for motions of a trapped dust particle in a bending magnetic field. Furthermore, we introduced sample dust particles into the TRISTAN accumulation ring and carried out an experiment to trap the dust particles in the electron beam, in a straight chamber with no magnetic field and observed their motion with a gamma-ray detector. The beam lifetime suddenly decreased when the sample dust particles directly under the electron beam were caught up into the beam. High-energy bremsstrahlung and a pressure rise caused by the destruction of the dust particles were also observed at the same time. After that, beam lifetime recovered gradually. Our theoretical analysis shows that vertical oscillation of a trapped dust particle with no magnetic field continues and that the dust particle is destroyed by the heat deposited by the electron beam in less than a second. The calculated variation in the beam lifetime coincides approximately with the actual variation in the beam lifetime. Compared results of the observations and experiment show that our theory for motions of a trapped dust particle is useful.

Experiments to trap dust particles by a wire simulating an electron beam

Motion of trapped dust particles has been previously analyzed using high-energy bremsstrahlung data obtained during dust trapping in the TRISTAN accumulation ring. Because it is difficult to observe the actual motions of dust particles trapped in an electron beam due to the strong synchrotron light background, we carried out experiments to trap sample dust particles with a Cu wire simulating an electron beam. A negative potential was slowly applied to the wire using a high voltage dc power supply. Motions of dust particles trapped by the wire were recorded with a video camera system. In an experiment using a Cu wire (1.5 mm in diameter) with no magnetic field, the charged dust particle made vertical oscillation about the wire. In another experiment using the same wire but with a vertical magnetic field (0.135 T) simulating a bending magnetic field, both vertical and horizontal oscillating motions perpendicular to the wire were observed. Furthermore, it was found that the dust particle moved in the longitudinal direction of the wire in the bending magnetic field. Therefore, it is expected that charged dust particles trapped by the electric field of the electron beam oscillate vertically where there is no magnetic field in the TRISTAN accumulation ring. It is also expected that trapped dust particles where there is a bending magnetic field oscillate horizontally and vertically as the particle drifts in a longitudinal direction along the ring.

Observations of dust trapping phenomena in the TRISTAN accumulation ring and a study of dust removal in a beam chamber

Using a gamma-ray detector and a television camera system for synchrotron light, high-energy bremsstrahlung and horizontal growth of the synchrotron light source were observed when sudden decrease in the electron-beam lifetime occurred due to dust trapping in the electron beam. Two types of beam current losses were found; one was a continuous beam current loss, and the other was a short-term beam current loss. High-energy bremsstrahlung at a location was observed in a short time and after that, the bremsstrahlung was not detected in spite of the occurrence of dust trapping phenomena. The fact suggests motions of the trapped dust particles in the longitudinal directions. Materials collected in the beam chamber are dust particles from ion pumps and dust particles made during the beam chamber processing for welding. Most of the collected dust particles were less than 2 mm in size and surfaces of some dust particles were melted with the electron beam. Simple analysis was carried out for the conditions necessary for a dust particle to be trapped, for motions of the trapped dust particle, and for interactions between the trapped dust particle and the electron beam. The analysis showed that a dust particle less than 3 mm in size, made of Al, can be trapped and that the trapped dust particle can move in the vertical and longitudinal directions. The analysis also suggested that a dust particle in size of about 2 mm can be continuously trapped around the electron beam without being destroyed by the electron beam. Furthermore, the analysis explained the difference between the two types of beam current losses observed in the ring. Experiments which simulate the electron beam using a Cu wire in an evacuated beam chamber show that a dust particle (less than 70 μm) is trapped sufficiently. The experiments also coincide with theory for an attractive force acting to a conducting small particle. The calculated electric field of the electron beam and the calculated electric charge of dust particles given through the photoelectric effect in the TRISTAN accumulation ring are 100 times and 104–106 times higher than those of the simulated experiments, respectively. In the ring, the attractive force caused with the average electric field and with the expected charge is 10–103 times larger than that of the simulated experiments. Therefore, a dust particle (less than 2 mm) can be trapped sufficiently. An electrostatic dust collector using an electron beam and an electrostatic force are effective in removing all of the sample dust particles in the test chamber for the simulated experiments. A method to remove trapped dust particles using electrostatic electrodes is also discussed. It is expected that such electrodes can be useful for trapped dust particles moving in a longitudinal direction.

Design study of new distributed ion pumps for the TRISTAN accumulation ring

Distributed ion pumps (DIPs) for the TRISTAN accumulation ring (TAR) have been recently designed and experimentally studied. Effects on the pumping speed are investigated in some geometrical conditions, under the spatially non-uniform magnetic field and on the distance between cathodes and anodes. The pumping speed per cell depends on the cell diameter. Furthermore, the following new facts are determined: (1) the non-uniform magnetic field reduces an effective cell diameter and causes the decrease of the pumping speed; (2) although the pumping speed per cell of the perforated plate-type anode is greater than that of the cylinder-type anode, the preference between these two anodes should be determined by considering also the total cell number and the structure of the whole DIP; and (3) there exists the most suitable value of the distance between cathodes and anodes for a given cell diameter. DIP of the cylinder-type anode with a cell diameter of 15 mm and with the distance between cathodes and anodes of 7 mm is found to be the most appropriate one for TAR in the magnetic field of 3.6 ≈ 11.5 kG. A pumping speed greater than 120 l s −1 m −1 at a pressure of ≈ 10 −9 torr can be obtained after baking.

High pressure–high temperature research using high energy synchrotron radiation at the TRISTAN accumulation ring (invited)

High energy synchrotron radiation emitted from the bending magnet of the TRISTAN accumulation ring (6.5 GeV) at the National Laboratory for High Energy Physics has been used for the high pressure–high temperature diffraction experiments using a multianvil press system, MAX80. Owing to the specific features of high energy synchroton radiation, significant improvements have been brought to the high pressure research. The wide energy range of diffraction spectrum leads to an increase in the number of observable diffraction peaks in an energy-dispersive method, resulting in an increase in the accuracy of the measurements of the lattice and thermal parameters. Due to the high penetrating power of radiation, diffraction patterns can be taken in a short time from materials containing heavy elements or materials surrounded by a metal foil. Typical examples of high pressure–high temperature experiments with high energy synchrotron radiation are also described.

Design and construction of beamline-NE1 for circularly polarized synchrotron radiation from the 6-GeV TRISTAN Accumulation Ring

The beamline for the circularly polarized synchrotron radiation at the 6-GeV Accumulation Ring for the TRISTAN project is now under construction. The insertion device of this beamline was designed to produce circularly polarized x rays at the photon energy range of 200 eV∼100 keV. The beamline is divided into the following three branches: (1) High resolution Compton scattering and magnetic Compton scattering experiments; (2) multipurpose experiments such as magnetic x-ray scattering and magnetic x-ray absorption; and (3) completely circularly polarized soft x rays.

TRISTAN Accumulation Ring as a High Luminosity Collider

Annals of the New York Academy of SciencesVolume 535, Issue 1 p. 567-571 TRISTAN Accumulation Ring as a High Luminosity Collider E. KIKUTANI, E. KIKUTANI AR B-Factory Group National Laboratory for High Energy Physics Oho-machi, Tsukuba-gun Ibaraki-ken, 305 JapanSearch for more papers by this author E. KIKUTANI, E. KIKUTANI AR B-Factory Group National Laboratory for High Energy Physics Oho-machi, Tsukuba-gun Ibaraki-ken, 305 JapanSearch for more papers by this author First published: July 1988 https://doi.org/10.1111/j.1749-6632.1988.tb51551.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Volume535, Issue1International Symposium on Production and Decay of Heavy FlavorsJuly 1988Pages 567-571 RelatedInformation

Photon stimulated gas desorption from pure aluminum

To investigate photon stimulated gas desorption from a sample inside, it is necessary to separate the gas desorption from the sample surface and the one from inside. When a sample has no inside gas content, does photon stimulated gas desorption soon become very small after surface gas is cleaned away? An experiment using a thin film carefully prepared at an ultrahigh vacuum can give this answer. The gas desorption experiments were carried out in a molecular-beam epitaxy apparatus made of aluminum alloys with special surface treatments. The apparatus is connected with the TRISTAN accumulation ring. Synchrotron light can be applied on samples in the apparatus. Pure aluminum films were prepared by vacuum evaporation (99.999% aluminum) on a silicon wafer in the pressure range from 10−9 to 10−8 Torr. Gas desorption measurements were made at a pressure around 10−10 Torr using ionization gauges and a quadrupole mass analyzer. Photon stimulated gas desorption of a pure aluminum sample was small compared to other materials. Now the experimental apparatus is being improved to measure the very low gas desorption yield more precisely. The final purpose is to make clear the relation between an internal gas content of material and photon stimulated gas desorption.

シンクロトロン放射光による「光化学反応」腐食

シンクロトロン放射光による「光化学反応」腐食

Disk-and-washer cavities for an accelerator

Studied is the behavior of disk-and-washer accelerator cavities, in which the single radial stem support is adopted. The support leads about 70% larger and 20% smaller rf power loss than that of the calculated value in the normal cell and in the end cell, respectively. The distortion of the field is limited in the region of the so-called coupling cells. The properties of the coupled cavities, as the dispersion curve or the effect of tuners on the relative axial field is measured and well explained by the biperiodic coupled resonator model. The manufacturing of the actual cavity is also described, in which electroplating and welding methods are developed. The transverse coupling impedance calculated for a multiple-cell cavity are comparable with the instability experiments made in the TRISTAN accumulation ring.

Z-shaped wire profile and position monitor for collimated synchrotron radiation using a single linear motion

A simple position and profile monitor for collimated synchrotron radiation (SR) using only one linear motion feedthrough was constructed and successfully employed to align the SR beam line of the TRISTAN accumulation ring.

トリスタン蓄積リング真空系の運転特性

トリスタン蓄積リング真空系の運転特性

Gamma Ray Source Using Internal Targets in the Tristan Accumulation Ring

As an alternative electron source TRISTAN AR is now operational, and is a$le to accelerate and store an electron beam of more than 5 GeV. We planned to extract high energy gamma rays by inserting a internal target into the AR, because a direct beam extraction is not easy. Two gamma ray lines are prepared by the two detector groups. Each detector group has its own target and gamma ray line. It is also required that the gamma rays should be simultaneously produced at the two targets with the least interference between them. The circulating electron beams gradually collide with the target and produce gamma rays, which are extracted from the AR through a Be-foil window. By a converter the gamma ray is changed into high energy electrons and positrons, which are finally used for the calibration of the lead glass counter. The momentum of the electron beam is defined by an analyzer magnet. At present two gamma ray lines, IT1 and IT4, are available as shown in Fig. 1, and are able to produce the electron beams for the two detector groups simultaneously. Target System Each internal target is located in the beam duct at a bending magnet gap and inserted horizontally from the outside of the beam orbit. The target is suffered from enormous synchrotron radiation and hence is made of molybdenum which is heat-resistive and easy to fabricate. The target head is 3 mm thick and 6 mm high, and is cooled by water flowing through a hole inside the target holder. The target position is monitored by a potentiometer and can be precisely adjusted within 0.05 mm by a remote control.

Development of an APS Cavity for Tristan Main Ring

Normal conducting 508 MHz cavities of alternating periodic structure (APS) with nine accelerating cells will be installed in the TRISTAN main ring (MR). Rationale for this choice was discussed in ref. 1. The structure is biperiodically loaded with straight disks. The cells are coupled only electrically through the beam apperture of a 100 mm diameter and the coupling constant is about one percent. The length of the coupling cell is 15 mm. The adopted dimensions are shown in Fig. 1. The parameters of the cavity were calculated by SUPERFISH and listed in Table 1. It was found that each accelerating cell frequency should be tuned well to obtain a high Q value. Thus, tuning plungers were installed to all of the accelerating cells. The shunt impedance was estimated to be 23 MΩ/m and this value was 85 percent of the calculated one. It was also found from model calculations that the frequency of the coupling cell fc should be higher than or equal to that of the accelerating cell fa to stabilize the power distribution among the accelerating cells. The cavity designed under this constraint was excited up to 220 KW (CW) which was 150 percent of the designed power dissipation. The measured shifts of fa and fc due to the thermal distortion arising from the power dissipation were in agreement with those estimated from a computer analysis of thermal distortion. The transverse instability caused by the deflecting mode of the cavity was observed in the TRISTAN accumulation ring (AR).

Operational Characteristics of the Tristan Accumulation Ring Vacuum System

The operational characteristics of the TRISTAN vacuum system is discribed. The vacuum system is made of aluminum alloys using specially extruded aluminum pipes. The best base pressure, on the order of 10 Pa, was obtained without any baking or discharge cleaning. The thermal gas desorption rate of the aluminum chambers was on the order of 10-10 Pa.1/s.cm2. For a time integrated beam current of 13.5 A.h, the pressure rise due to synchrotron radiation was 2.1 × 10-8 Pa/mA and the maximum beam lifetime was about 2 hours at several mA. The pressure rise is approximately inversely proportional to the time integrated beam current and is initially proportional to the beam energy, changing after about 7 A. h, to being proportional to the square root of the beam energy. A pressure independent lifetime of 357 min was observed. The lifetime at higher beam currents is proportional to the time integrated beam current. No thermal problems due to synchrotron radiation were observed. Corrosion due to high energy radiation in the presence of humidity was found in the aluminum windows for X-rays and y-rays. Heating problems due to wall current discontinuities did not occur in the dual flat mirror surface seal type gate valves made of aluminum alloys. They were observed in a current transformer, in the ceramic chambers, and in a normal, Viton sealed gate valve.