No abstract

Recently precise positioning devices with low outgassing rates have been required for production systems of very large scale integrated circuits, surface analysis systems, and scanning tunneling microscopes in ultrahigh vacuum. A bakable XYθ three-axis positioning table using a unique positioning mechanism utilizing friction and inertial forces caused by rapid deformations of piezoelectric elements was developed. The table has a hexagonal shape of 120 mm in diameter and is mainly made of aluminum alloys with an EX-process. The table has three feet with an Si3N4 ball on each bottom side and set on a plate made of Pyrex glass. The table was able to operate in an ultrahigh vacuum environment of the order of 10−12 Torr.

No abstract

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.

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.