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

Abstract

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.