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

Version 1

      Publication Details (including relevant citation   information):

      Rev. Sci. Instrum. 62(11), 2558 - 2567 (1991).

      PACS:

      29.20.dbStorage   rings and colliders

      29.27.EgBeam   handling; beam transport

      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.

      Address (URL): http://rsi.aip.org/resource/1/rsinak/v62/i11/p2558_s1