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

Version 1

      Publication Details (including relevant citation   information):

      Rev. Sci. Instrum. 62(4), 874 - 885 (1991).


      29.20.dbStorage   rings and colliders

      29.27.EgBeam   handling; beam transport


      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.

      Address (URL): http://rsi.aip.org/resource/1/rsinak/v62/i4/p874_s1