Gamma Ray Source Using Internal Targets in the Tristan Accumulation Ring

Abstract

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.