Long term displacement of the concrete floor in the TRISTAN ring

The TRISTAN ring, an electron-positron collider with 1 km diameter, is going to be modified as a B-factory. The B-factory consists of an electron ring and a positron ring, the energy of which are 8 GeV and 3.5 GeV, respectively. In the B-factory, the luminosity and the beam collision rate seem to be more sensitive to the variation of magnet positions. At the time of the operation of the TRISTAN, the drift of the beam orbit was observed, and its state is reported. If the main source of this drift of beam orbit could be found out, it will help the design of the B-factory ring. It is conceivable that the movement of magnet bases in the interaction region and the seismic motion of concrete floor at the expansion joints of ring tunnel blocks are responsible for the drift of the closed orbit distortion (COD). The latter is discussed in this paper. The TRISTAN ring consisting of 4 experimental halls, 100 m long straight sections on both sides and 4 arc sections is described. Gap sensors and hydrostatic leveling system were used to measure the variation of the gaps at the expansion joints and the tilt of the concrete floor. The state of variation of gaps and the state of movement of the concrete floor are reported. (K.I.)