PIA, the Positron Intensity Accumulator for the PETRA Injection

The storage ring PETRA is designed to store 4.1012 electrons and positrons in 2xfour 500 MHz rf buckets. Since the intensity of the positron linac is about 2.107 particles per 500 MHz bucket, 2.105 bunches are required for injection and accumulation in PETRA. In order to get reasonably short filling times the storage ring DORIS presently is acting as an intermediate bunch accumulation facility. This scheme has been successfully in operation since September 1978. Now the increased demand for elementary particle physics and for synchrotron radiation experiments at DORIS has motivated the construction of the small 450 MeV intermediate storage ring PIA, located between the positron linac and DESY. The circumference is 28,8 m. About 1 . 109 positrons will be injected at a rate of 50 Hz. A first harmonic cavity (10,4 MHz) accumulates positrons in a 0,8 m long bunch which is further compressed to 0,25 m length by a 12th harmonic rf system (125 MHz) for injection into the DESY 500 MHz system. After acceleration to 6,5 GeV in DESY single positron bunches are injected into PETRA.