Post Accelerator Beam Pulse Length Chopper

The CEA 130 MeV electron linac has a pulse length of 2.5 ??sec. The 6.0 GeV synchrotron accepts only a 0.76 ??sec pulse length to fill its circumference. To inject the entire 2.5 ??sec pulse length results in unnecessary radiation damage to vacuum chambers and various portions of the transport system. It is desirable to inject only a 0.76 ??sec pulse, and to select empirically that portion of the linac pulse that has the least energy spread. The unwanted portion of this pulse should be deposited on a suitably designed beam stopper. A magnet followed by a water-cooled collimator has been installed, which precisely chops the 130 MeV linac pulse. The system has been designated PAC for post acceleration chopper. The PAC system and our experience with it will be described.