A Precision Actuator and Shaft Encoder for a High Radiation Environment and Other Beam Component Developments at SLAC

A precision actuator and shaft encoder combination for remote handling in a high radiation and corrosive environment is described. The package allows accurate positioning of beam transport components in areas where liquid lubrication is not possible. The use of hexagonal lattice metals prevents galling or seizing of the rolling surfaces. The actuator translates rotary motion and torque supplied by a commercial radiation-resistant stepping motor into linear motion and force. Two actuators are in operation with a 7.5 cm output travel. Reproducibility is to ±1 step or 0.0015 cm. The shaft encoder resolves the turns of the motor in 1024 increments with cams and microswitches. The estimated dose rate of 1012 to 1013 ergs/g/yr in the vicinity of a SLAC high-power slit should present no problems. The second part of the paper describes a new quick-disconnect injected indium vacuum seal. Indium is extruded into a gasket groove of a flange through tapped holes by means of bolts. Finally, a blowout fuse employed in the beam stoppers of the SLAC personnel protection system is described. The fuse responds to thermal radiation from the surface of a beam stopper by melting a low-temperature eutectic diaphragm thus letting the vacuum system up to air.