SUPERHARP - A WIRE SCANNER WITH ABSOLUTE POSITION READOUT FOR BEAM ENERGY MEASUREMENT AT CEBAF

The CEBAF superharp is an upgraded beam wire scanner which provides ab solute beam position readout using a shaft encoder. Superharps allow f or high precision measurements of the beam's profile and position (Del ta x - 10 mu m). The Hall C endstation at CEBAF will use three pairs o f superharps to perform beam energy measurements with 10(-3) accuracy. The three pairs are installed at the beginning, the mid-point and the end of the Hall C are beamline. Using superharps in conjunction with a dual sensor system: the direct current pick-up and the bremsstrahlun g detectors, beam profile measurements can be obtained over a wide bea m current range of 1 similar to 200 mu A.