LH 2 Target Density in Hall A Experiment E 01 - 020

Experiment E01-020 1 consisted of a measurement of the H(e, ep)n cross section over a broad kinematical phase space using the Hall A 2 high resolution spectrometer pair. In order to calibrate our kinematics and check our cross section normalization, we measured elastic scattering in H(e, ep) using a 15 cm liquid hydrogen target with the “cigar-tube” cell. The normalization check involves knowledge of the liquid hydrogen density seen by the beam. In this paper, I show the results of a study of target density performed at fixed beam energy and with the high resolution spectrometers at fixed kinematics for varying beam current. For this study a “nominal” 2 mm × 2 mm square beam raster was used with the target fan frequency set to 60 Hz. For beam currents above 40 μA the density falls off linearly with beam current and also with position along the beam. No significant reduction was found near the entrance of the target cell even for the highest beam current employed, 111 μA. Below 40 μA, no significant density reduction was found.