High power cryotarget

Study of the elastic and quasi-elastic electromagnetic form factors of the few nucleon systems (H, H, He and He) at high momentum transfer requires target luminosities /> 10 cm sec. Similar luminosities are also required to study the weak neutral current form factors in the same systems. A major fraction ( 70%) of the experiments planned Hall A fall in this broad area of research.

To achieve the necessary luminosity within the limited target acceptance of a magnetic focusing spectrometer, targets operating at cryogenic temperatures and high beam currents are required. Given the maximum current of CEBAF (200 A) and target length acceptance of the HRS spectrometers, the power deposited by the beam in the targets will reach up to 1 kW. Although such power levels are not routine for previous cryogenic targets they can be handled. However, the low emittance of the CEBAF beam produces a beam power density at the cryogenic targets several orders of magnitude above previous experience. The CSULA group has investigated the problems associated with the realization of such a high power target, and a prototype has been build. Tests indicate that it will meet the performance goals, and funds for construction are needed as quickly as possible.

While the above mentioned prototype indicates that the required targets can be build, construction of an actual cryogenic target is not included in the construction funding profile of Hall A. This is the highest priority item for Hall A since, as described above, its physics research program depends totally on it.