Polarized Proton Target for the g2p Experiment

The $g_2^p$ experiment was completed in Jefferson Lab's Hall A in the spring of 2012. These data will provide the first measurement of the proton's $g_2$ structure function in the region $0.02~<~Q^{2}~<~0.2~GeV^{2}$. A large scale installation was required for the $g_2^p$ experiment, including a polarized ammonia (NH$_3$) target never before used in Hall A. Based on the principle of Dynamic Nuclear Polarization (DNP), microwave pumping is used to polarize irradiated ammonia in a high magnetic field at a temperature of 1K. In order to achieve the proposed kinematic range, the target magnet field was used at both 2.5\,T and 5\,T. Few studies of DNP have been done previously with a target field of 2.5\,T, making these data of particular interest. In addition, an experiment to measure the proton form factor ratio ($G_E$/$G_M$) ran concurrently with the $g_2^p$ experiment and required a different target polarization direction. Therefore, a rotatable target chamber was needed for transition between configurations. This talk will introduce the concept of DNP and describe the unique challenges faced in the design of the $g_2^p$ target. Performance indicators such as polarization decay rate and anneal time will be presented along with preliminary polarimetry results.