Approximately four years ago a decision was made to develop a new laboratory at Virginia to pursue research and development of polarized targets. There were two major goals of this laboratory: 1) to construct high polarization proton and neutron targets suitable for use at CEBAF and other electron facilities; 2) to investigate and develop possible improvement in the existing targets.
The first goal has been accomplished with the procurement and successful operation of an entire system suitable for use in Halls A and C, and with modifications in Hall B. The system consist of the following major components.
Research has continued in parallel on investigation of other materials and the optimum dose and means of irradiation of the samples. Irradiation of the ammonia samples has taken place at the electron linear accelerator at Saskatchewan and recently at CEBAF. The technique at CEBAF required stopping the 5 MeV injector beam in a tungsten target to generate an intense source of x-rays incident upon the ammonia samples. This was quite successful and we plan to continue this work. We will receive this summer another cryostat and magnet that will be a general purpose research device. The magnet is a superconducting solenoid capable of fields up to 9 tesla. The central refrigerator is interchangeable, capable of operation with either He evaporation units or a dilution refrigerator. This will allow us to continue our investigation of the optimization of material polarization with variable field and temperature. One of the eventual goals is the construction of a frozen spin system operating at lower temperature and reduced magnetic field.
The cost of procured equipment now totals $1.36M. Basel and UVA (Higher Education Equipment Trust Fund, Commonwealth of Virginia, the Commonwealth Center and the University) have contributed $1.11M. CEBAF has contributed $253K for the acquisition of the magnet and cryostat.
The manpower effort that has gone into the project is approximate 14 FTE, which includes senior physicists, research associates and technicians, but not students. The Commonwealth Center for Nuclear and High Energy Physics provided salary support for sixty percent of this work while the rest came from the continuing Department of Energy grant at Virginia.
In March 1993 the major components were shipped to SLAC. The target will be installed in end station A for operation in experiment E-143, a precision measurement of the spin structure functions, and , of the proton and neutron. The experiment is scheduled to run in the Fall of 1993.
The Universities of Basel and Virginia have been developing an improved method of electron beam polarimetry. The new technique involves magnetizing the iron foil perpendicular to the foil plane with a large field (4 Tesla). The target magnetization is continually monitored by a polarized laser beam.
The majority of the system has been procured with funds provided by the University of Basel, and is presently being tested at Basel. The total funds contributed at this time toward equipment for the polarimeter amount to $146K. In addition CEBAF has refurbished the large quadrupole necessary for separation of the Möller electrons. The items that remain to be built are the scattering chamber, the vacuum transport tubes for the beam and the detectors.
Because of the deflection of the incident beam by the high field at the target, it is necessary to install a magnetic chicane upstream of the target. CEBAF has ordered the necessary magnets and power supplies, and is now working on the final design of the beam rastering system.
The work on the large neutron detector was started about four years ago. The very early start was motivated by the possibility of using a smaller version in a series of experiments at the LEGS facility at Brookhaven. A system approximately 50% of the size needed at CEBAF has been in operation at Brookhaven for the last two years. The primary components of the detector are scintillation paddles, scintillator bars (10 cm by 10 cm by 1.6 meters), photomultiplier tubes, and all the associated electronics. The detector will be returned to Virginia this year and we will increase the number of elements. We will purchase an additional 32 scintillator bars and associated electronics.
When completed the detector equipment cost will be approximately $326K. The funds have been provided by the groups from UVA and Basel.
The effort of many scientists and the expenditure of considerable funds have put us in a position to carry out the G measurement at the earliest time consistent with CEBAF's schedule. All of the items will be built and tested by the end of 1993 and we will be ready to carry out the experiment in the middle of 1994.
With the present proposal we request full approval to run this experiment early in the experimental program of Hall C.