Magnetic Field Studies for Neutron EDM Beam Guide

Background The neutron Electric Dipole Moment (nEDM) project designs and constructs the apparatus required to execute the nEDM experiment, which will be located at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). Cold neutrons will be transported over a distance of~33 m and the goal is to combine the neutron-guide with a highly efficient polarizer. Two different schemes are being considered, a reflection-only (R) and a transmission-reflection (T-R) polarizer. While a reflection-only device is based on standard technology, the T-R polarizer is a new idea which could potentially increase the neutron flux into the IIEDM target cells by -40%. The T-R device will contain rernanent field magnetic super-mirrors, which have to be magnetized periodically. In addition, the geometry of the T- R device requires a magnetic field reversal over a very short distance. Scope This effort is part of the overall engineering design optimization for the nEDM project. We will develop a magnet that will generate anti-parallel fields of up to 200-300 0 within a short distance of each other over a time period of up to 1 ms. Two different techniques are being considered and will be tested: a) an Al foil septum placed. between the two regions alternating field, and b) and external quadrupole constructed of two current busses above and below the surface dividing the two regions. We will test different magnetization procedures using the Surface-Magneto-Optic-Kerr- Effect (SMOKE). The idea is to measure the change in linear polarization and ellipticity of linearly polarized light after reflection from the magnetized super-minor. This method could serve as a very useful diagnostic tool to check the uniformity of the magnetization. Absolute calibrations will have to be performed with neutron beams. Tasks The subcontractor will complete the following portions of the nEDM project by 09/30/2008: WBS Description Deliverables A) A measurement of the time and spatial profile of the magnetic field needed to magnetize a sample remanent supermi.rror polarizer. B) Experimental results on the feasibility of generating pulsed fields of the magnitude required by (A), using the foils septum and external quadrupole methods. C) Results on the feasibility of using the SMOKE to measure the magnetization of remanent supermirror polarizers. These deliverables will provide a key piece of information to help decide between using an R or T-R polarizer device.