Positron Accumulation

The Positron Accumulator has a trap composed of a 0.14 T solenoid magnet and 7 cylindrical electrodes. The first two electrodes are narrow, with a diameter of 12.7 mm each. The third electrode has a diameter of 30.5 mm, and the last four electrodes are the widest, at 200.7 mm each. Pure nitrogen gas is introduced into the trap through a gas inlet near the second electrode. The gas slowly diffuses downstream and occupies the entire trap volume. The three-stage electrode stack with varying diameters causes a pressure gradient to build up within the trapping volume. Nitrogen acts as a buffer gas and positrons bouncing axially back and forth in the trap lose energy to the gas molecules through collisions.

By applying appropriate potentials to the electrodes, the positrons over time are confined in the third stage of the trap. Since the fourth electrode is 6-way segmented, the rotating wall technique can optionally be employed to compress the positron cloud further, something that also increases the lifetime, as the cloud has a natural tendency to expand.

Once accumulated, the positrons may be ejected from the Positron Accumulator and sent to either a diagnostic station to be imaged or directly to the ALPHA 2 or ALPHA-g experiments.