Recent progress on the ATHENA Positron Accumulator

The Positron Accumulator for the ATHENA anti-hydrogen experiment at CERN, Geneva has recently been upgraded with a new 50 mCi /sup 22/Na beta /sup +/-radioactive source. Following this, rapid progress has been made in optimizing and characterizing the properties of the positron plasma. The rotating wall technique has also been implemented in the accumulation region and has been shown to lead to compression of better than a factor of 10 in density and markedly increased lifetimes, even when using the N/sub 2/ buffer gas as a cooling gas. Using these techniques we have routinely accumulated up to 2 * 10/sup 8/ positrons in a few minutes. The positron plasma has a FWHM of only 3-4 mm when using the rotating wall which compares with a FWHM of 15 mm without the rotating wall. (13 refs).