Experimental observations of resistive cooling in a Penning trap

Large numbers of anitprotons cooled by LEAR (CERN) to 2 MeV and subsequently cooled to a few hundred eV must be brought to much lower velocity in order to measure their gravitational acceleration by the earth. A sufficient number of antiprotons near an end-point speed of 5 m/s will be available if about 105 anti p's per extraction are in a thermal distribution with an average energy of about 10 K. Passive (resistive) cooling is a well-understood and previously demonstrated method which may be extended to achieve such a velocity distribution. This research demonstrates the viability of such a cooling method. By using a superconducting resonant coil with a 4 K Penning trap, resistive cooling of He+ ions is observed, with a minimum cooling time constant of 1.8+0.5-0.2 seconds. This value translates into an H+ or anti p cooling time constant of ∼0.5 seconds