Evaporative Cooling of Antiprotons to Cyrogenic Temperatures in a Penning Trap

Evaporative cooling has proven to be an invaluable technique in atomic physics, allowing for the study of effects such as Bose-Einstein condensation. We present the first application of evaporative cooling to charged particles stored in a Penning Trap. We have achieved cooling of a cloud of antiprotons to a temperature as low as 9~K, two orders of magnitude lower than ever directly measured previously [1]. Our measurements are well-described by appropriate rate equations for the temperature and number of particles. The technique has direct application to the ongoing attempts to produce a trapped sample of antihydrogen, where the trap depths are extremely shallow ($\sim 0.6~\mathrm{K}$ for ground state atoms). \newline [1] Andresen, G. B., \textit{et al} (ALPHA), Phys. Rev. Lett. \textbf{105}, 013003 (2010)