Patch Potential Induced Particle Loss in an Antimatter Penning-Malmberg Trap*

Even clean, gold plated, grounded metal surfaces inevitably generate anomalous electric fields. These fields are due to ``patch potentials,'' thought to be grain boundaries and charged oxide layers on the metal surfaces. These fields break the cylindrical symmetry of a Penning-Malmberg trap, and are investigated as the possible cause of observed anomalous antiproton escape, particularly in shallow traps with few antiprotons. An in-situ technique was developed for measuring the magnitude of these electric fields which involves using the patch potentials to move electron plasmas off-axis, and observing their subsequent orbit. We find fields on the order of tens of millivolts/cm. We present evidence that ultraviolet lasers used to probe the properties of antihydrogen atoms may strengthen these asymmetric fields.