Patch Potential Measurements in a Penning-Malmberg Trap

In the ALPHA-2 spectroscopy trap, positron plasmas heat more quickly after the trap is illuminated by laser light. In the new vertical ALPHA-g gravity measurement trap, positron plasmas expand to the trap wall in seconds, preventing antihydrogen formation. By measuring the displacement of electron plasmas from the center of the trap, we verify that these issues are due to variations in the electric potential along the trap surface (patch potentials). We also find that patch potentials can be worsened by laser light, that directing an electron beam toward the trap wall changes patch potentials, and that warming the trap can restore patch potentials to a nominal persistent magnitude.