Antimatter Plasmas and Antihydrogen Physics

Several antihydrogen experiments at CERN synthesize antihydrogen by mixing positron and antiproton plasmas confined in superimposed Penning-Malmberg traps. The antihydrogen atom itself can be confined by a superimposed minimum-B neutral particle trap. For example, in the ALPHA experiment, starting from roughly 0.1-0.5 trapped antihydrogen atoms per attempt, the antihydrogen trapping rate has increased by a factor of over 20 by implementing new techniques for plasma control. As many as 1000 antihydrogen atoms have now been simultaneously confined. Future developments in nonneutral plasma techniques, such as cavity cooling, may allow for trapping at substantially lower magnetic field strengths, thereby enabling further improvements in ALPHA's precision physics measurements. Using ideas from Fermi acceleration, a charge neutrality measurement has yielded a bound on the magnitude of the charge of the antiatoms to a precision of 0.7ppb of the positron charge. By modeling orbits as the trap fields are turned off, ALPHA set crude bounds on the gravitational properties of antihydrogen, with the ratio of gravitational mass to inertial mass M constrained to approximately +/-100. Building on the techniques developed over the last decade, the ALPHA Collaboration is deploying a new apparatus, ALPHA-g, to measure antimatter gravitation to 1\% precision. In this talk I will present the recent advances in nonneutral plasma physics that enable antihydrogen physics studies and cover the charge neutrality measurements and future gravity experiments.