Methods for plasma stabilization and control to improve antihydrogen production


The ALPHA (Antihydrogen Laser Physics Apparatus) collaboration creates and performs precise measurements on antihydrogen to test Charge-Parity-Time (CPT) symmetry. Prior to creating antihydrogen we must prepare the antiproton and positron plasmas to have optimal and repeatable parameters. This thesis presents the development of a new method to simultaneously control the number of particles and plasma density of lepton plasmas, developments that increased our antihydrogen trapping rate, precision physics measurements performed on antihydrogen, and other plasma studies still under development. The method to stabilize the number of particles was based on a zero-temperature plasma model, which states that the plasma's on-axis self potential and density uniquely define a plasma. It is the combination of two previously existing techniques, radial compression in the Strong Drive Regime (SDR) with Evaporative Cooling (EVC), thus we called it SDREVC. Experimentally this method has proven to be very robust in delivering nearly identical plasmas, and theoretical calculations applying a finite temperature plasma model indicate that temperature effects in our operating regime are insignificant. The development took place in ALPHA's Penning-Malmberg traps, and consisted of designing and testing potential well shapes that allowed the compression and evaporation to occur simultaneously. The standard deviation in particle number of our initial load of positrons in 2016 was 24%, a fluctuation which was previously uncontrolled, but the standard deviation after SDREVC amounted to only 3%. After implementing SDREVC in our experimental routines, the stability made it possible to optimize plasma manipulations for antihydrogen production runs and increase our antihydrogen trapping rate by approximately a factor of 20. This increase in the trapping rate played a major role in our recent measurements of the hyperfine transition and 1S-2S spectroscopy of antihydrogen, and the 1S-2S spectroscopy measurement is now one of the most precise tests of CPT symmetry.

Celeste Carruth

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