A 30 Years Perspective on the "Rotating Wall" Technique

The rotating wall technique enables essentially unlimited confinement time of non-neutral plasmas containing 10⁹ – 10¹⁰ charged particles in a Penning-Malmberg trap. The applied rotating wall electric field provides a torque that counteracts background drags, resulting in radial compression or steady state confinement in near thermal equilibrium states for period of weeks [1].

I will give my perspective on how the technique has evolved after being implemented in many laboratories around the world. In particular the “strong drive regime” [2] discovered by Cliff Surko’s group, and the “strong drive regime” combined with “evaporative cooling” developed in Joel Fajans’ group will be presented [3]. These improved rotating wall techniques provide unprecedented reproducibility of positrons plasmas, where density and particle number are controlled to 1% with a significant increase of anti-Hydrogen formation at CERN.

The RW technique is now used at 27 institutions world-wide, for studies of plasma physics, atomic physics, fundamental constants, quantum computing, and accelerator physics.