Reim, G, Phase Four says its RF thruster matches Hall effect performance, Aviation Week & Space Technology, 31 July-13 August 2023, p 48

In US, Phase Four has devised a radio-frequency thruster for very low orbit spaceflight. Radio-frequency energy heats a propellant such as xenon, krypton, iodine, water vapour, nitrogen or oxygen into ionized plasma that is then ejected by means of a permanent magnet. Performance is said to be equal to the conventional Hall-effect system used in satellite operations, and the permanent magnet instead of an electromagnet improves simplicity. Furthermore, an RF thruster could handle atmospheric nitrogen, oxygen and atomic oxygen then use them as propellants.