A reader points me to an Ad Astra Rocket announcement of the results of a PhD research study into the behavior of the magnetic nozzle for the VASIMR electric propulsion system. The results are important for maximizing thrust from the engine: Ad Astra’s Christopher Olsen Presents Groundbreaking VASIMR® Result in PhD Thesis Milestone – Ad Astra Rocket – Feb.2.2013.pdf (pdf).