This should dent Musk's ambitions for Mars, but one wonders how this will be more successful than the other nuclear thermal rocket designs.
"Russia’s plasma engine could reach Mars in 30 days, drastically reduce space travel time"
https://interestingengineering.com/space/russia-plasma-engine-could-reach-mars-early
"This engine utilizes hydrogen as fuel, accelerating charged particles—electrons and protons—to a remarkable speed of 100 km/s (62 miles/s)."