sentences:  The improvement in efficiency can be dramatic; existing experimental devices operate at about 10% overall efficiency, and it is believed "near term" devices will improve this as high as 20%.Further research in the fast ignition approach cast serious doubt on its future.By 2013, the US National Academy of Sciences concluded that it was no longer a worthwhile research direction, stating "At this time, fast ignition appears to be a less promising approach for IFE than other ignition concepts."