sentences:  Through the 1980s the estimated energy required to reach ignition grew into the megajoule range, which appeared to make ICF impractical for fusion energy production.For instance, the National Ignition Facility (NIF) uses about 420 MJ of electrical power to pump the driver lasers, and in the best case is expected to produce about 20 MJ of fusion power output.Without dramatic gains in output, such a device would never be a practical energy source.