Corrections and clarifications.
A table accompanying Christopher Anderson's article "Fusion research at the crossroads" (29 Apr., p. 648) incorrectly stated the length of time the JT-60-U machine at the Naka Fusion Research Establishment in Japan was closed for an upgrade. The reactor was shut down for 14 months between November 1989 and January 1991, not for a 4-year period between 1989 and 1993. The information in the table was supplied by the U.S. Department of Energy.