Energy Secretary Steven Chu announced that a DOE official is stepping down. (Evan Vucci/AP)

In an e-mail to department employees, Chu said Arun Majumdar, the acting undersecretary of Energy and the White House’s nominee to permanently fill the slot, is leaving next month. “Arun has been an invaluable resource to me, to the Department, and to the Administration, and we will miss his leadership,” Chu wrote.

Majumdar also is the director of the Advanced Research Projects Agency-Energy, an agency modelled on DARPA within the Energy Department, created in 2009 to encourage research and development of new technologies.

Eric Toone will replace Majumdar at ARPA-E and David Sandalow has been named as the Acting Under Secretary of Energy, Chu announced. Toone is ARPA-E’s deputy director of technology; Sandalow is the department’s assistant secretary for policy and international affairs.