Is it ensure, insure, or assure?
German-born American physicist who shared one-half of the Nobel Prize for Physics in 1989 with the German physicist Wolfgang Paul. (The other half of the prize was awarded to the American physicist Norman F. Ramsey.) Dehmelt received his share of the prize for his development of the Penning trap, an electromagnetic device that can hold small numbers of ions (electrically charged atoms) and electrons for periods of time long enough to allow their properties to be studied with unprecedented accuracy.