The Production and Acceleration of Metal Ions in the Harwell Variable Energy Cyclotron

The range of ions accelerated by the V.E.C. has recently been extended to metal ions. For example, a 5 to 10 μA beam of 48 MeV 58Ni6+ is now available and has been used by a customer. This beam has become possible as a result of success in adapting the normal ion source for the production of metal ions. The problem was to add to the ion source a controlled source of metal vapour without increasing the size of the ion source or adding separate oven heaters and controls. This has been achieved by inserting a graphite liner into the existing ion source chimney, the metal being embedded in the liner and out of direct contact with the arc. Provided the arc power exceeds a few kilowatts, the metal becomes molten and the vapour diffuses through the graphite into the arc which then becomes self-sustaining. With nickel (the most widely tested so far), intensity at full radius of between 10 and 20 μA of 6+ ions and 1μA of 8+ ions is readily obtained and source life averages about 4 hours. Other metals such as cobalt, iron, chromium and copper give similar results.