Production of ultrahigh vacuum by helium glow discharge cleaning in an unbaked vacuum chamber

For the production of ultrahigh vacuum in an unbaked vacuum system the effect of helium glow discharge cleaning as a wall conditioning technique has been investigated experimentally. A test chamber made of 304 stainless steel was constructed. Before the pump-down of the chamber it was initialized by air exposure. Then the discharge cleaning was done at the constant helium ion fluence of 0.5 Coulomb/cm(2). As an effect of the discharge cleaning it is shown that the pumping time to attain the pressure of order of magnitude of 10(-8) Torr is shortened after the discharge cleaning by one fourth compared with the pumping time without discharge cleaning. But the ultimate pressure at the pumping time of 72 h after the discharge cleaning is rather the same as that without discharge cleaning. The role of helium glow discharge and technical aspects to be taken care for the production of ultrahigh vacuum in an unbaked vacuum system are discussed. (C) 1997 Elsevier Science Ltd. All rights reserved.