Investigation of the properties of a MHD plasma valve

An ion beam has quite different vacuum requirements in different sections of an accelerator. Behind a stripper gas or after interaction with a gas target the vacuum conditions are poor, whereas in an accelerator module or especially in a storage ring the residual gas pressure has to be orders of magnitude better. As a new device to allow an ion beam to enter sections of different pressure we investigate a new kind of plasma valve [1,2]. The basic principle of the MHD (magnetohydrodynamic) valve uses the Lorentz force acting upon an ionized gas between an ultra high vacuum chamber and a gas reservoir up to a pressure of several mbar. When activated, the MHD valve is composed of a discharge plasma that fills a chamber with crossed electric and magnetic fields. Gas flowing from the gas tank into the UHV chamber is ionized by the discharge. The Lorentz force acts now upon the charged particles due to the crossed electromagnetic fields and repels them back into the gas chamber. By proper adjustment of the Lorentz force, the valve can allow any desired gas flow between the two chambers, or fully block any exchange of gas. The MHD valve can even act as an efficient vacuum pump to improve the vacuum conditions in the high vacuum section. High energy particles reaching the valve from the high vacuum side will penetrate the fields and the plasma. For heavy ion beams the MHD valve would therefore act like a window. The following Figure 1 shows one of the latest measurements of the pressure gradient between two gas chambers.