A new compact mass analyzer for extracting H− in a magnetized sheet plasma

Abstract

Magnetized thin sheet plasmas have been developed and used to generate H⁻ ion beams for various applications. The advantage of which is that the magnetic field that confines the sheet plasma separates the low energy electrons from the high energy electrons which is important in the volume production of H⁻ ions. The low energy electrons together with hydrogen create the negative ion and fast electrons destroy these negative ions. Therefore, the separation of these regions is highly advantageous in H⁻ production.
The previous method of extracting negative ions in a sheet plasma has a few setbacks. The solenoid that it uses to create magnetic field lines for mass separation is quite difficult to make and the fact that it uses DC current operating at a few amperes makes it impossible to monitor the negative ion flux for prolonged periods of time. It can also be seen that the magnetic field that it emits interferes with the magnetic field of the Helmholtz coils, which tends to distort the sheet plasma. More importantly, measurements 0 − 4.0 cm distances from the sheet plasma cannot be obtained because of its design limitations.
A new compact mass analyzer, which is simply a Wien filter, was designed and constructed to overcome these difficulties. The negative ions of the sheet plasma are extracted into the device and mass separated using its own deflector plates and the magnetic field produced by the Helmholtz coils ofthe sheet plasma. The new mass analyzer was designed such that it can be moved in a direction perpendicular to the sheet and it easily fits into any 2 ¾" standard knife edge flange. This device was first tested in the Sheet Plasma Negative Ion Source (SPNIS) of the Plasma Physics Laboratory, National Institute of Physics, University of the Philippines Diliman, Quezon City, and its initial results are presented in this paper.