| AVS 62nd International Symposium & Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS-ThA |
| Session: | Plasma Sources |
| Presenter: | Sofia del Pozo, TWI Ltd. and Brunel University, United Kingdom of Great Britain and Northern Ireland |
| Authors: | S. del Pozo, TWI Ltd. and Brunel University, United Kingdom of Great Britain and Northern Ireland C.N. Ribton, TWI Ltd., United Kingdom of Great Britain and Northern Ireland D.R. Smith, Brunel University |
| Correspondent: | Click to Email |
Details are given of a design of a novel RF excited plasma cathode gun that generates electron beams (EBs) for material processing applications including additive manufacturing, welding and cutting. Plasma EB sources offer solutions to the main problems with conventional electron beam guns, which use a thermionic cathode. Cathode wear from thermal cycling or ion bombardment is eliminated. EB power can be controlled by RF power modulation, which avoids the need for a grid electrode, and as a result reduces beam aberration. This technology has generated interest from various sectors of industry including additive manufacturing where rapid printing would be possible due to the high power provided by the electron beam, and at the same time fast beam pulsing can control material melting.
In this work, EBs were generated at accelerating potentials between 30 kV and 60 kV with beam powers of up to 1kW. The experimental setup allowed carrying out optical emission spectroscopy measurements simultaneously with beam current measurements.
A capacitively coupled plasma was generated in a cylindrical quartz chamber with 14 mm inner diameter. An RF power signal of 20 to 50 W at 84 MHz was applied between electrodes separated by 25 to 80 mm. Electrons were extracted from the plasma chamber to the vacuum chamber (at about 10-5 mbar) through an aperture (0.8 to 1.2 mm diameter) at the end of the plasma chamber by applying an accelerating voltage. Typically argon was used but EBs were also generated using krypton, helium and air. The pressure in the plasma chamber was controlled in the range 0.1 mbar to 1.5 mbar.
Optical emission spectroscopy measurements have been carried out in order to optimise plasma parameters for higher electron emission. This plasma diagnosis technique was selected as it is non-intrusive and allows estimation of important plasma parameters such as electron density and temperature. The spectra were correlated with electron emission. Ar – II lines were found to be much intense than Ar – I lines in those plasmas of higher electron emission. It was observed that the electron beam power was increased as the plasma chamber pressure decreased in one of the plasma chamber geometries. At any one plasma pressure, the beam power increased with RF power.
Further work is currently being carried out in order to increase the power of the electron beams generated. This includes revised plasma chamber designs and particle in cell simulation of the argon plasma.