研究目的

To investigate the influence of magnetic filter and magnetic cage in negative ion production in helicon oxygen plasma.

研究成果

Electronegative oxygen plasma in a helicon discharge has been characterised by using a two-probe technique using Langmuir probe measurements. Comparative changes in the charged particle densities, electron temperature, radial variation of electron density, and negative ion fraction in the expansion chamber of the HeliPS with and without using the magnetic filter and multi-dipole magnetic cage are analysed and studied. The negative ion, positive ion, and electron densities scale linearly with RF power except at the mode transition point where the jump in the density occurs. It has been found that the negative ion density becomes higher than the electron density or the negative ion fraction becomes greater than 1 even without the magnetic cage and the magnetic filter when the temperature ratio c is 10. By using the magnetic cage and the magnetic filter, the negative ion density increases with RF power and with the working pressure, and the highest negative ion fraction is found to be around 8 for c = 10 when the pressure is 1 × 10?2 mbar at the RF power of 1500 W. This shows that the magnetic cage and the magnetic filter can create a significant difference in the production of negative ions. Also, for the efficient production of negative ions, the RF power and the working pressure of the system at the given magnetic fields need to be optimised.

研究不足

The measurement of the negative ion temperature is difficult, and the value of c (Te/T?) has to be assumed. The electron temperature shows approximately no change with applied RF power, and the negative ion density depends on the negative ion temperature apart from electron temperature.