Measurements of electron temperature in radio frequency capillary helium glow discharges

Non invasive emission spectroscopy is used to measure the electron temperature in a radio frequency driven (28.4 - 36.6 MHz) capillary (r=0.8 mm) helium discharge plasma column, over the pr range (the product of the pressure p and the inside tube radius r) from to Torr cm. The results show that decreases significantly with increasing pr and is weakly dependent on frequency. The values of are few times lower than those reported in the case of low-pressure, capillary direct current helium discharges.