Double Probe Diagnosis of Surface-Wave Sustained Plasma Column

Abstract

A technique has been developed to diagnose the plasma column generated with Surface-Wave sustained plasma (SWP) source under different conditions. Principal physical properties, ion density and electron temperature were studied. Influence of several factors, such as the microwave power, the gas pressure on the ion density, the electron temperature was studied. The axial and radial distribution of electron temperature and ion density was also researched. The results show the Surface-Wave sustained plasma column is able to generate plasma of about 3ev electron temperature and 1011 cm-3 ion density. It is found in the experiment that at 2 Pa in gas pressure and 60 W in input power, the ion density and electron temperature are up to 6.8×1017 m-3 and 2.8 ev at 200 mm, 1.5×1017 m-3 and 2.2 ev at 1000 mm from the base. It is also found that the physical properties can be changed by adjusting the microwave power and the pressure. So, the Surface-Wave sustained plasma column is suit for the application of plasma antennas and other relative applications. Introduction Microwave and RF plasmas are finding increasing use in many fields. [1] A plasma column is constructed from glass tube filled with low pressure gases with the SWP source. This discharge style has many merits in plasma antennas [2]. The principal properties of the plasma, ion density and electron temperature have much influence on the application of plasma antennas [3, 4]. The diagnosis and the diagnosis method of the surface wave sustained plasma are not new [5-7]. However the diagnosis of the plasma column sustained by electromagnetic surface-wave, which is suit for the plasma antennas and lamps, is not done yet. So, it is necessary to study the properties under different conditions to guide the research in plasma antennas and plasma lamps. This paper mainly researches in the diagnosis of SWP plasma column. The Langmuir Probe double probe is used as the diagnosis technique in the whole paper. The influence of microwave power, the gas pressure on the ion density, the electron temperature was studied. The axial and radial distribution of electron temperature and ion density was also researched. Experimental Setup Figure 1 shows the schematic of the surface-wave sustained plasma experimental apparatus. It contains microwave generator, the glass vacuum room and the vacuum systems. LC-box [1] is regarded as the pump method. A copper cylindrical sleeve wrapped around the base of an electrodeless tube containing a low-pressure noble gas (typically, argon at ~10 mTorr). A matching network was employed to match the coupler to the generator. The wave generator produce 100 MHz microwave, passing through the glass window, and getting into the vacuum room to excite the plasma. The plasma tube, with 24 mm in diameter and 1200 mm in length, is made of glass. The apparatus can produce high density plasma without magnetic field. By adjusting the button of the wave generator, the reflected power can be changed. The base vacuum of the setup is Pa 10 4 3 − × . High purity gases act as the working gases. The gases were controlled with MFC. The input power of the wave generator is 1030 2nd International Conference on Electronic & Mechanical Engineering and Information Technology (EMEIT-2012) Published by Atlantis Press, Paris, France. © the authors tested by the power meter. The power is 20~80W. The Langmuir double probe which locates at every 200 mm from the base is made of tungsten and glass. The size of the tungsten lines in the double probe is 0.5 mm in diameter and 6 mm in length. The depth into the plasma can be changed by moving the probe tubes. The data can be attained from the V-I Figureures in different conditions. 30 40 50 60 70 80 0 1 2 3 4 5 6 7 8 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0