The Research Of Impedance Matching For ICP Source

Inductively Coupled Plasma Source plays an important role in Atomic Emission Spectrometry (ICP-AES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). They are very powerful techniques for quantitative and semiquantitative elemental analysis. Because of its sensitivity, low limits of detection and isotope ratio measurement capability, ICP-AES and ICP-MS are employed in environmental detection, food security, pharmaceutical science, geosciences and polymer chemists. In ICP source, the maximization of RF power transfer between RF generator and plasma calls for accurate knowledge of the plasma impedance. During the plasma ignition phase, the effective impedance of plasma varies from almost an open circuit to a very low impedance in a matter of seconds. So the impedance matching technique is an essential part in generating and stabilizing ICP discharges operated at fixed frequency 27.12MHz. Because of the weaker capability of endure reflected power, all of impedance matching issues for all-solid ICP source have been researched in this thesis.This thesis investigates impedance matching for inductively coupled plasma source, and consists five parts altogether.In the first part, the source of thesis topics, research purposes and research content are present firstly. The characteristics, configuration and developing history of ICP source are introduced. And then, the current research status and developed situations at home and abroad are introduced. Finally, a list of the major research content of the thesis is displayed.In the second part, transmission line theory and impedance matching principle are introduced. First, the hypostasis of transmission line theory is analyzed from the perspective of electromagnetic waves and electromagnetic fields. And then, impedance matching principle is explained from the perspective of electronic circuit. Smith Chart used for calculating impedance matching in RF and microwave area is introduced.In the third part, as a key part of ICP source, some circuit models in RF power are analyzed, including HF signal source, power amplifier and power combiner. The experiments of power amplifier and power combiner are taken by using dummy load and RF power meter. And the result of experiment shows the correctness of design proposal.In the fourth part, the design proposal of load matching box is introduced, including impedance matching network and phase detector. By means of emulating the impedance of load coil and plasma in Smith Chart, the method of reducing reflected power during the plasma ignition has been chosen. Auto impedance matching control arithmetic is taken to improve energy transfer efficiency and system stability. And the result of long time stability experiment shows auto impedance matching function makes excellent effect.In the fifth part, the process and result of the project are summarized, the shortages during research and development are pointed out, and the prospect of ICP source is put forward.There are three innovations in this thesis, including design proposal of circuit model in RF power and load matching box, impedance control method during plasma ignition, auto impedance matching function.