Computer Based High Signal-to-noise Ratio Langmuir Probe System

Langmuir probe possesses a lot of advantages in plasma diagnostics, such as simple equipment and operation, strong diagnostic ability, acquiring rich information etc, so it takes an important role in plasma diagnostics. But there are also some disadvantages need to be improved.Three noise elimination methods in Langmuir probe diagnostics were reviewed. Integrate-and-dump techniques: using integrate-and-dump network, which can suppress fluctuant noise effectively; filter: a filter using a translation line formed by a cascade networks has been developed to reject the rf(radio-frequency) noise; differential amplifier: using dual-cable circuit and differential amplifier, the induced noise due to the RC characteristic of coaxial cables can be eliminated effectively. The methods include noise elimination principles, noise elimination equipments and experiment results.In this paper, we designed a new Langmuir probe system based on integrate-and-dump network. Novel features of the system include: the use of integrate-and-dump techniques to implement the process of analog-to-digital conversion and to provide effective noise suppression; increase signal-to-noise ratio dramatically; and use data processing card to communicate with a host computer. Successful operation of the system has been demonstrated in the electrically noisy environment of an ECR plasma source.