Problem while constructing langmuir probe I am working on DC glow discharges and want to construct a langmuir probe. Circuit I am using is as shown in the picture

Also, I am applying ~1KV across cathode and anode.
Problem I am facing is that I am getting discharge btw probe and cathode. Which isn't unexpected, but destroys the purpose of probe, but then how to construct langmuir probe for DC glow discharges? What should be the appropriate circuit?
 A: you probably need a current limiting resistor in the part of the circuit containing the probe, either that or a way of isolating the probe ground from the power supply ground.  
A: To get something useful with the langmuir probe you will need to match the potential of the probe to the local potential of the plasma - can you vary the Vp potential to get the full range of 0-1kV?? If you match the potential of the probe to the plasma potential then you should not get the extra discharge in my opinion, but I have not worked with this system before. From your diagram I wonder how far into the plasma your probe is and also how large it is. I suspect you may need to have a small probe shielded by some insulator pushed further in, but this is a guess. 
I strongly suggestm that you look at this (apparently freely available) dissertation on a similar experiment.
p.s. an obvious thing to check as well is that the ammeter is not somehow pulling the potential of the probe to ground.... and that Vp is connected with the correct polarity - sorry obvious things to check that you probably have already done.
A: When designing a Langmuir Probe, there are a few things that you want to keep in mind with a DC glow discharge.
(1)  The distance between the anode and cathode, and the Langmuir Probe tip's distance to each of them.
(2)  The pressure of the gas you are using.
(3)  The gas (or mixture of gases) you are using.
All three of these factors go into Paschen's Law.  Based on those three factors (plus the electrode material), you can calculate the minimum voltage $ V_b $ required to cause breakdown of the gas to a glow discharge.  This voltage is important, because the same effect occurs between either electrode, and your probe tip.  Therefore, you want to choose your bias voltage, or range of bias voltages, such that no matter what, the voltage between the probe tip and either electrode is less than the breakdown voltages between the probe tip and either electrode.
If you do this, your probe tip will never "drive the plasma" and will always be measuring the plasma produced by your source.
