I am attempting to build a triple Langmuir probe and will need to select a power supply which can achieve the potentials and currents required.
I have found some literature stating bias potentials of +/-120 Volts, but these potentials were for use of a triple Langmuir probe in "voltage mode". I plan to use the probe in "current mode" - the literature states this is a more ideal setup for measurements of a pulsed plasma. Are the bias voltages required to be this high for a current mode measurement?
My plasma density is assumed to be in the range of 1e8-1e12 [cm^-3] with the electrons magnetized. The Larmor radius of the ions may or may not exceed the radius of the plasma chamber.This can be adjusted.
An additional question for anyone experienced with the use of this diagnostic. Is there a lower range of electron/ion temperatures which this diagnostic can resolve?
the bias voltage of such kind of probes is generally maximum +/- some ten volts (provided that you don't have unusually high plasma potentials, which can be the case if you are working with large additional electrodes with high bias in a plasma).
For probe measurements where you vary the voltage pointwise you will see when you reach the saturation region of your probe, so this is then about the voltage where you can stop increasing the potential.
It might be usefull to use a source meter or a four-quadrant power supply, though, as those usually allow to go directly from negative to positive potentials without changing the polarity of the power supply manually.
Thanks for the response Johannes.
I expect the RF produced plasma electron temperature to be no higher than 5eV, however because this will be a Helicon source some RF potentials will also exist within the plasma and may be much higher than 5eV.
Unfortunately I will not have access to a source meter at the facility for this particular measurement, but I will have access to a triple output power supply which ranges from 0-30V 0-3A for two of the outputs and 0-5V,3A for the third channel...which may not give me the capabilities required as I will need to change the polarity of one of those outputs somehow.
It appears using batteries for this measurement doesn't seem feasible if I am going to need to vary any voltages.
hmm, I would try with the 30 V power supply first, you might be lucky - however, you will have to change polarity manually.
Dear Nathan,
For Langmuir probe measurements in RF discharge plasma please check a book Raizer Yu P, Shneider M N, Yatsenko N A "Radio-frequency Capactive Discharges" (Boca Raton: CRC Press, 1995), Chapter 4. The question of RF discharge physics discussed in the other chapters of the book may also be helpful.
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