In the Pulsotron August test campaign I measured using langmuir probes to measure at the same time than optical methods using silicon shottky photodiodes. As result it was better to measure the ion temperature using the photodiodes.

I can advise you when the test report (with plots) is released here in researchgate.

There are many possible approaches to measure plasma parameters - it all depends on what you want to measure and which plasmas you are looking at. Here are some examples:

• electrical probes
• magnetic probes
• optical spectroscopy
• mass spectroscopy
• interferometry
• laser-induced flourescense
• thomson scattering
• ...

brilliant! thanks Javier, much appreciated! :) We have been using optical methods to look at laser ablation plasma and encountered some challenges with that, so Im very keen to learn more about your experiment and the results of your comparison - my motivation for asking this question is that we're keen to measure spatial variations in plasma density and temperature within our RF plasma chamber (its about 50cm in diameter with the antenna in the centre), and seeking alternatives to Langmuir Probe methods.

Jamie, try for hairpin probe and microwave spectrometer as well.

Best starting reference for plasma diagnostics is Hutchinson's 2nd Edition.

Retarding field energy analyser is one more device which is more suitable in case of RF plasma since the first grid eliminates the RF fluctuations and other RF noise in the plasma. You can make a miniature RFEA and study the ion / electron energy distribution across the plasma. Your plasma chamber is large, so you can easily do this. Langmuir probe is complex in RF environment.

If you are looking at atmospheric-pressure plasmas, chapter 8 of the book "K. H. Becker, U. Kogelschatz, K. H. Schoenbach, and R. J. Barker, Eds., Non-Equilibrium Air Plasmas at Atmospheric Pressure. Bristol,: Institute of Physics Publishing, 2005" provides a comprehensive summary of the various techniques, with many examples.

I think what Javier Luis López has is RF plasma which operates in low pressure.

I am sorry for the wrong name.  It is Jamie S Quinton instead of Javier in my above line of answer

We typically operate at pressures of around 10-100mTorr, though I will look into everything that is suggested as we're keen to learn more.

It is not clear either single probe or double probe. You can also use triple probe to measure floating potential, electron density and temperature as a function of time in time-varying discharges.

I used three Langmuir isolated probes to measure plasma speed and another three optical sensors aligned with the Langmuir. We found that there is a lot of resistance variation in the plasma. Also we had problems because there was cross conduction between the probes (the three probes were isolated between them but the plasma acted as a conductor between the Pulsotron-2 plasma ionizer electrodes and the probes) and because the  low resistance of the plasma was out of the range of our electronics, we need a different configuration to solve such problems and using a logarithmic amplifier. As result the optical sensors were a lot more accurate in our project at the moment.

Actually we work at 1Bar

Use non-contact methods wherever you can.

We released the August test report, there you can find a plot where it is compared results obtained from Langmuir probe and photodiodes (chapter 5, paragraph 9)

Technical Report Pulsotron-2 August 2014 Technical Test Report

I know that microwave transmission is a technique for measuring electron density, but it work only for a limited interval of electron density.

Optical emission spectroscopy can be used as diagnostic tool. Electron temperature can be determined from Boltzmann plot of emission intensity of several spectral lines. Electron number density can be obtained from Stark broadening of spectral line after de-convoluting the contribution comming from other broaening mechanisiums. This method is non perturbing and more favoured for reactive plasmas.

Thanks Abdul, I will look for.

Gianpiero, it is a good idea, you may say that the electron (or ions) shields the electromagnetic wave?, would 2.45Ghz or 890Mhz go well? (it exists plenty high power RF modules)

I need also a good filter in the receiver. The problem is when receiving a pulse in a LC filter reacts generating a wave which frequency is the same it was designed. LC or wave guide flters has bad response to high speed variying wave amplitudes.

I collaborate to an experiment, using MW transmission. The technique was used in princeton by the group of Richard Miles. I do not experience, but I attach a paper I was coauthor where different measurements on electrons where performed.

we use spectral and shadow methods in our experiments. they are bouth undisturbing but need some special equipment. 

Article Diagnostics of average temperature fields and electron densi...

Article Shadow photometric method for measurements of electron densi...

Dear Jamie S Quinton,

An external voltage in Langmuir probe can be used for plasma diagnostics as you mentioned. By analyzing the current drawn by the probe as function of the applied potential, one can determine the electron temperature, the electron density, the floating potential, and the plasma potential.

There are other equipment’s little different methodology could be used for plasma diagnostics of plasma bulk and film growth monitoring such as; Mass spectrometry, Ion energy analysis, Optical emission spectroscopy, Absorption spectroscopy, Laser-induced fluorescence, Plasma impedance, Spectroscopic ellipsometry, Interferometry, Quartz crystal microbalance.

The plasma bulk diagnostic techniques can be classified in many ways; for example; (1) by the particles they measure (electrons, ions, radicals, photons, etc.); (2) by being active (introducing additional signal into the system like a laser beam in laser-induced fluorescence(LIF) or external voltage in Langmuir probes); (3) by being passive (sampling neutrals in mass spectrometry or emitted light in optical emission spectroscopy(OES)); or (4) by the parameters they can help to assess (ne, nR, etc.).

Plasma diagnosticsare normally innovative and often measure a physical process from which information about a particular parameter can be deduced. Two plasma diagnostics types can be; one is active and another is passive plasma diagnostics. In active plasma diagnostics, the plasma is probed (via laser beams or microwaves) to see how the plasma responds. With passive plasma diagnostics, radiation and particles leaving the plasma are measured; this knowledge is used to deduce how the plasma behaves under certain conditions.

Here, a small amount of probe atoms mixed in the plasma are excited to metastable states by an electric discharge. They are further pumped up to the Rydberg levels by a laser beam, followed by decay to intermediate levels due to collisional transitions.

I have summarized with couple of equipment’s and classification methods can be used for plasma diagnostics. Hope this may be helpful for you.

Ashish