Plasma Diagnostics

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Presentation Description

we can study different quantities of plasma by various method & Instruments; Here i have mentioned langmuir probe. structure & its I-V trace at primary information.

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Presentation Transcript

Plasma Diagnostics : 

Plasma Diagnostics 1 Abhishek A. Gor (248) Plasma Diagnostics

Plasma diagnostics : 

Plasma Diagnostics 2 Plasma diagnostics Research about the tools & methods for the research in plasma is the main objective of plasma diagnostics. Various methods & Instruments are developed in plasma physics.

Various quantities of plasma : 

Plasma Diagnostics 3 Various quantities of plasma Nature Number density of particles Speed & Energy of particles Collision frequency Magnitude of Electric &Magnetic Field.

Langmuir probe : 

Plasma Diagnostics 4 Langmuir probe

Langmuir probe : 

Plasma Diagnostics 5 Langmuir probe Langmuir-probe, named after their famous inventor, allow us to infer plasma-density and electron-temperature from simple electrical measurements.

Slide 6: 

Plasma Diagnostics 6 Entire probe: length=66.5cm Probe tip: diameter=0.130cm

Construction of probe : 

Plasma Diagnostics 7 Construction of probe Probe shaft:- Stainless steel body Teflon plug 2 Metal caps Copper wire Glass tubing SMA co-ax connector Probe tip:- Tungsten wire Glass insulation Aluminum covering Ceramic casing (protects from plasma heat)

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Plasma Diagnostics 8

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Plasma Diagnostics 9

Probe : 

Plasma Diagnostics 10 Probe The cylindrical probe-tips are made from high-melting materials, usually tungsten. The probe area is of the order of a few (mm)2. They are embedded in AlO3-ceramics for electrical insulation.

Slide 11: 

Plasma Diagnostics 11

Langmuir probe : 

Plasma Diagnostics 12 Langmuir probe When probe is immersed into a plasma, it is exposed to a large flux of ions and electrons. This flux depends upon the density and the temperature (Thermal velocity) of the particles.

Langmuir probe : 

Plasma Diagnostics 13 Since the thermal velocity depends upon the mass of the particles, the electron-flux usually is much higher then the ion-flux. Due to high electron flux we assume the probe as negative potential Uf (thus repelling the electrons) to maintain its charge-balance. Langmuir probe

Slide 14: 

Plasma Diagnostics 14

Slide 15: 

Plasma Diagnostics 15

Langmuir probe : 

Plasma Diagnostics 16 Langmuir probe As long as the surface is biased sufficiently negative with respect to the plasma, the electrons will be repelled and one measures a (constant) negative current (the ion-saturation-current) determined by the thermal flux of the ions. From this current we can deduce the the ion-density.

Langmuir probe : 

Plasma Diagnostics 17 Langmuir probe When the voltage approaches the plasma-potential the electron-flux increases according to the boltzman-relation: n/n0=exp(-eU/kBTe) Thus in a logarithmic plot of the characteristic we find a linear slope which yields the electron-temperature.

Langmuir probe : 

Plasma Diagnostics 18 Langmuir probe The equation for the electron temperature & electric current is given.

Langmuir probe : 

Plasma Diagnostics 19 Langmuir probe Similarly the equation of charge density is also given. In case of neutral particle measurement of pressure is enough. i.e. (p=nkt)

Langmuir probe : 

Plasma Diagnostics 20 Langmuir probe All equations are for the Electron temperature, Electric current, Charge density are normalized from I-V trace.

Langmuir probe : 

Plasma Diagnostics 21 Langmuir probe Thus, langmuir probe is one of the important methods in plasma research.

Thank You……. : 

Plasma Diagnostics 22 Thank You……. Abhishek A. Gor (248)

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Plasma Diagnostics 23

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