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Table Top Plasma Experiments

LANL Critical Skills Program

John Kline

July 10, 2002

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Outline1. Why build small experiments?

2. Different Table Top Experiments

A. Double Plasma Devicei. Waves and Instabilities

B. Non-Neutral Plasmasi. Malmburg Penning Traps

C. RF Plasmai. Capacitively Coupled

ii. Inductively Coupled

iii. Helicon Plasmas

D. Dusty Plasmasi. Planetary Rings Experiments

3. Conclusions

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Why build small plasma experiments?

• Needs: That is all you need.

• Costs: Every scientist knows that funding.

•Proof of Principle: A small experiment used to prove concepts before building full scale experiments can be limited.

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Proof of Principle

DIIID Tokamak in San DiegoOperated by General Atomics

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Proof of Principle

These experiments study fusion directly

These experiments study RF current drive at WVU

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• The biggest draw back to small Proof of Principle experiments is scaling.• Do the experiments scale up in size?• Do the experiments scale up with the plasma parameters?

•DIIID Tokamak n ~ 1 x 1015 cm-3, Te ~ 5 keV, Ti ~ 15 keV•WVU Tokamak n ~ 1 x 1013 cm-3, Te ~ 3-5 eV, Ti ~ 0.3- 1.0 eV

Proof of Principle Experiments

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Double Plasma Device

The Pickett’s Charge Plasma DeviceAt Gettysburg College

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Double Plasma Device

Plasma

Magnets

Filament

Biasing Grid

RF Power Supply

Antenna for launching waves

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Plasma Parameters:

• Plasma Densities of n ~ 1 x 109 – 1 x 1010 cm-3

• Electron Temperatures of Te ~ 1 – 3 eV

• Ion Temperatures of Ti ~ 0.2 – 0.3 eV

• Ar Fill Pressure of No ~ 1 x 10-5 – 5 x 10-4 Torr

Double Plasma Device

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Space Plasma PhysicsPlasma Physics:

• Chaos and Nonlinear Dynamics

• Potential Layers

•Waves and Instabilities

•Velocity Shear Driven

•Drift Waves

Bo

Velocity Gyro-orbit size

Density

Radius

DiamagneticCurrent

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Non-Neutral Plasmas

• Most plasmas studied are quasi-neutral, i.e. ne ~Zni

• Small electric fields, perturbations, arise only at microscopic levels due to plasma waves.

• For Non-neutral plasmas, the plasma is made up of purely electrons or ions. This produces a net electric field in the plasma.

Plasma parameters:

• Densities on the order of n ~ 1 x 106 – 1 x 109 cm-3

Temperatures of a few (1-2) eV

• Fill Pressures of < 1 x 10-6 Torr

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Non-Neutral Plasmas

• Transport and Diffusion (neoclassical and classical)

• Vortex formation and Plasma Crystals

• Capturing of positrons and anti-protons

• Auto-resonance studies

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Malmberg Penning Traps

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A) the outer cylindrical electrode, B) the inner cylindrical electrode, C) the grids, D) the annular collecting

electrode and E) the filament.

Malmberg Penning Traps

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Plasma Crystals

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RF Plasma Discharge

• Radio Frequency plasma sources use high power AC sources to generate a plasma.

• There are three types of RF plasma sources: Capacitive, Inductive, and Helicon

Research areas:

• Plasma Chemistry: For example control of N+, N2

+, N, and N2; Break down of CH1 and CO2

• Plasma Processing, both etching and deposition

• Waves and instabilities

• Textile processing

• Bacterial removal

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RF Plasma DischargePlasma Parameters: Typically operated at 13.56 MHz; Many different fill gases.

• Capacitive

• Density on order of n ~ 1 x 108 to 1 x 1010 cm-3

• Electron Temperature Te ~ 3 eV

• Fill Pressure of No ~ 0.1 x 10-2 – 1.5 x 10-1 Torr

• Inductive

•Density on order of n ~ 1 x 109 to 1 x 1012 cm-3

• Electron Temperature Te ~ 3 eV

• Fill Pressure of No ~ 1 x 10-4 – 1 x 10-2 Torr (Atmospheric)

• Helicon

•Density on order of n ~ 1 x 1010 to 5 x 1013 cm-3

• Electron Temperature Te ~ 3 - 5 eV

• Ion Temperature Ti ~ 0.05 – 1.0 eV

• Fill Pressure of No ~ 1 x 10-4 – 1 x 10-2 Torr (Atmospheric)

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Capacitively Coupled Sources

MatchingNetwork

RF Source Plasma

CapacitorPlates

Vacuum Chamber

(GEC Reference Cell)

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MatchingNetwork

RF Source

Inductively Coupled Sources

Pyrex Chamber

Antenna

Alternative Antenna

Magnets(not required)

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Inductively Coupled Sources

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Inductively Coupled Sources

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MatchingNetwork

RF Source

Helicon Sources

Pyrex Chamber

Antenna

Magnets(required)

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Helicon Sources• Magnetically enhanced RF Plasma source with driving frequency between the ion and electron cyclotron frequencies: ci << < < ce< pe.

• A helicon wave is “bounded” whistler, a right hand circularly polarized electromagnetic, wave. Wave propagation helps to enhance the density production.

• Developed in 1970 by Rod Boswell looking for left handed circularly polarized waves.

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Helicon Sources

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Dusty Plasma Experiments

A dusty plasma is created by adding small particles (~ 10 um) to a plasma. The dust particles become charged and change the plasma dynamics, as well as, create a dynamical system of their own.

Because the presence of charged dust in plasma is relevant to environments ranging from industrial plasma process devices to the space plasma environment to the edges of fusion energy experiments, the study of dusty plasmas has recently become one of the fastest growing areas of plasma physics.

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Dusty Plasma Experiments

Photomicrographs of a) glass microballoons and b) Minnesota Lunar Simulant (MLS-1), a simulated lunar soil. All samples were sieved to select a 53-63 micron grain size. The frames are approximately 200

microns square.

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Planetary Rings Experiment

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Planetary Rings Experiment

A rotating magnet is used to generate a co-rotating electric field in the plasma.

If a cloud of microparticles is suspended in the vicinity of the rotating magnet, the electric field can cause the cloud to become extended into a ring-like structure.

Experiments will focus on studying the properties of driven and self-generated instabilities in the ring plane.

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Saturn

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Conclusions

• There are many interesting and scientifically significant plasma physics experiments that can be done on a table top.

• A well design and thought out experiment can be very productive.

• Other small plasma experiments:• Glow discharge

• Arc discharge

• Hollow cathode

• Plasma gun

• Filament sources

• Atmospheric plasma jets: for welding, material sprays, and contamination cleanup

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Cloud vs. Stream VelocitiesComparison of particle speeds in the cloud and the stream. Particles in the stream have speeds, vst ~ 30 to 40 mm/s. Particles in the cloud have speeds up to vmax ~ 2 mm/s. Dust

acoustic waves are also visible at the top of the cloud.

(The stream velocity vectors are shown in 3/8th scale relative to the cloud velocity vectors.)

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0 5 10 15 20 25 30

stream

cloud