Table Top Plasma Experiments LANL Critical Skills Program John Kline July 10, 2002 P-24 Plasma Physics

Outline Why build small experiments? Different Table Top Experiments Double Plasma Device Waves and Instabilities Non-Neutral Plasmas Malmburg Penning Traps RF Plasma Capacitively Coupled Inductively Coupled Helicon Plasmas Dusty Plasmas Planetary Rings Experiments Conclusions

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.

Proof of Principle DIIID Tokamak in San Diego Operated by General Atomics

Proof of Principle These experiments study fusion directly These experiments study RF current drive at WVU

Proof of Principle Experiments 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

The Pickett’s Charge Plasma Device Double Plasma Device The Pickett’s Charge Plasma Device At Gettysburg College

Double Plasma Device Biasing Grid Antenna for launching waves Filament RF Power Supply Magnets

Double Plasma Device 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

Space Plasma Physics Plasma Physics: Chaos and Nonlinear Dynamics Potential Layers Waves and Instabilities Velocity Shear Driven Drift Waves Bo Velocity Gyro-orbit size Density Diamagnetic Current Radius

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

Non-Neutral Plasmas Transport and Diffusion (neoclassical and classical) Vortex formation and Plasma Crystals Capturing of positrons and anti-protons Auto-resonance studies

Malmberg Penning Traps

Malmberg Penning Traps A) the outer cylindrical electrode, B) the inner cylindrical electrode, C) the grids, D) the annular collecting electrode and E) the filament.

Plasma Crystals

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

RF Plasma Discharge Plasma 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 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

Capacitively Coupled Sources (GEC Reference Cell) Vacuum Chamber Matching Network RF Source Plasma Capacitor Plates

Inductively Coupled Sources Pyrex Chamber Matching Network RF Source Antenna Magnets (not required) Alternative Antenna

Inductively Coupled Sources

Inductively Coupled Sources

Helicon Sources Matching Network RF Source Antenna Magnets (required) Pyrex Chamber Matching Network RF Source Antenna Magnets (required)

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.

Helicon Sources

Dusty Plasma Experiments 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. 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.

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.

Planetary Rings Experiment

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.

Saturn

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

Cloud vs. Stream Velocities Comparison 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.)