Laser-Induced Fluorescence for Plasma Diagnostics

Laser-Induced Fluorescence for Plasma Diagnostics

Designing and Testing an Optical Probe for Advanced Plasma Studies

Stephanie Sears

Advisor: Dr. Walter Gekelman

OverviewOverview

What is a plasma?What is a plasma? What kind of plasma was used for this research?What kind of plasma was used for this research? How was this plasma generated?How was this plasma generated? What exactly is LIF?What exactly is LIF? How was the experiment constructed?How was the experiment constructed?

The laserThe laser The probeThe probe Data CollectionData Collection

What were the results?What were the results? What were some of the problems?What were some of the problems? How does this contribute to further research in plasma physics?How does this contribute to further research in plasma physics? What is the next step?What is the next step? ConclusionsConclusions

Helium Plasma

Neon Plasma

Specifics of Our Plasma

• Fully-ionized argon (ArII)

• Dimensions=

• Density=

• Approximate electron temperature=

• Predicted ion temperature=

Creating the Plasma

• The plasma is pulsed

• Field Strength=

• Created with an electron beam

The Machine Schematic

North South

Machine Specifications

• 18 meters in length, 1 meter in diameter• 90 magnetic coils generate fields between 0.05 and 4 kG

• Barium oxide-coated nickel cathode• Molybdenum mesh anode• 0.55 meter cathode-anode separation• 450 radial ports• 60 rotating flanges• 4 mechanical pumps• 2 turbo pumps• 2 portable vacuum stations• Computer controlled stepping motors• Available working gases include helium, neon, argon, and hydrogen

The Machine Itself

The Cathode

The Anode

Inside the Chamber

What is Laser-Induced Fluorescence (LIF)?

Allowed Transitions of Argon II

Simple Energy-Level Diagram

Theoretical Spectrum

Actual, Doppler-Broadened Spectrum

Illustration of the Doppler Effect

Relation of Optical Intensity to Wavelength

Why is this worth looking at?

The Experimental Set-Up

Timing Diagram

The Laser

The Probe(Original Design)

Actual Design

Data Collection

The Data

Interpreting the Data

Problems To Overcome

• Very low signal-to-noise ratio

• Huge amount of scattered light

• Poor alignment of fiber with laser sheet

• The laser itself

Ways to Improve LIF Observation

• Better Filter

• Amplifier

• Better Probe Design

Design for a Future Probe

Conclusions

Acknowledgements and Thanks

• Dr. Walter Gekelman-Advisor

• Stefan Grunspan and Brett Jacobs-UCLA students

• Marvin Drandel-LAPD technician

• Everyone else on the UCLA plasma team

• Fellow REU students and friends

The EndThe End