A LASER SCATTERING DIAGNOSTIC TO STUDY THE ANOMALOUS FLUX DISSIPATION OF AN FRC Onnie Luk Advisor: Tobin Munsat http://www.ruggedelegantliving.com/a/images/solar.flare.2005.jpg
Some Preliminaries… FRC: Field-Reversed Configuration Magnetic configuration for plasma confinement Fusion energy research My summer project Design a laser diagnostic instrument for fluctuation measurement in FRC experiment at Los Alamos National Laboratory
What is Plasma? 4th state of matter Ionized gas with its motion controlled by electromagnetic fields 99% of all baryonic matter in the universe is made up of plasma Stars Interstellar gas Interplanetary space (solar wind)
What is Fusion? Need high temperature (~100 million K) to fuse atoms Deuterium Tritium + 3 He4 Neutron 2 Need high temperature (~100 million K) to fuse atoms good confinement ITER: fusion experiment under construction http://www.ofes.fusion.doe.gov/images/iter8x.jpg
Alternate Magnetic Confinement Configuration Field-Reversed Configuration (FRC) What's so great about FRC? Potential fusion reactor Simpler design than tokamak with better wall interaction Can possibly refuel tokamaks Study fast magnetic reconnection (basic science)
FRX-L: an FRC Experiment Field Reversed Experiment-Liner Located at Los Alamos National Laboratory Anomalous flux dissipation observed; possibly caused by lower hybrid drift instability Expected characteristic of the density fluctuation: λ = 26 μm Guess: ñ/n = 1%
Study of Density Fluctuation – Laser Scattering Diagnostic Detectors Plasma θ z Radius of Curvature Wavefront Beam Diameter Beam Divergence Gaussian Beam Diffraction Grating d φ mλ
Design Consideration: Laser Wavelength: 632.8nm (HeNe) High power: 17mW Beam pointing stability: <0.002° small compared to scattering angle θ Beam diameter: 0.96mm not too big and not too small Beam divergence: 0.05° Polarization: Linear
Design Consideration: Detector Power ratio : 2 x 10-5 Scattered power Ps: 3x10-7 W Size: Φ 0.23 mm compact, with active area similar to beam size (~ Φ2mm) Fast-responding: ≥ 20 MHz (fNyquist of digitizer) Noise Equivalent Power (NEP): 2.82x10-11 W as low as possible Signal-to-Noise Ratio (SNR): 1.2x104 SNR = Ps/NEP > 10 Nyquist freq: half of sampling rate Mounted High-speed PIN Photodiode (13 DAH 001): 2.86e9 freq