A LASER SCATTERING A LASER SCATTERING DIAGNOSTICDIAGNOSTIC

TO STUDY THE ANOMALOUS FLUX TO STUDY THE ANOMALOUS FLUX DISSIPATION OF AN FRCDISSIPATION OF AN FRC

Onnie LukOnnie LukAdvisor: Tobin MunsatAdvisor: Tobin Munsat

● 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

Some Preliminaries…

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

– good confinement– ITER: fusion

experiment under construction

1Deuterium Tritium

+ +

3

++

He4 Neutron

++

2

+

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)

k

k(=θ

i

f

21

2sin1-

z

Radius of Curvature

Wavefront

Beam Diamete

r

Beam Divergence

Gaussian Beam

Diffraction Grating

dφ

mλ

ik

nfluctuatiok

Laser

DetectorsPlasma

θ

nfluctuatioi kk

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

2222 ~41

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