THE DIGITAL C-BAND

REFLECTOMETER ON THE MADISON

SYMMETRIC TORUSChristina De Bianchi

Howard UniversityAdvisors: Ellen Zweibel & Jay Anderson

Summer REU 2009University of Wisconsin-Madison

Madison, WI

CONTENTS Brief background on the MST. What is a plasma? What are EBW’s? How can EBW’s assist the MST? Motivation Set Up Results. Conclusions. Future Work. Astronomy Community.

BACKGROUND ON THE MST. A reversed field

pinch physics experiment.

Fusion energy research and astrophysical plasma research.

The device was built to produce and contain near thermonuclear plasmas.

WHAT IS A PLASMA?

A hot ionized gas that requires a large number of particles.

Plasmas are confined by magnetic fields.

Quiescent plasma made at LAP.

WHAT ARE EBW’S? The Electron Bernstein Wave is an

electrostatic wave that propagates perpendicular to B0.

The variation of density creates the electric field of the wave. The gyro motion of the electrons carries the wave.

K (propagation vector)

E

HOW CAN EBW’S HELP THE MST? The EBW is a method of injecting energy

into a plasma to increase its temperature to reach fusion conditions.

Being able to heat the plasma will help us create a cost effective efficient fusion reactor.

MOTIVATION The diagnostic will

discern plasma properties during EBW launch;

Measure the phase difference between the forward and reflected waves;

Also used for diagnosis of plasma (i.e. temperature).

SET-UP: HETERODYNE CIRCUIT

SET-UP: HETERODYNE CIRCUIT

IF Transformers

Splitter

Mixers

BEAT FREQUENCIES The forward and reflected sine waves

are multiplied with a wave of 5.500 455 GHz with mixers.

Beat FREQUENCY: 455 KHz: dashed

11 GHz: purple

Red= 5.500455 GHz Blue= 5.5 GHz

SET-UP: ANTENNA

RESULTS: ANTENNA

In waveguide

Vacuum

λwg,e = 8.46 cm λwg,t = 7.68 cm.

Experimental error = 10.15%

5.5 GHz

λvacuum = c/fλc = 2πr/1.841λwg = λvacuum/√1-(λvacuum/λc)⌃2

SET-UP: QUARTZ

Motivation: Measure the wavelength in quartz.(We are using the quartz as a microwave window as well).We want the window to be ½ a wavelength thick for destructive interference and maximizing transmission.

RESULTS: QUARTZExperimental Results:λvacuum =7.003 cmλquartz = 3.35 cmλquartz/2 = 1.675 cm

Theoretical Results:λvacuum= 6.003 cmλquartz = none

Index of Refraction: n= λvacuum/λquartz n = 2.10 for quartz at 5.55 GHz

λ=360°/slope

CONCLUSION: A heterodyne circuit has been

constructed to measure phase differences between waves at 5.5 GHz.

This diagnostic, to date, has been used to characterize an EBW launching antenna and to help find specifications for a microwave vacuum window.

FUTURE WORK: The circuit will be an integral part of

EBW heating system in the MST.This is necessary for temperature diagnosis

of the plasma in the torus. Additionally, it will help measure edge

electron density.The phase between launched and reflected

waves indicates the position in the plasma where mode conversion (energy in one wave is converted to another wave) to the EBW occurs.

ASTRONOMY COMMUNITY?

The study of laboratory plasmas can led insight to astrophysical topics such as solar winds, accretion disks, and dynamos.

Magnetic fields in the MST configure itself in a fashion possibly similar to the manner in which it occurs in the solar corona.