The Digital C-Band Reflectometer on the Madison Symmetric Torus

1. The Digital C-Band Reflectometer on the Madison Symmetric Torus Christina De Bianchi Howard University Advisors: Ellen Zweibel & Jay Anderson Summer REU 2009 University of Wisconsin-Madison Madison, WI

2. 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.

3. 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.

4. What is a plasma? Ahot ionized gas that requires a large number of particles. Plasmas are confined by magnetic fields. Quiescent plasma made at LAP.

5. 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. E K (propagation vector)

6. 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.

7. 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).

8. SET-up: Heterodyne Circuit

9. Set-UP: Heterodyne Circuit IF Transformers Mixers Splitter

10. Beat Frequencies • The forward and reflected sine waves are multiplied with a wave of 5.500 455 GHz with mixers. Red= 5.500455 GHz Blue= 5.5 GHz Beat FREQUENCY: 455 KHz: dashed 11 GHz: purple

11. SET-Up: Antenna

12. Results: Antenna 5.5 GHz In waveguide Vacuum λwg,e= 8.46 cm λwg,t= 7.68 cm. Experimental error = 10.15% λvacuum = c/f λc = 2πr/1.841 λwg= λvacuum/√1-(λvacuum/λc)⌃2

13. 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.

14. Results: quartz Experimental Results: λvacuum =7.003 cm λquartz = 3.35 cm λquartz/2 = 1.675 cm Theoretical Results: λvacuum= 6.003 cm λquartz = none Index of Refraction: n= λvacuum/λquartz n = 2.10 for quartz at 5.55 GHz λ=360°/slope

15. 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.

16. 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.

17. 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.