MBI Phase Shifters

1. MBI Phase Shifters Or A Tale of Two Weeks Amanda Gault April 12, 2005

2. Outline • Why do we need phase shifters? • How does it work? • What tests do we do? • What preparation for tests? • What results? • What we still need to know?

3. What is a Phase Shift?

4. Why • To pick individual baselines out of the combined signal • To isolate the sky signal from noise

5. Faraday Rotators • Utilize a superconducting solenoid and ferrite to rotate the plane of polarization of the incoming signal • Rotation depends on current through device

7. input Rotate -90 output input Rotate +90 output Waveguide orientations

8. Assembly

9. Testing • Want to determine: • Maximum current • Reflection and transmission coefficients • Maximum Rotation

10. Testing: Maximum Current • Tests at San Diego show phase varying nearly linearly with current • Reach a max rotation angle of ~75 degrees • We need a 90 degree rotatiokn • If we can get a higher max current, we can increase the rotation

11. Testing: Coefficients • Utilizing the Vector Network Analyzer in Engineering, we can measure the amount of signal which is transmitted and reflected through our system • Reflection measurements are S11 and S22 • Transmission measurements are S12 and S21 • Ideally want all of the signal transmitted

12. Testing • Since the Faraday Modulator relies on superconductivity, it must be cold (<9K) to operate • Had to fit it into a test dewar

13. Waveguide Plumbing

16. A very tight fit

17. Applying lots of pressure

22. Sealed leak with apiezo

24. Resistance through phase shifter Keeping track of time, pressure, resistance, and temperature Thermometer readout

25. First Test • Leak • sealed with goop • Would phase shifter would not go below 11K • Difficulty filling liquid Helium • Unable to test at VNA since temperature did not get down far enough • Needed better heat-sinking

26. Prep for Second Test • Improved Heat-sinking • Added more short, thick pieces of copper connecting from the cold plate closer to the phase shifter • Rewired so that the brass wires connect to copper post on cold plate before connecting to the phase shifter • Damaged Thermometer

28. Tightening down the new pieces of copper

29. Original heat sinking Thermometer Post with wires New wires to adapt from brass to those on the phase shifter New heat sinking pieces

30. Same room temperature resistance before and after rewiring

31. Second cool down Towel Leaking funnel

32. Filling liquid Helium

33. Since Thermometer was damaged, relied on the changing resistance of the Faraday Modulator to estimate temperature • Cooled far enough for it to become superconducting • Carefully set it up at Engineering

34. Aligning the ports of the VNA

36. Highly accurate leveling system

37. Instruction on how to properly connect and tighten to the VNA ports

38. Complete set-up VNA display Ammeter and voltmeter VNA ports Power supply

40. Results • S12 and S21 measurements not identical • Probably at least partially due to slight twisting to fit set up into dewar • Assuming a cos2(θ) angular dependence, the Faraday Modulator gave a maximum rotation of about 25°.

46. Conclusion • Still not sure if the Faraday Modulator will perform as we need it to • Even better heat sinking needed • Will be testing another phase shifter designed by an engineering student here • The gold dewar is the Precious