1. Zack Conway, Georg Hoffstaetter
Quench Detection in SRF Cavities Using Oscillating Superleak Transducers
Ed Lochocki
Rutgers University
Zack Conway, Georg Hoffstaetter
Cornell Laboratory for Accelerator-based Sciences and Education

2. Planned accelerators are creating a large SCRF cavity demand
Why You Should Care
Planned accelerators are creating a large SCRF cavity demand
Demand currently cannot be met since a high percentage of cavities quench
What we must be able to do:
Identify quench spots
Do it quickly
Do it cost-effectively
OSTs are the way to do it
December 6, 2018
Cornell LEPP Template

3. Small surface defects create large EM fields:
Quenching 1
Small surface defects create large EM fields:
Pits & Bumps
Particles
Grain Boundaries
High RF losses in these regions generate heat
The heated SC surface becomes normal-conducting
December 6, 2018
Cornell LEPP Template

4. The cavity becomes thermally unstable
Quenching 2
The cavity becomes thermally unstable
The normal conducting region grows rapidly
All of the stored EM energy is converted to heat
December 6, 2018
Cornell LEPP Template

5. Superfluid He has temperature-entropy waves (Second Sound)
Defect Location
Superfluid He has temperature-entropy waves (Second Sound)
Cavity quenches generate temperature gradients
Temperature gradients generate SS waves
We use OSTs (SS microphones) to triangulate
So in one test, we can:
Do field measurements
Locate the defect
December 6, 2018
Cornell LEPP Template

6. OSTs in Action 1
December 6, 2018
Cornell LEPP Template

7. OSTs in Action 2
December 6, 2018
Cornell LEPP Template

8. OSTs in Action 3
December 6, 2018
Cornell LEPP Template

9. A previous program could
How Do We Do It?
A previous program could
Identify quench times
Identify wave arrival times at OSTs
Given a few cavity parameters, triangulate to find quench location
However, it was very limited
Only works with standard TESLA shapes
Cannot deal with cavities that have more than one radius at a given position
Tedious to modify
December 6, 2018
Cornell LEPP Template

10. What Do I Do? Fix Problems: Add functionality: Get data
Change code to work with a parametrically-defined geometry
Allow for easier adaptation to new shapes in the future
Add functionality:
Allow program to take input directly from oscilloscopes
Get data
December 6, 2018
Cornell LEPP Template

11. SecondSound 2.0 Image 1
December 6, 2018
Cornell LEPP Template

12. SecondSound 2.0 Image 2
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Cornell LEPP Template

13. Future SecondSound Image
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14. The End
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15. The Nature of an OST
What is an Oscillating Superleak Transducer?
(1) Thin millipore membrane
(2) Thick brass layer (140 V)
(3) Grounded aluminum
Superfluid passes through the membrane
When an SS wave arrives, the membrane oscillates
We measure changes in capacitance 2 3 1
December 6, 2018
Cornell LEPP Template