Identification of Quench Location inSuperconducting Radio-frequency Cavities

Ramesh AdhikariLee Teng Intern, Summer 2010

Berea College, KY

Mentor: Elvin HarmsAccelerator Division

Fermi National Accelerator Laboratory

August 13, 2010

Superconducting Radio-frequency Cavity (SRF)

Accelerating structures fornext generation of particleaccelerators

Made up of pure Niobium(Nb) , 9 cell

Very high quality (Q) factor( 2.7 x 1010) compared tothat of normal -conductingcavities (104 − 105)

Surface resistance- 10nΩ at 2K and frequency 1.3 GHz

Rf magnetic field at inner surface should be below thesuper-heating field (200-240 mT) which means maximumaccelerating field of 50-60 MV/m.

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Quench on a SRF cavity

While operating at an acceleratinggradient of 35 MV/m even a smallimperfection of the cavity surfacematters

Low thermal conductivity ofNiobium (125Wm−1K−1 at 4.2K)

Heat gets accumulated at one spotof the cavity and leads to a quench.

The quench is defined as a loss of a superconducting state.Therefore, it is NOT GOOD when we want to run our systemat temperature of about 2K to maintain superconductivity.

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Resistance Thermal Detectors (RTDs)

Figure: The arrangement of RTDs around a 9 cell cavity for the quenchlocation. Image courtesy: Ninoshka Fernandes, Lee Teng Intern 2009

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Second Sound

Phenomenon in which heatis transferred as a waverather than by diffusion.

Only observed in superfluidi.e. in this case, for Heliumat the temperature below2.17K (He II)

This wave is analogous to sound wave, and can also be heardthrough microphone!

In a cavity test, we can observe second sound generated atthe quench location.

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Oscillating Superleak Second Sound Transducers (OSTs)

Cylindrical in shape. Diaphragm atone end and a bronze coated wallconnected to SMA connector atthe other.

Porous diaphragm allows onlysuperfluid part of the He II totransmit.

Diaphragm oscillates as the secondsound arrives and causes changesin the biased voltage.

Can be modeled with acoustic circuit and the acousticcompliance of the second sound and transducer can be treatedas capacitor.

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Trilateration

Suppose the location of the OSTs are (xi ,yi , zi ), where i=1,2,3,4 for four OSTs andquench be located at (x, y, z). Then, thedistance between OST and quench wouldbe: (xi − x)2 + (yi − y)2 + (zi − z)2 = r2

i

Then,

M =

2(x2 − x1) 2(y2 − y1) 2(z2 − z1) s2(x3 − x1) 2(y3 − y1) 2(z3 − z1) t2(x4 − x1) 2(y4 − y1) 2(z4 − z1) u

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Trilateration

where, s = x22 − x2

1 + y22 − y2

1 + z22 − z2

1 − r22 + r2

1

t = x23 − x2

1 + y23 − y2

1 + z23 − z2

1 − r23 + r2

1

u = x24 − x2

1 + y24 − y2

1 + z24 − z2

1 − r24 + r2

1

Now, we can obtain the reduced row echelon matrix of theabove, augmented matrix to achieve the form:

M =

1 0 0 a0 1 0 b0 0 1 c

where, x = a, y = b and z = c - defines the position of the quench.

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Experimental Setup

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

...back to Trilateration

Now, we can ”see”the quench from theeyes of thetransducers

Sudden drop in RFsignal implies theoccurrence of quench.

Time delays between the occurrence of the quench and arrivalof second sound at each transducer can be measured.

Since the velocity is known based on the temperature, thedistances between OSTs and quench can be calculated. Then,position is calculated by using Trilateration.

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Software Development

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Software Development

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Conclusion

Based on Trilateration, the quenchcan be located quite precisely - onthe order of millimeters.

A program based on LabVIEW wasdeveloped to:- Perform speedy calculations ofthe quench location- Provide 3D visual display for theusers.

With computationally powerful programs like MatLab orLabVIEW Mathscript or Mathematica, one might be able tofind the quench based on the signals from as few as twotransducers and cavity geometry.

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Acknowledgement

Elvin Harms, Fermilab, USPAS

Eric Prebys, Fermilab, Lee Teng Internship Co-ordinator

Linda Spentzouris, Argonne, Lee Teng InternshipCo-ordinator, USPAS

Helen Edwards, Fermilab

William Barletta, USPAS

Carol Angarola, Fermilab

Erik Ramberg and Roger Dixon, Fermilab

Fermilab A0 staffs

Fellow Lee Teng Students

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities

Your Turn!

Ramesh Adhikari Fermi National Accelerator Laboratory

Identification of Quench Location in Superconducting Radio-frequency Cavities