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Single-Cell Standing Wave Structures: Experiments

This work presents experiments on single-cell standing wave structures conducted by Valery Dolgashev, Sami Tantawi, Yasuo Higashi, Toshiyasu Higo, and collaborators. The study explores parameters, pulse shapes, surface fields, grain boundaries, and low/high shunt impedance structures. Insights into pulsed heating effects, breakdown rates, and comparison of TiN-coated vs. uncoated copper structures are discussed. The results shed light on the differences between single-cell and three-cell structures. Various observations and findings from the experiments are detailed, emphasizing the importance of structure coatings and pulse characteristics.

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Single-Cell Standing Wave Structures: Experiments

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  1. Single-Cell Standing Wave Structures: Experiments Valery Dolgashev, Sami Tantawi (SLAC) Yasuo Higashi, Toshiyasu Higo (KEK) X-band Structure Testing Workshop KEK, Tsukuba, Japan, May 23-24, 2008

  2. This work is made possible by the efforts of • A. Yeremian, J. Lewandowski, C. Pearson, J. Eichner, D. Martin, C. Yoneda, L. Laurent, R. Talley, J. Zelinski and staff of SLAC Klystron Lab.

  3. Outline • Standing Wave Structures • Results • Low shunt impedance • One-Cell-Structures • Three-Cell-Structures • TiN Coated Single Cell Structure • High shunt impedance • Thick elliptical iris • Thin round iris

  4. Parameters of periodic structures

  5. Pulse Shapes

  6. “Square” pulse Input power Reflected Calculated Reflected Calculated Accelerating Gradient Calculated Pulse Heating Input pulse length ~175 ns Input pulse length ~380 ns

  7. “Shaped” pulse Input power Reflected Calculated Reflected Calculated Accelerating Gradient Calculated Pulse Heating Total input pulse length ~215 ns, flat part ~80 ns Total input pulse length ~310 ns,flat part ~150 ns

  8. Surface fields for 3 different single cell structures, shaped pulse(flat part: A5.65-T4.6-KEK-#1- 150 ns, A3.75-T2.6-Cu-SLAC-#1: 150 ns, A3.75-T1.66-Cu-KEK-#1 200 ns) Maximum surface electric fields [MV/m] Maximum surface magnetic fields [kA/m]

  9. Accelerating gradient and pulse heating for 3 different single cell structures, shaped pulse (flat part: A5.65-T4.6-KEK-#1- 150 ns, A3.75-T2.6-Cu-SLAC-#1: 150 ns, A3.75-T1.66-Cu-KEK-#1 200 ns)

  10. Grain boundary on iris of 1C-SW-A5.65-T4.6-Cu-KEK-#2 Grain boundary in high electric field area Grain boundary in high magnetic field area Lisa Laurent, 20 March 2008

  11. Cracks between grains and deformation of the grain on outside wall of 1C-SW-A5.65-T4.6-Cu-KEK-#2 Lisa Laurent, 20 March 2008

  12. Pulsed Heating Experiments Photograph of pulse heating sample Cu OFE 2 after rf processing SEM image showing large amounts of copper has apparently erupted through the cracks. SEM - Lisa Laurent

  13. All data for low-shunt impedance structures

  14. All data

  15. Low shunt impedance structures 1C-SW-A5.65-T4.6-Cu 3C-SW-A5.65-T4.6-Cu Solid Model: David Martin

  16. Low Shunt Impedance Single-Cell Structures • One-C-SW-A5.65-T4.6-Cu-KEK-#1 In after-test visual inspection the structure had visible discoloration, probably copper oxide • One-C-SW-A5.65-T4.6-Cu-KEK-#2 • After the first installation Faraday cups showed unusual breakdown currents at low rf power. After disassembly we saw traces of breakdown in rf flange. Flange was re-machined, structure was hydrogen then vacuum backed. • One-C-SW-A5.65-T4.6-Cu-KEK-#4 • Test finished, sent to KEK for inspection • One-C-SW-A5.65-T4.6-Cu-KEK-#3 • Test ongoing at ASTA, no measurable • dark current at pulse heating <30 deg. C.

  17. Dark current measured by upstream Faraday Cup at the end of processing of the Single Cell SW structures

  18. Two low shunt impedance structures, square pulse 1-C-SW-A5.65-T4.6-Cu-KEK-#1 1-C-SW-A5.65-T4.6-Cu-KEK-#2

  19. Two low shunt impedance single-cell structures, square pulse 1-C-SW-A5.65-T4.6-Cu-KEK-#1, 2

  20. Two single-cell structures, shaped pulse Single cell SW1 Length of flat part of amplitude Single cell SW2

  21. Three-Cell-Structures • 3C-SW-A5.65-T4.6-Cu-KEK-#1 • 3C-SW-A5.65-T4.6-Cu-KEK-#2 • Surface processing was done at KEK. The structure was installed with as dust-free as possible.

  22. Yasuo Higashi and Richard Talley assembling Three-C-SW-A5.65-T4.6-Cu-KEK-#2

  23. Particle counter

  24. Run-away condition for 3-cell structure

  25. Two 3-cell structures, square pulse Same max. gradient ~117 MV/m

  26. Two 3-cell structures, shaped pulse 3 cell SW #1 3 cell SW #2

  27. Single-Cell Structures vs. Three Cell Structures

  28. Comparison of Single-cell and 3-cell structures Run-away “recovery”

  29. TiN Coated vs. Uncoated Copper Structure

  30. Comparison with TiN coated structure, breakdown rate vs. gradient, flat pulse Single cell SW2 Single cell SW1 coated with TiN Single cell SW2 Single cell SW1 coated with TiN

  31. Comparison with TiN coated structure, flat pulse Higher breakdown rate for TiN structure

  32. High shunt impedance structures 1C-SW-A3.75-T2.6-Cu 1C-SW-A3.75-T1.66-Cu Solid Model: David Martin

  33. Two low-shunt impedance and two different high-shunt impedance single-cell structures, shaped pulse Length of flat part of amplitude 1-C-SW-A5.65-T4.6-Cu-KEK-#1 1-C-SW-A5.65-T4.6-Cu-KEK-#2 1-C-SW-A3.75-T1.66-Cu-SLAC-#1 1-C-SW-A3.75-T2.6-Cu-SLAC-#1

  34. Two high shunt impedance structures, flat pulse 1-C-SW-A3.75-T2.6-Cu-SLAC-#1 1-C-SW-A3.75-T1.66-Cu-SLAC-#1

  35. Two low-shunt impedance and one high-shunt impedance structures, shaped pulse 1-C-SW-A5.65-T4.6-Cu-KEK-#1,#2, 1-C-SW-A3.75-T2.6-Cu-SLAC-#1, 1-C-SW-A3.75-T1.66-Cu-SLAC-#1

  36. Some Observations • In all structures but one, coated with TiN, breakdown rate increases exponentially with either input power or pulse width. For structure coated with TiN the pulse-width dependence is weak. • There is no dramatic difference in breakdown rate for same electro-magnetic field and pulse width between single-cell and 3-cell structures. Same time, stored energy and input power ~2 times different. • At certain field and pulse width the 3-cell structure shows obvious run-away behavior. • All structures but one – coated with TiN conditioned in few hours with few breakdown trips. During further operation, the breakdown trips were very rare, even at high breakdown rate. TiN structure took a week to condition. • All structures had different amplitude of dark current (measured by Faraday cups) for the same field levels and pulse width. There was no obvious correlation between the dark current amplitude for the different structures and the breakdown rate.

  37. Summary We have a test setup with short turn-around time that produces useful data. The stand started working January 2007 and now has 9th structure (1C-SW-A5.65-T4.6-Cu-Choke-SLAC-#1).

  38. More slides

  39. Two low-shunt impedance and one high-shunt impedance structures, square pulse 1-C-SW-A5.65-T4.6-Cu-KEK-#1, 2 and 1-C-SW-A3.75-T2.6-Cu-SLAC-#1

  40. High- and Low-shunt impedance structures structures, square pulse 1-C-SW-A3.75-T2.6-Cu-SLAC-#1 1-C-SW-A5.65-T4.6-Cu-KEK-#1

  41. Two 3-cell structures, square pulse 3C-SW-A5.65-T4.6-Cu-KEK-#1 3C-SW-A5.65-T4.6-Cu-KEK-#2

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