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Spectroscopy of breakdowns

Spectroscopy of breakdowns. Breakdown physics workshop J.Kovermann 6.5.2010. DC measurements. High-power scaling laws. Breakdown diagnostics. How it fits into the CLIC study:. RF measurements. Comprehensive RF design. Breakdown simulation.

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Spectroscopy of breakdowns

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  1. Spectroscopy of breakdowns Breakdown physics workshop J.Kovermann 6.5.2010

  2. DC measurements High-power scaling laws Breakdown diagnostics How it fits into the CLIC study: RF measurements Comprehensive RF design Breakdown simulation New experimental techniques complementary to RF tests

  3. Breakdown diagnostics Plasma composition simulation and mat.sci. input Plasma size/position  simulation and design input Plasma parameters simulation input Spectroscopy, Integrated and time-resolved BREAKDOWN DIAGNOSTICS RF measurements, FC, XRAY  simulation and design input Missing energy ? OTR in nominal pulses  simulation and machine parameter input SEM  simulation and design input

  4. Spectroscopy in rf and dc Subject of my thesis: Comparative studies of rf and dc breakdowns by optical spectroscopy Task: Show validity of dc breakdown experiments for rf simulation and design Approach: Time integrated and time-resolved spectroscopy of dc and rf breakdowns Dc experiments are faster and easier, e.g. few CHF per sample, up to kHz rep.-rate with new power supply (end 2010) Two dc setups available at CERN, others under construction Less scheduling issues

  5. Int. ratio lines/continuum = 1/4 Time-integrated spectroscopySpectrograph and CCD camera Dc breakdown, 400MV/m, 0.93J

  6. Fast failure diagnostics! Time-integrated spectroscopySpectrograph and CCD camera Rf breakdown, 40MW, 200ns, 8J, SLAC C10

  7. Rf, 37MW, 200ns, C10, 17 BDs DC, 8kV, 0.98J, Cu, 499 BDs Time-integrated spectroscopyReproducibility and comparison  Remarkably reproducible after normalization to total intensity !

  8. Time-integrated spectroscopyReproducibility of line-ratios • Line ratios are constant over many breakdowns in rf and dc • TLM applicable? (dc: 4280K±9K, rf: 5366K±61K) • TLM not consistent for all line pairs!

  9. Time-integrated spectroscopyLine-ratios and total intensity • Line intensity / total intensity is spreading towards shorter wavelengths • Line ratios are only weakly connected to dissipated energy

  10. Light present when electric field is applied • Shoulder at 2.1eV (interband transition) •  OTR light present in dc and 30GHz rf, not found in X-band rf… Dc, 4.25kV, Cu, 600s int. Time-integrated spectroscopyNo breakdown  OTR Rf 30GHz SBS, 66MV/m 1h int.

  11. The Mo OTR mystery: • Why only these two lines? 694.7nm MoI Time-integrated spectroscopyNo breakdown  OTR 693.4nm MoI

  12. New way of measuring β close to the breakdown threshold (impossible with current dc setup) Time-integrated spectroscopyNo breakdown  OTR  field enhancement factor

  13. Dc Time-resolved spectroscopyPower and light waveforms Rf • Dc: Max. light emission after max. power • Rf: Light lasts longer than input power

  14. Acquired time-resolved with PMT, integrated by computer afterwards (20BDs averaged per bin) Time-resolved spectroscopyConsistency with integrated spectroscopy Integrated by CCD camera (single BD) • Time-resolved (PMT) and integrated (CCD) spectroscopy • show consistent results, even though the method and number of BDs are totally different

  15. continuum lines Time-resolved spectroscopyContinuum and lines • Dc: Spectrum consists of continuum and lines

  16. 522nm 516nm Time-resolved spectroscopyReproducibility of emission waveforms 518nm (background) • Dc: Waveform reproducible, lines emit longer than continuum

  17. Spectra of rf and dc breakdowns show Cu ions up two CuIII • Other elements were not identified (but still one unidentified broad line) • Main emission intensity originates from continuum • Continuum emission ends before line emission and is weaker • Total intensity of spectrum scales with line intensity and vice versa • Non-LTE plasma, temperature calculations are inconsistent • OTR emission seen in rf and dc • Cu OTR spectrum modulated by Cu reflectivity • OTR light is linear proportional to current (and rel. factor) • Can be used to get field enhancement factor close to breakdown limit • High electric noise environment, very low light levels, fast processes and (yet) unpredictable position (rf structures!!) complicates experiments a lot! Breakdown spectroscopyConclusion Thankyou!

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