1. CLIC meeting 14.3.2008Jan Kovermann

2. Task: Analysis of the light which is emitted by a breakdown Study the breakdown time dependence of the BD light emission See possible differences between DC and RF BDs Draw conclusions about BD physics, plasma temperatures and densities, development of the breakdown, ignition process, precursors I am using the DC sparc setup to optimize the spectrometer with the goal to have comparable measurements for DC and RF. Since the setup is much more accessible than the setup later in RF, it is a very good opportunity to tune the system and to study DC breakdown. Thank a lot to Sergio, Mauro, Antoine and Yngve!

3. The new spectrometer setup PMT, Hamamatsu R7400U-01, 300- 850nm, 0.78ns rise time Rotational stage, servo controlled, 250steps/nm Linear gauge, 1micron resolution, absolute position Ruled diffraction grating, 300 lines/mm, blazed at 500nm achromatic focusing lens 50micron input slit Fiber input with collimator

4. The light pickup inside the DC-setup 1mm glass fiber without optics

5. Some specifications Motor, scope (PMT readout) and linear gauge readout are controlled by a standard PC ~5nm resolution (higher resolution increases measurement time) LabView based software for calibration, alignment an spectroscopy operation Scope acts as ADC for the PMT(s), 1GHz bandwidth and 2.5GSa/s System takes data autonomous (~5h to take full spectrum in DC setup) Optical rails foreseen to integrate more PMTs resp. other detectors Fiber or free path optical input HeAr-reference light source for calibration very flexible design for future upgrades … a spectroscopy multitool! Goal: To have a working spectrometer that can be installed in CTF2!

6. First results in chronological order Still in 2007… first cw spectrum from an old fluorescent lamp:

7. First results in chronological order … and time resolved!

8. Latest results Last calibration done on Wednesday this week: After alignment: Calibration with OceanOptics HgAr- lamp delivers four points for calibration. Setup is linear as expected! position intensity 0. order 588.5nm 619.5nm 478.5nm 447.5nm

9. Measurements of overall light emission with time resolution in the DC setup: 0.order of grating focused on PMT, molybdenum under test

10. Measurements of overall light emission with time resolution in the DC setup: 0.order of grating focused on PMT, molybdenum under test, more detailed

11. Measurements of overall light emission with time resolution in the DC setup: 0.order of grating focused on PMT, molybdenum under test, even more detailed ~50-100ns width in 70% of all sparcs, probably correlated to voltage…

12. Measurements of DC sparc light emission with time resolution in the DC setup: time [ns] wavelength [uncal.] Limited by quantum efficiency of PMT… broadband light emission at the beginning of a sparc?

13. Measurements of DC sparc light emission with time resolution in the DC setup: … but there is also the white light: time [ns] wavelength [uncal.] Clustering?

14. Measurements of DC sparc light emission with time resolution in the DC setup: A preliminary spectrum (analysis ongoing): wavelength [nm] intensity [uncal.] 465nm Cu I 483nm 515nm Cu I 510nm Cu I 491nm Cu II

15. Conclusion: Too early to draw conclusion about DC-BD-physics, there might be still some problems in the setup New achromatic optics have been used for the last measurements, transmission spectrum unknown right now (coated) System can be used for the RF-BDs as it is after optimization, the setup will be in the gallery, light transport via fiber from CTF2 There is still a lot to do! Optimization of the spectrometer with the DC setup will reveals new information about DC breakdowns and prepares the spectrometer for the use in CTF2!