1. Ignition Studies of Low-Pressure Discharge Lamps M. Gendre - M. Haverlag - H. van den Nieuwenhuizen - J. Gielen - G. Kroesen Friday, March 31 st 2006 Experiments on CFL Ignition PHILIPSTU/e

2. PHILIPSTU/e 1/22 Goals of the study Set-up DC breakdown AC resonant ignition Summary Outlines  Goals of the study 

3. PHILIPSTU/e 2/22 Understanding Plasma Ignition Physics: better comprehension of dielectric-plasma phase transitions in general Technology: understand how compact fluorescent lamps ignite under various conditions Goals of the Study Motivations

4. PHILIPSTU/e 3/22 Interest of a better understanding Goals of the Study Courtesy of R. Richter, private communication 1900s

5. PHILIPSTU/e 4/22 Interest of a better understanding Goals of the Study 2000s

6. PHILIPSTU/e 5/22 Understanding Lamp Ignition Q: How does low-pressure breakdown work ? Townsend model: electron avalanche between electrodes Goals of the Study cathode anode E atom ion electron - homogeneous E field - infinite electrode extension Neglected by Townsend - inhomogeneous field - diffusion losses of charges toward the walls - wall surface charges

7. PHILIPSTU/e Goals and Approach 6/22 A: Thorough study of ignition in a ‘standard’ linear lamp studies: - different experiments on same lamp design - different lamp configurations (gas, pressures…) - control of experiments (repeatability, accuracy…) - cross-comparisons between results  Global Overview of the Phenomenon Goals of the Study

8. PHILIPSTU/e 7/22 Goals of the study  Set-up  DC breakdown Back to AC resonant ignition Summary Outlines

9. PHILIPSTU/e 8/22 Global Circuitry Set-Up RLRL HV probe camera controller ICCD camera lens TTL trigger Faraday cage lamp capacitive probe driver computer digital oscilloscope ch 1 2 3 ch 4 voltage regulator IFIF IGIG power amplifier function generator IAIA pulse generation  low-voltage waveform amplified to 200-1200V  double pulse scheme for charge clean-up  load resistor for lamp current regulation power amplifier function generator IAIA voltage regulator electrode heating  active electrode at 1000K for e - emission  electrode impedance constant over time  electrode voltage kept at constant value  no drift of electrode performances during the experiments time reference  same time base for all instruments  lamp voltage taken as the main reference  simultaneous triggering of scope and camera camera controller ICCD camera lens computer 1- optical imaging  fast iCCD camera for 50-500ns time resolution  one full lamp ignition for each image taken  20 to 60 images are added for each time step  data processed to give space-time diagrams capacitive probe driver 2- potential probing  custom-built floating capacitive probe  lamp potential mapping in time and space  7mm and 1ms space and time resolutions  data processed to give space-time diagrams IFIF IGIG 3- current recording  current measured at three critical points  sub-  s and  A time and current resolutions  current waveforms recorded by oscilloscope power amplifier IAIA Faraday cage lamp Faraday cage  critical for the accuracy of the experiments power amplifier IAIA

10. PHILIPSTU/e  probe rack - house and locate the probe  lamp - 145mm long, 10mm diameter  ITO window - transparent and electrically conducting  Faraday’s cage - stable electrostatic environment 9/22 Set-Up Experimental Frame of Reference  electrostatic probe - senses the lamp surface potential

11. PHILIPSTU/e Goals of the study Set-up  DC Breakdown  AC resonant ignition Summary 10/22 Outlines

12. PHILIPSTU/e -400 -300 -200 -100 0 V KA potential 11/22 Ignition Mechanism Overview 0 A 14 x (cm) K -500 +5000 light global evolution identical in both cases apparent lag of light emission (max 1  s) smooth evolution of lamp potential potential gradient in the wake of first wave DC Breakdown Argon 3 torr –600V Pre-breakdown wave: - starts at the cathode - propagates toward the anode - speed and intensity decreases Return strike: - starts at end of first wave propagation - propagates toward the cathode - speed and intensity decreases Argon 3 torr –600V Pre-breakdown wave: - starts at the cathode - propagates toward the anode - speed and intensity decreases time

13. PHILIPSTU/e 12/22 3torr Ar-Hg lamp : -500V dt=100ns Cathode-Initiated Breakdown DC Breakdown K A (0)

14. PHILIPSTU/e 13/22 DC Breakdown Argon 3torr –200V : Failed Ignition resolution  potential: 10ns optical: 100ns Argon 3torr –300V : Failed Ignition resolution  potential: 10ns optical: 500ns Argon 3torr –400V : Successful Ignition resolution  potential: 10ns optical: 500ns

15. PHILIPSTU/e 14/22 Pre-Breakdown Wave Position vs. Voltage - wave speed directly proportional to voltage - ignition condition: first wave has to reach the anode DC Breakdown 10 - 3 km/s 51- 44 km/s

16. PHILIPSTU/e 15/22 Lamp Net Charges vs. Voltage DC Breakdown - first wave charging effect increases with voltage - decrease of net charge only for successful breakdown - Ignition condition: charging threshold to be reached

17. PHILIPSTU/e 16/22 _ +  High radial/axial E-field component  Local Townsend-like breakdown  Wall charging and field displacement  Further ionization in front of cathode Global Overview of the Phenomenon DC Breakdown Qualitative model ee  Wave propagation toward the anode  Decreasing electron current flux  Field rotation and enhancement  Electrodes bridged, circuit closed  Steep current increase  Wave propagation toward the cathode  Global lamp charge decrease  Exponential current increase  Current stabilized by ballast - ionization wave driven by front field, rate of wall charge - wave speed dependent on E/p value - gradual decrease of field and wave speed during propagation - ignition condition : E/p high enough for 1 st wave to reach anode

18. PHILIPSTU/e Goals of the study Set-up DC breakdown  AC resonant ignition  Summary 17/22 Outlines

19. PHILIPSTU/e 18/22 Optical Recording AC Resonant Ignition

20. PHILIPSTU/e 19/22 Electrostatic Recordings AC Resonant Ignition

21. PHILIPSTU/e Correlation with DC Breakdown - synchronous propagation of K and A waves - importance of surface charge memory effect - easier ignition in alternating potentials as a result 20/22 AC Resonant Ignition

22. PHILIPSTU/e Goals of the study Set-up DC breakdown AC resonant ignition  Summary  21/22 Outlines

23. PHILIPSTU/e Global Overview - multiple diagnostic tools running simultaneously - cross comparisons between optical/electrical data - various experimental conditions investigated - correlation between wave propagation and lamp charging - minimum lamp charging required for successful ignition - new information inferred from data analysis 22/22 Summary

24. PHILIPSTU/e ANY QUESTIONS?

25. PHILIPSTU/e Global RC-Probe Circuit  Provides lamp surface potential vs. time/space R U Faraday’s cage Z + - - limited field disturbance around the lamp - Z chosen so total system transfer function = pure real - little need for post-experiment data treatment Set-Up x r

26. PHILIPSTU/eSet-Up Calculated Data from RC-Probe Output Measured:  =f(t,x) Calculated: radial E field: disp. current: linear charge: |E| field: <E field: axial E field:    total disp. current    total charge