Ignition Studies of

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Ignition Studies of Low-Pressure Discharge Lamps
M. Gendre - M. Haverlag - H. van den
Nieuwenhuizen - J. Gielen - G. Kroesen Friday,
March 31st 2006
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Outlines
Goals of the study Set-up DC breakdown AC
resonant ignition Summary
? Goals of the study ?
1/22
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Goals of the Study
Understanding Plasma Ignition
Motivations
Physics better comprehension of
dielectric-plasma phase transitions in
general Technology understand how compact
fluorescent lamps ignite under various
conditions
2/22
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Goals of the Study
Interest of a better understanding
1900s
3/22
Courtesy of R. Richter, private communication
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Goals of the Study
Interest of a better understanding
2000s
4/22
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Goals of the Study
Understanding Lamp Ignition
Q How does low-pressure breakdown work ?
Townsend model electron avalanche between
electrodes
- homogeneous E field - infinite electrode
extension
E
Neglected by Townsend - inhomogeneous field -
diffusion losses of charges toward the walls -
wall surface charges
anode
cathode
ion
electron
atom
5/22
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Goals of the Study
Goals and Approach
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
6/22
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Outlines

• Goals of the study
• Set-up ?
• DC breakdown
• Back to AC resonant ignition
• Summary

7/22
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Set-Up
Global Circuitry
8/22
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Set-Up
Experimental Frame of Reference
9/22
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Outlines

• Goals of the study
• Set-up
• DC Breakdown ?
• AC resonant ignition
• Summary

10/22
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DC Breakdown
Ignition Mechanism Overview
light
A
time
global evolution identical in both
cases apparent lag of light emission (max
1ms) smooth evolution of lamp
potential potential gradient in the wake of
first wave
0
11/22
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DC Breakdown
Cathode-Initiated Breakdown
3torr Ar-Hg lamp -500V dt100ns
A (0)
K
12/22
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DC Breakdown
13/22
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DC Breakdown
Pre-Breakdown Wave Position vs. Voltage
51- 44 km/s
10 - 3 km/s
- wave speed directly proportional to voltage -
ignition condition first wave has to reach the
anode
14/22
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DC Breakdown
Lamp Net Charges vs. Voltage

• - first wave charging effect increases with
  voltage
• - decrease of net charge only for successful
  breakdown
• - Ignition condition charging threshold to be
  reached

15/22
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DC Breakdown
Global Overview of the Phenomenon
Qualitative model
_

? 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 1st wave to reach anode
16/22
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Outlines

• Goals of the study
• Set-up
• DC breakdown
• ? AC resonant ignition ?
• Summary

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AC Resonant Ignition
Optical Recording
18/22
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AC Resonant Ignition
Electrostatic Recordings
19/22
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AC Resonant Ignition
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
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Outlines

• Goals of the study
• Set-up
• DC breakdown
• AC resonant ignition
• ? Summary ?

21/22
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Summary
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
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ANY QUESTIONS?
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Set-Up
Global RC-Probe Circuit
Z
U
-
Faradays cage

r
R
x
?Provides lamp surface potential vs. time/space

• - limited field disturbance around the lamp
• - Z chosen so total system transfer function
  pure real
• - little need for post-experiment data treatment

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Set-Up
Calculated Data from RC-Probe Output
Measured Ff(t,x) Calculated