Why does an excimer lamp produce a double filament discharge?

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Discussion Overview

The discussion revolves around the phenomenon of a double filament discharge observed in excimer lamps, specifically those powered by capacitive discharge electrodeless pulses. Participants explore the experimental setup, characteristics of the discharge, and potential influences on its behavior.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants describe the experimental setup involving a quartz tube evacuated and filled with a krypton and chlorine mixture, powered by a high-voltage pulsed source.
  • There are inquiries about the symmetry of the discharge and whether it appears as two distinct filaments when viewed from different angles.
  • Participants discuss the nature of the pulsed source, with some confirming it is bipolar, while others question the direction of electron travel.
  • One participant notes that the presence of permanent magnets previously distorted the discharge in a different experiment, raising questions about their effect in the current setup.
  • Concerns are raised about why two parallel discharges exist, as currents in parallel typically attract each other.

Areas of Agreement / Disagreement

Participants express curiosity and propose various hypotheses regarding the double filament discharge, but there is no consensus on the underlying reasons for the observed phenomenon or the influence of external factors such as magnets.

Contextual Notes

Participants mention limitations in their observations, such as the effect of the lamp's geometry and the positioning of electrodes, which may influence the discharge characteristics.

Who May Find This Useful

This discussion may be of interest to researchers and practitioners in the fields of plasma physics, electrical engineering, and experimental optics, particularly those working with excimer lamps and discharge phenomena.

VACUUMIST
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I am experimenting with excimer lamps powered as capacitive discharge electrodeless pulses.
The discharge, on a mixture of Kr and Cl, around 3 torr, appears a a double filament, why?
See picture.
P4.jpg
 
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VACUUMIST said:
Summary:: strange form of low pressure electric discharge

I am experimenting with excimer lamps powered as capacitive discharge electrodeless pulses.
The discharge, on a mixture of Kr and Cl, around 3 torr, appears a a double filament, why?
See picture.View attachment 270347
That's pretty cool. Can you describe how you built that experiment? How did you seal the tube and pump it down?
 
Interesting. Maybe @ZapperZ has some further insight when we know a bit more about the setup.
 
What does it look like from the side? Still 2 filaments? A cylinder viewed from the side (radially) would be brighter at the edges than the center, I would imagine. But this does look like two filaments to me.

Given the setup I would expect circular symmetry, except for the proximity of the table. One experiment would be to really set up true circular symmetry by suspending it above the table somehow.
 
Hi, thanks for your interest.
It is a quartz tube, that was evacuated in a high vacuum system (mechanical pump + diff pump), degassed, filled with krypton and chlorine and sealed off with blow torch.
Power supply approx 10 kV, at 50 kHz, pulsed source.
 
VACUUMIST said:
Hi, thanks for your interest.
It is a quartz tube, that was evacuated in a high vacuum system (mechanical pump + diff pump), degassed, filled with krypton and chlorine and sealed off with blow torch.
Power supply approx 10 kV, at 50 kHz, pulsed source.
a bipolar pulsed source or unipolar?
 
Hi DaveE
It is an electrodeless lamp.
Quartz is the envelope and the dielectric.
 
VACUUMIST said:
Hi DaveE
It is an electrodeless lamp.
Quartz is the envelope and the dielectric.
Yes, I see that. Which way do the electrons travel, one way, or both directions?
 
Is a bipolar pulsed source.
 
  • #10
excimer lamp.jpg

@VACUUMIST , Hey interesting stuff, can you please elaborate whether the lamp if viewed from the side looks like in my attached drawing and does the plasma that forms resembles the red one in my drawing?PS. what purpose is there the tape on the sides of the lamp and what seems like a wire running down either in the inside or outside the lamp ?
Are you using permanent magnets nearby to influence the shape of the discharge ?

Maybe if you can you can take a video of the lamp in action and show us.
 
  • #11
Hi artis

Both filaments seems to be paralell.
Tapes are just to hold the lamp to the table.
No wire inside or outside, just both external electrodes.
No alteration with a neodymium magnet.
I will try to prepare a video.
Thanks.
 
  • #12
VACUUMIST said:
No alteration with a neodymium magnet.
Really? I would have expected something.
 
  • #13
With an earlier essay, Kr + Br, the permanent magnet distorted the discharge.
I suspect that now, being the discharge so close to the lamp wall it is not noticeable any distorsion.
 
  • #14
I forgot to mention that the last magnet experiment was done with the electrodes repositioned, placed along the main axis of the lamp. That resulted in two discharges close to each electrode. Tomorrow some pictures.
 
  • #15
I prepared a new lamp, still at pumping station. Permanent magnet distorts the two discharges. Looking from an end doesn´ t seem that the discharges are as suggested by artis. Each discharge has its own start.
P5.JPG
 
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  • #16
A HV diode in series with the lamp reduces the irradiated power but keeps the two discharges.
 
  • #17
Interesting lamp, well in the first picture you attached i think i saw that wire along the lamp axis at the outside of the glass.

The thing I don't quite get is why are there two parallel discharges , because currents running in parallel tend to unite as they feel an attractive force
 
  • #18
No wires, just the 2 external electrodes.
I have the same question... why two parallel discharges?
 

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