by silver painting inside, and some examples...
Note: at any picture you can click and magnify to 1024 x 768 pix
I want to use maximum capability of corona preionizing electrodes (glass tubes) for my new
TEA N2 laser. At first time I was use only glass tube with inserted wire inside. Corona was
occur almost everywhere around, and inside this tube. I want only corona light between
this tube and anode in TEA N2 laser design.
Firstly, how I planned make setup with electrodes and preionizing wires:
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| Area where we expect main
discharge between anode and cathode must be preionized before this
discharge. I don't know exactly how long time must be this delay (maybe
few nanoseconds), but only what I know is that corona discharge occur
during charging peaking capacitors, and how fast will be this
charging depend of many factors (inductance of discharging
connections between spark gap and dumping capacitors, inductance of
peaking capacitors, space between electrodes etc.), until voltage reach
enough value for main discharge. At "?" place i need make experiments
for the best as possible distance between anode and preionizing wire
(glass tubes). Now, about this experiments: |
Huh,... I not want make handy
drawing diagram, because it may be bad for making some conclusions by
watching it. First need to found some programs for drawing diagrams. |
Look at this pictures why I need silver painting inside glass tubes:
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| This is glass tube with wire
inside. Above, and below this tube was white photocopier paper (which
fluorescence blue) for confirming UV light. |
Paper fluorescence. But, if you
carefully look inside tube and outside tube corona was present. I need
only outside tube. So, I need "fill" this empty space with some
conductor. |
With silver paint inside tube
corona occur only outside tube. Exactly where I need. Note: few blue-green dots inside tube are because silver paint peel of at few places. |
Now, how I make painting inside glass tube and few mistakes:
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| All you need for painting with
conductive silver paint inside tube. Paint have name "Silberleitlack"
(silver paint, or liquid silver) and come from Netherland. Just put one
glass end of tube in bottle with paint, make "vacuum", and paint is
there. Now, excess of paint push back to bottle. |
How looks beautiful this paint
inside tube! (but before drying)... |
I was put this tube to home
heater (about 80 °C) and paint was settled at many places along
tube inside. I think that is necessary rotate or roll tube during
drying to prevent this "peel off" of paint. Also, paint peel of when I
was try to put wire through tube. This mean, that before painting,
there already must be wire inside. |
There are few experimental distance at full and half pulsed voltage. Full voltage mean 15.6 kV,
and half voltage is because of peaker capacitor divide this voltage to half by "energy transfer"
from dumping capacitor to peaking capacitor. How it looks like:
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| During "energy transfer" from
dumper to peaker capacitor it occur as voltage divider to half of 15.6
kV. (Now, my apologize, because of "handy drawing") Half
voltage results:
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Now, full voltage (or energy)
reach experimental corona preionizing setup. (Definitively, I need make better drawing) :o( Full
voltage results:
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-------------Some_conclusions-------------- At almost "zero" distance from corona glass tube to "imitation" of anode electrode you can see big difference. At half voltage corona is very weak. |
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Left and right picture represent same distance of 0.8 mm. At left picture is no corona discharge, so this column will be an "empty" until end of whole table. Last distance where corona occur at half voltage is about 0.4 mm, so it is no worth to show. |
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At 1.2 mm there is no
significant change in corona power (only by observing at pictures - no
right measurement, because haven't instrument for this) Note: I wish to try put there some photo element and oscilloscope, but due to poor light, I afraid that only EMP will reach O-scope instead "right" pulse, and make wrong conclusions. |
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At 1.5 mm distance, light become weak. So, there is almost "end" of "usable" working distance. |
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At 2.0 mm distance, light is so weak, so there is now really end of usable distance (at this voltage). |
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Later, I was make with one alumina (or quartz tube - not sure). This also promise good results, but for now, haven't this tube with "right" outside diameter of 3 mm, and enough long (about 50 cm). |
Final conclusions: At half voltage of 15.6 kV results are disappointing. But, when once TEA N2
laser will be finished, I think use about 20 - 30 kV HV power supply, so when "energy transfer"
between dumping and peaking capacitors make divided voltage, then this will be about 10 - 20 kV,
which is enough for preionizing distance of about 1 - 1.5 mm which I think use.
"Bonus" pictures:
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| I was try test thin film (or
foil) of about 0.1 mm thick with silver paint as corona wire with
anode above dielectric. Result is
amazing, even at room light. But this foil is very sensitive to heating
by corona discharging at high repetition rate which I think to use
(about 20 pps), and can easy burn (or can be easy punctured by HV
pulses). |
Beautiful long streamers and
high intensity of corona light. But... :o( |