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Run those argons, people!

Event_Horizon

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Over the last few months I have been very busy with college, and I never got around to running my argon laser. I ran it a lot over last summer and about the start of September was when I put her away for a while. Well I never got around to using it until after Christmas. And man was that ever a mistake!

Around new years I pulled her out of the dusty corner of my bedroom and plugged it into the special 20amp socket I had installed specifically for my baby. I turned on the power and the fan came on. I adjusted the foam lining around the base of the fan, put on my safety goggles, set the current to 8 amps and turned the key. The passbank cooling fan came on and I waited the usual 30 seconds for the cathode to heat up. And then it began to start...

.... click

.... click

.... click

Nothing. The start pulse just kept firing, nothing else. I took off the goggles. No laser action, no sustained discharge. "Well, it's been a while, I'm sure it will start soon." 10 minutes later and still nothing happening. Oh crap.

Its winter here, so I took the laser head off and put in the shed. -8 degrees C should cool the tube and lower the pressure enough to start, right? I brought it in the next morning and tried again. Still no joy. Well, now what? The pressure is still to high. Alright, lets make it colder. The tube is made of BeO, which is a kind of ceramic, it should be able to take a big thermal shock when it does start, right?. So I took a quick drive down to the local chemistry supply store and bought 7 pounds of crushed dry ice (only $50, plus I had some left over!). I packed the laser and a thermometer in the dry ice, packed the dry ice into a box, packed the box into styrofoam and packed that into another box. I the took the whole thing and left it in the shed again. Came back the next morning. I check the thermometer, it was off the scale on the low end. Sounds good, lets do this! I brought the whole thing back inside, quickly removed the laser and wired up the power supply. I threw on the safety glasses, and flicked the power switch. The fan came on. Turned the key. Waited 30 seconds. The lights dimmed, the fan slowed, my life flashed before my eyes and the thing started to lase. I backed away, shocked that I actually managed to get it working. I left it. I didn't touch a thing for three hours. Then I came back and turned the current down to 6 amps. I left it for another three hours.

There are a few things to consider here. I needed to use dry ice to cool the tube to get it to start because I had left it so long, and worse yet, after I cooled it I brought it into the warm house and then started it. The thermal stress on the tube alone going from -60 to 5000 degrees C should have killed it. But even WORSE, the moisture in the air condensed on the laser head. The laser head running at 100 volts and 8 amps. If that moisture had condensed on the wrong place I could have been looking at a dead laser, a dead power supply, a dead laser AND power supply, or if I was touching it at the wrong time, a dead me.

So for God sakes people run your damn argons once in a while!
 



Hemlock_Mike

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Thank you ---

My ML ArIon took several tries to get started. Kept flashing but now going......

Listen to the man here.

Mike
 

Cyparagon

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You're supposed to WARM the head to lower the pressure.
 

JLSE

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Cyparagon said:
You're supposed to WARM the head to lower the pressure.


I recall someone in the forum baked theirs in an oven to get it started, interesting that either extreme will do.
 

GooeyGus

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Yeah warming lowers pressure.... that's good that it started though :D :D :D

In a 'pressurized' tube, cooling would lower the pressure. But since these tubes are under vacuum, warming causes the gas that is in there to expand, lowering the pressure. :cool:

I have a lasos head here that is high pressure. It lases with every click of the starter, so I know the tube is good, but I cant get the damn thing to fire. I've zapped the hell out of it with a tesla coil and it still wont sustain. The tube only has 2500 hours on it, too. Time to give it a good baking :cool:
 

GooeyGus

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I tried your ice trick and look what happened!!! :mad: :mad: :mad: :mad:








Three lasers broken!!! I'll be sending you a bill. It's only a few thousand....


;D ;D ;D
 

JLSE

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LOL, write the check to one GooeyGus :eek:

Hey at least you tried ;D


Dont they use any sort of glycol for the cooling system? Or are you supposed to be a resident of California to own and operate one?
 

daguin

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The "baking" trick is for LOW PRESSURE tubes that are almost worn out. You are trying to "bake" some of the argon back out of the metal. Baking is NOT for high pressure.

Peace,
dave
 

Cyparagon

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If a tube sits around too long, the gas that is usually buried in the tube lining seeps out, raising the pressure. Baking/running the laser re-buries the argon in the tube lining - lowering the pressure.
 

Event_Horizon

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Running the laser lowers the pressure as the argon ions are buried in the cathode material. Just baking the tube in an oven won't do you any good, because the gas doesn't get re-buried. A hot gas will expand, but since the volume stays the same the pressure goes up. This is great if your tube is old and is underpressure, but it will only make problems worse if the tube is overpressure from sitting for a while.

Leaving a tube for a long time releases some buried argon into the tube and raises the pressure. I cooled the tube down so that the gas molecules slowed down, lowering the pressure.

You might be confusing baking the tube in an oven with baking out a tube when it is being refurbished. This is something else entirely. That is when you open the tube up to your vacuum system and pump out all the gas, then you leave it like that attached to the pump and heat the tube so that any residual gasses are heated and more likely to enter the pump. This removes impurities from the re-built tube.

Also, GooeyGus, you ain't foolin' me! I don't recall seeing those first two pictures before but the third I remember was an Argon you had broken during shipping! And as such I do not believe the other two are the result of my procedure!
 

Hemlock_Mike

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I ran mine for 40 minutes last night after it got stable.  Tonight, I had to run the fillament for 10 minutes to get a beam.
Keep 'em HOT  :D
Mike

My SL 488 nM started like a champ !!!
 




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