Vacuum Levels and Plasma Extinguishment

John Futter · Post by **John Futter** » Tue Apr 26, 2016 2:33 pm

Torr should be a used with a Capital T after Torricelli the father of Vacuum and inventor of the Barometer
one of his famous sayings
"horrors et vacuui" after a vacuum implosion killed one of his servants

Rich Feldman · Post by **Rich Feldman** » Tue Apr 26, 2016 4:42 pm

With utmost respect for John F and Mr. Torricelli, and the unfortunate 17th century technician, I beg to differ.

When we write about newtons and pascals, hertzes, volts and amperes, farads and henries, etc., we don't use capitals. Except when the names are replaced by symbols: N, kPa, GHz, V, A, F, nH. Vacuum is great, but why should its traditional unit be treated differently?

John and I stand on the same ground, figuratively, that Torr is acceptable.
In fact, the regular spelling of Torr the symbol needs a capital T. That makes mTorr also OK.

I still maintain that torr and millitorr are OK, mtorr should be regarded as wrong, and milliTorr is abominable.

Dave Xanatos · Post by **Dave Xanatos** » Tue Apr 26, 2016 5:15 pm

Rich Feldman wrote:Dave,
Apparently you have a computer. If you don't have a spreadsheet calculator program, you need to get one.

...

I tend to script things manually... below is a script that outputs the pressure for every 0.01V increment...

Copy it, save it as something.htm and open it with a browser.

Code: Select all


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Untitled Document</title>
</head>

<body>

<table width=300 bgcolor="#cccccc" cellpadding=4 cellspacing=1>
<tr><td width=100 bgcolor="#ffeedd"><b>Voltage</b></td><td width=200 bgcolor="#ffeedd"><b>Vacuum (Torr)</b></td>
<script>


for (v = 800; v > 500; v--) {
	P = ((1.5 * (v/100)) - 12.125)
	x = Math.pow(10,P)
	x = Math.round(x*10000000)/10000000
	document.write("<tr><td bgcolor='#ffffff'>" + (v/100).toFixed(2) + "</td><td bgcolor='#ffffff'>" + x + "</td></tr>")
}

</script>
</table>

</body>
</html>

[soapbox commentary]

To each, their own

For me: mA, mV, mTorr, mH, GHz... I'm weird... it's a respect thing for me to try to remember to capitalize the letter of things named after people who spent their life working to leave behind the building blocks of our knowledge. Hertz, Pascal, Volta, Ampere, Henry, Torricelli, Faraday, Newton, Tesla... these are the giants upon whose shoulders we stand to gain a higher view than they could in their time. I like to remember that behind every mA, GHz, mTorr, there stands a man whose life work allowed us to know what that was, exactly.

[/soapbox commentary]

Rich Feldman · Post by **Rich Feldman** » Tue Apr 26, 2016 9:32 pm

Wow, Dave, you just helped me to do my first ever HTML script work.
Thanks!
Your program seems too small & clear to be hiding malware, and it worked here on the first try:

Then I successfully tweaked it to reduce the X and Y resolution. Went online & learned how to insert a comment in the source code. The result:

If you composed the program in something fancier than a plain text editor, I'd love to see how it looks in the UI.

Dave Xanatos · Post by **Dave Xanatos** » Tue Apr 26, 2016 10:06 pm

Happy to help! I designed websites for nearly 20 years... did a lot of custom scripting. I just used a text editor for that... looked just like it does in your editor.

Happy Scripting!

Rex Allers · Post by **Rex Allers** » Wed Apr 27, 2016 4:41 pm

When I posted a reply to Dave on Tue Apr 26, 2016 11:50 am, I also asked a question that nobody commented on.

Basically, what I understand as normal operating pressure for a fusor seems to be below any part of Paschen curves that I have seen. I was hoping that someone would tell me I got something wrong or explain how Paschen curves and fusor operating points relate.

For easy reference, here is a copy of what I posted earlier...

-----
As I understand these curves, a particular operating pressure and electrode distance gives a pd point. This will form a vertical line on the Paschen chart. If the vertical line that represents this value intersects with the curve, the vertical value of this point represents the minimum value of the HV needed to start a discharge. This seems to say you can have a discharge if the (pd, V) operating point is on or above the curve line. (Above also is to the right of the more vertical portion of the curve.) This would also imply that if the operating point is below (or to the left of) the curve, there would be no discharge.

*My problem / question*
Reading Richard's guide to operating a fusor, it is my understanding that the typical operating pressure, with D2 flowing for fusion, should be around 6-8 microns (or mTorr). For an 8" fusor, this would imply a pd of around 7E-2 Torr cm. Looking at a typical chart of Paschen curves on the wiki page for "Paschen's Law", this value is way to the left of whole chart. This seems to imply no plasma.

Have I gotten something very wrong in my understanding of Paschen curves or my numerical estimations?

Post by **Richard Hull** » Wed Apr 27, 2016 5:51 pm

The pressure it definitely and always preciesly what it is when the fusor is fusing. It can fuse over a very wide range, as I have noted. No one fuses at much over 25 genuine microns and only a tiny amount fusion is registered just below extinction. In short, if you are having problems, you are having problems because you or your gear is doing something wrong.

An old time fusioneer can be in the presence of a fusor that is misbehaving and immediately know what the issue is. Newbies are famous for not fully expressing things to the enth degree and typically have poor to non-useful supplies, miscal'd instruments, terrible neutron detction gear, etc.

A willing, would-be fusioneer might spend several weeks or months figuring out the sweet spot for their particluar fusor. VCU and the fusor team, here, had a terrible time solely due to a super professional $4500.00 high voltage supply that was current limited at 10ma. Current limiting, in a fusor supply, is like catching a bullet in the foot. Millisecond-plus, un-observable current excursions are extremely common in an amateur fusor. They absolutely doom a current limited HV supply to cutting off everytime you think you are close.

A full 9 ma at a "useful voltage" will fuse anywhere...anytime, in any fusor if the pressure is right and the chamber conditioned. All of this assumes a very sensitive and efficient neutron counter is at hand and the system can operate over a full ten minutes at this level. A stumbling newbie becomes a confident fusioneer only when all the foregoing are stable and under full control. It is an art and not a calibrated science. The fusor is far too crude, too simple and working in a ragged edged "no man's land" of pressure voltage and current within a leaking gas, "vacuum like" environment.

I spent one full year with two demo fusors, I & II, (1997-1998), learning all about what lights plasma in vacuuo and what doesn't, at what voltages and what pressures success was to be had. I didn't care about the Paschen curve or its failure to meet any sort of theoretical or empirical specifications related to my efforts. I learned by doing....constant doing. it's all about the journey and not the arrival.

Richard Hull

Rex Allers · Post by **Rex Allers** » Thu Apr 28, 2016 8:17 am

Richard, thanks for another great discussion of the realities of things that might matter. I think I was aware of the stuff you just described from reading several earlier posts. Unless anyone else adds anything enlightening, I guess I'll go back to not worrying about why Paschen curves don't seem to make sense to me at pressure and voltage points where I think a fusor typically runs.

If I eventually plod my way to actually assembling stuff and trying it, I was planning to spend a bunch of time with air, and then possibly hydrogen, before I start wasting any precious deuterium.

Post by **Richard Hull** » Thu Apr 28, 2016 2:13 pm

In the doing there are no secrets, just discoveries that lock into your gut far more intensely than a thousand words on a written page. Do not think I abhor reading. Quite the contrary. I find reading is the very pathway to doing things right and staying out of major trouble and danger in this business. Reading tells you what others have done and discovered. Based on reading you need to be doing and discovering along those lines for yourself.

Von Engels book "Ionized Gases" was my early guide. He was wise enough and experienced enough that after giving valuable equations and data related to ionized gases would quickly note that the equations only held for simple, rigidly controlled and narrow range conditions. In short, they were idealized. Very few, if any, amateurs on a limited budget, can support or hope to maintain rigidly conrolled conditions where curves and computations will prove spot on. This is especially true in the finely tuned, "bleeding edge" conditions where the fusor actually does fusion. You pay for its abject simplicity with having to have 5 arms and two brains all working at one time to find the sweet spot. Fortunately, once found, you OWN the klnowledge to bring to heel any fusor in future and from that point on, only one brain and a pair of arms suffice just fine.

Richard Hull

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Vacuum Levels and Plasma Extinguishment

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