First Plasma (April 19, 2017) - Most Recent Plasma

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Jackson Oswalt
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First Plasma (April 19, 2017) - Most Recent Plasma

Post by Jackson Oswalt » Sun Jul 16, 2017 5:01 pm

Hello all!

Before I begin, I'd like to say that I'm quite new to this forum so please forgive me if this is in the wrong section. Today I'd like to share my setup with you with the hopes you could give me a few tips and pointers. Maybe even help you out, though I doubt that. If you're an expert, then there are three questions at the bottom of this post that I could use some help with.

Alright, to begin: my setup.

As of now, my setup consist of a collection of Cf35, Kf25, and Kf16 fittings and adapters. The main component of the reactor is the 5-way CF35 Cross. Attached to 5-way cross is a series of adapters, two viewports, and an electrical feedthrough.
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Vacuum Chamber Shot #1
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Vacuum Chamber Shot #2
This is the electrical system I'm temporarily using until I get my -40kv power supply (picture below). It works well for demos, but it simply isn't enough. It consists of a 10kv Oil Burner Ignition Transformer (used to supply the bulk voltage), a Variac (used to control the voltage that goes into the transformer, therefore controlling the voltage that comes out of the transformer), and a high voltage rectifier that I made myself (which is used to convert the Ac current to Dc). Then, from the rectifier, it goes into the reactor.
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The Electrical System
Although I am not quite ready for deuterium fusion, I have made several advancements since my first plasma. For instance, in the beginning I could only run the reactor for 30 seconds at most. Now, I can run it red hot because there are 0 solder joints. In fact, this development took place today.

Now, for the actual plasma:
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Plasma Shot #1
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Plasma Shot #2
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Plasma Shot #3
Unfortunately my vacuum pump isn't quite strong enough to confine the plasma in the center, but I do have a Turbo Molecular Pump and eventually it'll be hooked up to the reactor.
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The Turbo Molecular Pump
I also noticed that the plasma would shift through different colors the longer I ran the reactor. As I mentioned, I can now run the reactor for a very long time, so I can truly observe the plasma. It starts off the normal purple, the fades to pink. Then it goes from pink to white and from white to blue. That's usually when I turn it off, but is usually has a few green spots. This might suggest it would turn green if it was left on longer. Anyone have an explanation for this? I realize different color plasma is created because of different types of gas, but the strange thing is that if I turn the Variac off and on the plasma starts over at purple. If it were a gas it should go back to whatever color it was when I stopped the glow of power. Sadly, by the time the plasma makes it to white it is way to bright to take a decent picture of.

Three questions:

1. Why does the plasma change color? Is it because of the gases in the chamber or something completely different?

2. How do I confine the plasma in the center? Am I right about needing to use the Turbo Molecular Pump?

3. Any suggestions? If you have anything helpful to share I'd love to hear it!

Thanks!

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Rich Feldman
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Re: First Plasma (April 19, 2017) - Most Recent Plasma

Post by Rich Feldman » Sun Jul 16, 2017 9:38 pm

Hi Jackson.
Let's leave behind our dialog in your first thread, where both of us might have been a bit off from our usual politeness.
As a "bottom line first" exercise for me: some respectful answers to your second question.

1. Yes, your plasma isn't forming a ball because its pressure is too high. You can infer the approximate pressure from the plasma configuration, as discussed frequently at fusor.net (please go look). Or from a vacuum gauge connected to your chamber, which you'll want to have plumbed up when neutron claim time comes around.

2. It's premature, and very common for neophytes, to blame the deficiency on the vacuum pump. Doesn't take much searching to find pictures of plasma balls and bugle jets, even "star mode"* plasmas, in systems with only rotary pumps.

The pressure around your grid is determined by an equilibrium between gas load (leaks and outgassing into the chamber) and pumping speed (commonly given in CFM or liters per second). The actual pumping speed and ultimate pressure, at the chamber outlet port, always fall short of those on pump nameplate. One factor is the connecting hose and its "vacuum conductance", which is also measured in CFM or liters per second. Conductance is a function of physical tube dimensions and the pressure regime. It's how fast gas would enter the hose if there were a perfect vacuum at the far end. It's why the vacuum spigots at lab stations on ISS are rated to deliver 1 mTorr, not lower. What's the value for your hose, and for your pump and hose in series?

I bet:
- You can get plasma balls and bugle jets without connecting the turbo pump.
- Fixing your leaks will be more fruitful than changing the vacuum hose, much less changing the pump. You need to do it anyway.
- The sooner you have a thermocouple or Pirani vacuum gauge on your chamber, the more time it will save you. You need it anyway.

*"Star mode" is a visible plasma configuration familiar to fusioneers. Named for the star shape. In at least one recent post, someone mistakenly thought it meant star nuclear reactions.

- - -
Now a non-technical response which was written first.

The primary answer to your question #2 is about the same as those given in the "enough is enough" thread.
"Please read the FAQs and do some forum searching first."
The subject has been discussed here, quantitatively and with pictures and theory, many times in the past. It really isn't that hard to find. Unlike many online fora, a large share of the readers here respect the value of archives and self-service Search tools, to complement the immediacy of Internet chatting at places where there be experts.

That second question is a New User question and belongs in the New User Chat Area. Because of its content, not its author or its style. You'd probably get good and correct answers right away, I bet from other new users who have been there a little longer.

Your pictures and description are very nicely done. Some might say they belong under Images du Jour, in spite of the formal description that warns of it being ephemeral. It's conventional to present progress reports there, even when they are short of neutron claims. Such threads are generally tagged by an administrator to make them persistent.

TTFN.
Richard Feldman

Sarvesh Sadana
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Re: First Plasma (April 19, 2017) - Most Recent Plasma

Post by Sarvesh Sadana » Sun Jul 16, 2017 10:40 pm

Without more information, I would attribute the color change in the plasma to a combination of the grid melting (see: viewtopic.php?f=18&t=11341) and the pressure increasing. What is your grid made of?

The pressure is far too high here. Based on the plasma, I would estimate it is a few torr, indicating you have large leaks in your chamber. It's probably too low to run your secondary pump. What is the minimum backing pressure needed to use your turbopump?

I agree with Rich completely. You really should read all of the FAQs, and the rules of the forum. This question would have been better in the new user forum.

Sarvesh

Jackson Oswalt
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Re: First Plasma (April 19, 2017) - Most Recent Plasma

Post by Jackson Oswalt » Mon Jul 17, 2017 1:25 am

Ok, so First, I'd like to apologize to Rich. It wasn't pleasant or mature of me to lash out at you on my first post. Thank you for making the effort to put this behind us and I will do my best to do the same.

Now to answer Sarvesh Sadana's questions. My grid is made of copper currently bent into the formation you see in the pictures. I understand that this is far from optimal, and I have parts in the mail that will make it official. You also mentioned that the color of plasma may have to do with the grid melting. I suppose this would make since, but the grid, when turned off, isn't glowing or anything. To reply to your second question, the turbo molecular pump doesn't require any pressure to start. At least that's what the seller said (who had used it for a good amount of time before selling it).

Next I'll answer Rich's questions. First off, I agree with your comment about getting a thermocouple gauge, and I have one in the mail now. I'm not sure about the "Conductance", but my pump is a 2 stage, 5 cfm Robinair vacuum pump. I understand now that my normal roughing pump may be enough to confine the plasma, but it is it truly enough for fusion?

I apologize for my laziness when it comes to searching for questions that have already been answered. I will do my best to avoid doing so in the future.

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Re: First Plasma (April 19, 2017) - Most Recent Plasma

Post by John Futter » Mon Jul 17, 2017 2:23 am

Jackson
Now that the formals have been done

You need to read the FAQ's
you need to lose any joint with teflon tape and soft solder those joints.
you need to get rid of both those ball valves
Many here have said they work I have measured dozens of different types some american others Asian on a helium leak detector
none where any where near vacuum tight as supplied. All leaked through the stem just under the handle.
It might be possible to disasemble and coat all the surfaces with High vacuum grease to get a TEMPORARY SEAL.
Again a ball valve with teflon seats will leak.

Get some vacuum rated backing line valves (rubber metal seal type are fairly cheap) you do not need bellows sealed valves on the backing line.

Now Yoda speaking
Much to learn this boy has

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Richard Hull
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Re: First Plasma (April 19, 2017) - Most Recent Plasma

Post by Richard Hull » Mon Jul 17, 2017 10:47 pm

There is no image of how you connect the vacuum pump to your chamber shown. If it is that tiny hose connected to the right, then it is too long.

2 feet of 3/8" diameter vacuum hose is ridiculous and is simply terrible and bad practice.... an embarassment. The vacuum forum FAQs stress this in the extreme. As Rich notes, it is all about conductance. Don't strangle the Robinaire by forcing it to evacuate through an effective soda straw.

4 inches of 1" diameter hose is nearly ideal between pump and chamber. 8 inches is way too long.
If you are not connected to a secondary pump, like a turbo or a diff pump, you need to jam the fusor chamber ontop of the Robinaire with the shortest length and largest diameter hose physically possible that you can manage. Only then will you pump out a chamber with any speed.

The colors you are seeing can due to backstreaming oil, water vapor, air, grid material and outgassing polymer from the long hose.

The above advice about short, large diameter hoses assumes you have no real leaks and that the Robinaire is doing its job and its oil is not loaded with water.

This is about the 5,953rd time I have noted the above....I had hoped the FAQ I wrote about this would be the last time I would need to stress this. The beat goes on.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Jackson Oswalt
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Re: First Plasma (April 19, 2017) - Most Recent Plasma

Post by Jackson Oswalt » Tue Jul 18, 2017 4:37 am

image.jpeg
Here, now you can see how it's connected. The hose is temporary, it was bought to connect the TMP to the roughing pump. Also, there is a humongous leak in the system. All the copper gaskets had been previously used by the seller. This info was;t shared with me until I asked.

The chamber has been disassembled entirely for it's major revamp.

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Richard Hull
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Re: First Plasma (April 19, 2017) - Most Recent Plasma

Post by Richard Hull » Tue Jul 18, 2017 5:19 am

Thanks for the pix and clarification, any issues with its length is offset by its generous diameter and its SS nature.

I see the small diameter clear plastic tubing is used to add insulation to the HV wire entering the chamber. What type of vacuum tight insulator are you using between the HV wire entering your chamber in the image and the grid support stalk?

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Jackson Oswalt
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Re: First Plasma (April 19, 2017) - Most Recent Plasma

Post by Jackson Oswalt » Wed Jul 19, 2017 2:30 am

Ha! It's pretty embarrassing. Right now it's only some more plastic tube, but the whole electrical feedthrough is crude. It's designed for low voltage (hence the metal), and has to be insulated so the high voltage electricity coming doesn't jump to the sides. Fortunately, I have a really nice electrical feedthrough set to be here on the 24 (picture below).
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Side view
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Side view
Attachments
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Vacuum side view

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Richard Hull
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Re: First Plasma (April 19, 2017) - Most Recent Plasma

Post by Richard Hull » Wed Jul 19, 2017 7:53 am

In your original post you inquired where all the colors were coming from. Add plastic vapors from your cobbled up feed thru from neutral bombardment to the mix of color producers.

No plastic, phenolic, bakelite, epoxy, grease or any number of metals (zinc, lead solder, etc.) can be inside the fusor chamber. If they are, lots of great colors, but no fusion and perhaps not much of a vacuum either.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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