Liam David Fusor Update

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Liam David
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Liam David Fusor Update

Post by Liam David »

I have now disassembled Fusor MK-1 to make way for MK-2. As of May 5, 2014, this is what I have.

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I have a threaded hole drilled in a rotatable 2.75" CF flange for a spark plug. This will be used as the HV feedthrough.

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The hydrogen regulator is 2 stage and has a maximum inlet pressure of 3000 PSIG and a minimum outlet pressure of 1 PSI.

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The main chamber is a 2.75" CF tee with 2 rotatable and 1 fixed flange. The regulator will be attached to the holes on the double sided flange (where the bolts are now).
I will use a how ever many stage multiplier wired to a 15kV NST to get 30-45kV.
A better vacuum pump than a 2 stage 3 CFM 2.3 micron pump will hopefully be supplied by George Washington University.
Fifty liters of deuterium will be purchased from Cambridge Isotopes.
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Dennis P Brown
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Re: Liam David Fusor Update

Post by Dennis P Brown »

I am no expert but I do not think that you will get enough power from a single NST to drive enough current in a voltage multiplier at 60 Hz to achieve 40 - 45 kV (I assume one needs at least 10 ma and twice is better.) Adding stages does not give extra current with voltage multipliers. The issue of ripple will be rather extreme with small caps and larger caps require too much current for the NST to supply without massive voltage drop out. Look up Chris' design using multiple lower voltage transformers coupled to a voltage multiplier circuit. That might address your needs.

You might want to ask if a spark plug can handle that level of power - I be surprised if it could ( 40,000 V * 0.02 amp/sec = 800 watts!)
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Scott Moroch
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Re: Liam David Fusor Update

Post by Scott Moroch »

Dennis just made a very good point that you should probably take into consideration regarding the spark plug. If you are looking to get up to voltages of 40-45 kv, a spark plug may not be in your best interest for a high voltage feed through. After reading about other fusors I learned that a spark plug may fail at around 20-25 kv and can potentially harm your power supply. I recommend you invest in a professional high voltage feed through that can handle the voltages you are looking to reach.

In addition, I noticed your main chamber is a 2.75 CF tee. The size of the chamber is acceptable, given the fact that fusion has been done in that size. However, 40-45 kv in a chamber of that size may be hard to handle and control. I am currently building a KF 5O 5-way cross fusor and so I understand the size you are dealing with. I would be careful with that kind of voltage in a small chamber. Also, as Dennis mentioned voltage ripple will be a concern with the type of voltage multiplier you are attempting to assemble using a 15 kv NST with hopes of reaching 45kv.

In addition, based on the size of your chamber and the price of deuterium, you do not need to purchase fifty liters of gas. 25 or even 10 liters may suit your needs.

Best of luck,

Scott Moroch
"In the middle of difficulty lies opportunity"
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

More parts have arrived!

First, a Series 275 Granville Phillips Mini Convectron Gauge with a KF 16 connector.
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The gauge is connected to the top of the KF 16 4-way cross. The left side of the cross is connected to the chamber via a CF 2.75" to KF 16 adapter. This adapter was made by silver brazing a CF 2.75" .75" bore to a KF 16 half nipple with a .75" OD tube. The bottom of the cross is an unused port. The right side is where the diffusion pump will be connected by it's loooong hose.
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This is the diff pump
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The HV feedthrough is now composed of a .25" OD .188" ID 12" long alumina tube. A CF 2.75" to .25" compression port seals to this rod via an o-ring. The end is capped with a .25" Swagelok end cap. The internal conductor for now is a wire.
Image

-Liam David
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Re: Liam David Fusor Update

Post by John Futter »

Dennis
I cannot fathom your quote about spark plugs not handling the power.
The central conductor is usually copper tipped with something like tungsten or for long life plugs platinum
I put many tens of amps through these as feed throughs into high vacuum systems
you do not multiply the volts and current together to get the spark plug dissipation
I x I x R is better
I have just measured a sparkplug it is 2.7 milliohms so 20 amps gives 20x 20 x 0.0027 = 1.08 watts
40 amps would make for 4.32 watts of dissipation in the plug ---probably about the maximum one should consider
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Re: Liam David Fusor Update

Post by prestonbarrows »

Dennis P Brown wrote:...You might want to ask if a spark plug can handle that level of power - I be surprised if it could ( 40,000 V * 0.02 amp/sec = 800 watts!)...
This is not quite right. The mistake is that voltage is measured across the component in question, not with respect to absolute voltage to ground. This is given by Ohm's law as V = I*R. In other words, you need resistance to maintain a voltage between two points.

A feedthrough is short and made of low resistance materials, something on the order of milliohms is a good guess. So, even pushing many amps through, the voltage across the feedthrough will be much less than a volt. In this case say, 40,000V on the outside terminal and 39,999.99V on the inside terminal.

In this case, the more relevant power relation is P = I * V = I * I * R. For these applications, order-of-magnitude values give 0.1[A] * 0.1[A] * 0.001[ohm] = 0.00001[W] as the power dissipated in the feedthrough itself. This is on the order of losses in any other wire in the system, which makes sense since a feedthrough is just a fancy bit of wire.
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Andrew Robinson
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Re: Liam David Fusor Update

Post by Andrew Robinson »

Looking forward to seeing your progress on your new power supply ;)
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Re: Liam David Fusor Update

Post by John Futter »

Preston
did you not see my posting immediately above your latest.
you are repeating but worse with conjecture. I did measure the resistance of a plug and did calculate the actual losses at two currents
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

The GFCI on my 15kV 30mA NST was just annoying the heck out of me. So I ripped it out. Now the NST varies voltage smoothly. I decided to test the newly modified NST by making some plasma, so I switched on my newish diffusion pump and threw the switch.

Image

The image is a horribly grainy, but I think I finally got a bugle jet shooting out the bottom of the grid. Still have no idea about the vacuum level because the seller gave me a fried circuit board. I'm guessing that the geometry of the inner grid is preventing me from reaching star mode. It's a bit oblong.

Image

-Liam David
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

Today I let my system pump out for twice as long and I think I got star mode.

Image

The images aren't very clear. I'll try getting better ones later tonight or tomorrow.

Image
Image
Image

-Liam David
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Richard Hull
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Re: Liam David Fusor Update

Post by Richard Hull »

Nice work Liam! I hope to have you in the neutron club soon. You are going at this correctly. Good luck.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

I still have a few things to work out, like the pesky ZVS driver for my 150kV x-ray transformer, a still broken vacuum convectron gauge circuit board, an the voltage and current metering stuff.
My HVAC backing pump runs blazing hot. I have to keep a rather large fan blowing on it for extended pump down.

-Liam David
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

Also, as a separate topic, I am working on a website. It is still a major work in progress.

http://liamdavid75.wordpress.com/home/

-Liam David
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

I let the system pump down using only the mechanical pump and switched on the power. The plasma appears exactly like the plasma with my diffusion pump on. The star doesn't become more distinct or star-like with the diff pump, so it doesn't appear like my diff pump is doing anything. Since my gauge is broken, I can't tell the pressure.
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Richard Hull
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Re: Liam David Fusor Update

Post by Richard Hull »

Without at least a known good TC gauge, you are dead in the water, vacuum wise. You will never know what you have or haven't got in the fusor environment.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

Finally I bought a Granville Phillips Series 275 Convectron Gauge with digital display (part # 275538-GQ-T). I powered it up and is displays around 750 torr when in the correct horizontal orientation.The gauge has a 1/4" female VCR connection, and I do not want to buy some outrageously priced VCR to KF-16 adapter. I brazed a washer to a male NPT fitting to allow it to seal with the gauge.
Image
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I hooked it up to the chamber, and was not happy with what I saw. With the roughing pump, I got the chamber down to 450 millitorr. With the diffusion pump, the pressure first rose to over 600, then dropped to about 250 millitorr, and then rose to stabilize at about 350 millitorr. When I closed the ball valve between the chamber and diffusion pump, the pressure rose at over 100 millitorr/second. Crud. Next step is to find the outrageous leaks (probably the HV feedthrough with compression fitting and hose barbs in the vacuum line).
-Liam David
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Richard Hull
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Re: Liam David Fusor Update

Post by Richard Hull »

Suspect your gauge connection kludge first. Connect the gauge to the forepump directly before anything else and see where you are. Step by step process.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Rich Feldman
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Re: Liam David Fusor Update

Post by Rich Feldman »

Yes, what Richard said.

Previous threads have mentioned changes in plasma color
when a tracer chemical is sucked into a leak.
Alcohol, acetone, dust-off spray, butane? :-)

You have at least one massive leak, findable with more primitive methods.
For example, pressurize the apparatus and apply soapy water to suspected joints.
Or evacuate the apparatus and apply vacuum oil to suspected joints. Pressure will drop as oil temporarily plugs the leak.
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

After re-brazing a conflat to KF adapter and replacing part of my vacuum line with copper pipe, I got my chamber down to 35mTorr after 45 minutes of pumping(not great, but an improvement over 400mTorr). The pressure rises at about 1mTorr/sec when I close the valve. I cranked up the voltage and got a dull, white plasma without a distinct star in the center, compared to purple distinct plasma I achieved earlier. I'll buy a bottle of helium soon for leak testing.
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

I discovered that one of the gas ball valves I use leaks, so I immediately suspected all of them. I bought a new vacuum butterfly valve for dirt cheap and replaced the ball valve. Now I can vent the mechanical pump and keep the chamber under vacuum. It leaks at about 0.5mTorr/s, and rises to 13 torr after 12 hours. Pictures probably coming tonight.
I suspect that the leak is at the cap of the feedthrough. The Swagelok cap broke off the end of the alumina rod, which is now rough. I'm still on the lookout for a cheap turbo pump/controller package and am still having problems with the high frequency transformer.
-Liam
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

It's been a while since I last posted. I have bought a 6 way 2.75" conflat cross to serve as a new main chamber. It will get here next week. Also, when I'm roughing the chamber out, the pressure drops to ~55 mtorr (still leaks) and then starts to slowly rise to 56 and then 57 as the pump starts to warm up. I disassembled and cleaned the pump, including one of the rotary vane stages, and got the chamber down to 55 mtorr, a 20mtorr improvement from before the cleaning. The rise in pressure still happens. Any idea what could be causing this?
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Richard Hull
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Re: Liam David Fusor Update

Post by Richard Hull »

What can the pump do at the head? Put a gauge directly at the pump inlet.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

At the moment, I am unable to deadhead the gauge. I got my new chamber in the mail today- it's a 6 way 2.75" conflat cross. Here is it assembled with used copper gaskets just for reference.
Image

Image

On a separate note, my school is building a 1MeV cyclotron starting next year. The project will be guided by Tim Koeth from UMD, and I had the pleasure of talking to him briefly after the school interest meeting for the cyclotron was over. Hopefully I will be fully involved in the project over the next few years- I am probably one of the more vacuum and high voltage knowledgeable students at my school currently (though I'm mostly still a newb), and I am sure that my "experience" building a fusor will help earn me a spot on the team.
-Liam
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Re: Liam David Fusor Update

Post by Nick Peskosky »

Just a quick note: I see that you're using some type of NPT threaded elbow adapter to connect the VCR flange on the 275 Mini, you did use a metal gasket seal between the VCR flange and the VCR->NPT coupling? These connections require silver plated SS crush discs which must be seated (and ideally centered) between the Male/Female VCR connections. I had a minor leak on my gas line which was affecting my ultimate pressure with the turbo on and the fix was as simple as utilizing vice grips and a wrench to tighten each VCR connection. Try placing ~90% isopropyl alcohol (denatured) or acetone on the flange seams and if you see the pressure climb even further than you've found your leak.

Just some food for thought.
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

Yeah, it's not the right fitting. I used it earlier by brazing a washer to the end to act as a rudimentary seal surface along with a cast solder gasket. It undoubtedly leaked and I'm replacing it with a VCR to KF adapter soon. It's just in the picture for "show". Do I need silver plated SS gaskets or can I use copper?
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