Liam David Fusor Update

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Liam David
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Liam David Fusor Update

Post by Liam David » Tue May 06, 2014 8:57 pm

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 » Tue May 06, 2014 11:45 pm

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!)

Scott Moroch
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Re: Liam David Fusor Update

Post by Scott Moroch » Wed May 07, 2014 12:53 am

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"
-Albert Einstein

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Liam David
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Re: Liam David Fusor Update

Post by Liam David » Sun Aug 24, 2014 8:54 pm

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.
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-Liam David

John Futter
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Re: Liam David Fusor Update

Post by John Futter » Sun Aug 24, 2014 9:03 pm

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 » Sat Aug 30, 2014 10:57 pm

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 » Sun Aug 31, 2014 5:34 am

Looking forward to seeing your progress on your new power supply ;)
I can wire anything directly into anything! I'm the professor!

John Futter
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Re: Liam David Fusor Update

Post by John Futter » Mon Sep 01, 2014 1:14 am

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 » Sat Sep 27, 2014 8:08 pm

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.

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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.

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-Liam David

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Liam David
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Re: Liam David Fusor Update

Post by Liam David » Sun Sep 28, 2014 4:49 pm

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

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

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-Liam David

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