Fusor Progress

For posts specifically relating to fusor design, construction, and operation.
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Emma Black
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Joined: Wed May 11, 2022 9:42 am
Real name: Emma Black

Fusor Progress

Post by Emma Black »

Power Supply: I'm using a big potential transformer, 110v-33kv running from a 240v variac & some 100kv cable. Fed up of moving the thing around its now on wheels. Metering via a couple of cheap ebay digital meters.

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Fusor itself is simple 6 way cross, with a marine surplus feedthrough and at the moment is only connected to the roughing pump (Edwards e2m18). Using an Edwards Pirani gauge, connected to a simple analog meter. This gauge has not been calibrated but

I was playing around with some different grids today, the one in the photo consists of stainless steel washers and m4 bolts to create a cage, I think this photo was around 14kv @ 19ma.

Next steps of course are to get the diffusion pump in place and tidy up the entire thing, build a proper grid.

I'm getting a weird issue with the voltage meter, there are no caps on this system but at lower voltages the meters reading fluctuates, second to second way more that I would expect. It's a panel meter with 10m impedance, connected via voltage divider. Analog meter works fine, maybe it's something silly.
Emma Black
Posts: 54
Joined: Wed May 11, 2022 9:42 am
Real name: Emma Black

Re: Fusor Progress

Post by Emma Black »

Making some progress on getting things into a more useable state, apologies if this is the wrong area to post this (feel free to move).

Fusor has now been racked some metering is now in place. Little concerned about the HV cable placement, it's rated up to 100kv but it's touching the back of the grounded rack, should I physically isolate it better?

Found the weird issue I was getting with the voltmeter was related to the two 500mohm resistors I was using for the voltage divider, it seems they were not rated at anywhere enough for the voltage needed. So I have switched to a pre-made HV probe while waiting for some new ones from China.

Current metering is via a self made shunt using nichrome wire.

Pressure measurement is via an Edwards Active Pirani Gauge, which outputs 2-10V depending on pressure. I'm getting 4.5v here which I believe works out to around 60 microns. How accurate this is I am unsure without calibrating the meter properly.

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Grid is still a simple couple of loops of tungsten wire on a bolt, but have a few tungsten wedding rings of different sizes off amazon which, plan to experiment with next and still have a diffusion pump to get up and running.

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Aidan_Roy
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Real name: Aidan Roy
Location: Massachusetts

Re: Fusor Progress

Post by Aidan_Roy »

Hi Emma,

So far that set up looks like it will definitely serve you well as you move forward. Is that transformer mounted in a military surplus ammo can? It looks great! I did a similar case with my own, and that sure is some beefy wire! If its the porcelain thats in contact it will be ok at lower voltages, maybe just as u practice getting plasmas struck and working with the pressure you are at. Once you get more into fusion voltages though however, it will rather jump to ground. I would watch for corona and isolate it as best as you can from any metal objects.
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Dennis P Brown
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Location: Glen Arm, MD

Re: Fusor Progress

Post by Dennis P Brown »

Looks good; my (far smaller & much lighter) x-former yields 30 - 33 kV and 25 ma continuous and 100+ ma surge so I assume yours can provide far more current.

Don't know if you have done this already but a metal case with a fusor inside should also have its own ground wire - not just for any possible HV issues but also if any 120/220 v shows up via a short from other devices. A good star grounding system insures that all major devices, besides the fusor, are properly grounded - a plasma arc can go a long way I've found. I use two independent grounds but I wired my own lab so such is available.
Last edited by Dennis P Brown on Wed Jun 29, 2022 6:19 pm, edited 1 time in total.
Emma Black
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Real name: Emma Black

Re: Fusor Progress

Post by Emma Black »

Aww thanks for the kind comments, it's getting there.

Yes its a ex British army motor box, theres the bridge stuff and ballasts inside in perspex tubs filled with oil with temp sensors. Box is oversized because I want to move the variac in there eventually and have it operate remotely via a motor, which it came with it. Box has since been painted and looks very snazzy.

Everything is grounded to a proper busbar, the shell, the pump, variac, server rack etc.
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Dennis P Brown
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Real name: Dennis P Brown
Location: Glen Arm, MD

Re: Fusor Progress

Post by Dennis P Brown »

Just a FYI; to make my 'cathode', I took a welding rod (for steel - so it is some steel alloy) and bent it around a 3.5 cm rod making four turns. Then reshaped these 'circles' to form a cage structure by bending three of them to different angles. Works well and the welding rod is 3 mm in diameter so heating isn't an issue even when I push 40 ma at 33 kV for a few minutes.

Here are some pics of my HV feed-thru and the cathode: viewtopic.php?t=14336

Not pretty (one could if they are more careful) but certainly works.
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