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Re: Archived - Tom McCarthy's Fusor Efforts

Posted: Fri Sep 05, 2014 3:56 pm
by Tom McCarthy
Lots more equipment; namely an Edwards RV3 mechanical pump, an Oerlikon-Leybold Turbovac 151 (with controller and cables) and Gamma Spectacular neutron detection set-up. I've also got my vacuum chamber sorted out, a 12" sphere with 10 CF ports. It's being made by [url][/url] and should be here some time in October. Ordering deuterium soon enough and more vacuum fittings en route. Need to get some more gas fittings and vacuum valves, but that's all really.

The Turbovac is newly refurbished, straight out of the box and the RV3 has only seen some moderate use. The previous owner said it should be pulling optimum vacuum after an oil change/clean-out.

Does anyone know anywhere to get a 3" sodium iodide scintillation crystal? There are BGO ones and some other types on sale on Ebay, but I'd prefer NaI.


Re: Archived - Tom McCarthy's Fusor Efforts

Posted: Wed Apr 08, 2015 12:56 pm
by Tom McCarthy
Been quite a while since the last update...There's been a little and a lot of progress at the same time. As stated before I've got 95% of the parts (only need to order deuterium + related piping) and I'm pretty much ready to go. I've been testing my fore pump and am about ready to hook it up to the chamber.

The guy who's giving me the power supply is keeping it until I've moved into a 3rd-level for supervision - This has been a bottleneck in progress for the past few weeks, but it looks like I'll be moving the setup to NUI Galway under their engineering department when all the safety items are cleared. I've also had trouble ordering deuterium, but I've been told it should be relatively easy to procure when I'm in a University.

My chamber's almost fully bolted, got the viewport and a load of blanks on and am going to fully blank out the other ports to test-run the vacuum pumps. Currently waiting on my boxing trainer (Works in a very good metal-work shop) to get back to me with some prototype grids - got 0.6mm tungsten wire as advised in the FAQs, but he's not sure how weldable it's going to be..

Hopefully I'll get moving a bit faster on the project now, looking to complete before June.

RV3 at the bench.

Re: Archived - Tom McCarthy's Fusor Efforts

Posted: Wed Apr 08, 2015 6:52 pm
by Richard Hull
Super impressive chamber! Good luck with the future fusion effort.

Richard Hull

Re: Archived - Tom McCarthy's Fusor Efforts

Posted: Wed Feb 14, 2018 11:41 pm
by Tom McCarthy
I knew it had been a while since I updated this thread, but didn't realise it was that long.

I have an awful lot more equipment now - deuterium, needle valve, swagelok connections, flow meter, orifice, Hb feedthrough and power supply (no cable), turbopump and roughing pump all ass,bled and pumping to 10^-6 as measured by Penning and Pirani gauges. Neutron detection also here.

Today I received a 6" CF throttle valve, exceptionally well packaged. It's pneumatically actuated, but has a micrometer for throttling. Also have some RG213 pictured that I'm using for a HV cable (many thanks to Rex Allers for his generous help, and also to Jeroen Vriesman and his fellow Dutch experts) and the HV supply I'm using.

Re: Archived - Tom McCarthy's Fusor Efforts

Posted: Thu Feb 15, 2018 12:58 am
by Richard Hull
When you are finished and working, this will be a really sweet fusion system. Taking it slow and easy will allow for a system that has a far better chance of success out of the gate.

Richard Hull

Re: Archived - Tom McCarthy's Fusor Efforts

Posted: Thu Feb 15, 2018 8:09 pm
by Tom McCarthy
Thanks Richard, looking forward to getting it working.

Re: Archived - Tom McCarthy's Fusor Efforts

Posted: Sun May 27, 2018 9:14 pm
by Tom McCarthy
I just finished leak testing my gas line and it’s in place now. Dad and I put together the clamp arrangement that holds the D2 lecture bottle in place. He welded it, as I have next to no welding experience.

My next step is to complete my RG58 HV cable, and connect my power supply to ballast resistor and then to feedthrough. I also have to put together a little HVPS control box. Handily, the power supply has voltage and current readout and control I/O. Getting there, bit by bit.

Also, not directly Fusor related, but I came upon a CNC lathe. It’s older than I am. I was told that the motors, mechanics etc. are good, but there’s something up with the software. Will boot it up and try and get it working as soon as I achieve fusion.

Re: Archived - Tom McCarthy's Fusor Efforts

Posted: Mon Sep 17, 2018 2:06 pm
by Tom McCarthy
I achieved plasma this weekend, on a run less than a minute long. It followed from wiring up and testing my high voltage line and supply.

The high voltage line consists of:
a DIY connector for the Matsusada supply
RG213 coax
100k, 100W resistor immersed in motor oil
grounding lugs/wires
Feedthrough and machined connector.

Also, though not shown in the pictures below, a 4" sewer pipe is placed over the exposed feedthrough and aluminium bar.

To control the supply I use the supply's I/O interface - connects to a panel I made myself, with 10k pots and 0-10v LED meters.
Voltage - varied 0 to max 6kV.
It drew a large current though, maxing out the supply at 20mA. Is this normal? My current meter was showing 9.99, so either I've wired up the control panel wrong, or the plasma current is very large. Perhaps there's some arcing going on, but I couldn't hear anything.
Pressure: ~10 microns.

When I return home next weekend I'm going to do another few runs, hopefully fusion too as I've the deuterium line in place already.

There's a video of the full run at this link - ... sp=sharing
It was too large to attach in a zip.

Many thanks again to the Dutch - Jeroen, Jerome and company that helped me out, and Rex Allers for his advice on the high voltage wiring.

Re: Archived - Tom McCarthy's Fusor Efforts

Posted: Mon Sep 17, 2018 8:51 pm
by Dennis P Brown
I certainly can't speak for your system but in mine, I could easily draw well over 100 ma at startup (max for my x-former was 33 kV and 28 ma continuous) using a 60 K-ohm oil submerged resistor. When the plasma first ignites, resistance can drop to near zero ohms in the fusor and the ballast resistor can do only so much. When this happened (nearly every start up) I'd simply dial back the variac to drop the voltage and hence, the current - often too much and I'd lose the plasma. Then I'd finely adjust the voltage upward until re-ignition, and then have to quickly but using small adjustments re-set the variac to stabilize the plasma. Then I'd use D2 flow to do fine adjustment on the current - this assumes one has already set their fusor's pressure to about its correct operational range (for me, 4 - 9 microns with 5 microns being the most common value.)

Be careful at start up - not dialing the voltage back and allowing the current to run full out could damage your transformer. Trying to ignite the plasma at the lowest easy working voltage is your safest method. The higher voltage systems can really conduct - at 5 microns, I'd get plasma light up anywhere from 18 kV to 24 kV.

Once the plasma remains 'lite', use both gas pressure and the variac to walk the voltage up to your desired setting. Often, the plasma will go weak (too much gas) so one needs to increase the voltage a bit faster or in some cases, finely adjust the gate valve. If current starts to climb too quickly, pressure can be used to control that parameter rather quickly. Setting one's diffusion or turbo gate valve is critical - both to conserve gas and make the system's response to fine gas valve adjustments better.

With experience, you will determine your "sweet spot" for your gate valve, fusor pressure, fine gas valve setting, and start up voltage. Once these are determined, and the chamber is seasoned, start ups are rather easy and so is maintaining the plasma - I could easily run an half hour: but my system did need to be watched - it could easily run away on its own.

Re: Archived - Tom McCarthy's Fusor Efforts

Posted: Tue Oct 09, 2018 3:27 pm
by Tom McCarthy
Thanks Dennis, appreciate the advice. I'm finding it harder than expected to operate the Fusor, haven't achieved a stable plasma at high voltages yet. I don't think I've got a stable deuterium plasma yet, as my D2 flow is too constricted, and I can't seem to throttle my turbo pump enough. The turbo is mated directly to a 6" gate valve. When I run the turbo though, a star mode emerges but is almost immediately extinguished as the pressure continues to drop. See the video at the link below - can't attach it here.

At the end of the video the plasma colour changes to a deeper pink from light blue/grey. Is this indicative of a deuterium atmosphere? I had deuterium flowing into the chamber while the turbo pump was started and think the atmosphere should have been mainly deuterium for a short while. What do you guys think?

Video here.
Screen Shot 2018-10-09 at 16.23.21.png