Matt Gibson Fusor

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
Post Reply
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Matt Gibson Fusor

Post by Dennis P Brown »

As for the lack of ceramic extension into the vacuum system, that isn't as bad as you might suspect - the plasma is both very conductive (over a volume) but has limits in any given small volume at low pressure (under 100 microns); so it is partly self limiting in the normal vacuum range that a fusor operates: 5 -20c microns. All bets off if you go a good bit above that pressure. Then the plasma can focus and support a considerable current. and at near torr range, support an arc.

If your worried, adding a glass tube extension that fits inside the ceramic tube and affixed with some furnace grade ceramic adhesive should work to insulate the rod.

Your turbo had better zero out a micron gauge for your system; an ionization or cold cathode will be required to determine the lowest value. Anything in the mid 10^-5 torr is good for a fusor as "clean" and vacuum tight.
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Matt Gibson Fusor

Post by Matt_Gibson »

So I think that I might have a leak…The new bspp to Kf25 flange didn’t come with an o-ring, so I took one off another fitting. This definitely helped things as before (no o-ring) I was pulling in the Torrs. After this improvised o-ring, it pulls into the mTorr, but now only gets down to 45mTorr after 10mins.

I’m guessing that while the o-ring helped, it’s needing something better. What else can I do? Better o-ring? Teflon tape on the bspp threads?

As of now, I’ve added a 8.5in length of steel tubing (Kf25 ends) and the turbo. I know that I shouldn’t expect the same performance as before these additions, but I expected better.

I have yet to hook up the chamber, so I’m expecting worse after that.
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Matt Gibson Fusor

Post by Richard Hull »

Every addition to a piecemeal tested vacuum system will suffer a reduction in performance due to any number of factors. Most often it is something stupid, poor sealing, ill suited additions, etc. The number one issue is that you brought you entire system up to air. Even with valves to close off a tested, partially assembled vacuum system, the new part will be loaded with all manner of water vapor and other vaporous materials that will either require many hours of system pumping or a tedious bake out to bring to a suitable vacuum level.

You are wise in following my vacuum system advice to assemble and test a system step by step. In this manner, you are confident in all the work done up to a point. (Seals are good and the system thus far assembled is good.) Each new addition imposes a trial period of sealing and pumping.

If you get a great idea and go back into the already tested system to add something great like a valve or a new fitting, you fight the battle all over again. Without a whole bunch of heat tape to bake out with, you are subject to long pumping periods and a lot of leak testing. Even technical vacuums can be frustrating to achieve. Scientific grade vacuum levels demand a special level of cleanliness. A good scientific level vacuum system, especially a complex one, is just never brought back up to air unless it is absolutely unavoidable. Such systems are loaded with top grade and expensive valving all along the vacuum path and all pumps are left on 24-7.

A good fusor needs a minimum of three vacuum valves, though two bellows seal valves will do in some cases. The fusor is trapped between a technical and scientific vacuum. Technical vacuum levels, (10 microns), just will not cut it and scientific level vacuums, (10e-6 torr), while nice, are just ridiculous over kill.

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
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Richard,

I have a valve meant to isolate the turbo from the foreline pump, just waiting on more Kf25 clamps :-)

I removed the turbo from the system and found that I can quickly (20 seconds or so) hit 12 microns at the end of the 8.5in steel tubing. I gave the bspp to Kf25 fitting a tighter twist and then reconnected the turbo to the system. It’s better (38 microns after 10 mins) but still not great.

Would this point you towards a better bspp to Kf25 seal?

All in all, the turbo is still able to rapidly drop to “zero” microns, I just can’t stand knowing something can be improved :-)
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Matt Gibson Fusor

Post by Dennis P Brown »

Don't over react to out gassing. What you describe sounds a lot like it. Don't assume a slow leak automatically. Just a minor aside, we tend to use microns here to be consentient.

When you can read below 10^-3 torr (using a vacuum gauge for those lower ranges), you can do real testing for small leaks and certainly determine if it is just out gassing or not.
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Dennis,

Got my units mixed up after looking at the Pirani so much lately…

I looked back at MTI site and see they sell a gasket meant to go with this converter. They didn’t include it, or make any mention of it. Despite it weighing like a gram, they want $23 to ship it. I’ll see what McMaster has.
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Matt Gibson Fusor

Post by Matt_Gibson »

Update:

Finally got my system bolted together and did some initial testing.

I am pretty limited in what I can determine right now because I don’t have any high vacuum gauges (any recommendations?). I have the Lesker Pirani and the MKS901 (needs to be installed still).

I am able to get to 0.1 microns (the limit for the Lesker Pirani) in under 10 mins (I need to actually time this). After 10 hours, my pressure creeps up to 252 microns. I tried spraying dust off into each and every connection point to see if it caused any jump in pressure, but it didn’t.

Haven’t done any baking…Would this pressure rise indicate moisture and not leaking?

Edit: Should add that there are a lot of loose ends and work to be done :-) I know I need to add an alumina tube to my feed through and some space on the main valve to the chamber, for example. Not thrilled having my hands so close to the frame, grounded or not.
EFFD34E1-DC9E-4C90-8C5E-64E68001A2E6.jpeg
14D07528-EDE0-4E8C-B6A5-EB36596D634E.jpeg
0D960366-73D5-46A5-BCA7-09967D9E8680.jpeg
Attachments
6BE98B20-329F-48C9-9BE1-33F0665E3552.jpeg
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Matt Gibson Fusor

Post by Dennis P Brown »

First off, very professional looking system.

Second, searching for a real leak when your system climbs just 250 microns in 10 hours is an utter waste of time; that isn't a leak at all - that is very little out gassing from a rather clean system. Baking would be of little value.

Your getting 0.1 micron (1 * 10^-4 torr, bottom of the reading) so are more then likely getting to 10^-5 torr and sufficient for a fusor (starting pressure.) Considering how very clean your system is and the gauge reading to 0.1 micron (bottomed out - likely much lower), you really don't need to measure below that value if you don't want to add another gauge/system. Again, you are essentially there.

If your power supply goes above 30 kV, that steel chamber can start to become dangerously transparent to x-rays; that window -depending on thickness/type of glass - could be a significant x-ray source even at 30 kV. Consider shielding if you determine these parts can't stop the x-rays. To be on the safe side, assume they will and just add sufficient extra shielding. Slate tiles would work nicely.

Remember, x-rays will travel 4Pi steradians so coverage below the fusor is important too - i.e. your lower body will be exposed in that setup too without proper shielding. Think of the fusor as a light bulb (ignore the metal) and that is where the x-rays go. That determines your shielding areas - the threat areas are places that you would be exposed by the 'light' (no shielding) when operating or working around a running system.

So, it looks to me that beside shielding, you just need deuterium and a neutron detection system and you could start doing fusion.
Last edited by Dennis P Brown on Fri Dec 10, 2021 1:47 pm, edited 1 time in total.
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Dennis,

Good to know the system is clean! I spent some time wiping down as much as I could (pretty much everything minus the turbo innards) with 99.9% isopropyl alcohol and handled everything with cotton gloves.

I was a tad worried that my chamber was a bit large for my relatively small roughing pump, but it seems like it’s fine actually.

My psu can go to 40kV @ 15mA, so X-rays are definitely a concern. The viewport is a Lesker Kodial glass type, which I don’t know much about…I’ll probably find some leaded glass to put on the outside. I’ll use my Ludlum to sniff out X-rays very early on so that I can avoid them.

-Matt
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Matt Gibson Fusor

Post by Dennis P Brown »

Your entire fusor could be transparent to x-rays at 40 kV and significant current. You might very well require extra shielding. Just look up penetration depths of x-rays @ 40 kV and you'll know if the steel case can stop that energy. Unlikely the view port glass will but again, look up the values for those energy x-rays.
Last edited by Dennis P Brown on Fri Dec 10, 2021 2:09 pm, edited 1 time in total.
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Matt Gibson Fusor

Post by Richard Hull »

A GM counter will scream at the viewport often before 20kv. It is the real danger for X-rays. A proper calibrated ion chamber will tell all about X-rays. Barring a proper ion chamber instrument. A good group of 3 dosimeters placed next to the fusor and at various ranges from the fusor will tell of total dose. Use only 100mr dosimeters. The yellow CD types are to read max doses of 600R! (Use the yellow dosimeters only after a total, world-wide, nuclear exchange as you venture out in the smoking rubble.)

My 100mr dosimeters read about 10mr when 1/2-inch from the fusor after about 1 hour of fiddling and doing fusion. At 2 feet, just off zero and in my shirt pocket 5 feet away, zero. This readings are taken at 40kv+
I shield only the viewport area very well with 1/8-inch lead. The fusor, I leave naked and unshielded.

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
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Richard,

Thanks for the tips! I’ll admit, physics wasn’t my strongest in college (I did electrical engineering and focused on power), so I’ve been wracking my brain trying to look for x ray penetration formulas!

I’ll grab some lead next time I order from McMaster (I bet they love me by now) to fix around the viewport.

Speaking of deuterium…I plan to use a 100mL syringe made for gases to capture the deuterium production from a fuel cell. I need a way to regulate the gas into the chamber still…Other than a bellows valve that I have installed, do I need to worry myself with needle valves or MFC’s?

Thanks!
Matt
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Matt Gibson Fusor

Post by Richard Hull »

When it come to lead sheeting try Rotometals.com. They have a full x-ray penetration chart and shopping page at the URL below. I see 1/16-inch thick should do you, but I would opt for a bit thicker. 1 foot square sheet of 1/16" is $23. (1/8" is $36 is Overkill). The issue with all metals is that sheet and wire are the most expensive forms of any metal and often command prices 5-20X the market price of bulk metal ingot. Lead is currently just over $1.00/lb on the market at 1000lb lots. The 1/8" square foot is 8 lbs. 36/8 = 4.5X. This is because lead is easy to work.

https://www.rotometals.com/lead-sheet-plates/

They are listed in the primary sources for any and all metals. I rarely have to order metals, but I always find them my best buy in small quantities from 8 ounces up to 100 lbs of metal, especially in rare or oddball metallic elements. Use the primary source forum.

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
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Matt Gibson Fusor

Post by Dennis P Brown »

To control deuterium into a fusor a 'leak' valve of some type is absolutely essential - standard vacuum valves (like bellows) simply do not offer enough control. A leak valve can be made or bought. High quality leak control valves are expensive even compared to vacuum valves but are available from vacuum supply companies. Making a valve that can perform in a somewhat similar manner has been done by people here. If I recall correctly they use a type of fairly inexpensive needle valve (AC grade) and add a very small capillary tube; one could also use a special micro-pin hole (companies make these for the medical industry applications.) Search the Fusor construction FAQ for leak valves - I believe that topic is covered there.
User avatar
Finn Hammer
Posts: 298
Joined: Sat Mar 05, 2016 7:21 am
Real name: Finn Hammer
Contact:

Re: Matt Gibson Fusor

Post by Finn Hammer »

An MFC is the gold standard of flow control.
I use one of the 10CCM variety, and it gives superiour controll of the flow, and thus the fusor pressure, which can easily be regulated to less than a microns presicion.
Get one, you won't regret it if you do.
And if you should ever contemplate to create an autotuning fusor, you will need one anyway.....

Cheers, Finn hammer
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Matt Gibson Fusor

Post by Matt_Gibson »

I’ll go the MFC route…I have been trying to keep ease of operation in mind over simplicity and cost. I quickly lose interest in a project if I have to hassle with it too much :-)

Any really good brands to look for other than MKS?

I’m going to hook my grounds and psu this weekend. Hoping for a plasma club entry soon.
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Matt Gibson Fusor

Post by Dennis P Brown »

MKS are excellent flow control devices. I've used them in the past with great success. But in buying any flow controller be aware they come in many flow volumes so get the right one. Besides the actual flow control unit, some require a separate power and readout display is also required. These devices have various connector options so if you use swagelok get that type.

New flow controllers are not cheap. Consider a good quality manual valve flow control valve for deuterium gas. These work very well (Yes, manual) and might be a good option, too.
User avatar
Finn Hammer
Posts: 298
Joined: Sat Mar 05, 2016 7:21 am
Real name: Finn Hammer
Contact:

Re: Matt Gibson Fusor

Post by Finn Hammer »

Trying your luck with making an offer on this unit might be a good idea.
Factory refurbished is the way to go with this kind of hardware, which is impossible to fix, for the average joe, if broken.
https://www.ebay.com/itm/304230386834?h ... SwHXlhlrcb
It is a helium calibration, but it should still work ok with H2.
You will need a + -15V supply to power it, a panel meter readout to read it, preferably with floating meter unit, we have been talking about them in another thread just the other day, and a 5-10 turn pot to controll it.

Good luck,

Cheers, Finn Hammer
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Finn,

Looks like we’re thinking the same wavelength. Here is one I placed a bid on:

https://www.ebay.com/itm/MKS-Instrument ... 632-2357-0
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Matt Gibson Fusor

Post by Matt_Gibson »

Alright! First plasma (no deuterium).

Strikes at 30kV (on fusor meter) and 5.5 microns. Immediately drops to 10kV and pressure climbing quickly.

So I’m confused here. The meter that I have connected from ballast resistor to ground shows 30kV but my PSU meter shows 34kv-ish. How can there be this much voltage drop? I’m using RG213 (3ft) as my HV wiring.

On the positive note, no sparking on the inside or the outside despite me putting 30kV+ on a 20kV insulator.

Edit: My Ludlum 3 with pancake probe starts screaming at 22kV (fusor) and almost maxes out at 30kV. This is about 2’ from the viewport. Time to get some shields in order.
061E8ED4-E926-44A5-B48A-B8D8EA8890B5.jpeg
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Matt Gibson Fusor

Post by Richard Hull »

Not a word about your current!!! Why bother reporting anything and then ask questions when you refuse to give all data. you gave two voltages, pressure and other details. Current is key!!! Why not multiply your current times your ballast resistor value and see what the answer is?? Data! Data! data! All of it!

I tell everyone all the time that at about 20kv a viewport will scream with nasty flesh burning x-rays. These x-rays are easily stopped dead in their tracks.

After my many FAQs dealing with construction, I can't understand why folks insist on pointing the viewport right at their gonads, or chests or much worse, at face level. The most sensitive organ in the body to radiation is the eye. Point all view ports to an outside wall or at the floor or anywhere where people aren't! View by point contact with a wide angle video camera or a less useful, mirror-telescope arrangement.

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
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Matt Gibson Fusor

Post by Matt_Gibson »

Hi Richard, 3mA. Even down to less than 1mA, or as high as 10mA, the voltage at the ballast (50kOhms) is roughly 4kV less than the PSU meter shows. There shouldn’t be more than a few hundred volts dropped across the ballast…Something else seems off?

Edit: As for the X-rays, I’m off to the side when operating. I held the probe such that the head was in line of sight of the viewport. Same with the camera for the picture.
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Matt Gibson Fusor

Post by Richard Hull »

I would suspect inaccuracies in the homemade voltmeter at the wire going to the fusor. How did you calibrate it. Such HV meters need to be calibrated using an accurate source %5 accuracy in 100 meg resistors will be in tolerance at 95 and 105 megohms. Four or five in series could be far out of tolerance to 10% or more so calculation could easily seem good but at 35kv could easily be 3-5Kv in error. You need to trim the string into correct reading using an accurately known source.

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
Matt_Gibson
Posts: 505
Joined: Thu Sep 23, 2021 10:36 am
Real name: Matt Gibson

Re: Matt Gibson Fusor

Post by Matt_Gibson »

Am I being needlessly redundant by having a second volt meter here? My max current from the psu is 15mA…That’s 750v dropped across the ballast if I ignore the resistance of the Hv wire to the fusor…Any reason NOT to go by the psu meter only?
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Matt Gibson Fusor

Post by Richard Hull »

That is fine +/- 500 volts is nothing at 35kv. Close enough for government work, as we use to say in the fusion biz.

If you lust for accuracy make up a little cheat sheet chart from 5 ma to 15ma with calculated drops for each current in your ballast and subtract the fusor operating current drop from you PSU meter reading. A much more accurate voltage to report.

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
Post Reply

Return to “Images du Jour”