Nathan Marshall - Fusor Progress

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.
User avatar
Mark Rowley
Posts: 625
Joined: Sun Dec 29, 2002 5:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: Nathan Marshall - Fusor Progress

Post by Mark Rowley » Thu Apr 30, 2020 5:25 pm

Keep it up Nathan, love the progress and Can-Do attitude.
I had limited success with the HF meters past 25kV. Exact same issues you and Jim have described and that's with copious shielding and grounding. Ultimately I opted for a nice Triplett analog meter which quickly solved the problem.

Mark Rowley

User avatar
Richard Hull
Moderator
Posts: 12434
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Nathan Marshall - Fusor Progress

Post by Richard Hull » Thu Apr 30, 2020 7:21 pm

Analog metering will never display the precision of a digital, but they will be around a lot longer and do good enough in the HV realm. No one here needs to know 36kv to better than +/- 200 volts. Harbor Freight meters are not good in high RF or EMP environments.... Few digitals are. It is extremely tough to kill an analog VTVM or VOM. (unless you drop it on a concrete floor - jeweled movement) Digitals will usually survive such a drop.

Choose all metering based on where and under what conditions it is built for. Hamfests are the best place to pick up a venerable old VTVM or lots of specific analog meter movements that you can turn into anything you wish. I have so many meter movements purchased over my lifetime that I have them in several large, cataloged boxes stacked up in the lab from 0-20ua to 5 amps. I tend not to buy voltmeters unless they are 0-30kv or the like, scaled, and have 50ua or 100ua movements.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

User avatar
Nathan Marshall
Posts: 37
Joined: Thu May 09, 2019 12:13 am
Real name: Nathan Marshall
Location: Hutchinson, KS

Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Fri May 01, 2020 2:49 am

Mark and Richard, you reminded me that I have an old analog meter that my grandfather gave to me years ago! I almost forgot about it. It has a 250 mV range so it is perfect for this application. I hooked it up and now even when the static EMPs occur there is no effect. The power supply is running great. The furthest I pushed it was 6mA at just over 30 kV. My Ludlum 44-9 probe starts to pick up x-rays even back where I am standing at that kind of power. So now I need to hook up the deuterium tank and regulator, and get some reliable neutron detection working.
Attachments
IMG_5637.png
IMG_5637.png (454.43 KiB) Viewed 964 times
IMG_5636.png
IMG_5636.png (430.78 KiB) Viewed 964 times

User avatar
Jim Kovalchick
Posts: 455
Joined: Thu Apr 14, 2011 12:00 am
Real name:

Re: Nathan Marshall - Fusor Progress

Post by Jim Kovalchick » Fri May 01, 2020 6:56 am

Nathan, I am certain you will be in the neutron club soon. I admire your careful work, especially the power supply.

Stay safe.

Jim K

Victor Gonzalez
Posts: 22
Joined: Wed Jul 17, 2019 2:16 am
Real name: Victor Gonzalez

Re: Nathan Marshall - Fusor Progress

Post by Victor Gonzalez » Fri May 01, 2020 11:03 pm

Do you have a reason to use these 2 capacitors?

I have almost the same setup for a PMT (I used an lm317 for voltage control), and the voltage output with and without these 2 capacitors are the same.
Attachments
IMG-20200501-WA0046.jpg
IMG-20200501-WA0046.jpg (33.54 KiB) Viewed 905 times

User avatar
Nathan Marshall
Posts: 37
Joined: Thu May 09, 2019 12:13 am
Real name: Nathan Marshall
Location: Hutchinson, KS

Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Thu May 07, 2020 9:48 pm

Victor: I was under the impression that the way to make a negative voltage multiplier was simply to reverse the diodes of a positive voltage multiplier. I haven't read any source that recommends removing those capacitors when making a negative multiplier so I never thought to. I'd have to do some simulations or experiments to decide if they really contribute greatly to the function.

Since my last post, I got everything ready for fusion. I did some tests of pumping down the chamber with the diffusion pump, throttling off the pump with a butterfly valve, and admitting air through my flow restriction setup to see if I could get stable plasmas and pressures. I found that my grid was too large. I was getting crazy negative resistance which resulted in wild oscillations of current and voltage. So I ditched my grid and made one that was a bit less than 1 inch in diameter and with two rings instead of three. This works far better. I was able to tune the pressure and get stable plasmas at ~30kV and 2-5mA. I did some hydrogen runs with hydrogen generated by an old PEM cell I was given in 6th grade. I used Mark Rowley's syringe method for storing the gas. The main reason I did this was to convince myself that I wasn't sucking gas in at high rates which would waste deuterium. Lastly, I hooked up the deuterium tank to the gas line with a used Harris 9200-50 H2/CH3 regulator from eBay.

Then came a major disappointment. I was going for my first fusion attempt this afternoon. I had everything set up and ready to go: diffusion pump running, BD-PND bubble detector set up near the chamber, and my power supply ready to rumble. When I opened the valve on my deuterium tank, the high pressure gauge didn't even budge... My heart sank. I obtained this tank over six years ago with the help of my high school chemistry teacher. That was my freshman year of high school, and I was naive enough to think I would be able to achieve fusion then. I didn't realize the time and money that it really took. It is a Sigma-Aldrich tank and was originally pressurized to 25 atm, and has a volume of 459mL. I wonder if over the years it slowly leaked since deuterium is such a light gas. To my surprise, when I turned the knob on the regulator I was able to get some PSI on the low pressure side. So, I went ahead with my test. I got a beautiful red 25kV 5mA plasma at 30 microns for just a minute before the gauge on the low pressure side went back to zero. Any thoughts on what went wrong here? Did the tank just leak over time? Or did I have some sort of leak? I imagine a leak of that rate would have been quite audible, and the fact that the high pressure gauge never even budged leads me to think it was basically empty to begin with.

Plasma without deuterium:
05-07-2020_10-59-12resize.png
05-07-2020_10-59-12resize.png (221.38 KiB) Viewed 838 times
Plasma with deuterium before it ran out:
05-07-2020_15-45-23resize.png
05-07-2020_15-45-23resize.png (208.89 KiB) Viewed 838 times

User avatar
Jim Kovalchick
Posts: 455
Joined: Thu Apr 14, 2011 12:00 am
Real name:

Re: Nathan Marshall - Fusor Progress

Post by Jim Kovalchick » Thu May 07, 2020 10:51 pm

Nathan,
Maybe your regulator has an obstruction. You should check it on another bottle or at least inspect the internals of the high side before assuming your bottle is empty. Also, cycle your bottle valve open and closed and open again.

I am curious about your short run. Did your plasma flash at the pressure you expected for your voltage. If it flashed at a lower pressure then it was just air in the line.

Good luck. You will be 'there' soon.

Jim K

User avatar
Nathan Marshall
Posts: 37
Joined: Thu May 09, 2019 12:13 am
Real name: Nathan Marshall
Location: Hutchinson, KS

Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Thu May 07, 2020 11:16 pm

Jim,
I did try opening and closing the tank a few times but to no avail. The pressure required in the chamber was higher than my runs with air. With air I was at about 5 microns on the baratron and for this short run I needed about 30 microns to get a similar plasma wattage. I'll take another look at the regulator like you suggested, but from what I could tell it appeared clean and in good condition. The fact that I got a little pressure on the low pressure side before it went away makes me think the bottle still had a bit of gas in it but then ran out. Thanks for the reassurance, I will soldier on! As one of the grad students I work with says: "It's always a fight."

User avatar
Dennis P Brown
Posts: 1996
Joined: Sun May 20, 2012 2:46 pm
Real name: Dennis P Brown
Location: Glen Arm, MD

Re: Nathan Marshall - Fusor Progress

Post by Dennis P Brown » Fri May 08, 2020 12:08 am

Sorry to hear; regulators aren't something that last - I've had some fail and a tank empties. But unless your primary valve (independent of the regulator) wasn't fully closed, the tank should have remained filled. Deuterium can't really diffuse through the lecture bottle (I've had one for over 6 years (in use) and it is fine but I always carefully and fully close the main valve fully tight. I will say, the residue gas in the regulator does leak away over a few days. Those small (read cheap) regulators can't be trusted to be the sole seal on the tank.)

I understand only too well getting ready to make one's first real fusion run only to take a hit. For me, my detector counter that zapped by the detector's HV supply. It is frustrating but you'll make it - your so very close. and have shown you can handle these issues.

User avatar
Nathan Marshall
Posts: 37
Joined: Thu May 09, 2019 12:13 am
Real name: Nathan Marshall
Location: Hutchinson, KS

Re: Nathan Marshall - Fusor Progress

Post by Nathan Marshall » Fri May 08, 2020 1:30 am

Dennis,
Well then perhaps it was my worst fear that occurred: the tank was full to begin with and something wrong with the regulator caused the whole bottle to leak in just the few minutes that I had the tank valve open... I should have closed it the moment that the high pressure gauge didn't budge. Hindsight is 20/20 and I think I was too blinded by the desire to go for fusion. Also if something is wrong with regulator, it once again goes to show that deal used buys on eBay usually lead to more frustration and money spent than just buying new to begin with. I still think that if the whole bottle leaked I would have heard some sort of hissing.

Post Reply