Update: fusor mods and star pics

[Ryan Catalano]

I just completed a series of upgrades to the fusor. I have added thermocouples for monitoring pump temp and chamber temp and have also replaced my faulty ion gauge with a new convectron. I also recently switched to a D2 bottle to supply my gas. My previous PEM setup wouldnt provide me with D2 very long and was lacking in purity so i switched over.

modified setup

I have also got my neutron detector fully functional and now serves as my primary method for detecting and quantifying neutron output. I calculated that my SNM-5 has an nvth of about 0.9 (compared it to readings from a bubble dosimeter).
Below I have attached a copy of my data

08312015 BF3 Verification experiments.docx

(134.52 KiB) Downloaded 502 times

I was preparing my system to conduct experiments on the effects of voltage and pressure on neutron output. In conducting my experiments, I found an interesting characteristic of my machine: pressure required to sustain the discharge is much higher than a traditional fusor. Someone has probably already experimented with this but I found that I needed to operate at pressures in the 30-40 mtorr range to maintain a decent voltage and current. It was in this region that I got my highest flux ever: roughly 43,000 n/s at a pressure of 35 mTorr, and 35 kV/5 mA on the grid.

With the new gas system, I have been getting extremely clean star mode discharges.

deuterium star

[Richard Hull]

Great pix and that is indeed a high pressure for operation of a fusor at that voltage. Most folks in there best moments at voltages in that range are working no more than 12-16 microns. Thanks for the report data.

Richard Hull

[Nick Peskosky]

Ryan,

You report that your D2 pressures are 30-40mTorr during runs as measured on your Convectron. Are these raw values taken by the gauge head or have you calibrated these against the published N2 standard curves provided by MKS (http://www.idealvac.com/files/manuals/2 ... 485_EU.pdf)? Due to its light molecular density deuterium usually reads higher than true pressure on most vacuum gauges.

[Richard Hull]

Thanks Nick for spotting this. I am so used to the use of my Baratron for pressure readings in my fusor which is free of thermal relationships for various gases that I just assume others are free of this as well. Bad assumption.

Richard Hull

[Ryan Catalano]

I apologize for the confusion. The 35 mtorr is the displayed pressure, but using the conversion chart that came with my gauge (KJLC 275i), I calculated that the actual pressure was roughly 29.1 mtorr, still fairly high for a fusor. I believe that the need for high pressure goes back to the Paschen curve. Since the electrode separation distance is so small on my machine and I'm operating on the left side of the Paschen curve, my the pressure has to go up in order to compensate.

[Richard Hull]

This increase in pressure has been seen on smaller fusors in the past. I am not sure, but I do not think any small machine under 4 inches across has ever hit the mega mark. 5-6 inch units have done it and a few sucessful 8-10 chambers have done even better. We have not yet seen big numbers from even larger amateur fusors as they tend to be rare efforts and are expensive and can waste a lot of D2.

I would say that it is rare for most in the neutron club to have ever hit the mega mark. Even though that list has grown, I think you could count the number of mega-mark folks on the fingers of one hand..........Maybe with a partial second hand, too. Most just want to say they have done it and never push the envelope. Often, they are never heard from again. Off to tilt at other windmills, I guess.

Side note:

Finally got to read all of Ryan's report submitted above in original posting. Great report, great work, Ryan!

It must be remembered that all BTI neutron dosimeters are set up for FAST neutron detection and that no moderator is required! A moderator may actually hamper detection as seen. The Russian tube did OK and that you proved beyond doubt with the moderator/no moderator tests.

Richard Hull

[Ryan Catalano]

Thanks Richard! I've began conducted tests at 40 kv and so far the results seem promising. I hope to get my neutron counts up so I can do a decent amount of activation in different materials. I have a NaI(Tl) gamma spectroscopy setup ready to go when the time comes.