Fusor Forums

It has been a while since my last post, but I've continued working on the device. There have been several significant upgrades:

- Feedthrough and ballast resistor changed to accommodate 60kV (with the assistance of mineral oil). - New 1kW 60kV power supply

- Pressure control using MKS 250 and 248

- Custom designed remote control panel (https://www.youtube.com/watch?v=gplmr2G ... e=youtu.be)

- 2M+ n/sec TIER

This can possibly be used as a neutron generator for real life applications. Try sputtering titanium to make a beam on target device. From a PM with Mr. Seltzmen, coating the grid would help more so than the walls.

But in all that is an extremely good system, especially for how small it is! Really good job and I wish you the best!

Ameen Aydan

I do not think I have ever seen a better presentation of co-joint functioning metering systems. (you tube)
Fabulous! a lot of thought and scaling went into this effort.

Richard Hull

I added a water cooling loop to the chamber to allow longer run times. (The thickness of the cathode already allows for long run times.) The main limiter seems to be electron beam heating of the walls which vaporizes material and poisons the fusion rate. The current setup can run for hours at 5mA and 1M n/sec.

The device seems capped at 3.2M n/sec for about a minute at 60kV and 15mA. The only option seems to be to raise the voltage to increase the fusion rate. (I’ve also considered changing cathode material and shape. Presently the cathode is aluminum.) I really want over 10M n/sec and it seems 100kV is probably required. I’m not sure the chamber geometry will support that high of a potential.

Based on the curves, 150kev is the limit on gain versus increased fusion as the curve's slope falls off fast.
Getting even 5meg n/sec seems an un-doable effort unless heroics and super shielding is brought to the effort. The x-rays would be lethal at 150kev.

Richard

That assumes that the ions gain the full cathode potential, but in our neutral collision dominated systems I don’t think that’s true. Of course the xrays are a problem. I do have a setup that’s controlled from 50ft away.

joer
It is not the ions that create the x-rays
It is the secondary electronsknocked off the grid that are accelerated to the fusor wall causing the x radiation

I know... I was referring to Richard talking about the D-D fusion cross section versus energy

Once again, John scores a direct hit. The electrons, typically from an emissive grid are indeed afforded, due to their tiny relative "size", a free ride to virtually full potential to the high-Z wall. Only a pitiful few interacting with the deuterium gas or deuterons in the fusor. The fusor is a near ideal x-ray tube of yesteryear! (gas x-ray tubes of the 1890s-1920's). The fusor is a far more efficient x-ray tube than a fusion reactor.

As long as folks putter around with demo fusors and never make over 25kv in a real fusor, virtually zero x-rays are emitted from their device, assuming a metal SS bodied fusor of typical .0625-inch wall thickness. However glass view ports and HV insulators are x-ray beam ports in all real fusors and are best pointed to the floor or the ceiling in their mechanical installations.

newbies.....See FAQ on positioning fusor components and x-ray warning FAQs.

Richard Hull

Richard,

I believe you are quoting the D-T cross-section curve (not the D-D cross-section) in your comment above. The D-D fusion cross-section doesn't fall off until a few MeV. Below is a graph of the different fusion reaction cross-sections vs energy taken from: http://www.kayelaby.npl.co.uk/atomic_an ... 4_7_4.html

Not that any amateur will push the voltages much above 100kV for the reasons stated above.

As a data point on neutron production I was just reading the Berkeley Compact Neutron Source (D-D beam on target) can generate 10^8 neutrons/seconds at just over 100keV using only a 10% duty cycle. A fusor is a different beast, but this might be useful as a data point. https://www.osti.gov/servlets/purl/824852

Bruce

I was indeed quoting and am familiar with the D-D curve. All easy, useful slope disappears at 100kev and it really is useless much beyond 200kev in amateur hands. Forget Xrays. The slope and return in fusion for all future 100kev advances are just not worth the extra 100kev effort. (shielding, state licensing, irradiating the cat or dog, other family members and the neighbors.

Finally, being a log-log plot one can't help but notice that going from 300kev to 3mev you get a 10% increase in cross section.... worthless.....
We can't help but notice a full order of magnitude increase from 40kev to 100kev, beyond which, the "forlorn hope" begins, slope-wise.

It is a matter of losing slope fast to the point and that pouring in more juice just ain't worth the hassle in amateur hands.

Reason and logic coupled with amateur hands in a family home limit us all in a fusion effort. Smart folks can observe the slope. Reason and logic, reason and logic.

Once you actually have 100kv applied and are still alive, 50kv or 100kv more heaped on, is a real stretch...How much of the tapering off slope is one willing to chase?

Beam on target in a well done system will always outperform a "simple amateur fusor" even at 10% duty cycle at most any voltage. When I say simple amateur fusor, this means no ion guns, no extra ionizing or suppression field control grids. This is the kind of fusor that is made here.

Richard Hull

I misinterpreted your previous post. I thought you were implying the D-D fusion cross section decreased above 150 keV. My Bad. Even though there is only a small increase in cross section between say 100 and 200 keV the neutron production rate more than doubles over this interval. However, as your rightly point out, this is really irrelevant for the amateur effort.

Joe, I apologize for derailing your thread.

Bruce

Bruce, no issue or scolding, just a restatement of limitations and realities in home grown fusion in a simple fusor. A clean and clear understanding is needed among newbies and the over unity hopefuls landing here.

While this thread is all about Joe working on his effort and to see it advance, we must also speak to those not currently doing beans on fusion to instruct in the practicalities involved, should they choose to start to actually do something. I often wonder how the very term "slope of cross sections" falls on ears that do not know what slope means. Such folks might do well to just move on as the far more involved work and understanding that lay ahead in a fusor effort is often, along with lack of funds, what kills an effort in progress.

Joe is certainly one of the most recent success stories and his efforts are expanding as he seems to be striving to see just how much he can wring out of his effort. Go Joe!

Richard Hull

At what energy do things start heating up again?

Beyond 2-3 mev, fusion backs off and the Oppenheimer-Phillips reaction takes over. This is called stripping where the deuteron is just dismantled into protons and neutrons in the D-D fusion scenario. It is why the cross section takes a nose dive beyond these energies. this has been in many posts here over the years.

https://en.wikipedia.org/wiki/Oppenheim ... ps_process

Richard Hull