More Upgrades

[Joe Gayo]

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

[Ameen Aydan]

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

[Richard Hull]

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

[Joe Gayo]

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.

[Richard Hull]

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

[Joe Gayo]

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.

[John Futter]

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

[Joe Gayo]

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

[Richard Hull]

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

[Bruce Meagher]

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