Neutrons / Second

26 06 2010

Our last fusion run produced results we can use to calculate the neutrons per second emanating from the fusor.

To help with converting from bubbles to neutrons per second I contacted Rob Noulty of Bubble Technology Industries – makers of the bubble dosemeter we are using. He says:

Hi Mark:
Did you run a control detector (to see what natural background bubbles you will get over this time)?  You must subtract these bubbles out assuming you have two detectors of roughly the same response (or you will need to scale).
Please note as well that you have a very small number of bubbles resulting in poor statistics (and a very large error). Based on 4 bubbles, the expected error is roughly 50%.
The calculation is follows:
1.     Divide bubbles by the sens in b/mrem
2.     This will give you the measured dose in mrem
3.     Divide by 3.48 x 10-5 mrem /(n/cm2)
4.     This will give you fluence (in n/cm2)
My detector has calibration: 24 b/mrem (2.2 b/uSv):
Here are my calculations:
This seems to ballpark agree with this fusion calculator:
Question to the community: where do I apply the error factor?
Also, I have yet to factor out the background reading I did previously: 1 bubble in 3486 minutes (2 days  10 hours  6 minutes).

Rob Notes:
There are two conversions, depending on dose conversion table to want use!
USA is going to ICRP-74 slowly, we use NCRP-38.
NCRP-38: 3.48 x 10-5 mrem/n.cm-2
ICRP-74: 4.16 x 10-5 mrem/n.cm-2




Context

26 06 2010

I’ve made this diagram to show where this project fits in the landscape of nuclear energy research:

UPDATE: I’ve updated this diagram with corrections provided by commenters.

Click for full size.





Background Reading

21 06 2010

All photos.

Just completed a background reading on the bubble meter. We saw 1 bubble in 3486 minutes (2 days  10 hours  6 minutes).





Neutron Club

9 06 2010

Yesterday I was officially added to the list of independent researchers that have achieved nuclear fusion, based on the result of our last fusion run. This list is maintained by Richard Hull, the first amateur fusioneer. Counting groups as a single entry, I’m the 38th person to make this list:

3. "The Neutron Club"

These people have operated a neutron producing fusor or fusion system.
(normally d-d fusion): 

          Richard Hull - 10e5 neutron mark 3/99
          Scott Little
          Joe Zambelli - Half mega mark 12/01
          Tom Ligon
          Michael Li - winner $75k Intel scholarship (fusor)
          Mike Amann
          Jon Rosenstiel - Mega neutron mark 10e6 11/02
          Gerardo Meiro - First non-US neutron Club member
          Phillip Fostini
          Carl Willis - advanced activation work
          Larry Leins - pulsed fusor work
          Craig Wallace - winner $1.5k Intel 2nd place (Fusor)
          Frank Sanns
          Brian McDermott
          Fergus Noble & Henry Hallam - first UK neutron members
          Adam Parker - winner of $10k Alabama scholarship in science
          Mark Langdon
          Thiago Olson
          Wayne Rodgers
          Eric Stroud
          Wilfried Heil & Noemi Zudor - Smallest fusor ~3" diameter
          Raymond Jimenez
          Alex & Ben Haylett - first to use heavy water electrolysis
          Steven Sesselmann - first Aussie fusion, New Star system design
          Andrew Seltzman
          ***********
          Utrecht University fusor group, poster is Benjamin Brenny
          Group includes: Sander Mann, Dick Abma, Thijs Krijger, Remco Van den
                          Dungen, Nivard Kagie
          ***********
          Bob Heil
          ***********
          Peninsula College - student group
          Ho Yee Hui, Derek Madison, Devon McMinn, Sarah Mangiameli
          Chris Milroy, Aaron Stoll, Jeff Zirul
          ***********
          Roman Radtke
          Louis Franzel
          Taylor Wilson - Youngest fusioneer - 14 years old.
          Thomas Rapp
          Tyler Christensen
          Ben Bartlett
          Doug Coulter & Bill Fain - first cylindrical fusor
          Matthew Honickman
          Jason Heidecker
          Mark Suppes




QUADRUPLE BUBBLE!!!!

6 06 2010

All photos.

With the vacuum pump working again, I assembled the fusor and attempted a fusion run last night. It was a day frought with challenges, but in the end the bubble meter saw 4 bubbles in 2 hours and 40 minutes:

This shows beyond a doubt that we have fused the atom. During previous attempts we only produced a single bubble… which suggests fusion, but does not rule out a cosmic ray.

Science Journalist Quinn Norton was at the lab writing a story for Gizmodo. She witnessed and documented the fusion run:

Previously we were having problems with transient voltages spikes or EMFs crashing the data acquisition (DAQ) card. Today was a big test for the new transient voltage suppression system . It FAILED big time. But I learned something in the process.

I began by intentionally creating an unstable plasma to test the transient voltage system.  This crashed the DAQ every time.

Next I disconnected all wires to the DAQ to determine if the interference is coming through the wires or the air:

Without computer control I needed some way to manually adjust  the MFC. I hacked together a quick voltage divider using a 2KΩ potentiometer and a 9V battery:

This proved to work very well.

To control the high voltage from a distance I used the emergency stop button:

This also worked very well. At this point the reactor is completely under manual control. No computer necessary. Which will turn out to be a good thing.

So now we can test the DAQ with no physical connection to the reactor.

Surprisingly, I was able to crash the DAQ every time, even with no wires connected to it!

Quinn noticed the USB hub flickering during the plasma sparks and suggested it may be the failure point. I removed it, and indeed the system seemed less vulnerable to crashing:

At this point the DAQ seems to remain running in the face of sparking plasmas. Good.

Next I tried connecting one channel to the DAQ… a digital output channel to turn the high voltage on and off. I created a duty cycle function in labview to make it easy to bake out the chamber without melting the fusor grid. This is what it looks like running:

Next I bake out the chamber for an hour using a deuterium atmosphere @ 10 mtorr. The high voltage power supply is set to it’s maximum: 30Kv @ 10mA and the duty cycle is set to 75% @ ~ 0.09 hertz.

At first the computer controlled bake out was running smoothly. About 15 minutes in I get a computer crash. Restart. It runs for about 7 minutes and crashes. Try again. 5 minutes and it crashes. The crashes in increase frequency until I am getting nowhere.

At the point I switch the system over to full manual control and begin the metered fusion run. A fresh bubble detector was unboxed and activated.

(so fresh and so clean)

For the main fusion trial the deuterium atmosphere was at 10 mtorr, high voltage set to it’s maximum: 30Kv @ 10mA. The procedure was to run the system at full power until the plamsa became unstable and started sparking. This instability seems to correspond to the grid becoming red hot, so the plasma instability may be due to thermionic emission.

The bubble detector was activated for 2 hours and 40 minutes. The plasma was running for some unknown fraction of that time. 4 bubbles were detected.

Challenges remain for controlling this wily beast with a computer.





Vacuum Pump Fixed!

3 06 2010

All photos.

The vacuum pump is back online!

Although Pfeiffer sent the wrong o-ring:

I was able to re-use the previous o-ring:

I’ll upgrade the o-ring to the new one when I get it from Pfeiffer.

Here is the removed broken vent valve:

The vent plug installed:








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