Ion guns and thick targets.

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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Richard Hull
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Re: Ion guns and thick targets.

Post by Richard Hull » Fri Oct 29, 2004 3:13 pm

Larry,

The 10 CPS background FREAKED me out! You definitely have a bad counter! If you meant 10 CPM, then you still have a very bad neutron counter and need it attended to immediately!

A very high background count would be 0.5 CPM and would typically indicate a bad tube or a grossly mis-set discrimantor level.

See my background posting in answer to a very recent question on the radiation detection forum.

viewtopic.php?f=13&t=5531#p37071

also

viewtopic.php?f=13&t=5531#p37073


Normal backgrounds from working and properly setup moderated BF3 counters using the stock 2" long N. Woods tube are in the 0.2 cpm to 0.02 cpm range. Only very large volume, very long, moderated He3 tubes can normally have multi-count per minute background counts. 10 cpm would be OK with one of these large neutron telescope systems.

Bad instruments used in neutron work will always lead to inflated figures for neutron results. This is why I always now counter check with the bubble detectors. Fortunately, all of my BF3 counters and my new He3 counter have checked out, first in the background area and finally in the actually neutron detection region as well.

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.

3l
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Re: Ion guns and thick targets.

Post by 3l » Fri Oct 29, 2004 3:26 pm

Hi Carl:

Thank you for your kind thoughts.
I use a 10 lb box of borax to back my setup.
Xrays have been reduced by using two stage acceleration method.
I simply took a piece of titanium shim and drilled a hole slightly larger than the ion apeture on my ion gun...that's my repeller electrode.(biased positive 100 kv).
To simplify mounting targets and electrodes are sealed by overlapping the conflat copper seal. With sufficiant pressure the conflat will work properly provided the shim you use is thin as possible.
I have eliminated the water cooling and gone back to oil.
I have done the 100kv in air with large spacing and proper insulation. It is taking too much space so I'm putting it all back to oil. It was just cobbled together on the work bench. I have moved it all into a tuperware tub. Oil makes it safer anyway. The tube ,Ps and auxillary ps stuff will be in the picture. The hardest part of the design was how to insulate the ion gun from the accelerating electrode. Normally the repelling electron would be as close as possible to the ion source but I used a long glass tube so I increased the ion source's extractor voltage to 1700 volts to move the extra distance. A small xray transformer with a diode string supplies the 100kv at 20 ma. The tube filament is run by an xray filament transformer.

Hi Richard:

The tube crapped out after my trip to college.
I took it back to the weak source it is flunking badly.
My prof checked my meter with a known working probe of the same type as mine ...it checked out. Bummer!
I have ordered the bubble tube and a replacement for my BF3 tube !
My old proff let me borrow the school' s Eberline for the morning .
I'll measure again (Sigh!)

Happy Fusoring!
Larry Leins
Fusor Tech

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Re: Ion guns and thick targets.

Post by 3l » Fri Oct 29, 2004 6:46 pm

Hi Folks:

Finally I have what I think are good neutron numbers.
I m curious to see what you guys get.
With a background of .12 cpm probe in moderator spaced 100 cm away
At 100 kv @20 ma
The count was 1.48 x 10 ^4 taken over a ten minute interval
At least it didn't fall throught the floor boards.
So I wanted to see where 10^7 lived so I cranked up the voltage.
At 120 kv @20 ma.
The count was 2.1 x 10^ 4 taken over a 10 minute interval.
Xray started going up too!
My supply will go up to 150 kv @ 20ma
I stopped at 140 kv due to insufficient shielding.
found an error.....low power at the wall...threw out the data on the last run.
Until I get a bubbler in my lab ,I will be a little doubtfull.

Happy Fusoring!
Larry Leins
Fusor Tech

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Richard Hull
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Re: Ion guns and thick targets.

Post by Richard Hull » Fri Oct 29, 2004 6:55 pm

The counters do not read in neutrons/second.

What was the raw, unreduced count and over what period so that we can back figure based on what is known about the PNC-1 and the N. woods tube. to get a figure based on our calcs. Both Carl and I are standing by.

The raw count needs to be presented as "x" number of counts total over a collection period of "y" minutes. Preferably over a relatively stable run period.

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.

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Re: Ion guns and thick targets.

Post by 3l » Fri Oct 29, 2004 8:13 pm

Hi Richard:

I have done as you have requested.
The previous post now has the count and interval.

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Richard Hull
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Re: Ion guns and thick targets.

Post by Richard Hull » Fri Oct 29, 2004 9:23 pm

Thanks Larry.

Based on my calc's which is based not on the simple math parameter assumption used in the past, but more on the relationship of two known functional PNC-1s to the far more accurate BTI bubble device, I figure you were producing about 9X10e5 n/s on the first run and about 1.3x10e6 on the second run.

This new calibration point which was only recently discovered, with the advent of the use of the BTI bubble detector, means that all of my past figures for fusor III were in error by as much as 40 to 50%. So I never hit 2.5X10e5n/s, but instead, reached a maximum of about 1.6x10E5n/s with the old fusor.

The new fusor IV has not produced even 10e5 neutrons yet. I figure my best run todate was about 8x10e4n/s. Again this is based on the much more accurate absolute data taken from the bubble detector.

This makes the old math still correct, but the assumption of the absolute efficiency factor for the BF3 tube was too low. The efficiency is now taken as being in the 2 to 3% range for the PNC-1 this means the old factor of 1% made the old numbers artificially high.

Restated, instead of us seeing and counting only 1 neutron in 100 we were actually seeing 2 counts/hundred. It is amazing how much this degrades the old numbers.

I am sorry for the old number error, but the BTI bubble detector is the real final arbiter today. This is mainly due to needing to make no assumptions regarding efficiencies within the device.

Once you obtain the detector, you will see what I mean. A word of warning........if you accumulate too many bubbles, >70, they will be tough to count without human error. So I now run the machine for a timed run with the bubble detector only for as long as it takes to get enough bubbles, say 50, and then note the time and end the run. Thus far at my low energy a ten minute run produces no more than 40 bubbles. A higher potency device might only need a 4 minute run to get 60 bubbles.

What sensitivity did you order?

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.

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Re: Ion guns and thick targets.

Post by 3l » Sat Oct 30, 2004 12:01 am

Hi Richard:

I'm greatful for you running those numbers for me.
I'm glad I did not get too many sunshine units.
I used my little dental xray for the first run.
I have a king kong tranformer that can top 200 kv easily on 220 volts.
This unit has only been up for a week.
I never hang around any test of anything really new.
I ordered the least sensitive bubble tube.
The last run @ 150 kv was in error due to the fact the power company lowered the voltage down to 80 volts on the mains.
Nim bins don't like that nor do wall clocks.
maybe I should only pay the 80% of the bill huh?
I'm going back to analog on voltage ...digital meters can fib.

Thanks Richard!

Happy Fusoring!
Larry Leins
Fusor Tech

3l
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Re: Ion guns and thick targets.

Post by 3l » Sun Oct 31, 2004 9:50 pm

Hi Folks:

I finally have pictures.
I had a devil of a time getting good ones .
The tub is bright blue if you can believe it.
Sorry about the angle.
The accelerator tube is on the top of the picture.
Dirrectly below is the insulative support that was a utillity commutation switch sans the switch..that I made into a support stand for the accelerator tube.
This particular device has a three way 2.75 cf connector and two glass insulative sections. One in the acceleratior section itself and the other to provide electrical isolation of the vacuum system.
The ion gun is at the far left of the tube and the target is at the far right.
The pyrex glass tube is rated at >500kv maximum voltage. (110 kv per cm on pyrex)
On the left hand bottom is the filament isolation transformer.
It has a rating of 150kv for insulation between primary and secondary.
On the right bottom the 100 kv dental transformer.
The arm from the right coil of the dental xray to the accelerator tube target bulkhead is the diode stack.
It has a rating of 150 kv at 50 ma.
The negative end is on the bulk head.
The entire device is covered with oil for insulation.
Told ya it was a simple gizmo.
The silver sheet on top of the blue tub is a sample of the target and repeller Ti material.
I have a new camera on order...I will replace these pictures when it comes.
Well here goes.

Happy Fusoring!
Larry Leins
Fusor Tech
Attachments
target2.JPG
target2.JPG (39.04 KiB) Viewed 3292 times

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Re: Ion guns and thick targets.

Post by 3l » Sun Oct 31, 2004 10:12 pm

Here's a better picture of the tube it self.
The filament connectors are on the left and the ion extractor electrode are the two large insulators out each side of the ion section. The only difference between this device and the original linac (this photo is of my original linac with another camera) is the target in the right endcap and the high potential electrode between the ion source and the glass insulator.
When my 21 year old helper finnally shows back after his hot date...I will reassemble the device on the bench.
My camera doesn't take good shots and yes I took that one under bright lights.
Attachments
target3.JPG
target3.JPG (19.69 KiB) Viewed 3292 times

ijv
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Re: Ion guns and thick targets.

Post by ijv » Tue Nov 23, 2004 5:47 am

Hi Larry,

it sounds like you've been duplicating some target fusion experiments done at the Uni. Wisconsin.

I've posted about it in the fusion theory forum, but the short of it is, that it seems like that embedded target fusion is important even within a standard fusor.

regards,
Ivan Vuletich

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