Ion guns and thick targets.

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
3l
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Ion guns and thick targets.

Post by 3l »

Hi Folks:

I've had pretty good success bombarding Ti targets to get neutrons.
At 100kv I've got the target cranking out 10^7 neutrons per second.
I use thick targets for my work.
Vacuum is at the usual 10 millitor region.
At first I thought that thin targets were required for the operation of neutron tubes....how wrong I was!
By thick I'm using 3/32" titanium shim stock off Ebay.
I cut 1 1/2 inch circles with a hole saw.
Then trimmed the the target to fit a 2 3/4 x 18" CF tube.
Insulator at the filament end and the target grounded to the case.
I pump the tube down to 1 milltor the back fill with D2 gas until the manometer reads reads 7-10 millitor. A twist if an old tank valve and volia a sealed ready to run neutron tube.
It takes a few minutes for the target to get filled with deuterium ions the surface few microns of the target gets saturated and the incoming ions start making neutrons. As a continous neutron source one fill will last several hrs. A thin titanium target fills in milliseconds but the advantage of a thick target is once it fills a lot of d2 is availible. This means that you can go to higher numbers without melting the target or running out of target nuclii to hit. A french firm has a new neutron tube reported at 10^8 neutrons per second in deuterium deuterium generation on a thick Ti target. And guess what ...it is a conflat device.

Happy Fusoring!
Larry Leins
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Jon Rosenstiel
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Re: Ion guns and thick targets.

Post by Jon Rosenstiel »

Larry,

Good going with the neutron tube. 10E+07 is nothin' to sneeze at. Can't wait to see the photos of your setup.

Jon Rosenstiel
3l
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Re: Ion guns and thick targets.

Post by 3l »

Hi John:

The neutron tube is nothing but a hunk of pipe!
I use the standard magnet ionizer next to my filament.
I was shocked at how x ray quiet these things are compared to say a pulsed design. The magnet does a really good job containing the
stripped electrons at the ionizer.
At first I used a Penning ion gun but it created loads of stray electrons and not enough ions. Too many xrays! Too few neutrons.
I went back to the Belljar and used the Ruby and Gow ionizer with three cheap ceramic magnets and a filament...Bingo.
He ran his cold but I have built both types. There is no difference really except you need an extra ionizer supply for cold discharge.
X rays fell by a substancial amount and the neutron count soared.
Runs at around 20 ma @ 100 kv.
The thick target hardly gets warm.
I've even thought of using Richard's design for a collider to hit a target from both sides.
I want to try stacking mutiple ion guns for more output and see if you can get 10^8 neutrons per second.
The efficiency is low as usual but the dice are easier to control this way.
Ti targets beat the hell out of the D2O Iceball targets.

Happy Fusoring!
Larry Leins
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3l
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Re: Ion guns and thick targets.

Post by 3l »

Hi Folks:

To clear up some issues the picture in the Belljar does not give enough info. The ion source has two flat electrodes glued to the top and bottom of the magnets. A rf signal is fed to these electrodes. A plasma column is formed in the center hole of the magnet. The number of ions is proportional to the number of watts the rf generator makes. I will make the math availible in a future post but you need 100 watts of Rf to get the ions for 10^7
neutrons per second. I used a one tube linear with a 14 watt CB radio as my source. The wavelength is roughly a 1/2 foot.
You can calculate it but take a flourescent tube put it at right angles to a CB radio xmitter antenna measure the glow. The length between the rf electrodes for the cross field ion source is an
even subdivision of lamda (wavelength) (l/4,l/8 ect) A Driven spark coil would work or sst.

Happy Fusoring!
Larry Leins
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Q
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Re: Ion guns and thick targets.

Post by Q »

ok, i had been looking at tbj's picture and found it to be lacking something.
also, i have been wondering if the neutrons are emitted in an isotropic manner or not. i know very little of targeted systems, so any information is greatly appriciated.

Q
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Richard Hull
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Re: Ion guns and thick targets.

Post by Richard Hull »

Q,

Neutrons, I would have thought, might not be emitted isotropically in a target system.

However, a wise and quick check with "the man", Carl Willis, shows that at real low energies, <100kev, the reactants will let the neutrons and protons go in almost any direction. However, as the energy of the bombarding particles climbs, there is a definite propensity to become a cardiodal pattern just due to simple line of bombardment kinematics.

Certain endothermic fusion reactions, on the otherhand, would be anisotropic from the get go.

It is to be remembered that our reactions, at such low energies, are true fusions and the exothermic nature of the fusion will allow the much higher energy emitted particles to go just about wherever they damned well choose at the moment of release.

So, intrinsically, at lower energies, a target system involving the D-D reaction IS isotropic in its emission of neutrons and protons as particles as well as tritium and He3 as nuclei.

OR

Restated, there will be no neutron beam from this kind of device using D-D reactions.


Larry,

20 ma @100kv will disappate 2000 watts somewhere!! Where is the heat if the target barely warms! This energy is enough to puddle most any thick or thin Ti target, especially in vacuuo. I just gotta know where that waste energy is going it certainly is not going into making neutrons with only 10E7 coming off/second. This is far less efficient than an equivalent fusor.

Fusors have a huge target shell area and it gets hot as a pistol real quick when disappating only 300 watts of input. If your input numbers are correct somethng MUST be nearly molten SOMEWHERE. One just can't spend 2000 watts and not get heat! Again, this is especially true in target systems which is always a given in this "fixed loss only" type of device.

One final question. How are you measuring those neutron numbers? (detector type, distance to detector from target, background count rate, actual timed count rate when pulling off neutron numbers in a data run, etc.)

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Ion guns and thick targets.

Post by Q »

hey thanks!
i was not sure what kind of pattern would be produced, but i was guessing it would not be an even emission unless there were several ion beams converging much like the farnsworth fusor.

with this in mind, it might be wise to have multiple runs and move the neutron detector to several locations. see if there is a "sweet spot" in the emission field.

Q
3l
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Re: Ion guns and thick targets.

Post by 3l »

Hi Richard:

You' re correct about the energy factor.
I use 5 to 10 minute runs to prevent heating.
Yes it does take 2 kw.
I am using the BF3 Eberline to measure the output At 100 cm.
I checked for radon daughters and the like.
Even tho I had It calibrated I took it to the school's weak neutron source just to be sure.
My instrument correctly measured the calibrated neutron source.
My background was nearly 3.6 cps on average of a day's counts.
I acumulated counts over 10 minutes time then averaged the counts to get the neutron counts per second of (adjusting for detector tube area) 5.16 x 10^2 in a 1cm^2. area.
Then took the distance of the probe from the neutron tube and calculated the isotropic yield of the tube at 6.12 x 10^7 neutrons per second.

I use a liquid cooled version for longer runs.
In my post the first experimental device was a small one (1.5" Target) that only produced 10^5 Neutrons per second that was the cool one. I should have posted that the 10^7 device had a liquid cooled target ...my bad.( I usually edit my posts but I had folks over) I only want the numbers of neutrons no mater the cost to test out the boiling water bit. This device will never breakeven. Once I get the numbers I desire it won't be run again. A Coffeemate boils water better than this thing! I didn't mean to confuse people but this device is only a prelude to future FUSOR developement.

Happy Fusoring!
Larry Leins
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Q
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Re: Ion guns and thick targets.

Post by Q »

since i am interested in the hybrid setup, this is a topic of much interest to me. the water boiling benchmark will be quite useful...

larry, are you going to be relying on this neutron tube solely or will the boron be present in this expiriment?

Q
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Carl Willis
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Re: Ion guns and thick targets.

Post by Carl Willis »

Hi Larry,

Thanks for calling me tonight: I always enjoy talking about this stuff even if I cannot find the time every day to drop by online. And your efforts with those document CD's are much appreciated.

If I'm not mistaken, 10^7 n/s would be establishing a new record for the amateur fusion community, and as such, I'm going to second a couple of wise voices here and beg for some pictures. Bring on the eye candy please! Not only is there a healthy skepticism, but with these types of systems the beauty often lies in the "little" details such as how your water-cooled titanium target is put together and how the high voltage and vacuum are handled. Of course, neutron metrology is always suspect even in the most experienced and capable hands, so I'll second Richard in particular in pleading for a full debriefing on measurement and derivation of the 10^7/s TIER number.

Don't feel rushed, but just know that there are guys here foaming at the mouth for the hard details on how they too can squeeze out 10^7 neuts / second with a DD neutron tube and the persuasive evidence that their efforts will pay off so nicely.

On another note, if you're confident in the 10^7 number it's prudent to consider shielding and distance for your own safety if you haven't done that yet. 10 cm from the target you are looking at up to about 1 rem / hour from fast neutrons (depending on which way you are facing), plus whatever contribution from x-rays is present. Keep your eyes out of the vicinity of the tube in particular, they're very sensitive to neutron injury.

Thanks Larry. Thanks for the preliminary report, good luck with your ongoing lab efforts, and keep the posts coming!
-Carl
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Richard Hull
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Re: Ion guns and thick targets.

Post by Richard Hull »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
3l
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Re: Ion guns and thick targets.

Post by 3l »

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
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3l
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Re: Ion guns and thick targets.

Post by 3l »

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
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Richard Hull
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Re: Ion guns and thick targets.

Post by Richard Hull »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Ion guns and thick targets.

Post by 3l »

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 »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Ion guns and thick targets.

Post by 3l »

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
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3l
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Re: Ion guns and thick targets.

Post by 3l »

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
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3l
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Re: Ion guns and thick targets.

Post by 3l »

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.
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ijv
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Re: Ion guns and thick targets.

Post by ijv »

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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Richard Hull
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Re: Ion guns and thick targets.

Post by Richard Hull »

Ivan is correct. U of W found that the embedded target fusion in a fusor lagged far behind the IEC transparent grid equivalent.

I have that report printed out and in my library.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Ion guns and thick targets.

Post by SteveHansen »

Hi Larry,

I was just browsing through some older posts and I noticed your reference to the Gow & Ruby ionizer but I was perplexed by the subsequent comments on filaments, RF, etc. Is this ionizer the the simple cold cathode ring magnet device that forms the anode region or something else?

Very good info on the thick Ti target.

Steve
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Re: Ion guns and thick targets.

Post by Doug Coulter »

Thanks for noticing this and bumping it up Steve - it's relevant to what I'm doing myself now.
Other sources I have indicate he should have been more patient and that neutron yield would have gone up substantially with a couple more days of pushing D into the target.

The fast-neutron guys use thin targets for a completely different reason. They want the reaction energy to be tight, with few low energy stragglers that have lost energy penetrating the target with no reaction yet. And for better cooling. For just making neutrons, a thicker target should be OK as long as you don't hydrate it so well it turns to dust - the other advantage of a thin target is a substrate that rejects hydrogen and doesn't get brittle.
Why guess when you can know? Measure!
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Re: Ion guns and thick targets.

Post by SteveHansen »

Most of the use of self replenishing targets I believe is in sealed neutron tubes where you also don't want a lot of "sponge" to soak up the deuterium or tritium. There's already enough that they need to have reservoirs, usually a zirconium filament, that can be heated to evolve the isotope and keep the tube at the correct pressure.

While I don't have anything set up for neutron production at the moment, might rethink that situation a bit. Got my hands pretty full with pulse devices and educational stuff.

Steve
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Re: Ion guns and thick targets.

Post by Frank Sanns »

Larry had a medical situation back a number of years ago so he he no longer has the ability to post on here and last I heard, he did not have access to read it either.

Frank
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We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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