Archived - Spark-Star Progress

[Tony1of5]

Hello Fusor Fans !

On Wednesday 25th September, I ran the Fusor for about 30 minutes and produced an AIR plasma at 12Kv and above.
The voltage was about 12Kv to 15Kv and the current was about 10mAmps. Vaucuum level near 5 to 15 micras (10-3 mbar). The balancing act on the edge of the Paschen´s curve cliff is not easy at all.

I have a car gasoline injector valve system to put air in the chamber and a closed loop monitoring a Edwards vacuum Guage voltage. It bounces around a lot. The amount of gas injected is too much and the diffusion pump too strong. Anyway staying near 12Kv-15Kv without the lights going out (in the fusor and the house!) is good enough for now. The feedthrough to inner grid had a glass jar column to protect it from ions, the tremendous heat of the Tungsten wire cracked the small jar, please see photo.

Apparatus setup : I have a second hand diff pump, an old varian/copy rough pump, an Edwards basic Vacuum gauage. also a Variac, large neon light testing transformer and a doubler rectifier.
Here are some air plasma and setup images images.

All the best
Anthony

[Tony1of5]

The following is an outline of the setup in use in the Spark-Star apparatus:

[Rich Feldman]

Nice work there, Tony. Welcome aboard.

Is your big clear dome / belljar a recent acquisition?

[charlie_mccartney]

Fusion with only 13kv?

[charlie_mccartney]

Nevermind, I just saw the doubler.

[Richard Hull]

No fusion here of course. None claimed. But definitely a plasma.

I hope you did not lose vacuum suddenly with the diff pump on. If so, it and its oil are trashed until cleaned and replacement oil in installed.

I have logged you to the Plasma club.

Richard Hull

[Chris Bradley]

Tony, the reason you have poor control with your injector valve (good work for building that into your system! Is that a first here?) is almost certainly that it has far too high a flow rate when it is open, even if it is open for a fraction of a second.

You should install a flow restrictor in the gas path, and this restrictor will then perform the majority of the flow control, while the injector does the 'fine tuning', so to speak. As it is not intended to be a vacuum-capable device, it might be best to create your flow restriction on the vacuum side of the valve.

I have written a FAQ on flow control that might be worth your time finding.

[Tony1of5]

Hi All

Thanks for the nice welcome.

When the glass collar/jar cracked on the inner electrode stem, there was a big pop and some sparklies but the external wall of the pyrex bowl held intact, so no problems. The glass bowl now has a great sun tan after a few weeks of x-ray PIXEs !

Regarding the injector valves, I got the idea from PFDC form the Madrid web site but I should have opted for a much better solution like the deuterium paladium diffussion cell. http://www.cientificosaficionados.com/d ... terio.html Thanks, Chris I will read your FAQ in the morning. The shortest electrical signal I can make to the valves is to open for 80 miliseconds, I looked at it on an oscilloscope. Then I made a resevoir behid the valve and I reduced the input pressure of the air to 20mBar to decrease the flow rate in the control pulse to the chamber... it works OK not great, then I put a variable voltage potentiometer (light dimmer control) on the heater of the diff pump to control the rate the pressure is dropping. Well it is is still bouncing around at about 5micra each firing, and about twice a second ... above 15Kv it is unstable. I do not recommend the car injectors to anyone

All the best
Tony

[Tony1of5]

A few more photos of previous trials. The teflon towers all outgassed with the heat of the nearby electrode and micra level vacuum was not possible for more than a few seconds

[Tony1of5]

An update of the fusor schematic diagram: Corrected BF3 to B10 and inserted flow restrictors.

[Tony1of5]

Hi Chris,

I have been looking at the flow restrictor designs that you mentioned. Many thanks. I have gone straight for the syringe needle with a wire placed through it. This is very cost effective.
I have made and experimented with these and have placed two in the gas input path. The behaviour of the pressure (vacuum) control has gone from bang-bang real time bad behaviour to a more damped delayed response. I can now operate near 8-12 Micras and have 10-20Kv oscillations, I have to put the gas reservoir at about 100mbar to keep the flow rate down. It is not so stable. I am amazed how fast the gas gets through a tiny gap in a blocked needle !!! I will put some photos here.

[Chris Bradley]

Do you mean 100 mbar gauge, or absolute. Particularly if you are having to run 100 mbar abs then you should decrease the flow rate of the restrictor.

Just try to find a needle/wire combination that give you the smallest annulus aperture, and work up. All you are aiming to do is run a flow rate that is 10 to 100 times faster than the virtual leakage of the chamber, to keep the input gases pure. If it is just a demo, you only have to match the virtual leakage rate to maintain a stabilised pressure, then crank down your chamber valve.

[Tony1of5]

I follow what you say. I do need to get the flow rate down by a factor of 10 or more.
We can agree the flow rate is a function of the aperature, the pressure ratios of in/out to the chamber and (in my particular case) also the on-time of the car injector valve. lowering any of these parameter values is good for fine gas control.

So you can understand my setup and reasoning. In the last photo, there is a T tube with a circular mechanical guage roughly indicating the atmosphere to inside gas pressure. On the left there is an orange tube coming from the electrolysis setup, also left side has an injector valve embedded as input to T tube and on the right side again another injector valve as input to the vacuum chmber then again an orange gas tube passing by a pirani on the way to the to the fusor chamber. The guage roughly shows zero when open to the vacuum chamber for a long time. The T and guage are actually the gas/D2 reservoir so backing off the pressure from 1 atm reduces the flow rate. I started at 1 atm with large flow rate and now operate at about 100mBar with OK but still too high flow rate.

bye
Tony

[John Futter]

Tony
sorry to dissapoint but the discolouration is not from PIXE but either oil from your diff pump or sputtering of your elements within your vacuum chamber.
Check carefully x-ray damage goes all the way through the glass not the surface and can be reversed by annealing the glass.

[Tony1of5]

The darkened colour extends deep into the glass, it appears to be a radiation effect. There is certainly outgassing when the ion beam blast off bits of Teflon on the feedthroughs, when the heat of the poisor cooks the Teflon and then also the base of the chamber (PVC with a glass plate to protect from mini sun). I guess there is also gas from the diff pump but it is probably in the lowest concentration of all this. All that said, there are no deposits on the glass when opening except a distinctive smell that gives me an allergy, hope it is not a fluorine compound from the teflon! the bell jar is a pyrex bowl (22cm) made for very hot/cold food use it is susprising how resistant to temperature, cost 10 euros !

[Tony1of5]

After check-out tests, I will give each sub-system a status of red (not fit for D day) or green (go for launch)

Regarding the "Spark-Star" Vacuum & vacuum control (Sub)system, I have been busy, fixing a inner grid and feedthrough and covering the feed through with a glass collar to try to minimise ion impacts and outgassing. With a new home made flow restrictor I can now leak gas from the dummy D2/air supply that causes 50 micras/minute increase in pressue in the main chamber. When the taps are closed to the chamber it has a leak rate of about 10 micras / minute (volume is about 3lires glass dome + 3 litres diff pump volume). so in theory, on "D" day (if I ever introduce D2 gas) my mix of gases in the chmber will be 4 parts D2 and 1 part air contamination. The back pressue behind the homemade leak is maintained automatically at about 200 mbar. Now with the rough and diff pumps running full blast these are capable of pulling the pressure below 6 micras and make the light of the poissor go out. A light dimmer control is used to back off the heater in the diff pump.

After many air tests, here is the behaviour/ results:
minimum vacuum about 5 micras, maximum voltage about 20KV RMS then the lights go out and the grid rattles like hell.
minimum stable vacuum about 8 micras max stable voltage about 14kv RMS. by stable I mean poisor on, no violent oscillations in voltage and all for more than ten minutes.

There is an outgassing problem above 15Kv where the ion generate gas by burning off the tefon at the base of the tungsten grid, this causes gas bubbles that auto-regulate the vacuum level and drive up the presssure and down the voltage. There is a worry about electrons "blast" lines appearing at high voltage after the poisor goes out. The worry that these will go through the 3cm PVC base and give me a surprise. Plastic is great cheap material to insulate high votage and work/glue/drill etc but it outgasses & melts etc.

so I now place the "Spark-Star" Vacuum & vacuum control (Sub)system on "orange" status .., it is not optimum but might just work later on, for a fusion shot.

[Tony1of5]

Regarding the neutron detection aspects.

In the few past months, I have bought,repaired and buildt and tested a number of detection setups.
Here are some that are working well. I will no go into nightmare stories like mad nancy wood BF3 tubes etc.

Detection setup
One querky Eberline ASP2e (software configurable) with variable tube voltage supply and variable threshold limits and counter box with a deafing trigger happy parot strangler sound inside .

above counter paired with one of the following Cold War ICBM Tubes:
*From the USA an AEC General Electric BP A7 B, B10 lined tube
*From the Soviet Union a SNM-19N with home made CSA.
* Also a SNM11n tube.

The GE tube and the SNM11n tube give nice large neutron pulses of about 400mv on an oscilloscope and are compatible with the Eberline counter box but the shm19n gives pulse of about 15mv and needed a

CSA amp connected close to the tube base, then the eberline could detect/ neutrons. ironically the SNM19N is the most sensitive of all but very susceptible to interference of a air filled xray sparkstar

type ! The SNM11N has near zero CPM noise and the AEC GE A7 has a large volume.

Here are my personnally determined voltage bias settings (passing a gamma exclusion test and an xray susceptibilty test, more info later on)
* AEC General Electric BP A7 B, B10 lined tube 700V
* SNM19N with home made CSA. 1700V
* SNM11n tube. 700V

[Tony1of5]

The neutron detector setup was debugged and developed using two tiny n sources, one of the non- optic smoke alarm type and another of the poor ladies clock hands type both totally sealed and giving a stunning combined CPM of 35 CPM, just enough to develop the charge sensitive amp and tube to counter connexions in the absence of an EM storm that a Fusor causes. The sources have now been disposed of one to the bottom of the mid Atlantic another to the centre of the solar system.



[Tony1of5]

The Eberline counter box was paired up with each of the B10 tubes(SNM11, SHM19 & GEA7) and tested for false n counts above background (1-20CPM) , the voltage and thresolds were determined where the tubes were not affected by the gamma sources present.

It was found that 700V was good for the SNM11& GEA7 and 1700V for the SHM19N this is below the spec sheet information.
See photo of the test setup, and the hot gamma goodies used to illuminate the cold war tubes.

[Tony1of5]

The next indispensable “null neutron test” is the x-ray interference test. The objective is to exclude the possibility that false neutron pulses and thus flase counts are being generate anywhere is the neutron counter/detector system. It is similar to the gamma ray test above but with x-rays.

It consists of firing up the Fusor with air/ He / H and going through different voltage ranges up as high as possible. Locate the counter detector and electronics near to the fusor. Any counts above background are cause for concern and are a test failure.
In my case, The fusor could reach about 20kV with AIR for seconds or lower voltages for minutes, before the poisor was unstable.

Test results,
The ASP2e counter and GE A7 tube pass , never any interference count rates always below 20 CPM
The ASP2e counter and SNM11N tube pass , never any interference count rates always below 2 CPM
The ASP2e counter and SNM19N tube with CSA amp are very susceptible to the EM interference (2K CPM ), I had to place one faraday cage on the CSA circuit at the end of the tube , this got the rate down to 200 CPM, then use another faraday cage ( two aluminium pots) on the whole moderator (paraffin wax) with snm19N inside. Then the holes where the cable comes out to the counter started to let in rays and false counts, so even small 1cm size holes in the external walls caused false counts.

Conclusions:
Gamma test “passed”
X-Ray test “passed” but the SNM19N is on probation.
Neutron detector (subsystem) green for go !

Photo shows a Radalert Geiger dosimeter near an air filled fusor near 12KV. It is counting x-rays.

[Richard Hull]

There are issues with you gamma null tests I will start a FAQ in radiation forum.

viewtopic.php?f=31&t=8904

Richard Hull

[Chris Bradley]

All that said, there are no deposits on the glass when opening except a distinctive smell that gives me an allergy, hope it is not a fluorine compound from the teflon!

It's likely not allergy, it's probably 'polymer flu' which is from the toxic pyrolytic products of teflon that can cause acute lung damage.

Never go sniffing around where teflon has been heated over 300 C. It can be lethal, apparently.

I doubt it'd have much of an effect if you have been constantly evacuating the chamber and there is only an odour remaining, but there are some pretty nasty things in teflon pyrolysis fumes.

[Tony1of5]

Thanks for the recent FAQ related to the B10 n tube setup !

Carl´s videos are truely educational and I have learned and reinforced concepts related to neutrons such as logarithmic energy decrement, moderator ratio, surprising fast neutron passage through lead and not plastics with many protons etc

Here is an example link for anyone interested http://www.youtube.com/watch?v=uQ8vwevCq8Q

In the past few months, I have followed almost identical steps for the B10 for snm9,11, si19n and GE Bp A7 tubes.

With all the B10 tube inferface circuits, I have put an oscilloscope output and have monitored signal traffic, I can see the neutrons typically ten times the magnitude of gammas and noise, with varying mV amplitude and same polarity, on some tubes they have a voltage crossing, (shape is like an s sideways on the x-time axis) , see photos below of SNM9 tube. The n penetrate lead and showup when surounded by moderator (HDPE or paraffin wax.) For weak n sources, making very long count duration increases confidence of you are detecting n and compensates somewhat for the low rate.

I continued to use the oscilloscope setup with the B10 tubes but hit the EM interference problem of the fusor. It gives off so much x-rays that seep into and any unshielded homemade electronics associated with detecting counting etc and make disheartening false pulses. This is why I suggested a practice run on an air filled fusor inorder to avoid to kid oneself later on if quoting high n rates.

Best

[Richard Hull]

Yes, B-10 tubes are far more suseptable to gamma radiation than BF3 or 3He tubes. This is why they can be tricky. I was considerably worried about your homemade neutron source recording such a huge count rate over background. You mentioned the use of a homemade source using smoke alarm based Am241 but gave no real uCi range used.

Richard Hull

[Tony1of5]

Hi Chris, regarding your last post ... Just posting again to let you know I am stil alive and well, cough cough

I think many fusors have a teflon base that gives way to the tungsten grid inner grid. this (circular) surface area presented to the mini-sun will be heated up ... and lot more than 300 degrees.

My design is worse because I put the poisor to the side of the telon feed tower and hung the inner grid from the top, like a steet light, it means the teflon feed is being heated laterally and outgasses more. I put it in a glass collar to protect it. Next time I will build with steel and ceramics !


I can speculate three way gases can get from inside the chamber to anyones lungs:
1) Run the fusor and then open it, everyone will open at some time !?
2) Running the fusor, then opening fully the rough pump air valve, some gas sucked by the rough pump will go into the room ??
3) If the exhaust vent of the rough pump is not channeled outside or if the exhaust pipe breaks or backs-up the gas will again enter the room and lungs.

Then the concentrations and risks no idea ... anyone ?