My fusor design with a lack of neutrons

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Alexander Lichte
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My fusor design with a lack of neutrons

Post by Alexander Lichte »

This is my 3rd fusor.
By changing the electrolysis to a PEM cell, the pressure and voltage inside the fusor camber could be doubled.
The fusor is operated with 18kV at 20µBar.
Neutron background radiation: 1n / minute
Neutrons with fusor operating: only 4n / minute

Here is my experimental setup:
IMG_4773_doku.jpg
1: Diffusion pump
2: PEM Cell
3: Gas chamber ambient pressure
4: Prechamber inlet nozzle
5: Electrical throttle
6: Prechamber (p=400mBar)
7: Reactor chamber inlet nozzle
8: Two-way cock for direct evacuation of the prechamber or the gas inlet
9: Capacitive pressure gauge CMR275 Range: 0.1mBar
10: Throttle valve to the pump
11: Pulse Generator to control (5)
12: HV Supply for NaJ photo multiplier
13: Astro Camera SV305
14: ignition plug
------------------------------------------------------------------------------------------------------
IMG_4774_doku.jpg
1: Regulating transformer for HV supply
2: Spectrometer
3: CHM11 BF3 neutron detector with d=2.5cm Paraffin and some Plastic
4: Power source for neutron detector I=5µA
5: NaJ scintillator d=63mm
6: Red Pitaya as MCA for NaJ and n detector
7: Reactor di=12cm, heated up to 60°C and isolated.
8: 10kV Neon Transformer & Voltage Doubler with 10nF Caps
9: Shielded Neutron Preamp
------------------------------------------------------------------------------------------------------
IMG_4768_kl.JPG
Actual Grid: 3 turns 0.5mm Kanthal A / d = 15mm

Earlier attempts with thin molybdenum wire were problematic because the glowing cathode had probably led to a strong flow of electrons.

Here the actual Operation:
Object-Name__000020__data.jpg
The neutron rate is very low with 3n / min.
Do you have any ideas how to further increase the neutron rate?

Thank you, Alex
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Richard Hull
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Re: My fusor design with a lack of neutrons

Post by Richard Hull »

Great setup Alex! This is about how I did fusion back in 1999 except I had no diff pump and, thereby, wasted a lot of tanked deuterium gas. Of course, I had more voltage, ~28kv, back then. That is what you need....More voltage. This will push you up the cross sectional D-D fusion graph curve and improve your neutron detection numbers, well out of the need to statistical analysis from possible background errors.

You presented very good photographic, labeled images and a rather full report on your kit and quantitative operational conditions. Keep on supplying us with this kind of detail. This is what we need, but only rarely get in the way of a report on fusion and fusor operation. If you get more voltage to the fusor, you will certainly see more neutrons. All the best of luck.

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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Liam David
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Re: My fusor design with a lack of neutrons

Post by Liam David »

There are several unknowns here that make diagnosis difficult. A few things stand out, however:

Your voltage is far too low and we have no idea what the current is. I don't see anything in your setup that measures either. Using a 10kV NST and a doubler to claim 18kV is not enough--the voltage of NSTs sag under load and they will not deliver full current at full voltage. Moreover simulating a full-wave multiplier (center-tapped NST?) of the specs you describe at ~10mA current draw gives you no voltage doubling and 50% voltage ripple. My guess is your voltage is <<18kV. Details of your supply?

How have you constructed your neutron detector and how well have you shielded the electronics? Given that it's an entirely homebrew system, more details are needed. Have you checked gamma sensitivity using a hot gamma source? The extra counts you see could easily be interference from the HV.

The plasma image looks purple/blue, which is indicative of air and not deuterium, which glows red. What is the spectrum from your spectrometer?

Do you dry the deuterium?

What is your base pressure?

It's a good start, and nicely done with the images and labeling. You have almost everything there for a good fusor, and I think your power supply is the main limiting factor.
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Dennis P Brown
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Re: My fusor design with a lack of neutrons

Post by Dennis P Brown »

Liam has hit many of the key points. That said, really excellent photo's and explanation for your setup! That's an A+ for prestation!

Liam is absolutely correct about your power supply. A 60 Hz NST will never provide enough power to run a voltage multiplier for a fusor. Your neutron count is very likely not real but as he mentioned, more likely noise (Boy, been there done that with my scintillation detector very recently - Richard was spot on.) I assume that is lead shielding for the detector but all electrical noise isn't easily deterred. However, you certainly put a lot of effort into that system - again, good work and photo. I will say that once you do real fusion, that level of noise will not in any way impact your signal. You will likely get many hundreds of counts per minute so 4 counts/min. baseline with a plasma is not significant noise. So, your shielding is likely sufficient for a fusor operating with proper voltage/current. One note: your lead thickness might or might not be sufficient; you should calculate what thickness is required. At proper voltage the x-ray (and to lesser extent gamma rays from fusion) could cause issues with the photo-multiplier.

Yes, as Liam points out deuterium generated by a wet cell process must be run through a dryer or the water vapor will "poison" your fusor reaction. So don't overlook that issue.

Also, I understand pressure change via a PEM cell within a chamber (of course) but not voltage - the plasma doesn't really change voltage per-se; rather, its conduction will affect voltage within the chamber but the voltage the power supply provides isn't a function of pressure or conduction within the plasma. That isn't really correct way to view that aspect nor is that really controlling the system voltage. One sets a voltage and uses the pressure to control the current.

The idea of adding a spectrometer is very intriguing - hope that leads to future experimental data to be posted here.

Hope these suggestions are useful - you have an excellent basic setup that includes some very professional additions. Solving the power supply (insufficient voltage and current) issue should be your focus.
Last edited by Dennis P Brown on Sat Jan 08, 2022 4:17 pm, edited 1 time in total.
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Richard Hull
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Re: My fusor design with a lack of neutrons

Post by Richard Hull »

Yes, I forgot to mention the sag of the neon transformer. What you measure from a doubler working from an NST is one thing in open circuit but it is never that under an ionized gas load in a fusor. I doubt if you have 10kv DC under load and you will never get the rated current from a neon transformer under load much less from a voltage doubler connected to it. The three things that must be reported to be taken seriously are:

1. A running, measured voltage to the fusor HV terminal.
2. The current supplied to the fusor gas load it at that voltage.
3. The pressure of the deuterium gas in the fusor during operation.

Good neutron counts, (fusion), well above background typically begin around 20-25kv applied, 6-12 microns of pressure and at a current of 8-10 ma.

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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Mark Rowley
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Re: My fusor design with a lack of neutrons

Post by Mark Rowley »

Excellent work so far.
My advice....... you have way too much plumbing between your deuterium source and fusor. 90% of that should be removed and replaced with direct feed from a 100mL prefilled syringe and a ss-ss4 type needle valve. Im almost positive your deuterium is highly contaminated with air resulting in probably less than 60% purity... hence the low neutron count.

I highly advise against direct feed from the pem cell. Direct feed will undoubtedly result in a considerably more wet product than a prefilled syringe. Additionally, a PEM cell by itself will not provide the deuterium flow needed for a new fusioneer learning the ropes of operation.

Dennis, Liam.... PEM cell deuterium captured by a large 100mL syringe is not wet enough to cause any noteworthy issues with the gas. There are countless posts about this in the past. No need to dry a pre-filled syinge. But direct feed from cell to the fusor is a doubly bad idea....wet AND not enough product.

Theres FAQ's on the proper use of using PEM cell deuterium. I'd also recommend a review of that as well.

Lastly, you will need at least 23-25kV to get the neutron numbers to a level where they are clearly distinguishable from background.

Mark Rowley
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Alexander Lichte
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Re: My fusor design with a lack of neutrons

Post by Alexander Lichte »

Thank you for your help!
Richard, you are so right: The colour of my picture is wrong. It was made by an astro-camera and anything that looks like an orion nebula is a good picture.

There is no air as you can see by the spectrometer:
VIS_Spektrum.png
I can't distinguish between D and H.
There might be some Cr ions from the cathode.
You can find them on the surface of the chamber.
However, even when using wet gas of a K2CO3 electrolysis the spectrum don't show any oxygen.
The red spectral line is out of the range of my spectrometer. A rearrangement of the mirrors would be necessary.
I think, the spectrometer don't help very much here.

My 50Hz NST is 10kV UNIPOLAR:
IMG_4776_kl.JPG
The voltage is measured behind the series resistor, direct at the cathode.
I measure the voltage with a DVM, 1MOhm impedance and a 100MOhm series resistor.
Another Resistor went to a Linux-µC.
Both measurements are the same +/- 3%

The cathode current is 2mA@18kV and 3mA@16kV.
Increasing the current further causes the connection cable near the cathode to glow.
That is interesting: this unisolated piece of wire consume approx. 50% of my current ... ?

Yes, there is a strong 50Hz ripple on the supply:
The Doubler powers the Capacitor for maybe 3ms. This result in a 17ms gap.
dU=I*dt/C = 2mA*17ms/20nF = 1700V (!)
The fusor is working in a pulsed way.
You can see it with the camera if you select 49fps as well.
Does that matter?

Although I don't have a neutron reference, I have confidence in my neutron counter.
The impulses are clearly different from the noise as you can see here:
n_Pulse_760.png
However, the spectrum of the MCA shows a wide range of pulse high. That is confusing.
Here a comparison with and without the fusor running:
n-vergleich.png
There is no lead shielding at the moment.
I will think about that when increasing the voltage further.
I performed some electrical shielding:
IMG_4778_kl.JPG
All I can see, sparks do not influence the measurement.
But I'm not 100% sure.
Good idea: I can prove the gamma sensitivity with a peace of nasturan from the Erzgebirge. My scintillator went in saturation with that sample.

To the gas:
That is critical and my main mistake in former experiments (except the low voltage).
Only the oxygen side is filled at the PEM cell.
Like Mark wrote, drying is not necessary for the first.
The PEM is always under ambient pressure.
I fill a balloon with the deuterium:
IMG_4779_kl.JPG
My steps:
1. stop PEM cell, stop D2 flow from the cell.
2. Open all valves
3. Evacuate "prechamber" and "Gas chamber ambient pressure" (the balloon) to 800mBar (not less!).
The balloon is absolutely empty now.
4. close the electrical throttle and fill a little D2 in.
5. Repeat 1-4 two times.
6. Evacuate "prechamber" to 2 µBar (outgasing)
7. Now it is time to let D2 into the prechamber.

I can't believe there is any air left in my system.
But maybe the balloon is outgasing and pollute my gas?
I will try Marks syringe.


To the gas flow:
My diffusion pump and the long connection causes a slow flow rate.
I need to dry the chamber very good. It holds pressure < 10µBar for many hours, maybe days.
50mA current to the PEM cell produce enough D2 for me.

If I turn power on with the fresh evacuated chamber, the pressure will rise if current begins to flow.
If the chamber is dry, the pressure will drop when current begins to flow.

I see following steps for the future:
- Increase prechamber for better gas regulation.
- shorten the cathode connection
- perform a gamma sensitivity test to neutron detector
Maybe insert some lead shielding
- Test Marks syringe

If I need to increase voltage:
- a new and high quality ignition plug (not the one of my old car)
- Longer Resistance chains on all places.

If I try it with my NST, I can maybe achieve 2mA@30kV max.
- A huger cascade
- Over voltage protection of the NST itself (i already lost one).
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Re: My fusor design with a lack of neutrons

Post by Dennis P Brown »

Extremely through explanations and good picture support. The spectral analysis was very good.

I do not think you need to do a gamma ray test of your scintillation detector - I think the total shielding is ok. Get fusion level voltage and power to your chamber (safely!) and use that to determine if the detector has issues with the x-rays/gamma; unlikely that is an issue - I'd think that chamber is reasonable steel thickness and since your scintillation detector is surrounded with lead sheeting a few millimeters thick(?) it should be pretty insensitive.

In a pic is that a 3He detector? They do not respond to gamma's. Or is that a BF3 detector? Nice to know; also, is the scintillation detector just for gamma or is it too a neutron detector system? You haven't explained much on your detector types or I missed it.

As for the NST, sorry but a pulsed system at even 60 Hz isn't going to power a fusor - not happening. The total power from that system will not be sufficient for a fusor in any case even if it was continuous (18 kV is too low to achieve fusion using any detectors you have.)

You get the differential voltage of 1700 v; your dt is 3 ms, and cap is 20 uF. Then your total 'current' during the discharge is equivalent to 1.3 A/s or about 20 ma for that time period; on average; where I used Icap = [20uF x 1700V/(0.017 )]. That looks good (18 kV and 20 ma) and if continuous would be 360 watts but it is a pulsed system. The 17 ms pulses occur fifty times so the average power is 0.02 of 360 watts or 7 watts total power per second. Assuming my logic is correct.

In theory I guess that would be enough for fusion during that 17 ms window (really, more like a few ms at best with enough current flow) but we know the probability of fusion at just 18 kV is too small in number for typical systems to detect. I just don't see someone getting a readable signal from that low voltage and short pulsed power spikes.

Aside: in the future, never use wood to mount high voltage components- yes, you have stand offs but wood will interact with the corona and could cause arcing. Ditto, it isn't a good practice to have all those exposed wires - that is asking for arc overs as well. A real fusor level supply is lethal - you need proper insulated wire and far better construction on that side of the power supply. Exposed HV is very dangerous and for fusor's can be fatal. Best not to use caps but if you do, bleed off resistors* are a critical safety feature. Most people build HV voltage multipliers under oil to prevent arcs and make them safer.

When you said you used a piece of peace of nasturan from the Erzgebirge, exactly what is that?

*If you don't know what these are used for you need to read up on HV capacitor safety!

Another aside: your copper shielding provides zero protection for that detector tube. The metal must fully cover and electrically connect to the tube and the the input/detector wires need coaxial connectors as well.
Last edited by Dennis P Brown on Sun Jan 09, 2022 1:57 pm, edited 1 time in total.
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Re: My fusor design with a lack of neutrons

Post by Andrew Seltzman »

Is that blue thing on your grid insulator electrical tape / heat shrink tubing? If so it has to go, plasma bombardment will make it outgas and contaminate the vacuum.
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Alexander Lichte
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Re: My fusor design with a lack of neutrons

Post by Alexander Lichte »

Hello Dennis,
as a German I do myself sometimes a little bid hard - a translation error? : nasturan - should be Uraninit (UO2).
You can collect that in Germany because the Soviets used to mine here in the past.

It's a BF3 detector. I performed background measurement for 1h and got 55counts with Uraninit on the top of the detector.
==> There is no influence.
Therefore, I do not expect x-ray influence caused by the fusor.
BTW: The copper shielding is connected to the tube (surrounding) and I use a coaxial cable to the MCA.
There is a common mode choke inside the supply cable to prevent sheath currents.

* * * * *

I tried the syringes today!
I've got only a 10ccm syringe. Only enough for a run with extremely low gas flow.
The result:
No sparks, controllable even at 20kV. A bit unstable because of the low gas flow.
Neutron counts: 85 neutrons in 19min 40s. Subtracting the background are there still 3n/min.
I need to buy some huger syringes!
My supply is over-driven completely with 20kV: Ozone and sometimes sparks all over the Diodes. Catastrophic!
Reorganization needed. OK: No wood :-)

@Andrew: Your are right: heat shrink tubing.
I am aware of that problem and are watching it.
I need to isolate the gap between the Ceramics pipe and the ignition plug to prevent sparks destroying the ignition plug.
How would you perform that?
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Re: My fusor design with a lack of neutrons

Post by Andrew Seltzman »

For isolating the gap, having the ceramic overlap is usually sufficient. Using several nested ceramic tubes may be required to get the diameters correct, but this is usually ok.
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Re: My fusor design with a lack of neutrons

Post by Dennis P Brown »

Go to an auto parts store and get spark plug wire. They should sell rolls of it - most can handle at least 25 kV or more. That will reduce the corona issues. You could try placing the diode multiplier under oil - synthetic oil is excellent for that purpose.

How are you getting 20 kV? Have you got a new power supply? Again, I do not think that NST will get you clean signals - 4 counts/min over background (BG) isn't too strong a signal; however, if you make a run with no modulator and with, and get the excessive count (only with the modulator) then you are starting to make a case for the signal being real. Also, proving your background signal is a bit problematic - runs with a stable plasma for those time periods and making many runs (both BG, and then with and without modulator) will start to make your case. Getting reliable statistics with only 4 counts/min. above BG will be a challenge - especially with a limited supply of deuterium.

Your efforts and build are impressive.

Thanks for the translation. Didn't know that.
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Alexander Lichte
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Re: My fusor design with a lack of neutrons

Post by Alexander Lichte »

I am building a better HV power supply with my NST now.
I think you will be more satisfy with it.
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Re: My fusor design with a lack of neutrons

Post by Dennis P Brown »

What voltage are you using for your BF3 detector?
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Alexander Lichte
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Re: My fusor design with a lack of neutrons

Post by Alexander Lichte »

I use a Voltage Source adjustable from 300V - 1200V and a 8M2 Series resistor.
The detector current is adjusted to 5µA. The current is important for me. I do not know the real voltage at the detector.
But I do not have the 1600V from the data sheet. This is only necessary for a 100M Series resistor.
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Re: My fusor design with a lack of neutrons

Post by Dennis P Brown »

Thanks for that information; I have less then no knowledge on voltage variation allowances of BF3 detectors and have one. Wondering if below 1600 volts that is generally called for/normally used is an issue for detector performance? I ran mine at 1600 volts and got good results on neutrons signals but blew my counter after a while. So have given up on it.

In any case, I look forward to your post on your new higher voltage supply - obviously, might take some time.
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Re: My fusor design with a lack of neutrons

Post by Richard Hull »

BF3 tubes are typically far more immune to gamma rays than 3He tubes by a factor of a full order of magnitude! While both tubes are already highly immune, the BF3 in a good setup is usually "photon bullet proof".
Unfortunately, BF3 tubes in large sizes require 2800 volts or more to function. This can lead to coronal and oscillatory noise factors if fed by less than plus-ultra bias supplies or poorly wired home built BF3 detectors, connected by noisy cables and failure to terminate in characteristic impedances.

BF3 tubes do not require the huge pressures found in 3He tubes and are often filled to pressures at or just below atmosphere.

Richard Hull
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Fusion is the energy of the future....and it always will be
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Re: My fusor design with a lack of neutrons

Post by Mark Rowley »

As evidenced with my system and the $150 Neutron Detector post (viewtopic.php?f=13&t=13216), I'll second what Richard is saying about BF3 detectors. Gamma, xray, and electrical noise blindness is excellent. If you elect to use an old Soviet 3He tube, expect it to be a headache when using it near an xray producing / electrically noisy fusor (as all fusors are). The Soviet 3He tubes are great for isotopic or static neutron sources like a fission reactor, Pu detection, Am/Be sources, and the like. But near a fusor you'll be registering a torrent of false counts from the noise.

Newer name brand 3He tubes from mainstream companies like LND seem to perform much better.

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Re: My fusor design with a lack of neutrons

Post by Alexander Lichte »

Nice to see your forum online again.
It was offline when I wanted to make the last post.

I've build a HV-cascade and it works fine.
There have been huge troubles with sparks:
There were sparks inside the reactor and these interfered with the neutron detector.
After all interference suppression measures were unsuccessful, I shielded the HV cable. This kept the interference away from the detector.
An iron powder choke in the HV supply line has significantly increased the stability of the gas discharge.

My setup:
Fusor_Vorderansicht_komplett.jpg
1: Backing pump
2: Diffusion pump
3: Throttle valve to the pump
4: 10 kV NST (NOT center-tapped)
5: HV Cascade, 10nF capacitors, went up to -35kV, 2mA@-25kV
5a: Washer as a field homogenizer
6: series resistor (transformer protection)
7: HV-Terminal
8: 200MOhm series resistor for voltage measurement (1:200 divider)
9: Shielding of the high voltage cable
10: Inductor with iron powder core in the HV-Cable:
Great EMI countermeasure!
11: Capacitive pressure gauge CMR275 Range: 0.1mBar
12: Spark gap as over voltage protection
13: CHM11 BF3 neutron detector with d=2.5cm Paraffin and some Plastic
14: Power source for neutron detector I=5µA
15: Red Pitaya as MCA for NaJ and n detector
16: Auto-transformer to adjust the HV

The D2 System is made completely new:
Fusor_Rueckansicht_Gaseinlass.jpg
1: PEM Cell
2: Pressure regulator for the PEM cell viewtopic.php?t=14483
3: Homemade needle valve
4: PEM Cell current
5: Throttle valve to the pump
6: ignition plug (extra insulated)
7: Shielding of the high voltage cable
8: HV-Voltage, 1:200 divider
9: HV current (3mA Range)

Yesterday I reached -26kV @ 2mA, Pressure: 16..18µBar:
Object-Name__000018__data_kl.jpg
I use a very solid steel wire d=0.8mm for the grid D=2.4cm (1 inch).
This gave me the highest dielectric strength.

I measure the neutron within 10 minutes - without / with moderator under the same conditions:
neutronen_gegenueberstellung.png
You can see approx. 1 neutron/min without moderator. That's the solar background radiation.
The first run was made one week before, with higher background.

With moderator, the count rate is always about a factor of 10 higher.

So I assume that this run released a significant number of neutrons.
There are not a lot of neutrons, but I'm sure Richard is right:
I need more power to achieve even more.
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Re: My fusor design with a lack of neutrons

Post by Richard Hull »

The image of the star tells me you are on the right track. You do need a bit more power, not much, however. Perhaps 5ma of current at close to 30kv then you should see many more neutrons. Really good work.

Question you should label the x and y Axis. I asume the x is in seconds? the Y is ????

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Re: My fusor design with a lack of neutrons

Post by Alexander Lichte »

Oh, Thank you for your praise!

I use a "red pitaya" as muti-cannel-analyzer:
http://pavel-demin.github.io/red-pitaya-notes/mcpha/
Many thanks to Pavel!

You can see a Histogram:
x-Axis: The Energy Level (in ADC counts)
y-Axis: The amount, how often this energy level was count.

Even if you cannot use it to measure the energy of the slow neutrons, the histogram gives indications when disturbances are affecting the measurement:
sparks_in_mca.png
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Re: My fusor design with a lack of neutrons

Post by Dennis P Brown »

You are running a bit on the low side relative to total power; certainly your neutron count shows that your device is clearly achieving fusion. The photo shows a blue plasma - this is due to your camera?
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Re: My fusor design with a lack of neutrons

Post by Alexander Lichte »

The color of the discharge is about right now.
The spectrum of the deuterium discharge consists mainly of the red 656nm D-α and the blue 486nm D-β line.
For me, the 486nm line is dominant.
For Liam David it is the 656nm line.
I don't know why.
Voltage - Current - Hydrogen Contamination?
To clarify this, I bought another spectrometer. But it hasn't arrived yet.
https://www.ebay.de/itm/143989529085
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Re: My fusor design with a lack of neutrons

Post by Dennis P Brown »

You are correct that the color varies. Appears that it turns out that both colors are generated but current density affects which dominates. LOL - didn't realize this fact. Follows with your lower current (2 ma) the bluer color occurs where as I have 30 ma and get the redder color (our cathodes both have 4Pi steradians of plasma discharge but only differ by available current supplied to the cathode.) See the discharge tube photo - both colors appear simultaneously but due to different current densities, the colors change depending on the tube diameter.
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Real name: Matt Gibson

Re: My fusor design with a lack of neutrons

Post by Matt_Gibson »

You guys are lucky to see anything at all. My cathode glows so brightly that I can’t see anything at all. No star, no nothing. Looks like a light bulb.
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