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Posts: 10
Joined: Fri Sep 30, 2016 1:31 am

Hello Everyone,

Today I got my demo fusor working. Following are pictures taken during the run.

Plasma pictures:
The Cathode HV tank (taken out of a High frequency X-Ray machine) has a 6.2kohm over 10Mohm voltage divider. I assume it outputs 5volts for its logic circuits measuring maximum voltage.
Doing simple math, HV*(6.2k/(10M+6.2k))=5v. HV= (5*(10M+6.2k))/6.2k =~ 8070v. The tank has a total ov 9 capacitor in series.
So 8070v x 9 = 72630v =~ 72000v. In this picture, I had the meter set to 2.5volt range. So a full scale will read 72000v/2 = 36000v on full scale.
The voltage reading on the fusor at around 31.5mA (according to shunt resistor voltage) is 0.1v which corresponds to (0.1*(10M+6.2k))/6.2k =~ 161.4v x 9 =~ 1452.5v

voltage across 100ohm shunt resistor is around 3.15v. V=IR. I=V/R. I= 3.15v/100ohm = 31.5mA
The vacuum pressure is.. Umm. all the way down.
The central grid mounted on a sparkplug. Please excuse all the sloppy workmanship,
Light blues are simple blutacks bought from stationary for quick sealant. The dark blue ones are silicon gasket makers.
The base plate is 10mm acrylic and the cover is around 3mm thick salad bowl.
The HV tank, IGBT circuit and High frequency driver circuit running at 100kHz. The 100kHz pulse
is supplied by the function generator. These high frequency circuits was initially used to run my Continuous Wave
Tesla Coil.
Plasma at much lower voltage levels.
And finally, my messy overall setup. Note that there are unutilized equipment's on the table as well.
After this my plans are to house keep my setup and save up for a micron pressure gauge to build an actual fusor. Living in a third world country will take some time to save up. But I strive to gain some knowledge that
is always more valuable than money.

Thank you for reading my post. Any help for my future work in building an actual fusor is highly appreciated.

Richard Hull
Moderator
Posts: 11711
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

### Re: Muhammad Faidzul Demo Fusor

Great work! While you fusor is crude and the vacuum not great, you have taken the time to instrument well and report accurately. This is something only a tiny fraction of first pass plasma folks bother with. You have done well and your instrumentation will guide you in learning the way a plasma functions as your vacuum gets better.

I spent one full year with fusor I and II before ever attempting fusion, just studying the glow discharge and plasma characteristics.

I have entered you into the plasma club.

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.

Posts: 10
Joined: Fri Sep 30, 2016 1:31 am

### Re: Muhammad Faidzul Demo Fusor

Thank you Mr. Richard.

The voltage in the chamber is saturated at around 1500v. I guess it shows that my chamber does not have enough gas evacuated to increase the breakdown voltage between the grids. I have read somewhere if the vacuum is perfect, the voltage should saturate at the maximum voltage that the power supply could provide since no current could flow.

I was thinking weather i can make a two plate capacitor probe, apply some voltage across it and read the current value to determine the vacuum. Then stick the probe in the chamber and compare it with sticking the probe direct into my vacuum pump outlet for comparison. By reading the current drained, i can figure out weather my chamber is leaking.

Noah C Hoppis
Posts: 56
Joined: Sat Dec 22, 2012 9:05 pm
Real name: Noah C Hoppis

### Re: Muhammad Faidzul Demo Fusor

The electrical conductivity of a gas at a given pressure is characterised by paschen's law (https://en.wikipedia.org/wiki/Paschen%27s_law). The mechanics involved can be somewhat complex, but in effect at 'high' pressures voltage breakdown is proportional to pressure, but at low pressures this relationship becomes strongly inverse.

What you just described is, in effect, a cold cathode ionization gauge, but operating under a different mechanism. CCIG's (and ionization gauges in general) have to rely on the ions actually moving to conduct a current, because paschen's law dictates at these low pressures an electrical discharge cannot strike directly across a chain of atoms (because there is not really a chain of atoms together, the pressure is too low). So a CCIG actually ionizes atoms on the plate of the 'capacitor' (or in very short range) and then uses the field between the two plates to transport the ion across the gap and conduct a current. Because the current relies on the availability of atoms in the electric field, the current in an ionization gauge is proportional to the pressure.

While CCIG's are excellent for measuring high(er) vacuums, they tend to not play as nice around the vacuum level you are describing in your chamber (due to continuous discharge). Normally CCIG's, inverted magnetron gauges, and the like start to function below the point that a thermocouple gauge pegs. Instead of building an ionization type gauge first, I would recommend either procuring a TC gauge (normally dirt cheap, around \$10 US is all I would ever pay for one) and characterizing it or building a full TC gauge from scratch (as described here: http://www.belljar.net/tcgauge.htm).
"No missile ever flew before 10 pm"

Richard Hull
Moderator
Posts: 11711
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

### Re: Muhammad Faidzul Demo Fusor

Good advice from Noah. With only a mechanical pump, a Thermocouple gauge is a must have item.

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.

Rich Feldman
Posts: 1171
Joined: Mon Dec 21, 2009 11:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

### Re: Muhammad Faidzul Demo Fusor

Are your X-ray transformer tanks from a Bennett system? They look just like mine, acquired almost 2 years ago. Yet another unfinished project, practically untouched since the last report here: viewtopic.php?f=18&t=9781&p=65697 You are way ahead of me on 100 kHz power inverters. Mind sharing your bridge and driver circuit details? How come you chose to use IGBTs? Is it all scratch-built, or made from boards available in Tesla coil hobby circles?

p.s. I thought God gave advice _to_ Noah.
noah2.PNG (4.35 KiB) Viewed 4837 times
All models are wrong; some models are useful. -- George Box

Posts: 10
Joined: Fri Sep 30, 2016 1:31 am

### Re: Muhammad Faidzul Demo Fusor

Noah C Hoppis wrote:The electrical conductivity of a gas at a given pressure is characterised by paschen's law (https://en.wikipedia.org/wiki/Paschen%27s_law). The mechanics involved can be somewhat complex, but in effect at 'high' pressures voltage breakdown is proportional to pressure, but at low pressures this relationship becomes strongly inverse.

What you just described is, in effect, a cold cathode ionization gauge, but operating under a different mechanism. CCIG's (and ionization gauges in general) have to rely on the ions actually moving to conduct a current, because paschen's law dictates at these low pressures an electrical discharge cannot strike directly across a chain of atoms (because there is not really a chain of atoms together, the pressure is too low). So a CCIG actually ionizes atoms on the plate of the 'capacitor' (or in very short range) and then uses the field between the two plates to transport the ion across the gap and conduct a current. Because the current relies on the availability of atoms in the electric field, the current in an ionization gauge is proportional to the pressure.

While CCIG's are excellent for measuring high(er) vacuums, they tend to not play as nice around the vacuum level you are describing in your chamber (due to continuous discharge). Normally CCIG's, inverted magnetron gauges, and the like start to function below the point that a thermocouple gauge pegs. Instead of building an ionization type gauge first, I would recommend either procuring a TC gauge (normally dirt cheap, around \$10 US is all I would ever pay for one) and characterizing it or building a full TC gauge from scratch (as described here: http://www.belljar.net/tcgauge.htm).

I realized that calling the plates 'capacitor' was way off. should have called it electrodes instead since it wasn't for storing charges anyway. lol. I remember the last time i read about paschens law on wiki. it took me weeks to understand it because i couldn't read a few sentence without falling asleep.

The thermocouple gauge seems like a nice and achievable project using some parts available lying around. thanks for recommending. Its simpler than it sounds. I don't think I'm going to buy anything yet. Better save money for a better option like this one: https://www.jbtoolsales.com/cps-product ... n-microns/ <--- Is it good enough for fusion vacuums?
I'm already regretting buying a 1 stage pump. Should have bought 2 stage from the start. I'm afraid a 1 stage pump couldn't support a diffusion pump.
Richard Hull wrote:God advice from Noah. With only a mechanical pump, a Thermocouple gauge is a must have item.

Richard Hull
Lol. Not sure if its a typo or a figured out pun
Rich Feldman wrote:Looks real good, Muhammad.

Are your X-ray transformer tanks from a Bennett system? They look just like mine, acquired almost 2 years ago. Yet another unfinished project, practically untouched since the last report here: viewtopic.php?f=18&t=9781&p=65697 You are way ahead of me on 100 kHz power inverters. Mind sharing your bridge and driver circuit details? How come you chose to use IGBTs? Is it all scratch-built, or made from boards available in Tesla coil hobby circles?

p.s. I thought God gave advice _to_ Noah.
noah2.PNG
Yes, Its from a Bennett system. Yours looks so clean. Mine is soaked in transformer oil. I drove it at 100kHz because that's what the brochure says so. It works fine. But i have never turned it on more than 1 minute since i was aware that the system wasn't designed for long run. Plus the resistor on the IGBT board got hot and kept releasing unpleasant cooking smell. By reverse engineering the kVp board, i could understand that, it runs on some form of PWM. its kind of weird for me because it was the first time i saw a full bridge inverter using PWM to adjust its voltage output. I didn't choose to use IGBT's. But it was lying around since the whole machine was disposed off. So it was basically free for me. I tried driving the Gate Drive Transformer (GDT) using a car audio amplifier that was lying around earlier that time, but the GDTs impedance was too low causing insufficient power from the audio amplifier, which caused significant voltage drop of Gate voltage thus could damage IGBT's at high power.

The small board you see is only a fraction taken from the original kVp board that is responsible for driving the GDT. I sketched it on a piece of paper last time, but i think someone threw it away (maybe it was me). I designed the board in Eagle PCB. I'll send the Eagle pcb file to you once i could find it if you like.

Richard Hull
Moderator
Posts: 11711
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

### Re: Muhammad Faidzul Demo Fusor

No need to keep quoting other folks posts in this thread. We can and have read all of the thread. Tons of quotes and little new text is a tiresome and tedious and often an odius effort for the reader.

I have corrected my mis-typed post.

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.

Posts: 10
Joined: Fri Sep 30, 2016 1:31 am

### Re: Muhammad Faidzul Demo Fusor

Ok, understood and noted.

Posts: 10
Joined: Fri Sep 30, 2016 1:31 am

### Re: Muhammad Faidzul Demo Fusor

Hi, So I bought this diffusion pump on ebay. Order was made 1st Nov, shipment on 10th Nov, received on 29 Nov.
I bought it because it was the cheapest yet i could find and it was the same one used by robofusor http://robofusor.haylett.ca/robofusor-2 ... cuum-pump/
By visual inspection, it looks good. But I need some advice from professionals since i have zero experience in diffusion pumps.
I have not tested the unit yet because I lack a step-down transformer and diffusion pump oil. Plus I doubt my Chinese 1 stage pump would be sufficient for roughing.
Bought from ebay on the same day it was advertised.
Once received, I stripped it down for inspection.
Bottom view of the Christmas tree
Top view of heat sink chamber
Bottom view of heat sink chamber
I didn't expect it to come with a throttle valve
Inside of the throttle valve
rated at 300 watts and 110vac
Cooling fan holder. I doubt the fan works because its not turning smoothly.
These two fitting are a bit loose. Is it a good idea to deform the female part so that it tightens up during slotting in?
Inside the chamber
Is it normal that nothing is holding the chrismas tree in position? Wont it shoot up when high flow of oil vapor shoots through?
Assembled unit
Assembled unit
Assembled unit
Will need to 3d print a new throttle handle