Steven Haid's Fusor

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Steven Haid
Posts: 12
Joined: Sun Feb 14, 2016 3:39 pm
Real name: Steven Haid
Location: Massachusetts, USA

Steven Haid's Fusor

Post by Steven Haid »

I am applying to the Neutron Club.

I apologize for not posting the construction progression of my fusor. I have just read the requirements for claiming fusion, and see that I should have been doing that. Hopefully I can make up for that with this detailed report.

I have made extensive use of this web site and doubt that I ever would have been able to make a fusor without the information provided in the forums.

I Joined fusor.net Feb 2016, and have made only 7 posts.

SUMMARY

Here is a picture of the Fusor. I started working on this January 2016. Looking back at my order history the first part ordered was "Allanson 15000 Volt 60 Ma Neon Sign Transformer", on Jan 4, 2016. It turned out this NST was not useful because when connected to a dummy load it's ground fault circuit breaker tripped, and there is no way to defeat the GFI on this NST. I later acquired a dental X-Ray transformer.
system.jpg
The screenshot attached below is from the data acquisition software. The values shown are from July 24 2017.
  • The upper left is the image from the camera.
  • The values shown in the black area near the top are self explanatory, except for NPHT, which stands for Neutron Pule Height Threshold. Pulse heights larger than this value are counted as neutron events.
  • The Summary graph at the bottom is a 300 second plot of the voltage, current, neutron counts/minute, and D2 pressure.
  • The Neutron ADC graph shows the pulse data collected from the ADC during a 1 second interval. Only pules that are larger than the NPHT are displayed.
Conditions:
  • Time Span = 1:30 minutes (20:20:20 to 20:21:50)
  • Average Voltage: 30 KV
  • Average Current: 6 mA
  • Average D2 Pressure: 15 mT
display1.jpg
A higher resolution screenshot and a screencast are here: DETAILS

Power Supply

I used a circuit similar to the what is described here viewtopic.php?f=29&t=4405 with the following changes:
  • a dental X-Ray Transformer is used instead of a Neon Sign Transformer
  • used 3 20KV 2A diodes in series
  • no capacitor
  • different metering resistor values, described below.
  • added a ballast resistor.
I have seen pictures of other fusor power supplies that have submersed all components in mineral oil. I chose not to do that, but instead use lexan for insulation and substantial distance between the components. I recall reading this would probably be okay up to 30 KV. I did test the power supply with it not connected to the fusor; at a voltage of 30 KV the current panel meter read 0.1 mA, and with the room lights turned off I did not see any discharge glow, so it seems okay. I am also running a dehumidifier in the basement to keep the humidity at 35% or less.

The X-Ray transformer fits snugly in a 1.5 gallon container, which is filled with 1 gallon of low viscosity mineral oil. I did not try to draw a light vacuum and add the mineral oil under the vacuum. Instead I did gently shake the container to attempt to dislodge bubbles (I didn't see any bubbles discharged), and the transformer has been resting in the mineral oil for months without being used while I was working on other areas. I did have a problem with the mineral oil slowly syphoning through the high voltage wires, This problem was solved by adding the vertical black wires on the end of 2 diode chains, and attaching the HV wire at a greater height than the mineral oil.

I used a 50K ohm 100W watt ballast resistor. At 40 mA, the power dissipated in the ballast resistor would be 80 watts. At a more typical fusor current of about 10 mA the power dissipated would be 5 watts, and the voltage drop is 500 volts.

The power supply has only been used under load for about 10 minutes so far. I am concerned that the X-Ray transformer may have some air bubbles and/or is being run at higher currents and duration that it was designed for. Therefore I have kept the fusor runs short.

The resistor used to measure current is 100 ohm 10 watt 5%. A panel meter and an ADC are both connected to this resistor. The ADC is connected to a Raspberry Pi computer. When the current is 10 mA the voltage across this resistor will be 1 V, which is a reading of about 200 on the ADC.

The voltage divider, used to measure the high voltage, is made of a 1G ohm resistor and a 100K ohm 2 Watt 1% resistor. A panel meter and an ADC are connected to the 100K ohm resistor. At 30 KV the voltage across the 100K resistor will be 3V and the ADC reading will be about 600. The 1G resistor was purchased from http://www.highvoltageresistors.biz/400 ... 60081.aspx and is specified at 60 KV and 13.5 watts.

The software that processes the date from the ADC computes an average over 1 second. The panel meters must also contain a built-in mechanism to average because the values they display are stable.

I was concerned that because a large 100K ohm resistor is used in the voltage divider, the input impedance of the panel meter and the ADC would affect the reading. The panel meter has 10M ohm input impedance, and the ADC has a 2M ohm input impedance. Using the formula to add parallel resistances of the panel meter, the ADC and the 100K ohm resistor yields 94K ohm. To account for this the software uses 94340 instead of 100000 when calculating the value of the high voltage. The KV panel meter will read about 5% low.

A problem I'm having is when the Raspberry Pi is turned on (which provides power to the USB ADC), the KV panel meter reading changes from 0.0 to -1.4. This Raspberry Pi is powered by a battery because I had suspected problems due to ground loops that might be resolved by using a battery for the power source. The software running on the Raspberry Pi compensates for this by adding 1.43, so that the software will display 0 KV when the HV power supply is turned off.
power.jpg
Vacuum System

The vacuum system is comprised of:
  • Welch 1402, Belt Drive Rotary Vane Dual Stage Mechanical Vacuum Pump, 5 CFM
  • 4 way KF-25 cross, with connections to: (1) Welch forepump, (2) Air admittance vent valve, (3) KF-25 bellows valve, leading to diff pump, (4) Thermocouple gauge (Varian 531)
  • Varian HSA Diffusion Pump, air cooled
  • CF 3.38" Manual Bellows Angle Valve, connecting the Diff Pump to the Vacuum Chamber
  • Gum Rubber Vacuum Hose Tubing,
  • KF-25 to Rubber Hose adapters
  • 90 degree Stainless Steel elbow, 1" tube size
To clean the Welch vacuum pump I followed the procedure, first used Flushing Fluid a couple of times and then filled with Duoseal Pump Oil. Following the cleaning, the pump achieved a pressure of 9 mTorr with just the Pirani gauge attached to the pump through a short length of gum rubber vacuum hose.

Even now the Welch pump is still dirty on the inside, and the pump oil turns brown after being used. I should change the oil again soon. Currently the Welch Forepump can pump the chamber down to about 20 mTorr.

The Varian HSA Diffusion Pump is air cooled, and is charged with 50 mL of KJLC 704 Diffusion Pump Fluid. The diff pump heater is plugged in to a current meter so that I know it is working. The heater is 115V, and the meter reads 2.7A. It takes 15 minutes for the oil to heat up and the diff pump start pumping. The cool down time for this pump is 40 minutes.

The thermocouple gauge is a Varian 531, and controller is Varian 804-A. The controller did not come with a cable. I purchased the cable from Dunimay Stockroom, they make the cable so it takes a few extra days. The controller has a knob to select one of 5 sensors. The switch contacts needed to be cleaned, so I opened the box, cleaned the switch with contact cleaner, and it works fine now. I calibrated the TC Controller against the Pirani Gauge. There is a calibration control on the rear of TC Controller.
vacuum.jpg
Vacuum Chamber

The chamber is made of 2 6" stainless steel hemispheres connected to each other with CF flanges (8" OD, 6" Tube Bore). There are 5 chamber ports:
  • vacuum port: 3.38" CF Half Nipple, with 2" OD Tube
  • electric feed through: 2.75" CF Half Nipple with 1.5" OD Tube
  • view port: 2.75" CF Half Nipple with 1.5" OD Tube
  • gas inlet port: 1.33" CF Half Nipple with .75" OD Tube
  • pressure gauge port: KF-25 Half Nipple with 1" OD Tube
Design considerations:
  • room was left on the right side of the chamber for the HDPE moderator and Neutron Detector
  • the Viewport is positioned in the back of the chamber, and at a downward angle so the X-Rays are directed into the ground
  • there are no ports at the bottom of the chamber, so that if a pieces of the electric grid were to break off it would not fall into a port
  • the gas inlet port is on the opposite side of the chamber from the vacuum port, so that the gas will fill the chamber prior to being evacuated through the vacuum port
  • the ports are located so that clearance is available to insert the bolts in the large CF flanges that join the 2 hemispheres.
When tightening the CF, I followed bolt tightening pattern that I found on the internet. And the bolts were re-tightened after 24 hours.

A Kurt J Lesker 275i Series Convection Vacuum Gauge, with KF-25 connection and Log-Linear analog output is used to measure chamber pressure. This is a "convection enhanced Pirani Gauge", with a range of 0.1 mTorr to just above atmosphere. This gauge has a digital readout and an analog output. A control on the gauge is used to calibrate the zero point and atmospheric pressure. I have connected the gauge's analog output to an ADC see Data Acquisition below. The gauge's manual provides conversion tables to convert the analog output voltage to pressure for various gases. The Data Acquisition software implements the D2 and N2 conversion tables.

Fortunately I had worked with someone who is now the owner of a machine shop. Most of what they do is CNC Turning & Milling, however they also have an older milling machine suited to making the holes in the hemispheres, and access to a welder who has done many vacuum chambers. I had originally thought that the holes would be drilled in the SS hemispheres, and that the holes would be smaller than the ports, and that the ports would be welded on the outside. The machine shop used a better approach:
  • attached the large CF flanges to each hemisphere, and bolted metal rings on the 2 large CF flanges to protect the knife edge
  • milled the holes in the chamber so that the fittings would snugly fit in the holes
  • welded the fittings on the inside
An interesting thing I learned when reading about welding vacuum chambers is what a "Virtual Leak" is. The vacuum chamber welds should be on the inside to avoid creating isolated air pockets inside the chamber that slowly leak into the chamber. A Virtual Leak probably doesn't matter to this fusor chamber; but does matter when constructing Ultra High Vacuum chambers, where even fingerprints on the chamber walls are a problem.
chamber.jpg
Camera

I used the Logictech HD Laptop Webcam C615. I chose this webcam because it's features include:
  • Premium autofocus for razor sharp images, even in close-ups
  • Record clear videos even with dim or poorly backlit settings thanks to automatic light correction
This camera seems to work well. I was surprised that it was able to image the fusor grid when the fusor is off with the minimal light that gets in the fusor through the viewport window, past the camera.

The images recorded while the fusor is running shows random sparkles. I'm not sure what causes the sparkles, perhaps they are due to the X-Rays.

The Data Acquisition software configures the webcam for 640x480 images, and provides pan and zoom capability, via keyboard commands, to select a subset of the 640x480 to be displayed.

D2 Gas Feed

Series of components
  • D2 Lecture bottle,
  • Single Stage Regulator, with needle valve and hose barb outlet
  • Flow Restrictor, details below
  • Bellows Valve connecting to the chamber
I tested the Flow Restrictor using the following procedure. This testing was done with air, not using the D2 gas.
  • closed off the input to the flow restrictor using barbed tubing plug
  • opened the gas valve and pumped down the chamber using just the forepump to about 20 mTorr
  • removed the tubing plug (actually cut it off) to allow atmosphere to enter the flow restrictor
  • waited for the chamber pressure to stabilize
  • note the pressure
My first Flow Restrictor is made up of 3 30" sections of stainless steel hypodermic tubing with an ID of .010 inches. These sections are connected together using .020" ID micro bore tubing. Adapters are used on both ends to convert the .020" micro bore tubing to 1/8" hose barb. All of the connections are encapsulated in epoxy (used Araldite standard Epoxy) to try to prevent leaks. This flow restrictor was tested using the above procedure, and the result was about 200 mTorr.

Hoping to achieve a lower pressure I built a second Flow Restrictor using 100 feet of the .020" ID micro bore tubing wound on a small cylinder. The ends of the tubing connected to a 1/8" hose barb adapter. This was also tested and also resulted in a pressure of about 200 mTorr.

Finally I connected the 2 Flow Restrictors in series, and testing this configuration yielded a pressure of 80 mTorr, which seems okay.

My D2 lecture bottle currently has about 600 psig. I had wasted some of the D2 during initial tests, before I realized just how little gas is in the lecture bottle, and became more careful not to waste it. A D2 lecture bottle at 850 psig contains just 25 L, or 0.9 cubic feet of gas at atmospheric pressure.

The regulator used is a "Harris HP704-015-170A Lecture Bottle Pressure Regulator, 0-15 psig, Brass" single stage regulator with Needle Valve. It is my understanding that some regulators will not handle the outlet being exposed to vacuum. The needle valve allows me to isolate the regulator from the vacuum.

Additional Info
  • CGA is abbreviation for Compressed Gas Association
  • http://www.airproducts.com/~/media/file ... ram-31.pdf Provides an overview of Cylinder Outlet Connections. This doc provides torque guideline of 10 ft-lb recommended for CGA 170 with washer
  • http://www.mathesongas.com/pdfs/product ... -Chart.pdf Provides cylinder information for various gas types. Indicates D2 cylinder can use CGA350 or CGA170. And "NOTE: The CGA 170 is authorized for non-corrosive gases packaged in lecture bottles. The CGA 180 is authorized for all gases packaged in lecture bottles.
  • Whenever the CGA 170 regulator is removed and re-attached to the cylinder a new washer should be used. Washers can be obtained from: https://store.mathesongas.com/cga-washers-teflon/
  • A disadvantage of a single stage regulator is that the output pressure does not remain constant; instead as the high pressure side of the regulator drops in pressure, the output pressure of the regulator increases.
flow_restrictor.jpg
Grid

The grid was constructed of a single Tantalum wire, diameter 0.065". The diameter of the grid is approximately 1.5", which is the maximum size that will fit through the electric feedthrough port.

I first practiced constructing a model of the grid using hookup wire. When satisfied with the technique I repeated the procedure with the Tantalum wire. A circular template was used to help bend the wire into a loop.

To insulate the stalk I used 2 nested Alumina Ceramic Tubes. The inner tube is 1/8" ID and 1/4" OD; and the outer tube is 1/4" ID and 3/8" OD. The Alumina Ceramic tubes were easy to cut using a small diamond circular saw blade. I made a jig to securely hold the tube, brought it outside, wore mask and goggles, and performed the cuts.

The grid was attached to the electric feedthrough by tightly wrapping the Tantalum wire around the feedthrough after carefully measuring for the desired location. I used vise grips to further tighten the wraps, to ensure the grid would not slide off during operation of the fusor. The inner Alumina tube rests on the top of the wraps, and the outer tube extends down to cover the wraps. The outer tube is a tight friction fit on the inner tube.

The pictures below illustrate the construction process. Shown is the model made of hookup wire, and leftover Alumina tubing.
feed_through.jpg
Neutron Detector

I am using an SI-19N He3 Neutron Detector Tube. I have seen information which says this is a corona mode detector. However the seller had tested this tube at a lower voltage using a proportional counter. I am using this detector at 1700 volts, where it works as a proportional detector. In the 2000 - 2800 volt range this detector is documented to work in corona mode, which would require more current than my Ludlum 2929 could provide.

The SI-19N is surrounded by 3-4 inches of HDPE on all sides to slow the fast neutrons that are released by the fusor to a speed that the neutron detector tube can detect.

The SI-19N Neutron Detector is connected to a Ludlum 2929 Dual Channel Scaler. The Ludlum documentation states this Scaler is usually used with an Alpha/Beta Sample Counter; but it can also be used with a proportional detector. This Scaler has a BNC connector on the rear that provides the final amplifier stage output. I have connected from this BNC connector to an ADC converter as described in the next section. The Alpha/Beta LED counter displays on the Ludlum 2929 are not being used.
neutron_detector.jpg
Data Acquisition System

Two Raspberry Pi computers are being used:

1) Computer Name = rpi_data, Program Name = get_data.
  • reads data values from the Voltage, Current, Pressure, and Neutron Tube ADC inputs
  • analyzes the data, for example identifies pulses from the Neutron Tube input
  • the analyzed data is sent to the other Raspberry Pi via Wifi
  • powered by a battery, because I was having trouble with AC ripple, which I suspected was caused by the Raspberry Pi power adapter.
2) Computer Name = rpi_display, Program Name = display.
  • receives the analyzed data over Wifi from rpi_data
  • reads the camera image from the USB webcam
  • displays the camera image, data values, and graphs
  • accepts user input for various controls, including selecting the Neutron Pulse Height Threshold (NPHT), and adjusting the camera image pan and zoom
  • records the analyzed data to a file so it can be viewed later in Playback mode
  • can run in Playback mode to examine the recorded data at a later time.
computer.jpg

The ADC for the Neutron Tube data needs to be high speed because the pulses are only a couple of microseconds duration. I found a reasonably priced ADC that can collect data from a single input channel at 500K samples per second. I was at first concerned that the pulses might be too narrow to be properly measured with this ADC, so I tried some simple circuits to widen the pulse. It turned out that these simple circuits did not do what I expected, and that simply directly connecting the Ludlum 2929 amplifier output to the ADC input works well.

I did have a problem with the low speed ADC (which reads the Voltage, Current, and Pressure) interfering with the High Speed ADC (the one reading the Neutron Amplifier Output data). The High Speed ADC FIFO would fill and enter an error state. I coded the software to detect this error and restart the high speed ADC; this happens twice per second. So instead of getting 500K samples per second, the software is receiving ~475K samples per second, which still is okay.

The software is freely available on github, and is licensed under the MIT License. The recorded data file from my first fusion run is available on Google Drive. The display program will run on a 32bit or 64bit Linux. For example I run the display program on either a Raspberry Pi or Fedora-20/x86_64 desktop computer. If you would like to try the display program these are the steps that can be used to build, install, and run the program on Fedora-20. It shouldn't be difficult to build and run this software on other versions of Linux as well. If you need help, send me an email, my email address is in the about.h file.

Code: Select all

# install additional software development packages
yum install SDL2-devel SDL2_ttf-devel SDL2-mixer-devel
yum install libjpeg-turbo-devel libpng-devel
yum install gnu-free-mono-fonts

# clone the git repo
cd ~
git clone https://github.com/sthaid/proj_fusor.git

# build the display program
cd proj_fusor
make display

# Download the 248M fusor run data file by browsing to:
#   https://drive.google.com/file/d/0B3Q10qVwU0_FZmc2VWZrSlNxQUU/view?usp=sharing

# run the display program 
display -h                                        # help on program options
display -p ~/Downloads/fusor_170724_192651.dat    # then use '?' for help
Since the pulse heights from the neutron detector are saved in the data file, the display program can be run in playback mode to observe how modifying the Neutron-Pulse-Height-Threshold (NPHT) affects the Neutron CPM values. The following pair of screenshots illustrates this, the top screenshot has NPHT=215, and the bottom has NPHT=200.
display1b.jpg

PROCEDURES

The following procedure focuses on the major steps. Steps dealing with the electronics are omitted. If you are interested see the following link for the full procedure that I used. https://drive.google.com/file/d/0B3Q10q ... sp=sharing

Initial Conditions
  • The 3 Bellows valves are closed.
  • Air admittance vent valve is open.
  • Regulator needle valve is closed.
  • Regulator pressure adjustment knob rotated counterclockwise and turning freely.
  • D2 lecture lecture bottle valve is closed.
  • Variac is turned off and set to 0 volts.
Deuterium Gas Setup
  • Open and then close the D2 lecture bottle valve, this will pressurize the inlet side of the regulator with enough gas to run the fusor. It is important to run with the D2 lecture bottle valve closed to avoid accidentally wasting the deuterium gas.
  • Turn the regulator adjustment handle clockwise until the regulator outlet gauge reads about 2 psig.
Pump Down
  • Turn on the diffusion pump fan.
  • Close the Air admittance vent valve.
  • Power on the forepump and verify the pressure quickly drops to 30 mTorr.
  • Open the forepump bellows valve and verify pressure again reaches 30 mTorr. This step pumps down the diff pump.
  • Open throttle valve and verify pressure again reaches 30 mTorr. This step pumps down the chamber.
  • Open gas valve, and wait about 10 minutes for pressure to reach about 25 mTorr. This pumps down the gas leak lines up to the regulator's needle valve.
  • Power on Diff pump heater.
  • Wait about 15 minutes for the chamber pressure (Pirani gauge) reading to reach about 0.2 mTorr. What I have observed is for the first 14 minutes the chamber pressure fluctuates but remains high; then the pressure drops quickly reaching 0.2 mTorr in a couple of minutes.
Obtain 15 mTorr D2 gas pressure in chamber
  • Close throttle valve until chamber pressure stabilizes at about 1 mTorr,
  • Open needle valve on D2 regulator, and wait for D2 chamber pressure to stabilize, at hopefully near 15 mTorr.
  • Adjust throttle valve for 15 mTorr D2 chamber pressure.
Create Fusion
  • Turn on the Geiger Counter and check it occasionally while the high voltage is on.
  • Turn on the Variac and slowly increase the voltage until the plasma ignites. At this point I backed off the voltage and slowly brought it back up again and the plasma re-ignited, this time drawing less current. I had also experimented with different pressures before settling on 15 mTorr.
  • Check Neutron CPM readout, and increase voltage if more CPM is desired.
  • After a minute or two reduce the Variac setting to 0 volts, and turn off the Variac.
Shutdown
  • Turn the regulator pressure adjustment knob counterclockwise until turning freely.
  • Wait for the regulator outlet gauge to drop to near 0 psig and close the regulator's needle valve.
  • At this point their still may be a substantial pressure reading on the regulator's inlet gauge. If there is enough pressure on the inlet gauge then the next time the fusor is used it may not be necessary to use more D2 gas from the lecture bottle.
  • Isolate the chamber by closing the gas inlet bellows valve. Wait a few seconds for the chamber to pump down. And then close the throttle bellows valve.
  • Turn off the diffusion pump heater and note the time. IMPORTANT: leave the diff pump fan and forepump on.
  • Wait 40 Minutes for the diffusion pump oil to cool down.
  • Close the forepump bellows valve.
  • Turn off the forepump, and quickly open the air admittance vent valve.
  • Turn off the diffusion pump fan.
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Richard Hull
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Re: Steven Haid's Fusor

Post by Richard Hull »

Great work! Probably the most complete report ever issued here. It is acceped and your name is placed in the neutron club.

You spent a lot of time, and probably money, in getting computerized data collection.

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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Dennis P Brown
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Re: Steven Haid's Fusor

Post by Dennis P Brown »

Very professional setup and neutron detector system. Very detailed construction/operation details (but a bit long for a read. Maybe should post operation and construction details on another thread in any future posts.) What was your base neutron detector system's count rate without the modulator but with full power on?
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Re: Steven Haid's Fusor

Post by John Futter »

Dennis
It is moderator NOT MODULATOR
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Steven Haid
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Re: Steven Haid's Fusor

Post by Steven Haid »

Dennis, I just ran the test you suggested, running the fusor at power for 3 intervals. The first and third interval did not have a moderator, and the second interval did have the moderator. The base count rate without the moderator and with full power is about 24 CPM. Refer to the following screenshot.
fusor_170815_194221_screenshot_1.png
This picture shows the neutron detector without the moderator, and with the moderator.
moderator_test.jpg
These are links to files saved on google drive from this run. The screencast is probably the most interesting. The screencast plays back at 5X speed. The Geiger counter reading during the 3rd interval was 900 CPM. It was located about 18 inches
from the chamber. I was about twice as far, so my exposure would have been about 200 CPM. The background
count rate in my basement is 25 CPM. I was not expecting that high a count rate on the Geiger counter.
The viewport window is on the opposite side of the chamber from the Geiger counter, so it was not picking up
X-Rays through the glass. I'm curious if this Geiger counter rate is what to expect from my setup.
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Re: Steven Haid's Fusor

Post by David Kunkle »

"The Geiger counter reading during the 3rd interval was 900 CPM. The background count rate in my basement is 25 CPM. I was not expecting that high a count rate on the Geiger counter.
The viewport window is on the opposite side of the chamber from the Geiger counter, so it was not picking up X-Rays through the glass."

2 thoughts:
1) X-rays penetrating the chamber walls?
2) Secondary x-ray emission from outside the chamber originating from primary x-rays making it thru the viewport, etc. ? Don't remember this subject ever coming up in reading old or newer posts.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford
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Rich Feldman
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Re: Steven Haid's Fusor

Post by Rich Feldman »

Congratulations to Steven for a very well done fusor project.

X-rays are scattered, not just attenuated, by air. Not as much as by denser material, but the air around a fusor is often pretty thick in the geometric sense. Not nearly as much as neutrons in a moderator.

Early radiographers learned that the intuitive model, "rays stream in straight lines from the source, with a loss of intensity that depends on material in the line of sight", applies only to most of the x-ray flux. Inevitably, some scattered radiation reaches the detector. Undesired effects range from loss of contrast to image artifacts, such as structures behind the detector revealed through backscattering. Tools and techniques to minimize them have been developed and practiced for generations.

I think a fair optical analogy would be projecting an image onto a screen in a smoky or foggy room. Even if the screen were black, or were replaced by an open window, everyone can tell when the projector is on and when it's off.

That's consistent with my own experience operating Coolidge tubes and Geiger counters at the same time. Intentional x-ray sources, even little ones like dental tubeheads, generate ionizing photons at rates that are huge compared to typical radioactive sources in the hands of hobbyists.

You could get a personal dosimeter, like the CD V-138 training units (200 mR full scale) left over from fallout shelter programs.
You can explore the inherent shielding afforded by a fusor shell, using free online tables and calculators. I like Rad Pro Calculator, at http://www.radprocalculator.com/XRay.aspx
radprocalc.PNG
All models are wrong; some models are useful. -- George Box
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Dennis P Brown
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Re: Steven Haid's Fusor

Post by Dennis P Brown »

Congratulations on one very professional fusor that does fusion! What are your future plans, if any for the setup?
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Re: Steven Haid's Fusor

Post by Richard Hull »

Counting with and without the moderator is always the ultimate tell whether you are doing fusion or not.

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: Steven Haid's Fusor

Post by Steven Haid »

I have a few ideas on what I might do next.

1) The setup has some mechanical issues with the table. Also the table being against the wall makes it difficult to access the rear of the chamber. I plan to fix these problems.

2) Before I found the dental X-Ray transformer I was studying how to make a power supply using a voltage multiplier, and had purchased a multiplier on ebay. My thought was to use a signal generator as input to an amplifier, connect the output of the amplifier to a transformer that would step the voltage up to 5-10KV, and then connect that to a 3 or 4 stage voltage multiplier. I was not able to find a suitable transformer. I did find transformer cores and documentation available on ebay, and perhaps could wind my own transformer. So, I might work on this.

3) And, I would like to study fusion physics and make a mathematical or computer model of the fusor. And finally compare the predictions of the model with the observed neutron counts.

Number 1 will probably get done this Fall; 2 and 3 will take some time.
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Steven Haid
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Re: Steven Haid's Fusor

Post by Steven Haid »

[INTRODUCTION

I have replaced my Fusor's power supply. My goal was to use components that are easy to obtain, and at a reasonable cost.

This new power supply did work in my Fusor, and produced 3000 CPM, as compared to 300 CPM from my previous power supply.

SAFETY

Extreme care is needed when working around high voltages. Do not touch anything until the voltages have diminished to zero. And always wear safety glasses.

This power supply uses capacitors that can maintain a high voltage for a significant amount of time.

What I describe in this post is a prototype, thus the high voltage components are not contained in an enclosure. I was positioned well away from the power supply while the fusor is running, but while building and testing the power supply I did get closer to high voltages. It is important to have reliable instrumentation to detect high voltage and to be extremely careful not to touch anything when a voltage is present.

EFFORT

I found this to be a difficult but interesting project. It will take more time to build than other power supply approaches on fusor.net. And this approach is not inexpensive. However, the parts should be easy to obtain. And the result was good on my fusor.

DESIGN

A high frequency AC power supply is used. The output from this supply is connected to the primary winding of a step-up transformer. The output from the secondary winding is connected to a voltage multiplier, and the output from the voltage multiplier is connected to the Fusor.

The HF AC supply used produces up to 60 volts peak (120 volts peak-to-peak), at 20KHZ. The transformer has a turns ratio of 70, so the output from the transformer is 4200 peak volts at 20KHZ. The Voltage Multiplier is 5X. The peak-to-peak input to the VM is 8400 volts, multiplying by 5 gives an output from the VM of 42 KV.

The reasons for using a high frequency AC power supply are:
  • An HF transformer requires fewer windings than what would be needed for a 60 HZ transformer. The transformer I wound has just 13 primary windings and 900 secondary windings.
  • The size of the capacitors needed in the VM are much lower. I used 14100 pf 10 KV capacitors in the VM. These are actually 3 4700 pf capacitors connected in parallel. These capacitors cost about $1.20 each. A total of 10 sets of 3 are used in the VM.
HF AC POWER SUPPLY

I used a Planet Audio 2600 Watt Bridgeable Car Amplifier to generate the 20 KHZ AC power. Bridgeable means that the 2 channels can be connected together to provide single channel output, at higher power. The 2600 Watts is described as 'MAX'. I believe this means that the continuous power output is substantially less than 2600 Watts.

Input to the Car Amp is supplied by a signal generator. The signal generator I used is a dual channel Direct Digital Synthesis model that can produce various wave forms. I didn't need such an advanced signal generator, as all I need is a sine wave at 20 KHZ and with an adjustable voltage. However, the DDS signal generator cost only $70, and the additional features are nice to have.

The Car Amp requires a 12 VDC power source. I used the Eyeboot 12V 50A DC Universal Regulated Switching Power Supply 600w. The first one I got failed, after a few months it wouldn't power on. It may have been defective or perhaps something I did. I sent a note to the manufacturer and they replaced it free of charge. And the new one has been working fine since then.

I used 2 pairs of 10 AWG wire to connect the 12VDC supply to the Car Amp. The Wikipedia AWG page says the Ampacity of 10 AWG wire is 30 amps, Since I used a pair of 10 AWG wires the total Ampacity should be 60 amps.

And I used 12 AWG speaker wire to connect the output of the Car Amp to the primary winding of the transformer.

I tried to measure the output voltage from the Car Amp using a multimeter set to measure AC voltage, but this did not work with my multimeter. Perhaps 20 KHZ AC is too high a frequency for some multimeters to measure AC. Instead I made a meter using an analog 1 mA meter, diode, resistor, and capacitor. The Car Amp output goes to the diode, which is connected to the resistor, and then the meter. Across the resistor and meter is the capacitor. The resistor value is 100K so that that a 100V output would result in 1mA current, a full scale meter movement. And the capacitor value is chosen for a time constant much longer than the 20 KHZ period.

Links to parts:
Signal Generator - https://www.amazon.com/gp/product/B071H ... UTF8&psc=1
DC 12V Power Supply - https://www.amazon.com/gp/product/B00YR ... UTF8&psc=1
Car Amplifier - https://www.amazon.com/gp/product/B003G ... UTF8&psc=1
12 Gauge Speaker Wire - https://www.amazon.com/gp/product/B079V ... UTF8&psc=1

ac_power.jpg

TRANSFORMER

The transformer core I used are 2 U-Core with Ferrite N27 Core Material. The N27 Ferrite Core is appropriate for use in High Frequency Power Transformers. See this link for information on Ferrite Materials:
https://www.tdk-electronics.tdk.com/en/ ... -materials

The 2 U-Cores are fastened together with a zip tie and wood shims are used to further tighten.

The Primary is 13 wraps of 14 AWG wire. The Secondary is 900 wraps of 24 AWG Copper Magnet Wire. The wraps ratio is approximately 70. It is easiest to adjust the ratio by adding or removing wraps from the primary. The Ampacity of 24 AWG wire is 2.1 A, which is substantially more than needed.

I tried to measure the insulation breakdown voltage of the 24 AWG Magnet wire used on the Secondary. The insulation did not break down at 880 VDC, which is the highest voltage that I tested. My Secondary has 23 layers with 39 wraps per layer. When the output of the Secondary is 4200 V, then the voltage per layer is 183 V, and the maximum voltage between adjacent layers is twice that, or 366 V. It seems that the insulation of the secondary magnet wire should be adequate. But, just for good measure I added a wrap of High Density PTFE Thread Tape between each layer. The PTFE Tape also helps to provide a smooth foundation for the next layer of wraps.

To wind the transformer I made a jig to hold the bobbin and the wire spool. The jig utilizes 2 Fishing Reel Line Winders to hold the Bobbin and the Wire Spool. The jig also provided an adjustable wire guide. The jig was very helpful in making uniform windings and getting the secondary wound in reasonable amount of time.

I designed the Bobbins on Tinkercad, and 3-D printed using Treatstock Kasza Printing. The 3-D printing cost was only about $23. Here are links to the bobbin designs on Tinkercad:
https://www.tinkercad.com/things/eO75SV ... ombul-wolt
https://www.tinkercad.com/things/guosA7 ... nky-bigery

Links to parts:
U-Cores - https://www.mouser.com/ProductDetail/87 ... 0A0002X027
Secondary Wire - https://www.amazon.com/gp/product/B01NA ... UTF8&psc=1
PTFE Tape - https://www.amazon.com/gp/product/B008H ... UTF8&psc=1
Fishing Reel Line Winder - https://www.ebay.com/itm/LS-2B-Fishing- ... 2749.l2649

transformer.jpg

VOLTAGE MULTIPLIER

Wikipedia has an article on Voltage Multipliers.

A voltage multiplier multiplies the peak-to-peak AC voltage to a DC voltage. For example, a 2X VM using household 120 VAC input would create a 670 VDC output. This is because the 120 VAC is RMS voltage, the peak voltage is 1.4 x 120, or 168 V. And the household peak-to-peak voltage is 336 V.

As mentioned earlier, I used 5X VM, to be able to multiply the 4200 VAC peak output of the transformer (8400 V peak-to-peak) to 42 KVDC.

A voltage multiplier is a circuit consisting of diodes and capacitors. I had read an article that stated that the voltages within the VM are equally distributed among the capacitors. So, when using a 5X VM to generate 40KV, the maximum voltage across a capacitor would be 8 KV. To confirm this, and to help determine what the values of the capacitors need to be, I decided to write a computer program to simulate basic electric circuits. There are plenty of existing programs which simulate electric circuits, and they are probably all better than my program.

My circuit simulator program showed that 14100 pf 10 KV capacitors should work well for a Fusor at 35 KV and 7 mA. There is more about my Circuit Simulator program later in this post.

The diodes I used are 20KV 2A (PRHVP2A-20), and available on ebay for about $2 each. These diodes can't be tested using a multimeter diode tester. I recall having measured the voltage drop across these diodes to be about 15V. So, I think these diodes are actually constructed from 20 1KV diodes in series, encapsulated in epoxy.

The capacitors I used are 4700pf 10KV Ceramic Disk Capacitors, available on ebay for about $1.20 each. I used 3 of these capacitors in parallel (14100 pf), for each capacitor needed in the VM circuit. These capacitors need to be in oil for the 10KV rating. I read a spec that says these capacitors will work at 5KV when not in oil, and when in oil will work up to 15KV.

Links to parts:
Capacitors - https://www.ebay.com/itm/US-Stock-10pcs ... 2749.l2649
Diodes - https://www.ebay.com/itm/1-4-8-10pcs-PR ... 37BR1E7QgA
Mineral Oil 1 Gal - https://store.steoil.com/crystal-plus-f ... 0fg-1-gal/

vm_5x.jpg

INSTRUMENTATION

My initial attempt to measure the voltage output from the VM was to use a voltage divider and multimeter to measure the voltage across the smaller resistor. This did not work well, when I repositioned the multimeter's leads the reading changed dramatically. I suspect that the HF or RF radiation from the VM or Transformer was being picked up by the multimeter leads, and affecting the reading.

Instead, to measure voltage, I used the multimeter, in uA mode, in series with the 1G ohm resistor. Thus a reading on the multimeter of 30 uA would indicate a Fusor voltage of 30 KV. This seems to work well, but presented a problem of how to get this reading communicated from the multimeter to my data collection software. To solve this problem I found a Bluetooth Multimeter, the Owon B35T Multimeter, and also found sample code on GitHub which showed the method to access this multimeter via Bluetooth using the Linux gatttool program.

To measure current, I employed a similar approach with a second Owon B35T Multimeter, this time set to read mA. The current measuring multimeter is connected from ground to the ground side of the transformer secondary which is also connected to the ground connection of the VM.

I did have trouble establishing reliable connection from the Raspberry Pi to both of the multimeters simultaneously. I think the problem was due to both of the multimeters being positioned right next to each other, causing bluetooth interference. When I repositioned the meters about 1 foot apart the bluetooth connections became reliable.

The software to read the Owon B35T multimeter is here:
https://github.com/sthaid/proj_fusor2/b ... owon_b35.c
The software also monitors for failed bluetooth connections and when a failed connection is detected the software attempts to re-establish the connection.

Link to parts:
Owon B35T Multimeter - https://www.amazon.com/gp/product/B017R ... UTF8&psc=1

BLOCK DIAGRAM

block_diagram.png
  • V1: 12 VDC Power Source for Car Amp
  • T1: 70x Step Up Transformer
  • R1: 50K Ballast resistor
  • R2: Safety ground connection in case of M1 failure
  • R3: 1G ohm resistor
  • M1: Fusor milliamp meter
  • M2: Fusor voltage meter, 1 uA reading = 1 KV
Thanks to https://www.digikey.com/schemeit for the tool used to make this block diagram. To create the png file I printed to pdf and then used Fedora Linux Shift-PrtScn to captue the screenshot png file.

SOME PROBLEMS ENCOUNTERED

Various problems were encountered. None too serious, but they did take time to resolve. I would guess that if someone else makes a power supply like this that they would run into different problems.
  • The 12 VDC power supply for the Car Amp failed and was replaced for free by the manufacturer.
  • The 5V 2A power adapter for the Signal Generator failed. I replaced it with a 5V 3A power adapter.
  • Bluetooth connections to the 2 Owon B35T multimeters were not reliable. This was resolved by moving the multimeters apart by about 1 foot.
  • The Owon B35T Multimeter measuring fusur voltage started oscillating instead of displaying a stable voltage. This occurred during testing without the fusor connected to the VM's output. This was resolved by repositioning the transformer's secondary ground wire so that it no longer was in contact with the transformer core.
  • When testing the power supply with the fusor ignited, I tried increasing the power to the fusor, from 7.5 to 9.3 mA. After about 10 seconds running at 9.3 mA the power supply failed. I traced the failure to a capacitor in the VM. And replaced the capacitor, which resolved the problem. I don't know why the capacitor failed, I guess it may have been defective, or perhaps extreme conditions within the VM at this higher current caused the failure. After replacing the capacitor I ran the fusor again for about 4 minutes at 36 KV / 7 mA, without problem.
RESULTS

Here is a screenshot from a fusor run using the new power supply. Compared to my previous power supply the voltage applied to the fusor has increased from 30 KV to 35 KV. And the neutron count rate has increased from 300 CPM to 3000 CPM.

fusor_191214_102144_screenshot_3.png
system_view.jpg
transformer_and_vm.jpg

COST OF THE MAJOR COMPONENTS

Code: Select all

Signal Generator                            70
Planet Audio Car Amp                       100
12Vdc 50A power supply                      55
2 U-Cores  ($51 each)                      102
3D Printed Bobbins                          23
Secondary Wire (791 ft)                     30
Secondary Bobbin Winding Jig                40
VM diodes  10 @ $2.00                       20
VM caps    30 @ $1.20                       36
VM Mineral Oil (1 gallon)                   20
1G resistor                                 40
2 Bluetooth Multimeters ($55 each)         110
                                          ----
                                         $ 646
ADDITIONAL INFO - UPDATES TO MY FUSOR SOFTWARE

To accommodate the new method of obtaining the Fusor Voltage and Current from the Bluetooth Multimeters, the software ...
  • Still using the 2 Raspberry Pi computers.
  • The get_neutron_data program on one of the Raspberry Pi computers is now dedicated to reading and scanning the ADC data from the Ludlum Scaler, to count the number of neutrons detected.
  • The display program running on the other Raspberry Pi collects the data from the Webcam, Pirani Pressure Gauge, Voltage and Current Bluetooth Multimeters, and receives the neutron detector CPM from the get_neutron_data program running on the other raspberry PI. These data values are displayed and graphed, and are saved to a data file so they can be reviewed later.
The Software is available at https://github.com/sthaid/proj_fusor2.git

ADDITIONAL INFO - MY CIRCUIT SIMULATOR PROGRAM

Other, probably much better, circuit simulators are available, and free to use. For example LTspice. I have not tried them.

My circuit simulator software is available here https://github.com/sthaid/proj_circsim.git

How it works ...

This program simulates circuits that are comprised of resistors, capacitors, inductors, diodes, and AC or DC power supplies.

The eval_circuit_for_delta_t routine, in model.c, is the core of the simulation. This routine determines the new circuit state (voltages and currents) after a short time interval (delta_t). Kirchoff's current law, Ohms law, and the Current-Voltage relationship for capacitors and inductors are used.

The eval_circuit_for_delta_t routine does the following
  • Loop over all nodes, and for each node determine an estimate for the next voltage following the short delta_t interval. This estimate is computed by choosing a voltage that satisfies Kirchoff's current law, using the values of the components attached to this node and state of adjacent nodes as input.
  • Based on the voltages computed in step 1, determine the current passing through each component, which is equivalent to the current at the node terminals that the component is attached to.
  • One might expect that the sum of the currents, for each node, calculated in step 2, would be 0. However, this is not the case because the next voltages calculated in step 1 do not incorporate changes in the voltage of the adjacent nodes. So, step 3 will sum the current for each node, and if any node's total current is significantly not zero then repeat from step 1. After a sufficient number of iterations all of the nodes currents will be nearly zero, in which case this routine has completed computing the next circuit state.
To evaluate the circuit for a long time interval (many delta_t), the eval_circuit_for_delta_t routine is called many times until the circuit has been simulated for the desired interval.

Tests ...

Various test circuits are in the tests directory. For example test/r3 solves the problem of determining the resistance across a single resistor in an infinite grid of 1 ohm resistors. See screenshot attached below, which shows that a 1 volt power source connected across a resistor has 2 amps of current. Using ohms law the resistance is 0.5 ohms. This is the correct answer, but this resistor problem is really meant to be solved using logic and not by a circuit simulator.

circsim_resistor_grid.jpg

And here is a simulation screenshot of the 5X voltage multiplier used in this power supply.

circsim_vm5x.jpg
User avatar
Richard Hull
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Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Steven Haid's Fusor

Post by Richard Hull »

Fantastic power supply effort! I believe one other person has done this here and it worked Ok for them as well. However your rather complete exposition here far exceeded what most would supply and should stand as a great post on its own forever.

I suggest that you post this entire effort on the supply in the fuosr power forum! Right now it resets in the tail end of your original fusion win post, which itself stands as one of the finest examples of fusion win claims ever written.

Naturally leave this post here, but please post it anew in the Fusor power supply forum as a fabulous post on how you can make a fusor supply of some merit.

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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