Since I started this project, and as I stated in a previous post, the goal of Fusor 1 has been to take what I have learned with the very crude demo Fusor 0 and apply it to actual fusion with scientific-grade parts and systems. Sunday morning, I came one step closer to achieving this goal when I turned on Fusor 1.1 and generated plasma within the metal chamber. The successful first light of Fusor 1 has not only demonstrated that fusion is not impossibly far away, but will also open up lots of interesting (although certainly not yet novel) avenues of research for me to pursue.
With the bottleneck of first light squarely achieved, many potential upgrades to Fusor 1 can be undertaken in parallel which will speed up progress exponentially. I am already in possession of a fusion-capable 30kV transformer, have recently purchased a much more advanced vacuum pump, and am working on designs for more advanced systems incorporating these components.
This post outlines the Fusor 1.1 design, first light, and next steps. This post is also potentially needlessly in depth, but I would rather be too verbose than not clear enough about my process.
Fusor 1.1 Design:
The design for Fusor 1.1 (named as such to differentiate it from the many Fusor 0 designs) is very basic and follows many of the principles advocated for on fusor.net.
The chamber is a 6" conflat 4-way cross chamber to which I have attached 6" to 2.75" conflat reducers on all sides. I have attached a borosilicate viewport, high voltage feedthrough, conflat to 1/4" NPT adapter, and conflat to KF-25 adapter to those reducers. A Varian 531 thermocouple gauge embedded into a KF-25 flange is attached to the KF adapter and a 1/4" NPT to barbed hose adapter is screwed into the 1/4" NPT port on the conflat flange.
The vacuum system is, as of now, very crude: simply a piece of PVC hose connecting the chamber barbed adapter to a cheap HVAC pump. Due to its design and the parts I have on hand, I have not been able to conduct a true bulkhead test with this pump, but in a test where the hose is connected to the Varian 531 thermocouple tube via the two conflat adapters attached directly together with a Viton gasket and vacuum grease, it pulled an end vacuum of approximately 550 microns on the Varian 804-a thermocouple controller.
The variable high voltage supply is based around a 12kV 30mA neon sign transformer (NST) fed by a 0–120V variable auto transformer (variac). The output from the NST is rectified with a full wave diode rectifier under oil and sent through the feedthrough to the grid. The grid is made of a single tantalum wire wrapped in a geodesic grid shape. The long end of the tantalum grid is tightly wrapped around the feedthrough stalk and insulated with a long ceramic tube. I bought the grid and feedthrough already attached. The steel vacuum chamber is grounded to a star ground terminal made with a single bolt connected to ground. The NST case is connected to the star ground in series with a 10Ω resistor. All electrical connections were made with either spade or ring terminals.
There is a Sparkfun VC830L multimeter connected to the AC output leads from the variac used to accurately measure the variac input to the NST. The high voltage DC output from the rectifier is measured with a Fluke 80K-40 high voltage probe connected to a Fluke 27 multimeter and grounded to the star ground bolt. A Fluke 117 multimeter measures the voltage drop over the 10Ω resistor which can be used to find the current at the grid.¹
I monitored the chamber itself with a Sony A7iii camera recording 1080p video. I changed the exposure settings throughout the test to prevent the video from becoming blown out.
Test 1:
I achieved first light of Fusor 1.1 on November 14 at 11:14 AM (a little bit of serendipity there). From first activating the pump to re-pressurizing the chamber, the test took about than 30 minutes overall with plasma being generated for approximately 8 of those minutes.
Procedure:
- All metering activated and confirmed to be at ambient levels
- Vacuum pump activated
- Upon reaching below 700 microns of pressure within the chamber, the variac is switched on
- Variac dial turned up at intervals of 10 volts (measured on the multimeter), plasma within chamber is observed between turning up the variac
- At some point, variac turned to 0V and is switched off. As a precaution, if pressure within the chamber ever increases above 2000 microns, the variac is immediately switched off
- Vacuum pump switched off
- Immediately after the pump is switched off, the KF-25 thermocouple connection clamp is removed and the vacuum seal is broken, repressurizing the chamber (this is done to prevent oil back-flow into the chamber from the vacuum pump)
This procedure is very standard for a demo fusor, the only thing (to my knowledge) differentiating it from other demo fusor procedures on fusor.net is the relatively high pressure at which the variac is activated. This is, unfortunately, mandated by the sub-par and very leaky vacuum pump that I am currently using.
Results:
Outstanding Success! Plasma was generated within the chamber at various NST input voltages and chamber pressures!
The chamber was pumped down to approximately 650 microns before the variac was turned on. Plasma began appearing on the grid at approximately 9 Volts AC NST input.
Plasma increased in intensity but changed in character as I turned the variac dial up. This was likely due to the increase in power sent to the NST as well as the increase in pressure as the test progressed.
Below are the recorded values for each NST input voltage:
I decided to stop the test before testing the full range of variac supply due to the spike in chamber pressure. After I turned off the variac, the chamber pressure began to drop again to about 700 microns before I deactivated the pump and removed the TC KF-25 flange.
Analysis:
There are two primary differences between Fusors 0 and 1:
Firstly, obviously, the Fusor 1 chamber is made entirely out of conductive steel while the Fusor 0 chamber is of a dual-plate design. I do not have the background to quantify this numerically, but intuitively this would seem to encourage the plasma to concentrate more within the grid as electromagnetic force would be exerted from all sides instead of from two plates. Additionally, this would mean that more surface area is subject to picking up electrons and carrying them to ground, presumably decreasing the resistance of the chamber.
Secondly, although I have never accurately measured the pressure within the Fusor 0 chamber, it is clear that the conflat seals of Fusor 1 leak significantly less. This would make the vacuum within Fusor 1 deeper than in Fusor 0 which, by Paschen’s law,² would have an effect on the plasma and the energy required to light it.
I cannot change these characteristics separately, so I must interpret my data as a result of both. Ascertaining how much of the difference between Fusors 0 and 1 was caused by either change individually will require much more data.
Fusor 0 Comparison:
Comparing the Fusor 0 and Fusor 1 data, these differences in chamber design have clearly had an effect upon the system:
Current and power were clearly not greatly effected by the metal chamber, but voltage exhibited dramatically different characteristics between the two chambers. It is likely that the lower pressure within Fusor 1.1 allowed plasma to form at lower voltages while Fusor 0 required over 200V more for plasma to form. Once the plasma formed in Fusor 0, the amount of energy required to sustain it decreased, leading to the drop in voltage.
My theory is that in Fusor 1, this did not happen as the initial voltage required was already so low that sending more power to the NST raised the voltage along with the amperage since the increase in conductivity due to generation of plasma was less dramatic.
As to be expected with the distinct differences in grid voltage and pressure, the visual characteristics of the plasma in Fusor 0.4 and Fusor 1.1 are notably different.
At an NST input of about 10 volts, plasma has not even began to form in Fusor 0, while it has already formed clearly within Fusor 1. Additionally, the grid voltage is significantly higher in Fusor 0 as there is not yet any load on the system.
At 20Vac NST input, plasma has just began to form on the Fusor 0.4 grid while in Fusor 1.1, there is a significant amount of plasma within and around the grid. Additionally, there is significantly more voltage being drawn in the 0.4 test at the cost of some amperage. I believe that this is due to the lower pressure in the Fusor 1.1 chamber requiring less voltage to ionize the air as per Paschen’s Law.
At this NST input voltage, plasma is just beginning to form in Fusor 0 while there is a significant amount of plasma in Fusor 1. It is worth noting that when compared to the Fusor 1.1 picture at 20Vac input, the area of higher intensity in the center of the grid in this Fusor 1.1 picture is more diffuse and the plasma appears more blue-ish.
Until writing this post, I had not fully realized how significant the increase in efficiency between Fusor 0.4 and Fusor 1.1 was. It is clear looking at the images side by side that Fusor 0 required significantly more power to generate plasma than Fusor 1.
I think that the sparkling on the Fusor 1 grid, which began at 40Vac NST input, is due to imperfections on the grid (oxidization, vacuum grease accidentally brushed onto the grid, etc.) being vaporized and ejected, or sputtered, outward. I am going to need to do more research, though, because I do not have enough information to support that belief.
At 50Vac, there is still very little plasma in Fusor 0, but some very minor sparkling on the grid has begun to occur. This seems to imply that the sparkling is more a function of amperage than voltage or pressure, but there are too many differing variables between the two tests to say conclusively.
It is also interesting that the plasma in Fusor 1.1 continues to look more diffuse as input voltage increases. This does not seem to be a direct result of pressure, as pressure has dropped since the 40Vac sample, but more closely linked to amperage and power.
At this point, I halted the Fusor 1.1 test. I have more Fusor 0.4 data at higher NST input voltages, though:
Interestingly, and perhaps importantly, in Fusor 1.1, even at 0.41W (although moreso at 2.22W) plasma concentrated in the center of the grid. Conversely, in Fusor 0.4, plasma seems to be concentrating around the sides of the grid instead. I am almost certain that this is due to the significantly higher pressures within Fusor 0.4 preventing plasma from existing far from the grid.
Even at twice the power of the final Fusor 1.1 test 1 input voltage, I still do not think that there is any plasma in the center of the grid. The plasma that appears to be in the center is actually plasma around the back edge of the grid.
With this amount of power being supplied, the steel grid glows red hot and begins to warp. This is not a problem that I will have with the tantalum Fusor 1 grid.
It is clear that even at over 5 times the input power, Fusor 0 cannot generate comparable plasma to Fusor 1 due to the higher pressure.
Next Steps:
I have already conducted another Fusor 1.1 test that I have not discussed here in the interest of keeping this post somewhat focused. That test has raised many questions that I am going to attempt to answer in the near future and will discuss in another post.
Other than that, I would like to run a test of the system, using the variac to keep the NST supply at 5mA so that I can make more direct comparisons to the visual gauge data on fusor.net³ to confirm that my pressure metering system is calibrated properly.
I have ordered a Precision D-25 vacuum pump on eBay that will, hopefully, allow me to pump down to sub ten micron levels of vacuum. This will exponentially increase the amount of plasma study available to me and be another huge step forward in my fusion project. I am very lucky to have the help of Mr. Price at LDS Vacuum who has been willing to help me design a high quality valve system to go between the pump and my chamber.
I am also beginning to explore the Arduino based control and metering system discussed in a previous post. I am now thinking that this should be split into two distinct units:
A relay-based control unit using an Arduino and an analog control board to control various relays turning things like the NST and vacuum pump on and off.
This will be fed data by a separate metering system using op-amps and microcontrollers to measure and record electrical and pressure data. Not only will this be a lot more convenient than my current way of recording data, it will also allow me to implement several automatic cutoff procedures in the interest of safety so that I do not destroy my fusor.
In a fusor.net post that I have not been able to find again, Richard Hull states that a mistake that a lot of aspiring fusioneers make is that they move too fast, blowing past the demo stage to fusion, without taking the time to do the scientific exploration that is the whole point of the project. I am determined to not make this mistake. Although I already have a 30kV transformer and will soon have a Precision D-25 pump, I am going to take my time investigating plasma characteristics and learning more about how everything works.
With that said, I do want to attain lower pressures within my system rather quickly as that opens up even more research opportunities. The new pump is arriving Monday and I have the entire week off from school for Thanksgiving, so I will probably make a lot of progress then.
As it stands, writing these posts is actually the most time consuming part of this project, so I will probably consolidate many tests into fewer, even less frequent posts that I can spend time writing while I wait for parts to arrive or time to do tests.
I am so excited to have reached this major milestone in this project and look forward to even more progress and exploration soon!
Notes & Citations:
¹ https://www.fusor.net/board/viewtopic.php?f=29&t=4266
² and plasma dynamics that I do not know enough about
