A New Cube, or Two

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Jon Rosenstiel
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Re: A New Cube, or Two

Post by Jon Rosenstiel »

I can see that a lot of thought and work has gone into cube V2.0. 1e8 here we come!

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Liam David
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Re: A New Cube, or Two

Post by Liam David »

I've been on a bit of a break now that the spring semester of grad school is over, which means I've spent some time working on the cube system. I haven't had the chance to upgrade the cube itself, but have made some notable changes.

Deuterium now enters directly at the chamber (via 1/4" VCR) instead of the vacuum manifold below the chamber. This helps with gas purity and flushing contaminants out as the chamber gets cooked. The pressure of the gas line is monitored by a 0-75 psia Precise Sensors pressure gauge.

PXL_20230524_213137321.jpg
New gas line to chamber with valve.
New gas line to chamber with valve.

The other port on the flange (1/2" VCR) connects to an Inficon 100 mtorr capacitance manometer. It has a superb resolution of 3e-6 torr, an accuracy of 0.4%, and is heated to 100C to avoid condensation of contaminants. The gas-independent response is also really nice, as is the 2 ms update frequency. This gauge will allow me to properly calibrate the two Piranis in my system and should give me a much better idea of the pressure in the chamber while it's fusing. The gauge I previously used can be seen at the bottom of the following image.

PXL_20230524_213019379.jpg

Since my chamber is aluminum, the conflat ports seal via o-rings rather than copper gaskets. This has allowed me to electrically isolate the chamber from the rest of the system using Kapton tape. I insulated the bolts from the vacuum manifold flange and placed a layer of tape between the flange and chamber. I tie the chamber to ground through a 1k resistor and can use my oscilloscope to measure the current through the plasma with nanosecond resolution. The gas line, being VCR and hence metal, includes a ceramic break for isolation which can be seen in the image above.

This tiny resistor isn't particularly suited for the role... to be upgraded in the future.
This tiny resistor isn't particularly suited for the role... to be upgraded in the future.

The final upgrade, and one that isn't anywhere near completion, is a change to data acquisition system. The convenience of the current system for analyzing data on the fly with sub-second resolution has been really nice, but I've run out of ADC modules, and adding more will only reduce the sampling frequency. Behold, the Adlink DAQ-2206, a 64-channel, 16-bit, 250 kS/s (total), variable gain PCI ADC card. It also has 24 digital I/O channels, 2 16-bit counters, and 2 12-bit DACs. It will go into a PC located at the fusor and stream data to my computer via ethernet. At full speed, it can do almost 4 kS/s when all channels are active, which is overkill for all but perhaps the capacitance manometer.

PXL_20230524_205637942.jpg
PXL_20230522_195400253.jpg

I'm working hard on my next cube iteration which will hopefully be done in December.

system.png
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Richard Hull
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Re: A New Cube, or Two

Post by Richard Hull »

The new acquisition system is amazing! Nice to know it is out there. My head swims at the rapidity of technology. My first job, I bit-banged the early RISC 6502 at the individual instruction level and then moved to an assembler within months. Still had to hand wire the PIA 40 pin chip 2- 8 bit digital ports and one nibble port. No AtoD.... that needed a single channel 24 pin 8bit AtoD chip. JEEZ!
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: A New Cube, or Two

Post by Dennis P Brown »

Nice system. I really hope you have upgraded that ground system - that is an accident waiting to happen.
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Liam David
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Re: A New Cube, or Two

Post by Liam David »

Over the winter break I had some time to work on my next cube iteration. Unfortunately, I wasn't able to get it to a fusion-ready state, but updates are still in order.

The new data acquisition system is mostly up and running with the major holdup being a ground loop issue. All the custom electronics, gauge power supplies, umbilical cable, etc. are in, and interface with, a 3U rackmount chassis. It's currently incomplete but in a basic functional state.

A while back I picked up some big laser supplies and a water distribution block that were conveniently in a pair of blue rackmount boxes, so I've moved all the controls and power supplies to those racks. Here is a picture of the stack next to the 3D model. From bottom to top: NIM crate with 2x detector channels; a Vacscan RGA controller; -100kV 20mA Teslaman PSU; my control box; 2x turbo pump controllers; the PC with the DAQ card; a scope to monitor the fusor current and detector pulses.

Rackmount control system
Rackmount control system

A rapid-fire list of some changes:

The main body of the cube chamber is unchanged, but the endcaps have been upgraded and are encased in 3D-printed water blocks for cooling. Each endcap has titanium targets and quartz windows.

I purchased a 1.6kW water chiller unit because by the time I designed a sub-zero system of similar capacity, I realized the cost would be about the same and it just wasn't worth the extra hassle.

The feedthrough has been upgraded with a Stewart platform for very fine positioning of the cathode in all 6 degrees of freedom. I will be using a parallel projection method to align everything.

Based on some static charging I observed with the feedthrough, the lower ceramic insulator was modified and the problem was eliminated.

An oil cooling system was constructed and includes a micropump, heat exchanger, pressure sensor, flow sensor, filter, and supply/return thermocouples. It circulates mineral oil through a set of 3D printed cathodes that I will be testing. I have successfully operated a low-voltage plasma with oil circulating through the cathode.

The deuterium system has been reconfigured to be much simpler and to have better conductance for maximal gas purity.

A pneumatic gate valve was added between the chamber and vacuum system, and likewise a pneumatic valve added to the gas line, to isolate the chamber for both diagnostic and safety reasons. I use CO2 cartridges and a solenoid valve to control these with pushbuttons and eventually some relays for digital control.

The frame was made more rigid using laser-cut brackets on each corner.

The brackets that connect the vacuum system to the frame were lengthened, thinned, and their material changed from aluminum to stainless steel to reduce heat transfer to the frame during bakeout. Additional cutouts further reduce heat transfer. A few other brackets and mounts for other components were changed.

Anti-seize was added to each bolt since I've been having problems with seized bolts needing to be cut off.

The next iteration will include additional ceramic spacers to properly isolate the cube and allow for nanosecond current measurements.

Pre-bake configuration
Pre-bake configuration

Oil cooling system
Oil cooling system

While not fusion-ready, I have made some plasma. Here's a beam as viewed through the quartz windows on the endcaps.

Low voltage deuterium beam
Low voltage deuterium beam

Due to the geometry of my cathodes, they're extremely sensitive to gas purity and surface cleanliness. The maximum bakeout temperature of my cube is ~150C due to its aluminum construction and a variety of o-ring seals, which unfortunately isn't hot enough to get the cathodes clean. I'm biting the cost bullet and putting together a separate 6" conflat chamber for the sole purpose of low temperature (<150C) and high temperature (ideally 400C) bakeout of vacuum components and the feedthrough stalk/cathode assembly. It will be pumped with a big 330 l/s turbo and have a small VCR connection to my main chamber so that I can use the RGA to monitor bakeout progress. I have a gate valve on the front that acts as an easy-access door. The bakeout procedure for aluminum components that go into the cube is a 150C bake for a to-be-determined time. For stainless and titanium, I'm aiming for 400C. Copper will be something in between. Everything will then be baked again at >100C when on the fusor vacuum system. The downside to all this is that the time between testing different cathodes will be something like a week, limited by all the baking that has to be performed. I might add dry nitrogen venting to help things out.

Bakeout system, work in progress
Bakeout system, work in progress

I'm still aiming for 1e8 n/s in an unassisted glow discharge. I might be crazy, but I'm already thinking about upping the voltage to 200kV... we shall see.

Future plans
Future plans



A largely unrelated point, but I neglected to post about this a year or so ago. Below is an image comparing a new (right) and used (left) temporary aluminum plug that I was using to protect on-axis threads in my old endcaps. The marring is due to my use of pliers to remove the plug from the endcap, but the absence of the hex socket is the result of the electron beam emanating from the cathode. It was apparently narrow enough to melt the front surface despite the high thermal conductivity. My guess is that I was dumping a few hundred watts into a sub-mm electron beam. Food for thought.

Nuked thread protector
Nuked thread protector
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Dennis P Brown
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Re: A New Cube, or Two

Post by Dennis P Brown »

Incredibly impressive build; maybe start aiming for helping the French with their Tokamak build? ;)
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Liam David
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Re: A New Cube, or Two

Post by Liam David »

Hah, no-thank-you. Getting from the previous iteration to here took a year of planning and a month of hands-on work. Can't imagine the logistics for ITER. Tokamaks just aren't for me.
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Richard Hull
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Re: A New Cube, or Two

Post by Richard Hull »

Ryan, your work is not fusor work any more. It is more like trying to achieve the best electrostatically operated fusion assembly. As you noted in many posts in this thread, the simple fusor, as is commonly built here, is self limiting for a myriad of reasons. Your work now is pure research far beyond the best ever seen here and outside of the purse of the best amateur, yet it remains pure IEC!

What sets you far above others is you have learned a lot and shared a lot with all here. You are also well aware that among the best of we observers only a small cadre can follow your work along the more complex lines. However, share you do for its own sake and what understanding it may bring to the amateur effort.

You share not only the physics but the engineering mechanics of system assembly and share your hard won knowledge that so many of us engineers and experienced hands-on doers have learned. We all learn that theory and reality often diverge in practice due to the unexpected within the doing. Von Engels, in his book on ionized gases, repeatedly gave warnings that the equations were idealized examples with idealized, hard fixed conditions. This relates to the more modern common phrase. Your mileage may vary

Your work now rivals many academic efforts of the past. Your struggle to understand the physics of IEC fusion at an intimate level shines through. The great thing is that the search is not for power fusion, for IEC looks like a big loser in fusion. You see it can be improved perhaps by a few orders of magnitude if pressed to some as yet unknown limit.

I personally thank you for hanging in there with us lower level folks sharing your results. Certainly, you will publish your results in some peer-reviewed paper in future, perhaps to attain higher degrees, if you have not done so already.

Liam, for this thread, your research and your continued assisting others on fusor.net, I have made you a 3 star elite fusioneer!

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: A New Cube, or Two

Post by Liam David »

Richard, thank you for the kind words and encouragement. Back in 2014 when I registered, I never thought I'd be quite so deep into IEC or even at a place like PPPL doing fusion research. This project has significantly affected by path through life and if not for it, I might be doing something wholly unrelated to fusion. Even if I have moved past most members here on certain specific topics, I still have lots to learn on a variety of fronts and have many to thank for advice and input along the way.

It probably goes without saying that I'm keeping some of the details of my system, namely the cathode and chamber geometries and some other details, mostly obfuscated at the moment. I want to be clear that I don't intend for this to be a permanent decision. When I (hopefully) achieve 1e8 n/s with proper verification with calibrated detectors, I will release some of the important details that would allow more experienced members here to replicate the results. I'll also discuss the important plasma physics phenomena that contribute to my device.

However, I'm not overly thrilled about putting detailed instructions for a 1e8 fusor on the internet, especially one that doesn't require a massive 300 kV, 100 mA supply like UW used to achieve the same. I think that the final design will be only marginally more complicated than a typical fusor. The classic 1e6 fusor is one thing, but 1e8 and above is a whole other thing. The barrier to entry has to correspond to the radiation hazards. I'm open to any thoughts on the matter, for when the time comes.
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Richard Hull
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Re: A New Cube, or Two

Post by Richard Hull »

A wise precaution on your part for our sake. We respect that.

The grand complexity of your work would surely, hopefully and blessedly keep out effectively, all who would seek such dangerous numbers in fusion. However, thinking ahead, should you reach 10e8 n/s, one might rationally think that all your grand complexity was research generated and the epitome of the finished process might not require all that complexity to merely replicate, once expounded upon.

We still have people here who can't seem to obtain a simple TC gauge, voltmeters and ammeter setups to enter the plasma club to report accurate data on their efforts. 90% are in the middle somewhere. It is rare to see someone come here with big money, purchase all new and make the neutron/fusioneer appellation virtually overnight. Often, this rare breed just might try to go 10e8 with no knowledge of the danger they may step into. Such rare folks might not study and learn from a long-fought battle over time which normally allows for study and reflection in often expensive pauses in their work to just do fusion at any level.

I have often noted that fusion, for its own sake, when judged against lofty professional power goals, is "easy". However, it is just difficult enough for the amateur scientist or would-be fusioneer that deeper pockets and a good bit of self-directed learning slows the process in a manner which keeps the applicant from just whizzing past key parts of the process that keeps them safe during the effort.

In the end, from my point of view, it is your decision should you come out of your effort in total success, provide to us that which you wish to share.

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: A New Cube, or Two

Post by Dennis P Brown »

I agree with Richard - your separating into a rarified air that none except University level Proff's have traversed. Not just impressive but the level of determination is an order of magnitude above any.

Now for the down to Earth stuff - since I do not know about your shielding this suggestion is more than likely irrelevant but I would, just in case, do be extra cautious on radiation issues. I do not know your voltage but certainly an x-ray shield should be part of that advance device. And if you really expect such neutron levels (and why shouldn't you?) do consider neutron thermalizing/shielding as well.
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Liam David
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Re: A New Cube, or Two

Post by Liam David »

I've done quite a lot of work simulating neutron shields, so I have a pretty good idea of what's needed to reduce fluxes to acceptable levels. I'm hesitant to add any moderators/shields before having a proper calibration with known detectors. After that I'll have to see. Ultimately, for the highest activation yields, it would be advantageous to encase the whole chamber in moderator with large reflecting volumes.

X-rays, as you mention, are by far the more dangerous product and I have quite a lot of lead for just that purpose. I might even shield the feedthrough assembly with lead due to the large amount of scattering off the ceiling and walls of the shop. That will require oil immersion which I have most of the parts to do. Not looking forward to that step.

Regardless, for the high voltage/power runs I will be running remotely. I have a 100ft umbilical cord for a completely remote operator station with hardwired interlocks.
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Richard Hull
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Re: A New Cube, or Two

Post by Richard Hull »

Thank goodness for the inverse square law. Nothing protects like distance. Shields are nice, yet costly. Getting the hell out there and away is always free. Remote operation is always best if you are pushing voltages over 80 kv. Sadly, D-D fusion in a common fusor doesn't win much at 80 kv over 60 kv. The only thing dramatic at 80 kv+ are the increased costs, extra effort demanded and increased danger.

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: A New Cube, or Two

Post by Dennis P Brown »

I'd be shocked if your ceiling could reflect any significant X-rays (infamous last words of doubt relating to a safety issue.) But certainly a short exposure to a 10e8 neutron flux would not be an issue. So, that is not a pressing issue till then. I highly suspected that you had the X-ray issue well in hand.
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Liam David
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Re: A New Cube, or Two

Post by Liam David »

The fusor sits near a metal garage door (often open and so above the fusor) and on concrete, so while not significant compared to the raw x-ray output, I still see many mrem/hr reflected to ~10ft away that originally came from the feedthrough or other small holes. It's definitely not dangerous, but enough that I didn't run long in those configurations without additional shielding.
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Richard Hull
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Re: A New Cube, or Two

Post by Richard Hull »

Dennis,

10e8 FLUX is deadly!

Use flux correctly (neutrons per square centimeter per second)

We never use flux as it is pitiable.

10e8 total isotropic emitted radiation or 10e8 TIER

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: A New Cube, or Two

Post by Dennis P Brown »

Oops, once again, being sloppy; Good you point that out because, frankly, this is how people get confused and I need to be more careful with terminology.
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Liam David
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Re: A New Cube, or Two

Post by Liam David »

As much as I sometimes wish I could get 1e8 n/s/cm^2, that's a level of radiation a hobbyist just can't handle. Sometimes I'm a bit sloppy too and have occasionally said flux when I meant TIER.
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Liam David
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Re: A New Cube, or Two

Post by Liam David »

"Obligatory" bi-yearly update:

Given some things I learned in December and January, I found it necessary to reconfigure the system once again. This go around, most of my time was spent on the data acquisition system and getting the kinks worked out, although some limited work was done on the vacuum system and on turbo pump maintenance. I significantly reduced the measurement noise by adhering to good grounding practices and using differential inputs on my ADC card, which allows me to significantly increase the sample rate without loss of accuracy.

I moved all support systems and diagnostics out of both the fusor frame and blue rack boxes and into a new 42U open-frame rack (a cheap Craigslist find). This moves all electronics away from water/oil cooling systems and makes things less cluttered. Also, the rack castors are no small quality-of-life improvement over shuffling around heavy boxes full of power supplies and such.

Some other changes:

The main vacuum hub has been changed from a 2.75" conflat 6-way cross to a 2.75" conflat cube for compactness.

The deuterium lines have been reconfigured for maximum gas purity and no longer contain flexible metal bellows. I use a combination of VCR and Swagelok tube fittings.

I'm adding an additional deuterium flow control valve (an old MKS-248) that will pipe deuterium directly into the cathode. This requires floating the valve at the cathode potential, hence my inquiry in another thread about passing DC analog signals to an HV platform. I have what seems to be a viable cheap solution based on Toslink digital audio components and a super simple valve driver circuit. The 10 sccm Brooks mass flow controller that I've been using will still pipe deuterium directly into the chamber. Additional pneumatic valves have been added, both at ground potential and floating, to act as shutoffs.

I started working on a standalone multi-channel counter separate from my integrated fusor data acquisition system to allow for digital monitoring of a variety of neutron and other detectors.

The large bake-out chamber is slowly coming together. It's for both pre-assembly component bake-out and processing of my new cathode, the latter of which is vital for its success.

Finally, I'm working on how to best encase the fusor in HDPE, lead, and water for maximum x-shielding and neutron activation ability.

More updates to come next vacation from school.


PXL_20240615_155420600.jpg

PXL_20240611_222542241.jpg

Testing various gauges and systems
Testing various gauges and systems

Current end-goal
Current end-goal
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Richard Hull
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Re: A New Cube, or Two

Post by Richard Hull »

Thanks for the timely update.

When I was in college, I barely found time to work on my old 57 Ford. ( a big deal in the 60's). Life was one of study,study, study. In the summer it was work, work, work to earn my tuition for next year. Worked loading/unloading hot freight cars for Reynolds Metals (yes I paid my way through college). It was cheaper then.

You are a powerhouse! Keeping busy while learning is a smart move if you can do it. I learned far more after college than when in college. Self-directed learning with a voracious curiosity about all of the sciences drove 100% of my spare time. No getting married until 29 and no children as a conscious decision afforded me vast amounts of spare time.

You are progressing at a pace that dizzies my perception of youth who apply themselves. Rare in this day.

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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