Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA-9mA

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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman »

I've tracked down the source of x-rays coming from the fusor. I had initially thought the 15mR/h was some of the higher energy x-rays coming through the lead glass, or stainless shell, however it turned out to be coming from the viewport near the vacuum gauge. Some of the secondary electrons from the grid were getting up into the conflat cube and generating x-rays. A lead foil cap over that viewport has now eliminated any measurable(on a ludlum 17 ion chamber, minimum resolvable rate ~0.5mrem/h) x-ray flux from the fusor. I'll still need to add lead shielding around the vacuum chamber when I start running at 70kV, but for now the x-ray issue is solved.
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Richard Hull »

The shell starts to go transparent on the standard .060 inch thick SS shell at about 35kv applied. At the shell, working at 40kv, using a victoreen ion chamber, I get about 10mr/hr. It will only go up from there. Any window or view port will be much higher at lower voltages as the lower energy x-rays produced will pass through the glass as electrons strike the shell on the opposite side. This is much the same as old x-ray tubes.

The lead cap trick over the view port was used by Joe Zambelli in his 2001 fusor. I avoid it by pointing my view port straight down into the concrete floor through the video camera. View ports are the most dangerous emitters of radiation in the amateur fusor and all that danger is x-radiation. Neutrons from fusion are of no real consideration for the average successful amateur fusioneer as few will use more than 40kv applied.

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: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman »

I recently scored an URSA multichannel analyzer on ebay and am hooking it up to do neutron activation analysis
SAM_5159.JPG
The system was calibrated with a Cs137 check source
SAM_5161.JPG
Cs137.jpg
And an Am241 source(smoke detector)
Am241.jpg
All of which showed distinct peaks.

Spectra was also taken of the x-ray emission of the fusor
At 25kv (with the lead shielded cap off)
fusor-25kv.jpg
At 30kV (with the lead shielded cap on)
fusor-30kv.jpg
At 40kV (with the lead shielded cap on)
fusor-40kv.jpg
It's interesting to see how the 30-40keV x-rays are just starting to get through the 1/8" stainless shell, while the 25keV ones are blocked entirely unless the lead cap is removed.
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Richard Hull »

Great work Andrew! I have noted this above and for some years. Your work puts a real fine point on this. Thanks for the excellent report.

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: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman »

Additional progress is being made on the liquid cooled grid to address the heating of the field control cap that covers the lip of the ceramic by brazing it to the cooling lines on the grid. Cusil brazing alloy (72% silver and 28% copper eutectic) was used in the brazing with a boron modified flux(Superior No. 601B/3411)
SAM_5190.JPG
The allow has reasonable wetting properties on stainless and only contains vacuum compatible materials(no zinc or cadmium)

A test braze was completed on an older grid, shown after sandblasting and some cleaning
SAM_5191.JPG
SAM_5192.JPG
SAM_5194.JPG
The braze seems structurally and thermally sound and generally wetted ok on the stainless, though the gap may need some tuning to get good flow down into the area between the cooling lines and the cap.

Additionally, the neutron detection system is being upgraded to use He3 detectors instead of the older BF3 detectors that were previously in use. The new detector is about 7x more sensitive then the BF3 tube on the system. This should allow the time constant on the constant neutron flux control system to be reduced for tighter regulation while still remaining stable.
SAM_5195.JPG
SAM_5196.JPG
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Steven Sesselmann »

Andrew,

It's really good to see you make these small incremental improvements it means the technology is being refined and becoming more mature.

By the way I have one of those LND He3 tubes, and I'm interested in knowing where you got the connector. Does it come like that with the threads or is it something you have custom made?

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman »

The connector is a TNC bulkhead mount adapter to clamp on coax, the clamp on section has the same 7/16-28 as the TNC and the LND tube. the other fitting is an Amphenol 79675 Adapter TNC to BNC adapter, a small spring connects the pin on the end of the He3 tube to the center pin on the other adapter
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman »

Pictures of the molybdenum cap glowing under ion bombardment after about 40sec of operation at 17mA
SAM_5200.JPG
Pictures of the molybdenum cap glowing under ion bombardment after about 40sec of operation at 17mA
SAM_5201.JPG
The old grid was removed and inspected prior to the upgrade to the version with the brazed cap. The macor ceramic has held up extremely well with no signs of thermal or arcing damage.
SAM_5210.JPG
SAM_5211.JPG
A cooled grid with a brazed field control cap has been installed and is currently being tested
SAM_5217.JPG
SAM_5218.JPG
The new grid was tested for several minutes at ~2.5e6n/s with no discernible heating of the field control cap
SAM_5220.JPG
The current limit for operation time is now the heating of the vacuum vessel which will require some additional fans to keep cool .
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Richard Hull »

I have never really worried about the shell heating which tends to reach about 200 deg F after 1.5 hours of running. (electron bombardment and neutral crash area).

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: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman »

Mine seems to have localized spot heating near the ion sources. I think the fraction of the deuterium beams that is neutralized or charge exchanged at the focal point is being accelerated outward and striking the shell near the injector ports on the opposite side.
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Steven Sesselmann »

Andrew,

Did I understand this correctly, the cap was initially not brazed to the cooled grid and so became heated from the ion bombardment, so you have now brazed it to the grid so it now stays cool?

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman »

That's correct. The previous version had a molybdenum cap for shielding the lip of the ceramic. The cooling lines just stuck through, making electrical contact, but without making good thermal contact. The new version has a brazed stainless cap.
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Richard Hull »

Thanks for the info. My shell has no ion sources pointing at one another across the sphere. Those beams on delecate parts in the chamber would be a bad thing.
So much for taking the time to critically align stuff during assembly.

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: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman »

The beams seem very well aligned, the fact that they are hitting near the ion injector ports is due to the electrostatic lensing effect from the grid. The grid consists of 3 rings, and while it resembles a spherical source at a distance, nearer to the grid the discrete effects of the grid rings are noticeable. An ion beam fired directly radially inward at +-45 degrees to the midplane of the vacuum vessel will pass through the grid and bend towards the midplane. When exiting the grid it will be at an angle nearer to horizontal and will strike the shell about halfway between the midplane and the opposing injector port.
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman »

I've been working on converting my older CAD files on the fusor into autodesk inventor, here's what I have so far
core1high.jpg
Cross sectional view
core3high.jpg
Grid Detail
grid.jpg
Grid insulator box detail showing cooling lines
grid_box.jpg
Detail of machined macor grid insulator
grid_tip.jpg
grid_tip2.jpg
grid2.jpg
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Richard Hull »

Nice CAD work. Very professional. Fabulous images of what the finished product will resemble. Boy, times, they do change.

I took two classes in engineering drafting while in college in the mid-sixties. We joked about the drafting requirements, saying that should we fail as electronics engineers, we could always find work with International Havester designing self-propelled manure spreaders.

I bought the drafting table and a super nice set of drafting instruments and used them into the early 70's for my own work and pleasure. I still pull them out on occasion, but tend to use simple Computer drafting programs for mechanical stuff and schematic programs for electronic circuit printouts. I have never considered CAD, as I can doodle out a 3-D mechanical impression and see issues develop on that front. Without free access to CAM, I always felt CAD, by itself, a bit over blown. CAD-CAM need to be fully wed and implemented together. My thoughts.

As the brain ossifies, I currently only attempt to learn that which is supremely valuable immediately which is free of any cost. As I am retired, the only new stuff I need to know is that which presents itself in the press of advancing my own personal efforts. I don't have to impress any one person or employer any more. I have a lifetime accumulation of hard won knowledge, about 60% of which is useful now only for campfire stories about how it was in the "old days". This sort of specific, focused knowledge and its application, which the young folks here strive for now, will be part of their campfire story collection in later life, as well. There will always and forever be "this new thing" leaving the bulk of your past efforts and hard won experience, a relic on the trash pile of what was once the cat's pajamas.

All that past effort in life, as you advanced, served to put bread on the table, pay for the car, etc. However, just as the bread ultimately ended up in the sewer system as consumed waste product and the car, in the junk yard, having ferried the family around so valiently, so hot, current, specific skill sets in focused endevors will also fade from being of any real value in future.

This is why I can see the sage, yet sad, Yogi Berra quote in my closing salutation as truly humorous on many levels.

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: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Robinson »

Glad to see you pushing into some newer CAD software Andrew. Nice attention to detail. I keep trying to reinforce the usefulness and application of CAD here. With your level of past attention to detail, I know I don't need to try to convince you. I know it can be a daunting task to model everything but very rewarding in the end. We're now pushing into the 1000's of hours on our current model. I'd be happy to talk CAD with you. I'm sure we both have some tips and tricks we can share. Keep it up and as always, I continue to look forward to your progress.
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Robinson »

Andrew,

You may be particularly interested in the thermal and flow characteristics we're modeling currently off your original design. Note the continuous feature via 3D sketches to enable the flow and thermal simulations of the grid. This was an early (and incomplete) 3D test and unfortunately I'm not at the office currently so I don't have our updated models or data to share at the moment, but like I said, send me a message sometime. We're investigating heavily into this area and building on your previous success. I would love to share data between teams.
Capture.PNG
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Robinson »

Hey Andrew,

I fired off a few emails to you, but I'm not sure if I have the correct email address. I wont post it here in plain text due to crawlers but are you still at the university/using that email address? Looking forward to hearing back from you.

Cheers,
Andrew
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman »

I'm here(same address), I sent you a response via email.
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman »

The fusor has been tested with the new molecular drag pump and dry diaphragm pump. The MDP was mounted to the high vacuum solenoid valve on the fusor and was running off of it's built in AC power supply, while the diaphragm pump was running off of the fusor's 24Vdc supply. Vacuum performance was generally good. The solenoid valve between the fusor and MDP was opened at ~100s while the fusor was at ~100mTorr, pump down into the high 1e-4 range occurred with generally good performance. Deuterium pressure was held at ~8mtorr and the fusor generated ~2.3E6n/s at 40kV and 17.6mA, also generally about the same as running with the turbo station.
fusor-mdp.jpg
MDP mounted on fusor
SAM_5865a.jpg
Plasma
SAM_5866a.jpg
My last deuterium tank had run out of pressure, having only ~90psi when I got it, it lasted about a year of intermittent use. New deuterium tank has ~1750psi in it and should last a significant time. The tank is now mounted inside the fusor frame(more compact and better protected) and all VCR fittings have been upgraded to copper o-rings rather then the nylon washers I was using for testing.
SAM_5870a.jpg
The fusor's going to be hooked back up to the old turbo station until I can get the new one with the MDP built though.
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Re: Mark3 operation and upgrades

Post by Andrew Seltzman »

A recent upgrade to the mark 3 has replaced the 6 way conflat cube with an 8 way kimball physics vacuum hexagon. The hexagon is considerably smaller and more compact, and has 2 more ports then the cube. The hexagon is connected to the core with a brazed ceramic isolator with copper conflat o-rings, which replaced the PEEK plastic isolator with viton o-ring. In addition the hexagon mounts an MKS 901P with integrated display, x-ray shielded 1.33CF viewport, deuterium inlet valve, Pfeiffer EVI 005 vacuum valve, an electron collector probe on a BNC feedthrough, and a germanium viewport for IR measurements. This upgrade replaced 1 plastic insulator, 2x 2.75CF viton o-rings, 1x KF40 Viton o-ring, and 1x KF16 o-ring with all metal parts, is about 4kg lighter then the previous unit, and significantly more compact, which will allow a diaphragm pump / turbo pump system to be integrated into the frame. The MKS 901P is the RS485 version which will allow several vacuum gauges and the turbopump to talk on the same bus.

The Pfeiffer EVI 005 valve was the one tested in this post
viewtopic.php?f=10&t=12155

The deuterium inlet valve was welded with this procedure:
viewtopic.php?f=6&t=12284

CAD designs on the hexagon are attached below
vac-hex.jpg
vac-hex-half.jpg
6way-frame.jpg
Pictures of the completed hexagon
SAM_6445.JPG
SAM_6448.JPG
Comparison to the old vacuum cube:
SAM_6452.JPG
Vacuum tests of the new system are very encouraging, the lower conductance of the smaller valve is offset by the removal of the viton and plastic; the system now archives considerably better vacuum performance, and will max out the gauge at below 1e-5 torr.
First pump down with bakeout starting at ~700s and pressure rise with valves closed.
6way-vac.jpg
6way-rise.jpg
In addition a new digital control system is in the process of being designed, which will replace the older analog feedback controllers with an arduino controller and provide a touchscreen display for monitoring and control
SAM_6456.JPG
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA-9mA

Post by Richard Hull »

Fabulous upgrade Andrew!! One of the better systems out there and a fusioneer that has been around a while. Thanks for the upgrade. I am envious of the valved off 1000+ second hold to about 50 microns. I am at 100 microns after about 360 seconds, but I have operated like this for about 9 years now.

Again, nice stuff! ( as an old friend used to comment to me).

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: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA-9mA

Post by Andrew Seltzman »

Latest upgrade progress:

Diaphragm pump, rough vacuum gauge, and turbo pump to be installed on fusor frame.
SAM_6520.JPG
CAD design of mounting position:
turbo-mount.png
Vacuum gauges and turbo pump will share an rs485 bus for communication. The USB to RS485 dongle used for turbo pump testing is the following:
https://www.amazon.com/gp/product/B010K ... UTF8&psc=1

Pump actual speed, set speed, and controller current, voltage, and power.
turbo-test.jpg
Matlab control program for pfeiffer turbo pump:
Pfeiffer_TC100_rs485_plot_data.zip
(2.27 KiB) Downloaded 500 times
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA-9mA

Post by Andrew Seltzman »

More upgrades for the fusor:

Upgrades for mounting internal vacuum pumps, custom backing and mounting bracket for the TPD011 turbo pump
SAM_6850.JPG
Front and back of bracket, replaces the NW16 backing connector and provides 4x 10-32 tapped threads on a 1.75"x97mm pattern
SAM_6849.JPG
Turbo pump and diaphragm backing pump
SAM_6852.JPG
Mounting plate to hold vacuum pumps
vacuum-system.png
Locations of vacuum pump within fusor frame
vacuum-system-location.png
Thermal camera mounting system on vacuum hexagon to observe grid temperature
vacuum-hex-optics.png
Right angle bending mirror
SAM_6853.JPG
Optics path
optics-path.png
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