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

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

Post by Andrew Seltzman » Fri Mar 18, 2016 8:48 pm

Some power supply upgrades are coming to the fusor allowing increased voltage operation. Earlier this year I got a second spellman PTV power supply on ebay for $200 with the intent of paralleling the outputs for increased current
http://www.ebay.com/itm/Spellman-Lunar- ... 7675.l2557
Unfortunately the seller had one positive and one negative polarity and sent me the positive polarity one, which had to be returned. Kuba got the other one that had the negative output.

Fortunately Bern spotted a spellman x-ray supply on e-bay which I managed to win. It's a -70kV, 8.56mA spellman power supply(DXM70N600X3547)
http://www.ebay.com/itm/Spellman-Power- ... 7675.l2557
The manuals are listed here
http://www.spellmanhv.com/DXM
http://www.spellmanhv.com/~/media/Files ... XMMAN.ashx

It has digital control of the output(serial, usb, and ethernet)
s-l1600.jpg
though it does use an unusual connector, a Claymount Mini Federal Standard X-ray connector, identified as a model CA11
http://www.claymount.com/en/products/hi ... /connector

I managed to find some short cutoff cables for testing of the supply
http://www.ebay.com/itm/Claymount-Xray- ... xyMZ5RnAlY
But I am looking for the screw ring for the connectors and longer cables that I can adapt to my system if anyone knows where to get them.

My grid system is in the process of being upgraded to prevent arcing from the tip of the ceramic insulator and prevent outgassing by replacing the boron nitride with macor and alumina. With the grid removed the fusor will easily pump down into the 1.5E-5torr rang and into the high E-6 range with help from the bakeout heaters and ion sources to desorb water from the walls, so the grid BN ceramic was definitely causing the vacuum problem. With the bakeout heaters on and the fusor shell in the 80-90C range, the vacuum will hold in the mid E-5torr range, so it should still have 99% deuterium purity when operating in the mid E-3torr range. Leakage through the few remaining viton o-rings still lets in some water, but the vacuum is getting progressively better.
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman » Thu Mar 24, 2016 7:19 am

The old grid was modified to remove all boron nitride components that were causing vacuum problems due to their porosity and water retention.
Deposition on old boron nitride grid insulator
SAM_4889a.jpg
Arcing damage to top of old grid insulator cracked the quartz tube
Still0003a.jpg
Still0008a.jpg
Still0012a.jpg
New grid system with macor deposition shield, alumina insulator stalk, and molybdenum field control ball
SAM_4900a.jpg
molybdenum field control ball fits over the tip of the alumina stalk preventing any sharp edge from being exposed to the plasma like on the last grid design. Sputtered metal deposition will eventually make the lip of the insulator conductive leading to arcing. The molybdenum ball fits like a cap over the tip of the ceramic rod presenting only smooth surfaces to the plasma.
SAM_4899a.jpg
The new macor bushing adapts the quartz vacuum feed through to the alumina rod and includes a deposition shield, the bushing has a machined in pump out duct to vent the inside of the grid assembly to prevent a trapped volume
SAM_4898a.jpg
Design of bushing and molybdenum cap
SAM_4908a.jpg
SAM_4909a.jpg
Operation of new insulator
SAM_4907a.jpg
Unfortunately the new design arcs at 25-30kV at 10mTorr at the base where the alumina rod meets the macor bushing. This only occurs when exposed to plasma, in a neutral gas at 10mTorr with the ion sources off to prevent any plasma breakdown the insulator will hold off 40kV. This design needs to have additional bushings outside the alumina stalk like on the boron nitride grid. These will be machined out of macor and added to the system.
grid-rev4-down2a.jpg
The vacuum performance of this grid is perfect with no outgassing or water retention. The system will easily hit the mid 5E-5 torr with the grid installed, macor is definitely the way to go.

Preliminary tests are being conducted on the new Spellman DXM supply. It turns out the supply is brand new, with no logged hours on the HV on hours counter. The supply can be controlled and monitored over an ethernet connection, or with analog inputs.
SAM_4911a.jpg
Matlab program generating a 5kV ramp waveform of the voltage output
spellman_kV_rampa.jpg
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by John Futter » Thu Mar 24, 2016 7:52 am

Andrew
I have had various results with the ethernet control program as supplied by Spellman with our 6kW 140kV unit
it disappeared from our intranet when we needed to shut it down urgently due to excessive x-ray production in our experiment ie counters went over 300mSv.
So we now have a kill switch wired through the interlock connector.
Not sure why you are having so much trouble with the BN insulator.
As for o-rings some of our equip has nearly a 100 meters of viton o-ring and it sits at around 2x 10^-8 millibar base pressure with a single 300L/S turbo, the RGA does not show appreciable water signal we see a weak air signal N2 O2 H2 Co2 and heavier hydrocarbons probably fingerprints and grease ,backing pump oil etc.
Pyrex makes very good shields as it is slightly conductive and defines the "E" field with a nice gradient.
I do not like MACOR for this as it is too insulative and the field can concentrate in the wrong places IMHO

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

Post by Andrew Seltzman » Thu Mar 24, 2016 4:43 pm

John,

I definitely plan to have a hardware interlock/kill switch on the final setup.
The problems with the BN insulator were mainly due to it having 7% porosity and a boric oxide binder, which is hygroscopic. It soaks up water vapor and then released it when it starts to get warm.

I'm trying to avoid any non-quartz glasses like pyres since they benin to get conductive when heated by direct ion bombardment. This is especially a problem at the lip next to the grid. The quarts has much less problems and can tolerate much higher temperatures, but still needs to be shielded from direct bombardment at the top lip. It's also kind of brittle and can fracture during an arc. Alumina will not fracture like quartz, but has much lower dielectric breakdown strength.

The macor is something new I'm trying due to it's machanability, I hope to make something similar to the BN insulator but with macor shields, an alumina core, and a molybdenum field control ball at the top to prevent any ion bombardment if the insulator lip. I really think the re-entrant molybdenum ball will greatly increase grid insulator life by preventing conductive deposition on the insulator lip by the grid from initiating field emission discharges.

Do you have any experience using macor under intense ion bombardment, like near the focal point of a fusor? Does it begin to melt/degrade/outgass etc...?
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Robinson » Sun Mar 27, 2016 6:13 pm

Great to see you're still making progress on this design. We're running into some of our own operational challenges with our liquid feed through. Always great to see the challenges you are running into. It has helped us immensely in the past to avoid some costly mistakes. Thanks Andrew!
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman » Mon Jun 27, 2016 2:10 am

Latest upgrades to the mark 3:

A complete rebuild of the grid cooling system has been completed.
The old system was removed
SAM_4966a.jpg
and replaced with an upgraded version consisting of a compact thermometric heat exchanger designed around an all in one waterblock pump combo (swiftech apogeedrive 2) http://www.swiftech.com/ApogeeDrive2.aspx
SAM_4976a.jpg
as well as a new radiator and low noise fan
SAM_4975a.jpg
An acetal block is machined to hold a second copper waterblock that fluorinert flows through
SAM_4989a.jpg
SAM_4980a.jpg
A thermoelectric cooler transfers heat from the fluorinert to the water cooling loop
SAM_4999a.jpg
A CPU retention plate is outfitted with extension standoffs
SAM_4988a.jpg
Allowing the apogeedrive cooler to clamp down to the thermoelectric cooler and fluorinert waterblock
SAM_5002a.jpg
Dimensions of the acetal block
SAM_4994a.jpg
SAM_4995a.jpg
The newer system is considerably more compact
SAM_5003a.jpg
A stainless reservoir stores fluorinert for the cooling loop
SAM_5039a.jpg
SAM_5040a.jpg
Complete system mounted in reactor frame
SAM_5044a.jpg
SAM_5046a.jpg
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman » Mon Jun 27, 2016 2:42 am

Upgrades to the grid system have also been completed

The arcing problem on old grid design was traced back to the area between the alumina insulator and the macor bushing
SAM_5024a.jpg
SAM_5025a.jpg
This was only a problem when exposed to plasma bombardment. In a vacuum it would hold off 40kV, but arc at 25kV under plasma bombardment

A new design with a macor insulating cap and new bushing with a overlapping interface that prevents any scattered plasma from forming a conductive path
SAM_5011a.jpg
SAM_5019a.jpg
SAM_5021a.jpg
The new version will operate without arcing at 40kV in a plasma and will not produce any outgassing(unlike the boron nitride version) allowing continuous operation of the fusor
SAM_5054a.jpg
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Robinson » Mon Jun 27, 2016 2:53 am

As always, fantastic work Andrew! Both myself and my team always look forward to updates on your grid design and have been following them with great interest.

You have caught my particular interest with Macor. Will need to read up on this ceramic. Thanks!
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman » Mon Jun 27, 2016 2:56 am

Latest operation data from the new grid and cooling system:

The new macor insulated grid allows significantly better vacuum performance due to it's zero porosity and lack of binders. There is no discernible outgassing as the ceramics heat up, allowing continuous operation.

Latest operation at 7.2mTorr, 40kV, and 8.8mA
SAM_5051a.jpg
Generated 70 bubbles (30bub/mrem) in 60 sec at 3.5"(8.89cm) from the center
SAM_5068_counta.jpg
SAM_5067_counta.jpg
Current best neutron output is 1.08E6n/s
fusion-6-26-2016-7,2mtorra.jpg
Next on the to do list is connect the second PTV supply in parallel to run at 40kV, 17mA, and hook up the new 70kV, 8.5mA spellman supply for higher output.
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Richard Hull » Tue Jun 28, 2016 9:04 am

Fabulous report and great work across the board. Few folks who have done fusion here have hit the mega mark. Probably as few as 10%. You kinda' have to stick with it once you have done fusion to get numbers up. You system is clean and very well executed. You can now easily do activation on a significant scale, far from any need for satisitcal back up.

You might try to calibrate a fixed silver activation set up against your BTI bubble detector, if that is your only neutron indicator. When the bub dosimeter craps out, you can rely on the silver activation as a crude but calibrated indication of future performance. (assuming you don't want to blow the coin needed to replace the BTI when it goes south.)

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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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