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

For posts specifically relating to fusor design, construction, and operation.
Andrew Seltzman
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Re: Mark3 operation 3e-4 torr / quad ion source @ -40kV, 1mA

Post by Andrew Seltzman » Wed Mar 29, 2017 12:01 am

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.
MDP mounted on fusor
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.
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.
Andrew Seltzman

Andrew Seltzman
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Re: Mark3 operation and upgrades

Post by Andrew Seltzman » Sun Jul 08, 2018 9:50 pm

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

The deuterium inlet valve was welded with this procedure:

CAD designs on the hexagon are attached below
Pictures of the completed hexagon
Comparison to the old vacuum cube:
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.
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
Andrew Seltzman

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

Post by Richard Hull » Mon Jul 09, 2018 6:15 pm

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Andrew Seltzman
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Joined: Mon Feb 02, 2004 1:02 am
Real name: Andrew Seltzman

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

Post by Andrew Seltzman » Mon Sep 03, 2018 9:58 pm

Latest upgrade progress:

Diaphragm pump, rough vacuum gauge, and turbo pump to be installed on fusor frame.
CAD design of mounting position:
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: ... UTF8&psc=1

Pump actual speed, set speed, and controller current, voltage, and power.
Matlab control program for pfeiffer turbo pump:
(2.27 KiB) Downloaded 10 times
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