Fusor Vacuum System Completion

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
Post Reply
User avatar
Cade Neely
Posts: 28
Joined: Mon Dec 30, 2019 9:06 pm
Real name: Cade Neely
Location: Southern Indiana

Fusor Vacuum System Completion

Post by Cade Neely »

After several months of work, testing, and delays, I have completed the vacuum system for my fusor. I will make this post reasonably detailed as I will reference it in my neutron club application in the hopefully not to distant future. So without further ado, this is my vacuum system.


System Description:

The system is built around two pumps, the Pfeiffer Pascal 2021 rotary vane pump and the Edwards nEXT 240 turbomolecular pump. The backing pump has a pumping capacity of 14 cfm and an ultimate pressure of 3 microns. I bought this pump refurbished on Ebay, and it works like new. The Edwards nEXT 240 is the high vacuum pump for my system, and this was obtained as lab surplus. These two pumps are connected by a 12" foreline, NW25 bellows valve, and 4-way cross. On the 4-way cross is a Pirani gauge which measures the pressure of the foreline. On one of the turbo's ports is the TAV vent valve. This valve is a solenoid valve that brings the system up to ambient pressure. A series of adapters on top of the turbo lead to an NW40 bellows valve. This valve acts as the throttle valve for the fusor. Just before a ten inch foreline leading to the chamber is an Edwards WRG which stands for Wide Range Gauge. This gauge takes readings from a pirani gauge and inverted magnetron gauge to measure pressure from atmospheric down to 10^-10 torr. The NW40 foreline leads to a 4-way 2.75" conflat cross which is my fusor chamber. I have a simple USB camera mounted to view the grid.
A view of the system
A view of the system
Another View
Another View
Chamber
Chamber
One of the design factors for my system was remote operation. I wanted to operate the fusor from a distance of 16 feet to cut down on radiation shielding/hazard and protection from high voltage - the high voltage supply will be mounted on the cart. In order to accomplish this goal I designed a module to control the pumps, fans, TAV vent valve, and transmit the gauge information to the turbo controller. I will discuss this in greater detail in a future post.

On the control panel is an Edwards Turbo and Instrument controller. The turbo is controlled by this device but it also controls the vacuum gauges, and TAV vent valve. This is a very useful feature as it is a very compact way of controlling many of the vacuum parts.


Problems encountered during construction:

One of the problems encountered during construction was failure of the WRG. With my first one, I pumped down the system with the fore pump to 15 microns and then started the turbo. The pressure dropped and stopped at 5 microns. I thought I might have a leak but realized 15 microns could have never been pulled by the backing pump with such a serious leak. I returned the gauge and received another one. Similar results were experienced with the second gauge. My third gauge worked, but after several hours of operation stopped working. After a visual inspection and input from members of fusor.net, I cleaned the gauge and was able to get it to work. I hypothesize that these gauges deposit a material as they work and must be cleaned regularly.
The second problem I experienced was outgassing. The NW40 foreline was soiled upon arrival, and I cleaned it with isopropyl alcohol. This worked and after application of a hair dryer while under vacuum, the pressure in the system was reduced to 10^-6 torr. When inspecting the system, I found oil condensation on the view port and a thin layer of oil on the vacuum components inside. The whole system then needed to be cleaned because of this and the foreline replaced. I cleaned the components using acetone, isopropanol, and an ultrasonic cleaner. After cleaning, the system was cleaner than before, and I was able to pull a vacuum of 5.4x10^-6 torr.

Conclusion:

In conclusion, I would like to thank the members of fusor.net that helped me with my WRG issues. There are several upgrades and advances I plan on adding to the vacuum system. I plan to add a stepper motor assembly to the fusor throttle valve so that it can be controlled from the control panel as well as a homemade high voltage feedthrough. I will keep you all updated on future progress.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Fusor Vacuum System Completion

Post by Richard Hull »

A really fabulous and detailed report on a very well done vacuum system, indeed. You experienced a fairly normal set of issues in getting the system to where you are confident in its abilities.

I have tended to operate my systems in a manner that accounts for gravity. The mechanical fore pump is on a lower deck or on the ground, the secondary, high vacuum turbo or diff pump on the next upper level and the fusor or main chamber placed upon, yet, another third deck level. I note your mechanical to turbo foreline "dives" into the turbo making the turbo outlet well below the mechanical pump's inlet. This might, over time, invite oil to accumulate in the foreline "ripples/ridge valleys" or even as far as the base of the turbo pump. Hot oil mist is not totally ruled by gravity, for sure, but can be governed by it to a degree. It is just something to consider over the time of operation of your system.

Thanks again for the great 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
Post Reply

Return to “Images du Jour”