Open Ultra High Vacuum System

The Internet has made information previously only accessible at universities available to almost anyone with an internet connection, anyone can study courses and acquire knowledge at a fraction of the cost! But as is often with science and engineering, this is only half of the equation. The hardware used for professional research is often prohibitively expensive and often custom made, and often when an experiment or project is finished or a grant is received, this perfectly usable hardware is simply discarded.

This Instructable is about recycling and lowering the cost of entry into the fields of high sciences, by reusing discarded or used hardware, and using modern technology and engineering to make it work for a new purpose. To take hardware from different time periods and different manufacturers, and make it all work together as one unit to accomplish the same goal new hardware would, using things like Arduino, 3d printing, and home CNC machining. After all, we work far too hard as a species to gather this knowledge just to keep it from those who may have interest in it simply because they weren't invited to the party, like me. Knowledge is a human right, and treating it as a commodity is a waste.

Other people have done projects like this before of course, but I want to do this as professionally as possible, as if I was doing this in a university setting, so I can learn as much as possible, on a very meager budget. Like, super meager. The intent of this is to recycle retired lab gear and parts that are normally thrown away, and all of my files, code, and drawings are made available to be modified and published to further the reach of this project.

This project is intended for multiple uses, and is designed to be partially modular to enable a variety of experiments to be carried out. The first proof of concept experiment of this system will be a Farnsworth Hirsch Fusor. This system will be able to achieve a very high level of vacuum capable of making a very functional fusor. The Vacuum chamber's upper window lid will be modular and set up for different experiments, for example, when set up as a fusor there will be a high voltage feedthrough in the upper window lid for the inner grid and gas valves, while having a seperate sputter coater lid that can be quickly exchanged for a different project.

Among many others, a primary use for this project could be for coating glass with metal via the sputtering process to create DIY LCD panels, thin film transistors, or partially silvered and fully silvered first surface mirrors for use in high accuracy laser systems.

To start with, we need to acquire the mechanical parts:

• A high vacuum pump, like a turbomolecular, oil diffusion, sorption, or cryostat pump
• A chamber with thick walls to withstand atmospheric pressure
• a viewport
• vacuum gauges, both roughing and high vac
• a roughing pump, like an hvac pump
• electronics to connect everything and make it work
• some sort of stand to hold it all
• plates adapters and connections
• tubing and wiring
• optional components like, bakeout heaters, gas valves and purge gas, chamber sealing valves, liquid cooling etc.

This ultra high vacuum system utilizes a surplus 4 inch liquid cooled fluid baffle Daia DPF-4z oil diffusion pump and 2 stage rotary vane pump to achieve very high levels of vacuum. The Diffusion pump is majorly overkill for this project, but it was found for a great deal on ebay, and was impossible to pass up.

The Rotary vane pump is a harbor freight special pump, made by US general. It isn't the highest quality pump, but it will be operated relatively rarely, and only used to pump air, and not refrigerants as it was originally intended.

A Varian 841 vacuum Ionization gauge was acquired on ebay for a small price in questionable condition, with the intention of repair as sub small project. Repairing old equipment like this and integrating into your designs are a great way to learn about how to fix electronic devices and engineer your own! However, I ended up using an MKS 903 series inverted magnetron transducer cold cathode ionization gauge (mouthful!) and an arduino to interpolate the data.

The actual vacuum chamber is a CF flanged tube from a larger system also acquired from ebay, but as we do not need a large chamber volume, this small chamber will work perfectly.

There is also a cooling system for the pump, various electrical work, an adapter plate that needed to be machined to interface the pump to the standard CF flange chamber.

The most integral part of this system is the high vacuum pump, used to increase vacuum levels farther than typical mechanical means can achieve. A roughing pump, the US General rotary vane pump pulls the initial rough vacuum needed in the chamber and the diffusion pump, and the diffusion pump then activates as the second stage, increasing to the final vacuum level.

This specific diffusion pump operates on the oil diffusion principle for gas molecule removal, by which in the bottom of the diffusion pump, oil is boiled and vapor travels up the chimney, and the vapor is ejected out to capture as many gas molecules as possible, and fired downwards towards the outlet of the pump to carry the gas to the mechanical vacuum pump. Now, we do not want this oil splashing into the main chamber, so there is a liquid cooled baffle used to cool and condense the oil before it can get into the chamber.

To mate this non-standard Japanese pump to the standard CF flange chamber, I needed to engineer an adapter plate out of aluminum. I used a desktop CNC machine to mill out a plate of MIC-6 toolplate to keep a perfectly flat surface, as the o-ring mating surface needs to be perfectly flat, while supporting the weight of the pump and chamber.

The system after being adapted then needs to be mated, the pump head has an o-ring groove for sealing against the bottom of the plate, and the plate has a groove machined to seal against the bottom of the vacuum chamber. High vacuum grease is used to properly seal the o-rings against the mating surfaces. The diffusion pump then had its outlet tube modified to connect to the roughing pump.

This diffusion pump is large, and subsequently liquid cooled, so a water cooling system must be utilized. I made a cheap liquid cooling loop by modifying and reusing an old office water cooler, and adding a pump and cooling lines to connect up with the diffusion pump. This water cooler has a stainless steel bucket that contains the liquid, in this case methanol, with the copper refrigerant coils wrapped around it, and a ceramic pump that pumps the cooled liquid around water jacket of the diffusion pump, and then returns it to the bucket to be cooled again.

The water cooler was picked up from its way to the dump, and was modified in the following ways, the entire cooler was shortened to half its height by folding the coils over on the back of the unit, and the entire system was cut in half, removing the water filter unit. A small water pump from eBay was installed, and plumbed into the system. The electrical system was then modified to power the pump when the cooling is on, and the thermostat turned down to prevent overcooling.

Now that I have a cold cathode vacuum gauge, I need some way to interpolate the logarithmic gauge pressure to voltage. Arduino..? Arduino.

For my first foray into c++, I chose this as a first code project, and I recommend starting simpler, as this took weeks of learning.

The code below simply sets A0 as a floating point unit for voltage, which
is 0-5v from the voltage divider. Then it is calculated back up to a 10v scale and interpolated using an equation based on the voltage/pressure table provided by the manufacturer.

The equation is P=10^(v-k) where p is pressure, v is voltage on a 10v scale and k is the unit, in this case torr, represented by 11.000. It calculates that in floating point, then displays it on an LCD screen in scientific notation using dtostre. This code was the first program I have written from the ground up, and it was pretty daunting at first, but it was made easy and super rewarding by the community! :3

#include 
<br>#include 

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

// the setup routine runs once when you press reset:

    void setup() {
      // initialize serial communication at 9600 bits per second:
      Serial.begin(9600);
      pinMode(A0, INPUT);              //A0 is set as input
      #define PRESSURE_SENSOR A0;
      
      lcd.begin(16, 2);
      lcd.print("MKS  Instruments");
      lcd.setCursor(0, 1);
      lcd.print("IMT Cold Cathode");
      delay(6500);
      lcd.clear();
      lcd.print("Gauge Pressure:");
      
    }

// the loop routine runs over and over again forever:
   
    void loop() {

      float v = analogRead(A0);        //v is input voltage set as floating point unit on analogRead
      v = v * 10.0 / 1024;             //v is 0-5v divider voltage measured from 0 to 1024 calculated to 0v to 10v scale
      float p = pow(10, v - 11.000);   //p is pressure in torr, which is represented by k in the equation [P=10^(v-k)] which is-
                                       // -11.000 (K  = 11.000 for Torr, 10.875 for mbar, 8.000 for microns, 8.875 for Pascal)

       Serial.print(v);

       char pressureE[8];
       dtostre(p, pressureE, 1, 0);        // scientific format with 1 decimal places
      
       lcd.setCursor(0, 1);
       lcd.print(pressureE);
       lcd.print(" Torr");

    }

The next step after our system is plumbed, is to load the pump with oil, power up your roughing gauge and let the rouging circuit pump the system down for leakdown. When you reach ultimate vacuum for your mechanical pump, the second stage can be started, turning on your high vacuum gauge and high vacuum pump.

Now is when you will find big leaks, as high vacuum pumps and sensors are extremely sensitive, so even air trapped in screw threads will set off your gauge.

If you have it, you can perform a helium leak test with a helium tank and detector. Helium is an extremely light and small molecule, so it will find its way into leak paths even nitrogen has trouble going through.

This project is a work in progress, results of leakdown will be posted here, follow me for updates!