DIY Ultra High Vacuum Research Project

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Introduction: DIY Ultra High Vacuum Research Project

About: Maker, Engineer, Geek Girl.

This instructable details a project that has been in the works for many years, a nuclear physics project done out of a sheer wish to learn and to hopefully inspire others to do similar. I desire no monetary gain, this is not a college project nor is it aimed at any specific goal. This is a personal project that was simply started out of a desire to understand the details and complexity of the various subjects of physics you typically only get to see in universities. Things that are normally only available to the rich or lucky. I want to demystify and make knowledge like this accessible to all humans. 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.

I learn in a very practical way, and actually doing projects that require so much detail teach me the most. I took interest in this project some years ago after seeing a video of Ben Krasnow's on an ultra high vacuum system used for an electron microscope which he has also used for DIY sputter coating to make conductive glass. This project was very far outside my realm of possibilities and experience at the time, so I decided to start my own project from the ground up, engineer every part and work out every issue on my own to expand my knowledge of engineering and science. You don't just learn from the research I want to do with this project, you learn so much about engineering that you can't learn from a book or the internet.

Other people have done projects like this before, 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.

Step 1: What Is This?

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 will be exchangeable to set it up for different experiments, for example, when set up as a fusor there will be a high voltage feedthrough in the upper window for the inner grid and Deuterium gas backfill.

Another use for this project could be for coating glass with metal via the sputtering process to create DIY LCD panels. Creating thin film transistors, or partially silvered and fully silvered first surface mirrors for use in laser systems.

Step 2: Components

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, 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.

Step 3: The Diffusion Pump

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.

Step 4: Connections and Cooling

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.

Step 5: Software?? Electronics??? Code????!

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");
    }

Step 6: Testing and Leakdown

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!

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    4 Comments

    Nice project! Definitely educational, fun, and also a really cool thing to have in the garage. :)

    A few tips that might save you some hair:

    Below about 10^-6 Torr the seal types become very important. Plastic/rubber seals allow noticeable amounts of gas to diffuse through them. How much varies from plastic to plastic, with Teflon and Viton generally considered to have the lowest diffusion coefficients. There are certain vacuum compatible epoxies available for permeant seals as well.

    Also, below about 10^-4 Torr the gas remaining in a vacuum chamber is mostly water. The water sticks to the internal surfaces and gets pumped out very slowly. The water can be driven off with external heat or internal UVC (aka germicidal UV) to achieve a lower ultimate vacuum.

    If you need to weld anything exposed to vacuum, TIG/Heliarc is the way to go. That's the only technique that doesn't produce pinholes or 'virtual leaks'.

    Finally, FYI back in the day they used to use solder and copper pipe to make vacuum connections and it seemed to work fairly well. However this method has been abandoned in modern labs, probably for the same reasons as why we use TIG welding.

    You can also get vacuum parts, particularly things like ion gauges, from Duniway Stockroom. They're a pain to deal with (you have to call them on the phone for everything), but they do make good products.

    1 reply

    Thank you for all this information! I wasn't aware of the issues with certain seals, I was just going to buy buna-n o-rings, but will definitely try to find viton or the like. I will most likely have a set of high current coils that get wrapped around the chamber to produce some heat and drive off water, however it can double as a plasma cleaner if I backfill with other gasses and use a high frequency.

    Speaking of Duniway, they are fantastic, they provided me with the manual and circuit diagram to my old Varian Ion gauge controller.

    I appreciate your approach to this project! You will go far with an attitude of learning like this.

    1 reply

    Thanks so much! :)