Diffusion Pump Tests

Over the Holidays I got a few of the parts I needed to test out the diffusion pump.

I caped off the beam line port with a NW-40 blank off flange, installed a new DV-6M thermocouple gauge at the head of the diffusion pump and filled it with 50 cc of fomblin 25/6 (Generally a mechanical pump oil, but has a decently low vapour pressure). I pumped down the system to 15 microns and plugged in the diffusion pump heater. After 20 mins of heating up, the pressure dropped and bottomed out the thermocouple gauge read out at the head of the diff pump (on the right):

In order to use the diffusion pump in my lab (a.k.a my room) I had to make a self contained cooling system. It consists of a plastic jar of water with an aquarium pump that pumps the water to the water cooling lines of the diffusion pump. The only issue is that the water warms up pretty quick. For now I add ice as I go along, but in the future I will try to come up with some sort of way to cool it (Perhaps a peltier thermoelectric cooler).

Vacuum System Testing

I did some testing and my second thermocouple gauge destined to read out the pressure at the top of the diffusion pump is dead...

I started up the foreline pump, isolating the foreline from the rest of the system with 2 valves. It took 10 mins for the pressure to hit 15 millitorr (microns of mercury) in the foreline, which is normal since the pump and fittings have been sitting around accumulating moisture. After, I turned off the pump, brought the pressure back to up to atm pressure and started the pump and it pumped it from 1atm down to 15 microns in 3 mins :

I could just stick in the dead thermocouple gauge and try out the diff pump anyways, but the beam line port is open to air. Until the beam line gets installed I need a NW40 blank flange to cap off the beam line port to test out the vacuum system.

So the Need to Acquire List :
-DV-6M Thermocouple Gauge
-NW/KF 40 Blanking flange

Until I get a hold of these parts, I will start working on designing and building the High Voltage power supply in order to supply the accelerating potential.

Vacuum System Assembly

My vacuum system is put together with NW fittings. Why? Because these were the ones I managed to get a hold of. Also, they are readily available for replacement and reasonably cheap second hand. Most of the fitting were donated by George Solomom from Vacuum Technology Incorporated including the diffusion pump and the valves. The rest were bought on eBay:

In order to connect the roughing pump to the system, I soldered an adapter to a scrap copper pipe and soldered that to some fittings that matched the threads on the input to the robinair pump:

This connects to a a 3 terminal fitting : one of the other two terminals goes to the foreline of the diffusion pump via a valve, the other goes to a flex tube to the high vacuum assembly via another valve and in the middle is a thermocouple gauge to measure the foreline pressure. The High vacuum 4 way cross assembly is connected to: the inlet of the diffusion pump, the "yet-to-be-built" beam line and the other flange in capped off with a blank. Hopefully I can get a hold of / design & build a high vacuum gauge such as an ion gauge to go in the place of the blank. (For previous accelerator, I had built some sort of cold cathode ion gauge, but it was pretty worthless...)

I haven't turned the vacuum system on yet, I will have to clean out all pieces with solvent and fill the diffusion pump with oil.

Here's what it looks like:

If you have any suggestions for a better design, let me know!

The Vacuum System

 The most important part of any accelerator is the vacuum system. You can find all kinds of neat ways to push along particles and it won't matter if they just smash into something else in a matter of a few nanometers.


The accelerator tube will be about 1 meter long, so a mean free path of 1 meter or more is needed. For this, a pressure of about  10⁻⁴ Torr is required. 

In order to achieve this level of vacuum, first a roughing pump bring the pressure down to about 15 millitorr :

This is a 2 stage Robinair Vacuum pump. These are normally used for servicing refrigerators and other cooling systems.

After the roughing pump brings the pressure down into the millitorr range, the diffusion pump gets turned on :

This pump uses jets of boiling oil to collide with remaining molecules and direct them to the roughing pump and out of the system.

Now, these pumps usually cost lots, but they were donations. The robinair from a refrigeration servicing company and the diffusion pump from a specialty vacuum company.

Next, hooking them up and getting a decent vacuum... (not as easy as it sounds)

Building a Homemade Linear Accelerator (On the Cheap!)

A couple years ago, I built a small linear accelerator loosely based on old plans from the Amateur Scientist section in Scientific American. It was a functional device, but nothing too exciting. My goal now is to build a new acceleration, versatile and useful for some basic experimentation.

The original accelerator was built on a budget of 100 $. For this one, the max budget is 350 $.

These are mains components to a linear accelerator :

-Vacuum System
-High Voltage Power Supply
-Ion gun or Ion Source

I will start building soon. All feedback, ideas and suggestions of all sorts are very welcome.