Superconducting Magrid IRL

30 09 2009

WOW. Check out this part we just got from prometal:


There is some slight warping, so the lid doesn’t fit as tightly with some of the faces. This can be corrected with machining, but some extra material would need to be built in.


It really helps to hold the shape in your hands. Amazingly this process is inexpensive. These two pieces cost ~$110. So we can afford to do about 10 iterations, more if necessary. Pretty cool.

Previously we used the 420 Stainless Steel +Bronze, which is magnetic. This time we used the 316 Stainless Steel + Bronze hoping it would be non-magnetic –  but unfortunately it is magnetic.

With superconducting cable:


Pump Update

29 09 2009

So yesterday the pump arrived refurbished from the manufacturer (for $3,500). yay!


I attached the pump to the chamber and tried it out. All good.

For about 10 minutes.

Then i start hearing this intermittant “not good” sound. But maybe it’s just some rattling right?

We’ll the rattle turned into a shriek. When the pfeiffer tech heard the sound on the phone he said to send the unit back.

What a drag.

Mass Flow Controller

27 09 2009

So I’m making good progress building out the computer control and data acquisition system for the reactor. Currently we have a manually controlled needle valve to regulate flow on the deuterium handling system. I want to replace this with a computer controlled mass flow controller.

A new mass flow controller costs roughly $1,100. There are plenty available on ebay starting from $70.

A mass flow controller must be calibrated for a specific gas. Some can be calibrated on demand with a digital interface, and some are hard wired to work with a specific gas. I’m wondering if we can get away with using a hydrogen calibration for our deuterium system?

The next parameter is flow rate. Here is some background on flow rate nomenclature: flow rate nomenclature. Although mass flow controllers meter based on mass flow rate, they confusingly are rated using volumetric flow rate metrics like SLPM (standard liters per minute), SCCM (standard cubic centimeters per minute) or SCFH (standard cubic feet per hour). Conversion between the two must be done at standard temperature and pressure, and must take into consideration the density of the gas: details.

So before I can spec a mass flow controller I need to calculate our midpoint flow rate needs.

Some facts:

The chamber holds ~6,500 cm^3

The turbo pump removes gas at the following rates:

N2 -> 56 liters/sec

He -> 48  liters/sec

H2 -> 36  liters/sec

So the mass flow controller meters how much fuel is flowing into the chamber. We also want to control how much fuel the vacuum pump is pulling out of the chamber. This requires a gate valve or butterfly valve. Many of them include an integrated bellows connection (which is great), and are pneumatically actuated (not so great).

Adding a gate valve will require us to redesign the welded sled; and I bet it won’t be the last design change. To keep it flexible I’m going to take another page from Andrew and switch to 80/20.

Now my naive attempt to calculate flow rate needs:

Without a gate valve the pumps will remove 2160 l/min. Now the typical mass flow controller seems to max out at 10 SLM (l/min)…. so the pump will remove fuel far faster than the mass flow controller can supply it. And this will waste expensive fuel.

I think these calculation work for pressures in the laminar flow region (> 1e^3 torr). We are working with pressures between the laminar flow domain and the free molecular flow domain – I don’t know how the calculations change at this point.

ps. Wolfram Alpha seems to be useful for density calculations.

Small Steps

22 09 2009

Today I added a tap point for analog reading from the ion gauge. Pins 3 and 7 according to the manual.




Eventually I’d like to use the digital interface, but for now this gets the job done.

Next I added a proper connector to the bench-top power supply (pulled from an old PC):


This works a lot better than the wire jumper which kept falling out.

We received and tested the 100A/100mV ammeter shunt resister:

IMG_4085We will use this shunt to take current reading going into the superconducting magnet.

Next up we tested out the IGBT:


Using this schematic:


It successfully switched 10 mA. Next to try it with more amps.

Hacking the DC Magnetometer

21 09 2009

Today I hacked the Alpha Labs magnetometer to add an interface for the DAQ. Here is the finished product:


Here is how:

First I got some info from the manufacturer:

DCM output instructions

Easy! Now we cut a shape out of prototype PCB by scoring and snapping:


I used a small circle file to remove the corners we cannot score and snap:


Here is the finished PCB fragment:


Next we solder in some jumpers, mount the piece and solder the cable tie-downs to secure the assembly:


And wire it all up:


I plugged it into a differential channel on the DAQ and…


We have a DC magnetometer sending data to the computer. Regarding interpreting the results, Andrew from Alpha Labs says:

The Gauss conversion to output voltage is 200mV at full scale. So if you are in the 20,000 range and you are reading 5000 Gauss, your output should be 50mV. If you are in the 2000 Gauss range reading 1500 Gauss, your output should be 150mV. So the output jack gains by 10 WITH the range control switch.

Reactor Controller / Data Acquisition

17 09 2009

Since the pump broke I’ve been working on the reactor controller / data acquisition system. This will allow us to record:

Voltage reading (via voltage dividers and ammeter shunts); low power voltage reading from magnetometer, thermocouple, pressure gauge, etc; on the output side: voltage control of power supplies, servos for needle valves, triggering IGBTs; Our ion gauge has the option of digital over RS485.

I purchased an NI USB-6008 (manual, driver):


Unfortunately the driver for this does not work with Snow Leopard yet. I’ve already upgraded my main laptop to Snow Leopard and I really don’t want to downgrade to Leopard so I dug up and old G4 running Tiger. Had to swap out a broken CD drive:


This G4 will be a challenge to upgrade to Leopard as it lacks a DVD drive, although it may be possible to install without DVD.

I was able to install the driver NI-DAQmx_Base. I opened up NIdatalogger and performed a successful grab of voltage data on the analog input:


I would like to get this ruby adapter working. So far I can’t get it to build on Tiger (it makes it further on Snow Leopard). I’m working with the creator to get it installed and working:

make -f Makefile.swig install
swig -ruby -Fstandard -I/Applications/National\ Instruments/NI-DAQmx\ Base/includes -o daqmxbase_wrap.c daqmxbase.i
make: swig: Command not found
make: *** [daqmxbase_wrap.c] Error 127
make -f Makefile.swig install
swig -ruby -Fstandard -I/Applications/National\ Instruments/NI-DAQmx\ Base/includes -o daqmxbase_wrap.c daqmxbase.i
make: swig: Command not found
make: *** [daqmxbase_wrap.c] Error 127
I just needed to install SWIG. Although this took roughly 6 hours! It installed without a problem.
I AM UP AND RUNNING with data acquisition in my native programming language ruby.

New Arrivals

9 09 2009

Got the first bubble detector today:


Unfortunately without the pumps it’s all dressed up and nowhere to go. These have a shelf life of 90 days, and must be stored in their airtight cigar case:


I had to purchase 3 of these. Each will ship as the last expires, so I’ll have 270 days of coverage.

Also got two IGBTs today:


These can switch 200A 600V.


Fuji A50L-0001-0260/A


Pretty heavy duty! I expect to use these on the next run with the superconducting magnet to quickly disconnect the power supply from the magnet.


Get every new post delivered to your Inbox.

Join 639 other followers

%d bloggers like this: