Lab Time

16 05 2010

Spent some time in the lab. Really loving my new photo blogging capabilities. Shoot first, answer questions later.

Friday’s photo stream.

Saturday’s photo stream.

Received a bunch of parts from mouser. Including the protection diodes.

Prototyping board for NI USB 6008. I should have ordered two!

Did a tour of my shop neighbor’s guitar workshop:

Made progress on the coil power supply chassis:

And played around with ferrofluid:



25 04 2010

Last night I controlled the fusor from LabView. I put together a simplified version of Andrew Seltzman’s Marc III controller. So far I can:

  • graph the chamber pressure in realtime
  • enable/disable fuel
  • set the fuel flow in SCCM
  • see actual fuel flow rate from mass flow controller
  • enable/ disable high voltage
  • set frequency and duty cycle for high voltage

The HV duty cycle lets us do fusion trials without melting the grid.

Something I’ve noticed: when the plasma becomes unstable and sparks… it crashes the data acquisition card. I’m guessing the sparks are creating powerful EMFs. We may need shielding.

USB Geiger Counter

15 12 2009

Got the sparkfun USB geiger counter working today.

The replacement PCB is a newer iteration. It bleeds the high voltage automatically. Nice upgrade.

You can read the data from the virtual com port with this command:

screen /dev/tty.usbserial-A800czX2

Each geiger count produces one random bit:

Fusion Run Data Graphs

17 11 2009

Here are graphs from the fusion run. The x-axis is time in minutes.

I used google charts to produce these graphs. This code produces the chart from data in mysql. This code transforms the voltage reading to its corresponding instrument value.

I did a quick and dirty downsampling like this:

resamples = samples.in_groups_of(samples.size/number_of_data_points).map{|slice| slice.average rescue 0}

I’m not certain this is all working correctly, but it seems to add up. One oddity: the voltage drops into the negative; perhaps from disabling the high voltage, I’ll have to confirm that.

This is primarily an end to end test of the data acquisition system.

Remote Control

14 11 2009

Now that our Fusor seems to be working, I must operate it from a safe distance. Last night I did the first successful remote run. I connected an iSight to the Fusor mac (G4 running OS X Tiger). Then I used VNC to remote control the Fusor mac from my laptop:


I made headway with the command line program to control the fusor and record data in mysql via ruby. It’s currently setup to record vacuum chamber pressure, voltage and current according to the Glassman, and the effective flow rate of the mass flow controller. Currently I can enter commands to turn the high voltage on/off and set the flowrate of the mass flow controller. Next I want to control the voltage and current on the Glassman.

I also got a geiger counter:


It takes two D batteries. There is a BNC connector for headphones. I have a BNC connector on order with mcmaster. In the meantime I improvised a connection to some computer speakers to test it out. Seems to be working. It picks up the expected background radiation producing that erie clicking sound. You can definitely hear an uptick in the clicks when I run the Fusor.

I’m working towards producing a comprehensive mapping of this device’s performance envelope using computer control to search the parameter space and record the results.

This is all so fun and exciting.

Computer Controlled Sorensen Hack

7 10 2009

Sweet! Just got the high current (120 Amp) Sorensen power supply working with computer control (to power the superconducting magnet).

Here is a video:

Details after the jump.

Read the rest of this entry »

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.

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