F.I.C.S. Gets Faraday Cage

Pictures du jour here.
Forum rules
This is a good place to put pix of your lab or shop intended to produce the drool reaction. If topics get lengthy here, we may want to move most of the discussion to where it fits in the org scheme here (such as it is). Good place for announcements of things you just got working and so on. Respecting readers who may not have large bandwidth, try and keep the pictures to about one megapixel -- we have the BW and the storage here, no problems, but some readers may not.

F.I.C.S. Gets Faraday Cage

Postby Steven Sesselmann » Mon Jun 11, 2012 4:28 am

Hi Guys,

The last couple of weeks I have been busy with upgrades to the F.I.C.S. reactor. First of all the gas handling system needed improving, the laser drilled orifice with a 5 micron hole, which bleeds gas into the cathode was either too small or clogged, probably the latter, and the system stopped working. I have replaced the leak with a Swagelok 1/4" needle valve. This valve almost leaks too much when closed, but with my 100mm turbo pump, I can still maintain a steady 10 micron pressure by slightly opening the big gate valve. the needle valve can be adjusted via an acrylic rod from a safe distance (trick learned from John Futter).

Unlike a normal fusor, the F.I.C.S. reactor has an exposed cathode and floating gas system, the whole thing was pretty risky, and I was concerned about accidentally touching the components, so I have added a Faraday cage, built from 4.5 mm acrylic sheet and bird wire. This might also shield out some RF and keep my instruments quiet.

Further I have added a National Instruments DAQ, so I can record the pressure, cathode voltage, neutrons and current during my experiments using the simple version of LabView.

There are a few remaining issues that need to be sorted out before I can get on with round two of my experiments.

1) The Gamma High Voltage (RR100-6N) is on the blink, it intermittently cuts out.
2) Need some more Swagelok fittings to connect sample cylinder to main cylinder for filling.

I should get around 30-60 minutes of experimenting from each refill to 2 bar (50cc sample cylinder)

DSCF0206.jpg
FICS Prototype fusion reactor with Faraday Cage



DSCF0208.jpg
Floating gas cylinder with gauge and needle valve.



DSCF0207.jpg
Acrylic rod for adjusting needle valve without getting zapped.



DSCF0195.jpg
LabView DAQ, running on Mac hardware with Windows 7 installed



IMG_0465.jpg
The lower half of two Tungsten hemispheres, being the reaction chamber inside the FICS cathode, note new installation of tungsten mesh over aperture. During operation the mesh gets hot and acts as a thermionic emitter, thereby maintaining a degree of ionization in the beam line, which in turn fuels the secondary ionization inside the cathode.



IMG_0485.jpg
Old stainless steel cathode mesh showing spot where beam focus has burned a 1 mm diameter hole through the mesh.



Steven Sesselmann

http://www.beeresearch.com.au
http://www.beeresearch.com.au....take a difficult problem and find a simple solution!
User avatar
Steven Sesselmann
 
Posts: 24
Joined: Wed Aug 25, 2010 8:41 pm
Location: Sydney - Australia

Re: F.I.C.S. Gets Faraday Cage

Postby Doug Coulter » Mon Jun 11, 2012 9:41 am

This is starting to look seriously good! There's another benefit of the faraday cage (though you might want to make the mesh finer) - protection of the rest of the room from both EMI and just picking up a DC charge from any exposed really high voltage - it can really zap you if you pick up a few kv, then wave your arms (you are a wimshurst machine) and then really get hammered (ask BillF about that one).

Even tiny, current limited arcs can make quite the mess, and ruin your HV supply. I have a 50k ballast on mine - which limits arc events to an amp - at 50kv - that's 50kw and will easily fry nearby laptop computers (they aren't as well shielded as tower cases, but those have their own little problems - all the wires are antennas to bring the nasty stuff into the box). I've knocked out about 3 computers with my setup, but with the cages on the HV - that stopped happening. The risetime on an arc-emi pulse can be very quick, into the ghz and get through wide mesh, FWIW.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: F.I.C.S. Gets Faraday Cage

Postby Steven Sesselmann » Mon Jun 11, 2012 5:47 pm

Doug,

The ceramic ballast resistor you see in the photos (standing upright) is around 8M ohm, this takes the load off the power supply in the event of an arc, and still allows me to run the PSU at its maximum 6 ma. The resistor only gets slightly warm during operation.

Need to get onto Swagelok this morning and order some fittings, so I can complete the gas handling system. I really should have had a another shutoff valve above the needle valve, because the needle valve can not be shut off completely, this means I will waste around 100 ml of gas with each experiment.

Cost of a Swagelok valve vs the cost of wasted deuterium ?

Even at the horrifically high price I paid for my deuterium, 100 ml is only $2.00.

Steven
http://www.beeresearch.com.au....take a difficult problem and find a simple solution!
User avatar
Steven Sesselmann
 
Posts: 24
Joined: Wed Aug 25, 2010 8:41 pm
Location: Sydney - Australia

Re: F.I.C.S. Gets Faraday Cage

Postby Doug Coulter » Tue Jun 12, 2012 9:31 am

Yeah, I paid pretty rich for my D too - knee high (but fat) tank was around $2k, for 5-6 9's pure. For me, it's more the hassle than the cost - they didn't make it easy for me to get the stuff. But I'm only using a fraction of a CC per run here - I do batch mode mostly and even that big tank just doesn't take much to get to an indicated 2e-2 mbar or so. I used these tiny solenoid valves I found surplus, driven off a timer circuit and a pushbutton to let in small increments of gas, and a larger solenoid valve between the turbo (which is idling at 1/4 speed during a run) and the forepump to let out little chunks of gas - it's all discrete, and a little clunky but it works - and zero leaks.

Joe machined some hydrogen type tank valves with different threads so we could put D into those small aluminum oxygen tanks we get surplus for the price of the metal. I put around 300-400 psi into those, and use a two stage regulator (will go below one bar) on the setup - that way a leak or accident can only lose one of those little tank's worth.

If you have to "float" your gas input, things get interesting (an earlier setup of mine did that). Silicone tubing doesn't seem to let D out, but it does let air in slowly, so you lose purity. Ditto teflon and just about every other flavor I tried. I went to pyrex (with a tiny SS capillary glued into one end to control flow) and had a very interesting oops moment. At the time, the length of this tube was several feet, and there were about 2kv between the grounded tank and the other end. Under some conditions after I'd close the D valve - the tube would make Paschen's law happy and I had a purple "neon" tube, which was kinda hard on the ion source power supply, though it was pretty.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA


Return to Eye Candy

Who is online

Users browsing this forum: No registered users and 6 guests

cron