Langmuir Probe Creation and Design

For posts specifically relating to fusor design, construction, and operation.
User avatar
Mike Beauford
Posts: 419
Joined: Wed Apr 25, 2007 6:24 pm
Real name:
Location: Morton Grove, IL

Re: Langmuir Probe Creation and Design

Post by Mike Beauford » Sun Apr 25, 2010 5:00 am

Hi Brian,

My bet is it's the impedance of the power supplies that is causing the curves to be different. I'm wondering if there is a way to massage the data to remove any type of impedance mis-match?

My 2 cents!

Mike Beauford
Mike Beauford

User avatar
Richard Hull
Moderator
Posts: 12277
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Langmuir Probe Creation and Design

Post by Richard Hull » Mon Apr 26, 2010 2:09 pm

I'll go along with Brian on the impedance issue. Like Chris noted, put a large external capacitor across the supply output and do the work. I am with you that the old Kepco might be the correct supply to use here.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

bk8509a
Posts: 40
Joined: Sat Oct 31, 2009 8:47 pm
Real name:

Re: Langmuir Probe Creation and Design

Post by bk8509a » Mon Apr 26, 2010 9:31 pm

Center probing. I'll tell you guys how it goes in a few days.
We're in the process of taking our finals.
Attachments
DSC_8267.JPG
DSC_8257.JPG

DaveC
Posts: 2346
Joined: Sat Jun 30, 2001 5:13 am
Real name:

Re: Langmuir Probe Creation and Design

Post by DaveC » Tue Apr 27, 2010 7:38 pm

Brian -

My question was not so much about what "floating" or "isolated" meant , but how you will or are making this measurement. In other words, How are YOU isolating your power supplies? (That's was behind the schematic request.)

Most low voltage power supplies will bring into the circuit the internal impedances to ground of the supplies. At low plasma potentials, this is rarely a problem. But at multi-kilovolt potentials, a low voltage power supply's insulation resistance will be broken down.

At times this issue is circumvented by using batteries in some sort of insulating housing, long range potential adjustments with plastic rods, voltmeters and ammeters surrounded by corona shields and possibly suspended by monofilament fishing lines, or supported on plasctic cups, ... you know the "good" experimental procedures that Feynmann seemed to appreciate most. (See his comments about experimental work at Princeton vs MIT in "Surely You're Joking Mr Feynmann")

Regarding your latest adventure with measurements at the center of fusor, these will bring the isolation issue into sharp focus, since the ion potentials would be expected to approach HV supply voltages.

So be careful about floating low voltage supplies here, you may breakdown the isolating resistance. A good HV isolating transformer (see one of the earlier threads) would work well to preserve the hardware.

Dave Cooper

bk8509a
Posts: 40
Joined: Sat Oct 31, 2009 8:47 pm
Real name:

Re: Langmuir Probe Creation and Design

Post by bk8509a » Thu Apr 29, 2010 7:50 am

I will have a bigger post on this later. I'm writing my senior thesis right now. Best data yet. I'll let you have your opinions.
Yes, it is repeatable.
Attachments
TemperatureMid.png
Maxwellian.png

Post Reply