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Creating a neutron source

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klugesmith

Thu Dec 13 2012, 03:25AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Andy wrote ...
This is the formula I'm using
B = unI
permeability =1
Amps =10000
number of turns =10
distance =0.01
amp turns =10000000
Tesla =40000

and
F = Amps*Length*B
Amps 50000
distance 0.01
Tesla 40000

Force newtons/meter 20,000,000

Are these the right formulas to use in these situation, what would I be missing?
I'm trying to squash the arc, with the coil current going clockwise and the spark field going counter clockwise. ...

Hi Andy. First a couple of basic questions. Why do you want to make neutrons? What makes you think you have ideas that 1) will work and 2) have not, as far as you can tell by cursory searches on the Internet, already been developed by others?
As people keep telling you on fusor.net: Your ideas are flying high, but you need to put boots on the ground. Learn more about physics and electricity. If you are not in a position to learn them in a classroom, you can teach yourself using the Internet. Then get some adult supervision, and build and measure a basic subsystem such as a vacuum chamber or high voltage power supply. It looks like you're off to a good start.

Now about your first calculation.

We can't read your mind, but you started with the formula for magnetic flux density B inside a "long" solenoid -- one whose length is >> its diameter. For the lineal winding density n, are you using 10 turns per 0.01 meter, with current I of 10,000 amperes? Then where did 10^7 ampere-turns and 40,000 teslas come from? 10^7 amperes per (lineal) meter, I could understand.
In SI units, the permeability of free space u0 is 4*pi/10^7 teslas per (ampere/meter). So I figure about 12.6 teslas (that's 4 * pi), a pretty respectable magnetic field. If the coil length is 1 cm, its diameter should not exceed 2 to 3 mm if you want to satisfy the "long" condition of the B=unI formula.

As an exercise for you: for how many microseconds can a 1-mm-wide copper wire carry 10,000 amperes before it overheats? You get to choose the other dimension of wire cross-section, and the maximum temperature rise. Let's compare your 1E7 amperes/meter with the linear current density in world-class Bitter solenoids, which exist in a few research labs. With state-of-the-art water cooling and mechanical restraint, and multi-megawatt DC power supplies, they can run at around 3E7 A/m, and sustain B values between 30 and 40 T.

No time to get into your question 2, except: Please clarify the orientations of your B field and your plasma current density field.

p.s.
When talking about those formulas, please don't get in the habit of casually interchanging
the names/symbols of constants or variables, with the names/symbols of units of measurement.
Are 250 and 6-8 LeBron James's pounds and feet and inches, or his weight and height?
Are 98.6 and 37 our normal body degrees F and degrees C?
We say "current = 10 kA", not "kA = 10". One appears naturally when working out a formula; the other does not. I have tried to make a good example in this spreadsheet:

Unfortunately, there is one near-exception that can lead newbies astray.
It's popular, in fact practically universal, to use the word voltage (and symbol v or V) for the thing that is measured in volts (V).

Good luck!
[edit] I see you posted a nice drawing while I was writing this tome. I have some issues with it.
1) the B fields from the two wires labled "coil" will cancel each other along the line you have labeled "spark".
2) If the "coil" wires are part of a helix then their current is oriented along the circumference of the enclosed space. Why will spark current have any component with that orientation? I think you need to study Z-pinch (and perhaps theta-pingh) some more. Hint: dB/dt.

Andy

Thu Dec 13 2012, 04:18AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Cheers for the infomation

Hi Andy. First a couple of basic questions. Why do you want to make neutrons? What makes you think you have ideas that 1) will work and 2) have not, as far as you can tell by cursory searches on the Internet, already been developed by others?

I was trying to follow the z pinch theroy, but instead of useing 100 thin wires ,A spark would be the wire(repeatable). I saw the pinch Mark Rowley on fuser.net had, and was duplicating it, but wanted to know if it could fuse D. The neutron source was for a isotope battery.

We can't read your mind, but you started with the formula for magnetic flux density B inside a "long" solenoid -- one whose length is >> its diameter. For the lineal winding density n, are you using 10 turns per 0.01 meter, with current I of 10,000 amperes? Then where did 10^7 ampere-turns and 40,000 teslas come from? 10^7 amperes per (lineal) meter, I could understand.
In SI units, the permeability of free space u0 is 4*pi/10^7 teslas per (ampere/meter). So I figure about 12.6 teslas (that's 4 * pi), a pretty respectable magnetic field. If the coil length is 1 cm, its diameter should not exceed 2 to 3 mm if you want to satisfy the "long" condition of the B=unI formula.

The 10^7 were amp turns/meter. I didn't know the coil had a length to diameter function, I was planning to have 1cm length, and a diameter of 30cm radius to maximize the area for inductance. I will had 12.6 Tesla to the equations.

The heat thing , 1mm wire 20.95ohms/km for ten meters 0.2095ohms. P = I^2*R ,20950000 watts/second . Copper specific heat is 386. 20950000/386 = 54274/50gram = 1085 C/second

klugesmith

Thu Dec 13 2012, 06:40AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Andy wrote ...
The 10^7 were amp turns/meter. I didn't know the coil had a length to diameter function, I was planning to have 1cm length, and a diameter of 30cm radius to maximize the area for inductance. I will had 12.6 Tesla to the equations.

I think you'll like this reference.

Magnet formulas for many configurations, including a current loop (which is like the coil you describe). Also, beware that common solenoid inductance formulas may have large errors for your ultra-stubby aspect ratio.
I think your plan is original and unique to employ "a diameter of 30cm radius".

Andy wrote ...
The heat thing , 1mm wire 20.95ohms/km for ten meters 0.2095ohms. P = I^2*R ,20950000 watts/second . Copper specific heat is 386. 20950000/386 = 54274/50gram = 1085 C/second

You will go far, young man. But I think your heating rate answer is too low by a factor of 1000. Perhaps the specific heat value is for kilograms, while the wire mass is in grams. The unit for P is not watts/second, it's watts. Same as joules/second.
Time to learn how to use a spreadsheet calculator. It makes it easy to document and review calculations like that, and very easy to tweak the variables. Dedicate a column for the units of measurement. And don't mix unit-conversion formulas (even kg to g) with physics formulas -- use separate cells.

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