SmCo Grid for Deuteron Deflection

For posts specifically relating to fusor design, construction, and operation.
Post Reply
Joshua Guertler
Posts: 107
Joined: Fri Apr 21, 2017 2:59 pm
Real name: Joshua Guertler

SmCo Grid for Deuteron Deflection

Post by Joshua Guertler » Mon Apr 29, 2019 8:13 pm

Greetings,

In the hopes of reducing the amount of collisions that occur between my grid and the incoming deuterons, I have been searching fusor.net and other sites for potential manners to optimize grid transparency and deflect 40 keV deuterons.

After doing so, I came across a few sources, one of which included an old post by Jeroen Vriesman back in 2015 (see here: viewtopic.php?f=18&t=10265&p=68448&hilit=SmCo#p68448).

In the post linked above, the OP talks more about how he desires to use this for reducing the current pull of the fusor. However, it has occurred to me that the magnetic field produced by the magnets may be used to deflect the trajectories of deuterons in the slightest fashion to reduce collisions with the grid.

Thus, I propose that a typical grid configuration comprised of two loops made of nickel-coated samarium cobalt may be used to reduce collisions with the grid. The new grid would be made up entirely of this SmCo magnetic material (beyond the nickel layer), thus, the high voltage would be applied to it. The grid would look somewhat like the item below:
fusor grid.jpg
I am considering this design for my magnets, but perhaps without the center/equatorial ring.
fusor grid.jpg (12.95 KiB) Viewed 3617 times
The apparatus that I am using has a -40 kV 400 W power source (the likes of which are still being modified). The magnetic SmCo grid will have an outer diameter of 1.25” and shall be placed in a stainless steel hemisphere of a 6” outer diameter. At the moment, I am not planning on using an ion gun, but its addition may prove tempting in the future.

If I succeed in getting this grid operational, I am planning to move onto more geometrically transparent designs (such as those modeled by the University of Wisconsin-Madison). Thus, I will be able to determine if the use of magnetic materials (SmCo magnets) are able to decrease the number of collisions with the inner grid wires.

Thus, I was curious if the individuals on this forum (who are far more experienced and knowledgeable on this topic than I) have any input on my design and whether or not the use of magnets would do any useful work to prevent deuterons from colliding with the grid.

If it happens to be that my proposed magnets are of no use for deuterons deflection, I was curious if they might be useful for some other purpose (i.e. decreasing current draw). Thank you.

Sincerely,
Joshua Guertler

User avatar
Rich Feldman
Posts: 1138
Joined: Mon Dec 21, 2009 11:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

Re: SmCo Grid for Deuteron Deflection

Post by Rich Feldman » Tue Apr 30, 2019 4:12 am

Interesting idea, Joshua. Reminds me of original polywell fusors (?) with ring-shaped electromagnet coils inside.

Issue 1. How do you propose to orient your permanent magnets? All north poles up? All north poles away from the sphere center? Each arc magnetized along its length, or transversely in the plane of the spherical surface?

How will the resulting static magnetic field be oriented in space outside the magnets? How is it supposed to deflect moving ions away from hitting the grid? Do you understand the basic f = q times (v cross B) formula for force on a charged particle in a magnetic field?

There's an inherent magnetic field from the HV current in any fusor, but its magnitude is negligible compared to, say, the geomagnetic field, or the weakest intentionally permanent magnets.

Issue 2. How do you propose to cool the grid, to keep high energy magnetic materials from overheating? SmCo is much more tolerant than NdFeB, but its useful temperature range is all lower than the useful temperature range of ordinary soldering irons.
Mike echo oscar whisky! I repeat! Mike echo oscar whisky, how do you copy? Over.

User avatar
Trent Carter
Posts: 23
Joined: Tue Dec 20, 2016 8:38 pm
Real name: Trent Carter
Location: Melbourne, Florida
Contact:

Re: SmCo Grid for Deuteron Deflection

Post by Trent Carter » Wed Sep 04, 2019 9:18 pm

The concept wont work, but you should still do it as you will learn a lot. Major scientific advancements were the end result of experimentation without merit. Heck Nikola Tesla did not even believe in electrons!

1. Your SmCo will get very hot very quickly and will reach the point where its dipoles can flip on their own, resulting in magnet-no-more
2. The SmCo will trap the plasma in pretty plasma rings. Take some pics, it will be cool, but wont last long. See (1)
3. The Deuterons wont deflect much while traveling quite a handsome chunk of the speed of light, accelerated by your 40keV. However your electrons at 1/4000 the mass of the p+n will deflect more. However electrostatic forces are already in your favor there.
4. If you switch to a 2D cathode then you could use an external helmholtz coil to reduce the electrons hitting the chamber by turning them in the B field, much like a magnetrons magnets. You could do some research there. But does not fit your theory.
5. Most commercial / research grade fusion devices uses magnets. Mostly electromagnets, even more often high temp superconductive ceramics at >> Teslas, but its a start.

Good luck

Trent

John Futter
Posts: 1451
Joined: Thu Apr 22, 2004 2:29 am
Real name: John Futter
Contact:

Re: SmCo Grid for Deuteron Deflection

Post by John Futter » Thu Sep 05, 2019 8:05 am

Trent
Protons deuterons do not get anywhere relativistic with 40kV acceleration
from memory when i did work this out years ago somewhere around 1000km/sec
all of this due to the difference between electron mass and amu mass

User avatar
Trent Carter
Posts: 23
Joined: Tue Dec 20, 2016 8:38 pm
Real name: Trent Carter
Location: Melbourne, Florida
Contact:

Re: SmCo Grid for Deuteron Deflection

Post by Trent Carter » Thu Sep 05, 2019 10:23 pm

Yes, 1% is not "near" C, however its way too fast for a magnet to have much affect. I had to make a quick XLS on this, as I recalled it being around 50% of C, but that was an electron at 40keV. I stand corrected.

Correction: I used the mass of a proton, obviously the Deuteron is just over 2x the mass of a proton. So more like 0.65% C. updated image below
Screen Shot 2019-09-05 at 7.39.23 PM.png
Screen Shot 2019-09-05 at 7.39.23 PM.png (99.56 KiB) Viewed 776 times
Last edited by Trent Carter on Thu Sep 05, 2019 11:41 pm, edited 2 times in total.

User avatar
Rich Feldman
Posts: 1138
Joined: Mon Dec 21, 2009 11:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

Re: SmCo Grid for Deuteron Deflection

Post by Rich Feldman » Thu Sep 05, 2019 11:03 pm

Let's do a SWAG without looking up any coefficients on the Internet.

Rest mass of electron is about 500 keV. Proton is about 1800 times more massive (900 MeV); deuteron is twice that.

Velocity of deuteron with kinetic energy of 40 keV:
m * v^2 / 2 = 40/1800000 m * c^2.
v^2/c^2 = 4/90000 = 1/22500
v/c = 1/150
v = 2000 km/s. Nice how the answer is a round number. 2 mm per nanosecond.

An electron at 40 keV, neglecting relativity, is 3600 times less massive, so 60 times faster.
v/c = 0.4.
v = 120,000 km/s. In a nanosecond it travels 120 mm, comparable to the scale of our fusors.
The correction for relativity, in the electron case, is on the order 8%. (ratio of kinetic energy to rest mass)

Now who wants to figure the radius of gyration in a magnetic field?
A starting point could be the numbers for a cyclotron, for someone who remembers the values.
Size, field strength, and particle energy.

As I warned Joshua, I think the temperature and magnet strength problems are not as fundamental as the geometric issues, for what he wanted to do. Trent had some specific suggestions along those lines.

[edit] 40 keV deuteron has same curve radius as 80 keV proton.
10 times smaller than in a cyclotron delivering 8 MeV protons or 4 MeV deuterons.
I figure radius of about 2 inches at B = 1 tesla, which is a much stronger field than Joshua's magnetized grid can produce in a space of that size.
Trent, want to check my numbers? I was surprised at the roundness of the answer (when given in inches).
Mike echo oscar whisky! I repeat! Mike echo oscar whisky, how do you copy? Over.

John Futter
Posts: 1451
Joined: Thu Apr 22, 2004 2:29 am
Real name: John Futter
Contact:

Re: SmCo Grid for Deuteron Deflection

Post by John Futter » Fri Sep 06, 2019 9:12 am

thanks Rich
i'm out by a factor of two

not bad for an old git who did a few calcs 25 + years ago while designing implanters with mass selection magnets

User avatar
Trent Carter
Posts: 23
Joined: Tue Dec 20, 2016 8:38 pm
Real name: Trent Carter
Location: Melbourne, Florida
Contact:

Re: SmCo Grid for Deuteron Deflection

Post by Trent Carter » Sun Sep 08, 2019 12:17 am

Mr Feldman; sure I will check your numbers...

I get 1.61 Inches. ...but pretty close to 2.

Magnetic forces apply a centripetal force F=mv^2/r. Then F=qvB
qvB=(mv^2)/r
r=mv/qB
v=Speed m=Mass q=Charge B=Magnetic field strength

Static:
Deuterium Mass: 3.35E-27
Deuterium Charge: 1.60E-19
Voltage: 40kV
B Field: 1 Tesla

Calculated:
Velocity: 1.96E+06
Radius: 1.61 In (40.912mm)
Screen Shot 2019-09-07 at 8.15.13 PM.png

Post Reply