#fusionblogging

[archacovercosine]

??????

New fusion startup proposal to transmute mercury into gold by using fusion neutrons. Apparently the correct isotope can act as a neutron multiplier too. ?

[archacovercosine]

wake up honey, another fusion scheme just dropped: magnetic confinement, but in space!

Launch YC: Zephyr Fusion: In-orbit fusion power | Y Combinator

Powering tomorrow's industrial revolution in space

linking the ycombinator (lol) page because their website has even less information

basically, the thinking seems to be confinement time ~ major radius^2, and in space we can use a floating dipole magnet and make the field as big as we want.

notable questions to answer include

- how are you going to capture the power

- where is the power going to even go

- what reaction are they aiming for? this thing has no blanket or anything so sustaining a tritium cycle is definitely not possible.

- isn't all your fuel just going to diffuse out into space

[archacovercosine]

i dont think it understood what i was going for here but this is pretty fun

[archacovercosine]

loll apparently a shot on SPARC costs like 100k (for ~10 seconds of useable plasma).

i wonder how they calculate that, is that just operational costs or is price of the machine part of it?

[archacovercosine]

while doing research into the spherical tokamak limit I also managed to stumble onto an alternative confinement scheme that I was previously unaware of: the spherical tokamak with a plasma central column. So instead of having a magnet to run the current through they have a set of electrodes on the top and bottom of the vacuum vessel and the current runs through a plasma discharge.

this is kind of cursed but also kind of interesting, unfortunately it looks like actual devices using this idea have been fairly limited, but there is one operational right now in Italy called PROTO-SPHERA.

I might have to look more into this idea, it seems to approach a spheromak in a way.

[archacovercosine]

How low can you push an ST aspect ratio from a physics perspective? Supposing we magically solved the engineering problems e.g. with new superconductors that let you make the central pillar way thinner (without giving you a stronger overall field strength)

right, I've finally had time to look this up so.

I am interpreting 'physics perspective' here as macroscopic magnetohydrodynamic (MHD) stability. For confined plasma configurations, this stability is typically determined by the ratio of plasma kinetic pressure (p = n k_b T) to the magnetic pressure (B^2 / 2 mu_0), and this ratio is typically called beta.

Now, it is possible to work out the critical beta that keeps the plasma stable against the most important instabilities (in a tokamak, that is the external ballooning mode). As long as you stay below that critical value, from a physics perspective the plasma shape is stable.

What is nice about the spherical tokamak is that the critical beta scales with the aspect ratio (ratio of major and minor radius), so the more spherical the tokamak is the higher the allowable plasma pressure.

So in a sense, the spherical tokamak is more stable from a physics perspective the thinner you make the central pillar. I at least have not been able to find any plasma physical limits that kick in as the aspect ratio approaches 1.

For the actual derivation behind this, I will have to refer to Freidberg, Plasma Physics and Fusion Energy, but I hope this provides a semblance of an answer.

[archacovercosine]

a stack of helium-cooled lithium-lead pebbles, call that my TBR pile

[half-orc]

sAM EVOLVED INTO IVY SAUR