sballin

Joined 8 years ago

Karma

Submissions

Member since

Nov 27

Recent submissions

Fusion grad student here. HL-2M is very similar to the US DIII-D reactor in size, magnetic field strength, and plasma current. HL-2M will have 11 MW of heating power in its first stage compared to 23 MW on DIII-D according to Wikipedia, though this will likely be upgraded. But consider the fact that DIII-D was built in 1986.

JET, currently operating in the UK, is the tokamak closest to producing more fusion power than absorbed heating power. It would be a nice surprise if it achieved this in its upcoming research program using deuterium-tritium fuel. But to reliably pass this milestone and get closer to producing electricity, we need to build tokamaks bigger, like ITER, or with a stronger magnetic field, like SPARC. Neither one will produce electricity, but they will allow us to study the potentially different plasma environment and materials issues at high fusion power.

Electricity-producing tokamaks are in the extremely early conceptual design phase (DEMO, ARC) and will require much more research on tritium breeding and materials that can withstand insane levels of heating and irradiation.

HL-2M specs (paywalled): https://doi.org/10.1016/j.fusengdes.2015.06.106

Comment · 7 years ago

If you have Alfred, you can sort of do this with an extension I made: https://github.com/sballin/alfred-search-notes-app

The default search looks for folder names too, so searching "[folder name]" will bring up all the notes in that folder, and "[folder name] [note name]" will bring up the specific note in that folder, as of the latest commit a few minutes ago :)

Comment · 7 years ago

I'm a PhD student studying turbulence at the outer edge of plasmas in fusion experiments. Turbulence degrades plasma confinement, which makes it difficult to keep the plasma burning and produce power. I'm interested in whether different machine designs or operation procedures can help reduce turbulence.

At the moment I'm analyzing data from W7-X in Germany. It's a really cool device off the beaten path of tokamaks but seriously catching up in performance [1].

[1] See fig. 15 of https://iopscience.iop.org/article/10.1088/1361-6587/aaec25

Comment · 7 years ago

The fast ion loss probe used in fusion energy research is relevant to your last point. See figure 1 of [1], or if you have access see [2] for a good explanation.

[1] https://w3.pppl.gov/~szweben/Papers/coauthorpapers/DarrowRSI...

[2] https://aip.scitation.org/doi/pdf/10.1063/1.5039311

Comment · 7 years ago

East of Eden (John Steinbeck) is one of my new favorites of all time. Once you get past the opening descriptions of valleys and farms, the story is relatable, gripping, and unexpected.

Comment · 8 years ago

I'm not the expert on this, but I was curious so I looked into it a bit. I don't believe it required significant resources or crazy algorithms, but a clever selection of physics criteria to optimize. It was a ~20-dimensional Neumann boundary value problem [1], and a code named NESCOIL was used to figure out the shape of the coils that would produce the required magnetic field [2], which it did using Fourier series.

By the way, the unusual shapes of the coils can be understood intuitively from this picture: https://imgur.com/a/Bq3ABfQ. A plasma needs to be confined with a magnetic field in order to be heated to extreme temperatures, and a toroidal field (produced by the currents in the red coils) is unstable due to particle orbit drifts. You need to add a twist to the field for it to be stable (using the green coils). But if you unroll the surface of the torus, you can approximate the currents in both green and red coils using the discrete blue coils, and they're easier to build.

[1] https://aip.scitation.org/doi/abs/10.1063/1.860481 [2] http://iopscience.iop.org/article/10.1088/0029-5515/27/5/018...

Comment · 8 years ago

I guess the word pinhole is misleading here, I think it's a few cm in diameter. Behind it there's an array of lenses that projects the view onto a fiber bundle, then a lens at the other end of the bundle projects that view out. That light goes through a beam splitter which shares it between our camera and another one in the shielding box.

Most imaging in fusion is done like this because of space constraints, magnetic fields, and neutron fluxes.

Comment · 8 years ago

I operate a fast camera at W7-X. It's a normal high-speed camera that records light in the humanly visible range, and the plasma emits in that range and reflects off the walls. IR cameras are most often used to gauge the temperatures of vessel wall components.

Our camera looks through a pinhole in the vessel wall, but it sits a few meters away from the machine and gets that view through a bundle of optical fibers. There wouldn't be enough space to place the camera right at the pinhole because of the magnets and their cooling systems, and the magnetic fields would be pretty high. The camera needs to be shielded from the fields for its electronics to work properly, and the shielding box perturbs the magnets' field, so moving the camera far away is a good idea. We don't worry about neutrons, because W7-X plasmas are fueled with stable helium and hydrogen (no deuterium or tritium so far, mainly due to onerous nuclear regulations in Germany), and these fuels don't produce many neutrons at all.

Comment · 8 years ago

Here's a source, unfortunately paywalled, from 1989: https://www.tandfonline.com/doi/abs/10.13182/FST90-A29178

I do research at W7-X, so I can confirm that to the best of my knowledge, the design was computed a long time ago. Building the actual device took a while.