I’m guessing you’re referring to HL-2M which indeed in testing. But that tokamak is not designed to generate electricity but rather to study long pulse durations (~5s) at reactor relevant temperatures.
Author of that article and plot here. SPARC is projected to have energy gain Q >=2 and potentially up to 11[1]. ITER is projected to achieve Q of >=10[2] so I would guess that SPARC's expected triple product would be in the same ballpark as the projected ITER datapoint, perhaps slightly lower, though potentially the same. We'll see!
Most of the ports are used for diagnostic equipment, things like laser interferometers to measure plasma density or other devices to measure plasma temperatures. Also some ports are used to inject neutral beams for heating.
I’m working on this exact issue. You can view all fusion energy companies here and filter by location.
https://www.fusionenergybase.com/organizations/
You can view each of their funding histories on the company detail page, just click on the company name.
ITER and Commonwealth can (and in my opinion should) be seen as complimentary endeavors.
ITER has been designed with relatively conservative magnet technology and will very likely provide the physics results that need to be understood in order for fusion power to become a reality. This includes experimental tests of the physics of plasmas where the heating is dominated by high energy alpha particles rather than external heating. This is a regime that's not yet been studied in a laboratory and there is important research to be done there.
Commonwealth is pushing the envelope of high temperature superconductor magnet technology and is relatively high risk compared to ITER's magnets (and this is a good thing). Lots of ITER technology will be useful to Commonwealth even before ITER turns on. For example decisions about which low activation steels and the huge amount of physics work that's already gone into planning for ITER.
I think the most likely outcome is that both accomplish their goals and contribute to making commercially viable fusion energy a reality in the future.
The typical design for a fusion power plant that runs on deuterium tritium fuel is to place a lithium "blanket" around the plasma. 80% of the energy released in the deutrium - tritium fusion reaction comes out in the energy of a neutron which would be absorbed in the blanket, heating it up and also generating tritium fuel which could then be fed back in as half of the fuel (the other half being deuterium which is abundant in seawater).
You would then run a heat exchanger from the hot lithium to create steam to then turn a turbine and make electricity.
There is also direct-capture in some fusion designs where the charged by-products are electrically decelerated, producing current. I don't believe this is possible in the standard Tokamak design, but the efficiency gain is a selling point for those designs which do allow it.
That’s right, there are other fusion fuels that have only charged fusion products which could be directly converted to electricity. This is in contrast to deuterium - tritium which releases 80% of its energy in a neutron which has zero charge.
Examples of fusion fuels whose main reaction produces only charged products are deuterium helium-3 and proton boron-11. These reactions however require higher temperatures and better confinement characteristics.
The reason why deuterium tritium is the major focus of most (though certainly not all) research is that it has the highest reactivity at the lowest temperature compared to other fuels. Unfortunately it produces a high energy neutron which makes the conversion to electricity more complex.
Direct capture cannot capture a neutron, as it is not a charged particle. Charged particles are relatively trivial to block with the lithium blanket. Not sure how direct capture could possible be more efficient. Do you have a reference that explains what you are talking about?
There's just the matter of getting the temperature up to 10x of an ordinary D-T fusion plasma. Non-equilibrium reactors like the polywell try to bypass the problem entirely, but (to my knowledge) it's very hard to maintain a non-thermal state.
There are a few reasons why the investment is flowing.
1) New enabling technologies, including high temperature superconducting tape, algorithms for plasma control and diagnostics which take advantage of new hardware (GPUs), and advanced manufacturing techniques are now available.
2) Optimism that private companies can synthesize the past 70 years of plasma physics research with these enabling technologies to develop transformative approaches to fusion.
If you're interested I wrote a short article about this topic a few months ago,
> algorithms for plasma control and diagnostics which take advantage of new hardware (GPUs)
I don't know about that. Here's a few bullet points from [1] (which someone else linked to in this thread; it describes the approach taken by these guys at TAE) that don't inspire a whole lot of confidence:
"Our prior is “reasonable”, but is it really the marginal distribution over all possible plasmas? hahahahhahahaha. We model many effects, but plasmas are complex beasts and we do not model all. We only have one measurement, of much smaller dimension than our unknowns. We never sample from the tails. takes too long to get samples. by definition you can’t really validate them. Will we ever know we’re right about anything? we have zero golden data"
I remember reading recently that a Nobel Prize was won a few years ago for work with chirped pulse laser amplification using titanium sapphire lasers that can apparently achieve nano or microsecond energy pulses in the terawatt range. A potential contender for a non-fission fusion spark, but still does not solve the containment problem. The article says the laser could generate a magnetic field somehow?
And a startup hoping to try it, run by the guy who came up with the idea decades ago: https://www.hb11.energy/
There are several groups doing experiments with it, and it seems to be going really well.
There are two lasers. One hits a target that generates a magnetic field; it'd be hard to describe without a picture but see the articles at the first link. Basically the laser blasts electrons off a metal surface, they hit another surface and flow through a coil. For a nanosecond there's a 4000 tesla field. (An MRI machine generates around 3 tesla.)
The second laser is faster and more powerful: 10 petawatts or more, for only a picosecond. That hits the fuel. It's enough to kick off fusion by itself, but the magnetic containment creates an avalanche effect that multiplies output. Then it all blows up, you harvest the energy and cycle in another target.
Thanks for the link. It is a much more thorough explanation.
How fast is the fuel used up within the field? Would there be a way to inject the actively fusing reaction with a steady fuel input rate for long term generation (neutron bombardment embrittles superconducting metal containment with the D/T reaction, unlike boron encased in supposed laser induced magnetic field?)
I'd imagine this would occur in a sphere (closed and contained). Tokamak designs aren't spheres, but also closed relying on magnetism to push back against a reaction that is pushing out as fusion occurs:
To produce thrust - what if it was a half sphere somehow? Propellant implies ejection of something, and a fusion reaction ball is magnetically interactive, with no radioactive material byproduct? What if a fusion thruster harvested some energy from the reaction to "push" back against an actively fusing pellet feed rate? Could this propel a craft or am I missing something fundamental here?
The magnetic field disappears in a nanosecond, the fuel pellet gets used up, and it explodes, destroying the coil that generated the field. So you just send in another target assembly and fire the laser again, every second or two.
There's nothing wrong with a pulsed system like that. Lots of fusion designs are pulsed. A gasoline generator with an internal combustion engine is a pulsed system too.
Add a magnetic nozzle and you could definitely turn this into a rocket. Thrust would be low but efficiency very high, so it'd be useless for launch but great for long-distance travel.
There is a very general problem with pulsed systems for fusion. The issue is that plasma-facing surfaces are confronted with extreme instantaneous power levels. The depth to which heat can diffuse is proportional to (pulse length)^(-1/2). A nanosecond pulse will deposit heat in a tenth of a micron thickness, or less.
This forces any fusion reactor that uses pulses to have a sacrificial ablative layer on these surfaces that must be renewed (and to deal with the forces from the explosive vaporization of this thin layer). This is problematic if the reactor also requires high vacuum. The scheme for p-11B fusion that this subthread was talking about, for example, has been presented with a direct conversion scheme that uses a megavolt level vacuum capacity. Imagine what happens to such a capacitor when its surfaces flash superheated vapor.
Interesting. But if the direct conversion works, then the magnetic field removes most of their kinetic energy from the charged particles before they get to the walls. All it gets is the x-rays. There has to be some radius where that's no longer a problem. Each pulse in this design would be about 300 kWh; offhand I don't know what percentage is x-rays.
If it's too hard to maintain vacuum, then reverting to a plain ol' thermal cooling could be a backup plan.
A magnetic field leaves the kinetic energy of a charged particle unchanged.
The electric field is supposed to reduce the energy of the alpha particles, but (1) the alphas from p-11B are not monoenergetic, and (2) what is keeping the electrons (that are inevitably liberated in the extremely energetic explosion of the target, the impact of the alphas with the collecting electrode, and photoelectric emission from all surfaces exposed to photons from the plasma) from shorting the whole thing out?
To produce thrust - what if it was a half sphere somehow? Propellant implies ejection of something, and a fusion reaction ball is magnetically interactive, with no radioactive material byproduct? What if a fusion thruster harvested some energy from the reaction to "push" back against an actively fusing pellet feed rate? Could this propel a craft or am I missing something fundamental here?
Mach's principle. Why is there a "preferred" rotational frame of reference in the universe? Or as stated in this Wikipedia article,
"You are standing in a field looking at the stars. Your arms are resting freely at your side, and you see that the distant stars are not moving. Now start spinning. The stars are whirling around you and your arms are pulled away from your body. Why should your arms be pulled away when the stars are whirling? Why should they be dangling freely when the stars don't move?"
The two most obvious solutions to the thought experiment presented are either 1) space is absolute in some way (i.e. the classical Newtonian response) or 2) the behavior of space "here" is affected by the by distribution of matter "over there". General relativity gives us a strong argument in favor of (2) by showing that a) many physical principles thought to be absolute are actually relative and b) showing that mass "over there" affects the shape of space "here".
To say anything more concrete requires requires defining the question much more precisely. I believe there is still some disagreement on the interpretation of Mach's principle in light of general relativity. For example, see https://en.wikipedia.org/wiki/Mach's_principle#Variations_in... (and a couple sections above, the 1993 poll of physicists asking: "Is general relativity with appropriate boundary conditions of closure of some kind very Machian?"
The unsatisfying mathematical answer is that it is impossible to have a uniform distribution of rotational speeds, therefore there must be a preferred one.
It's the same reason the universe has an average speed (unlike what you might expect from special relativity), although it is unclear if this is true for the entire universe or just the portion we can see. We can measure how fast we're moving w.r.t the cosmic microwave background radiation though (it is red-/blue-shifted in a particular direction).
This is an interesting argument! Wouldn't it also work for positions, though? That is, either the universe is finite, or, since there can't be a uniform distribution over an infinite space of positions, there must be some preferred "center" of the universe?
You'd think, but of course we know that not to be the case. It's hard to pinpoint the exact reason though. Sure we know time and space are rather special, but its hard to say exactly why.
In the end though I reckon the most obvious reason is that speed is a property that directly corresponds to energy, therefore for each region of space to have a well defined energy (which is required for e.g. general relativity) every region of space needs to have a well defined distribution of speeds.
I suppose this does leave open a small loophole, as you can easily correlate speed with position in order to get a distribution that is uniform in both (but correlated). But this goes against our assumption that the universe is uniform everywhere (which might turn out to be false, but so far it's holding up well).
