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Comment: Re:Mills Mess (Score 1) 59

by hattom (#42371953) Attached to: Juggling By the Numbers

It's what happens when a long story about the original motivation for him wanting to develop a method (a story which does indeed feature mills mess) gets edited for an article.

I guess you could say that mills mess is what started him thinking, and by the time he'd got something simple and usable out of the idea - it was no longer about where the throws were made (eg mills mess), but when/what they're made (eg siteswap).

So of course, siteswap has nothing to say about mills mess - but that should explain why it's mentioned in the article at all.

Comment: Team Shreddie Crunch (Score 1) 59

by hattom (#42371283) Attached to: Juggling By the Numbers

http://juggling.tv/12550 - Team Shreddie Crunch 2

A great sample of mainly siteswap and numbers juggling by some of the British best technical ball jugglers. (Link to the more recent video).
There are plenty of good examples out there, but this is one of the best.

Disclaimer - I'm friends with most of these guys, just lucky enough to have lived in the part of the world with the possibly the highest concentration of technical jugglers.

Comment: Re:Extracting the heat (Score 1) 318

by hattom (#39445383) Attached to: Ask MIT Researchers About Fusion Power

Fusion creates incredibly high energy neutrons, which are unaffected by the magnetic field, that pass through the plasma, heating it slightly, and leave the plasma.

The solution is (as many have said here already) to create a blanket of lithium around the device, and for the neutrons to pass into* the blanket, collide with the lithium, and cool down. This heats the lithium as well as breeding tritium fuel. The heat in the blanket is passed to create steam at a heat exchanger, steam powers turbine... electricity.

*creating the steel to hold the blanket in place without it becoming too damaged by the neutrons is also tricky.

Comment: Re:NIF (Score 1) 318

by hattom (#39445265) Attached to: Ask MIT Researchers About Fusion Power

If they can do what they can currently do once (last I checked) per day 100 times per second, yes. Its research is interesting plasma physics, interesting laser physics, and transferable in many cases to other fields - but an electricity generator NIF is not.

It does do a very good job of nuclear weapons research given a ban on testing though.

Comment: Re:Scaling of Tokamaks (Score 2) 318

by hattom (#39445221) Attached to: Ask MIT Researchers About Fusion Power

I think fusion reactors scale somewhere like r^4 in terms of Q value. As size increases, confinement time increases, and given the temperature and pressure gradients that can be sustained, the core temperature and pressure can increase.
I can't prove that it's r^4, but I'm sure I remember it being approximately r^4 or maybe r^3 (or somewhere between the 2).

With regards D-D/D-T, when tokamaks such as JET, MAST, ITER and the like run with deuterium, their aim isn't to allow fusion. So a typical deuterium Q value would be 0 or very close to 0.

The reason is that getting deuterium and tritium to fuse isn't the difficulty - so it's not something they have much need to practise. Working in a purely deuterium mode provides the same plasma physics challenges - but without the added difficulty of using tritium (for example, once a tokamak has had tritium in it, human access to the machine is very strictly limited).

With all that's learnt using deuterium and tritium, if a machine such as JET goes for a D-T campaign as it did in 1997, and another campaign was considered recently, then it gives a data point to show performance, proves that progress has been made, and may be useful if they were interested in studying ash (helium) in the plasma.

Studying effects of neutrons is usually done elsewhere - leaving a sample in a source of neutrons for long periods of time (such as in a fission reactor), although a Component Testing Facility is planned in the longer term to expose components to high energy neutrons (14MeV is much higher energy than neutrons in fission).

So not a huge amount is to be gained by running D-T regularly.

Comment: Re:The talk is always about break-even with fusion (Score 1) 318

by hattom (#39441945) Attached to: Ask MIT Researchers About Fusion Power
It was removed from the initial ITER specification to save money (and that it would only serve for PR / demonstration purposes) and improve access to the machine. Unless they've added it back in in the last year. They will however do this on DEMO, and potentially add one later to ITER.

Comment: Re:What could you do with unlimited resources? (Score 2) 318

by hattom (#39441817) Attached to: Ask MIT Researchers About Fusion Power
I was told that a similar question was asked of someone in the UK fusion programme about 2 or 3 years ago by the director. The guy went away and did some sums to answer the question: Given the money to build it now, how well could a fusion plant be constructed, and what would be the cost of electricity produced. His answer was something like as follows: To build a power plant now would require working around the current problems (such as ELMs) by creating a machine to run in L-mode (low confinement mode) rather than H-mode (ELMs only occur during increased-efficiency H-mode) and so creating it much larger than it should need to be - therefore it can be run at low power, "easy", and low risk* mode, ie run a large machine incredibly conservatively, which isn't incredibly efficient. The cost per kilowatt hour for the lifetime of a machine would have been about 50p (~80cents). So an improvement of ~10x would put it viable. And given the conservative nature of the machine calculated, that's not far away (running in H-mode would make a large difference for example). On the other hand, to put ICF's recent claim that they will beat ITER into perspective, I believe that at NIF they are currently firing the lasers maybe once per day, then replacing the inner optics between each shot, and carefully placing and targetting the ~millimetre target between shots. I think the point at which they reach viable fusion is 100 times per second. Last I knew they were awaiting the invention of a solid state laser capable of achieving their requirements - which was by no means on the horizon. To reach ~100 times per second, the target would need to be fired into the chamber at ~100m/s, and then still be hit by all 192 beams simultaneously on the millimetre scale target. Then again, NIF's goal is really for studying nuclear weapons. If they've made progress recently, and are closer than I think, then I'll be pleasantly humble, but ICF's wild claims that they'll do it this year don't go far to dissuade the outside view of scepticism towards any claims about how far off fusion may be. Said claims haven't been helped by the delay of 20 years over the building of ITER. So when people say "20 years is up, where's fusion?" in reality 20 years ago MCF researchers were waiting for the same thing they're now waiting for. In the last 20 years much has been learnt, understood and improved... but it's still the same 20 years away as it's still the same machine away. On an aside, the probably problem was that in the 50s or thereabouts, someone performed the calculation to see how big a reactor would need to be to break even according to the Lawson criterion. It was relatively tiny, order 0.5-1m (I don't remember exactly). At this stage they figured that 20 years should be enough. In the next 20 years, turbulence was found to be more than "something we might need to account for" and in fact it's the main heat transport mechanism going on in a hot plasma. Then it was found that larger machines were needed, and from that last 50 years, ITER should be painfully close to finishing the work (some argued that ITER should have spent a little more to include lithium blankets needed for extracting energy and breeding tritium - which would be great for PR to show that it could put energy out to a grid... but extra cost, reduced access to the machine for improvements and essentially no benefit. That should be the purpose of DEMO (the next machine after ITER - a demonstration powerplant)). *risk of not working/elms/disruptions, not risk to people.

Comment: Re:Helium 3 (Score 1) 318

by hattom (#39441377) Attached to: Ask MIT Researchers About Fusion Power
D-T (deuterium-tritium) has a larger reaction cross-section that He_3 + H. And given the vast abundance of deuterium (a bathtub of seawater contains a human's approximate lifetime energy suppy of deuterium for fusion) and the availability of lithium (a laptop battery likewise for lithium (and hence tritium)). So I can't see why you would suggest helium-3 at all. On the subject of breaking even JET got close to break-even in 1997 - the last time it tried. It's known that D-T reactions can be done on JET, so no additional plasma physics is learnt during D-T reactions that isn't learnt during D-D experiments. The only difference is that D-T produces fusion power, looks great in the press, but irradiates the tokamak, which on a constantly upgraded research machine, is rather impractical. If JET performs another D-T spell soon as was recently stated, then it's likely that it will beat break-even. Of course that's thermal power output, electrical conversion isn't fitted on JET, but thermal efficiency is expected to scale with R^3, hence the 20+ year need for a machine larger than JET.

Polymer physicists are into chains.

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