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Comment Re:Are Tokamaks practical? (Score 1) 318

ITER's baseline operating scenario (fairly conservative, known regimes etc) is for Q=10, i.e. 10 times as much fusion power produced as input externally for 400 second shots, quite a large positive return. More advanced scenarios aim for Q=5 but running continuously. Of course none of this fusion power will ever go into the grid; ITER is an experiment, and will only have test blanket modules, and no steam turbines. Once operation with a "burning" plasma (where most input energy is coming from fusion) has been demonstrated, blanket modules and divertor designs tested, the next step planned is a demonstration power plant DEMO.

Comment Re:lower limit on tokamak design (Score 1) 318

Yes. The lower limit to transport in a tokamak is given by "Neoclassical" transport, which is what you get assuming all turbulence has been suppressed. Assuming current magnetic field limits of a few Teslas (above which most superconductors stop being superconductors, and the forces on coils become enormous), and that the temperature is around the peak cross-section for D-T fusion (about 10 keV, or 100 million oC), this gives a minor radius of a meter or so for fusion ignition. The Joint European Torus (JET) has a toroidal field of around 3-4 T, and a minor radius of about 2m. Assuming all turbulence could be suppressed, JET would probably ignite.

Comment Re:Capture the Energy Produced? (Score 5, Informative) 308

Actually the front-end optics in NIF are usually replaced after each shot using modular Final Optics Assemblies, because debris from the exploding pellet and hohlraum is deposited onto surfaces. In a fusion reactor the optics would also need to withstand the flux of 14 MeV neutrons, without degrading excessively. Besides this there are several major hurdles to overcome in turning NIF's (impressive) performance into a source of power:
  1. The definition of "ignition" here means laser energy onto target vs. fusion power out. Current laser technology is not efficient enough at the high powers needed for ICF. It's still meaningful because in laser fusion the target physics is largely separated from the lasers so once the principles work an improved laser can be developed.
  2. The glass lasers used in NIF need to cool down for several hours between firings, whereas in a power plant the lasers need to fire at 10-15 Hz. High-power solid state lasers need development.
  3. The indirect drive scheme used in NIF is too inefficient to be used in a power plant. NIF uses a hohlraum to create a uniform implosion, but the conversion of laser energy to x-rays on the target is only a few percent.

I've been around NIF and it is an amazing machine. It's also designed (and funded) to study warm dense matter physics like equations of state at high density for nukes, not fusion. Use of NIF for fusion is a great side-benefit and hopefully they can get useful data from it.

The HiPER project to design a fusion reactor based on fast ignition has been though an initial concept design phase, but is now waiting further development. There is still a lot of research which needs to be done in target physics, lasers, and materials before ICF is ready to build an ITER-like machine

The physics behind the ITER tokamak on the other hand is quite well understood at this point. Sure there are outstanding issues which are still being worked on (ELMS, divertor detachment, RWM control spring to mind) but we're pretty confident it will work. The design of ITER started in 88, and before that the INTOR project in '78, but it has taken a long time for politicians actually put some serious resources behind it. Hopefully it won't take that long for ICF projects like HiPER to be taken seriously and funded at a level which will make them happen

Comment Re:yet more biblical contradictions (Score 1) 916

When you say "know", you must be using a very low threshold for proof. Personally I'd take a claim that someone lived for 1000 years as a very good reason to doubt the source, rather than something interesting to be taken as fact and explained. The simplest explanation seems to be that it's a fairy tale told by bronze-age parents to their kids

Comment Re:Rephrase: Politicians should never make laws (Score 1) 214

The different ancient Greek states had quite different systems, but variants on the Athenian one were common:

Membership of assemblies was either by lot (similar to jury duty now), or consisted of those who wanted to be there (sort of like a parish council I guess). Public offices were often allocated by lottery from a pool of people who nominated themselves. From the wikipedia article:

Selection by lottery was the standard means as it was regarded as the more democratic: elections would favour those who were rich, noble, eloquent and well-known, while allotment spread the work of administration throughout the whole citizen body, engaging them in the crucial democratic experience of, to use Aristotle's words, "ruling and being ruled in turn" (Politics 1317b28–30). The allotment of an individual was based on citizenship rather than merit or any form of personal popularity which could be bought. Allotment therefore was seen as a means to prevent the corrupt purchase of votes and it gave citizens a unique form of political equality as all had an equal chance of obtaining government office.

Whilst there are good things about this system, I'm not 100% sure it's preferable to the current system. At the time it was criticised for allowing the many to tyrannize the few (mainly the rich).

Comment Re:Monarchy is an abomination. (Score 1) 456

Whilst I generally agree with this sentiment, there are aspects of constitutional monarchy (e.g. in the UK) which are very useful. The main one is to separate the head of state from the head of government: the king/queen has little to no power in practice (though may do in theory), but is a figurehead. This means people can criticise the head of government (prime minister) without appearing unpatriotic. This in contrast to presidential systems where the head of government is also head of state. Having a monarchy (and institutions like the Lords) is a little odd, and ideologically not very democratic. In practice though it has some good points, and seems to work well enough most of the time.

Comment Re:Ok (Score 3, Interesting) 221

Wholeheartedly agree that for trains and walking / cycling would be an excellent alternative. I own a car, but haven't driven it for over 6 months as I simply haven't needed to: walk to work (20 mins each way), walk or cycle to the shops and take the train for longer journeys.

Whilst driving can be enjoyable, there is nothing fun about motorway (freeway) driving. For long distances I'd much rather be in a train where I can walk around, stretch my legs, have a table to do some work on, even use Wifi on many of them. If I need a car where I'm going, hiring one at the other end is often pretty cheap.

Unfortunately, this is possible because I live close to the middle of town within walking distance of public transport. The dreams of living in bigger houses with individual transport far from the unwashed masses which the GP seems to object to, have lead to sprawling suburbs where it's almost impossible to walk anywhere. Either it's simply too far or because the planners assumed everyone would drive and made pavements (sidewalks) which end in 4 lane highways.

The options are then pretty limited: develop better, greener individual transport, or large-scale demolition and rebuilding in higher density areas which can be served more efficiently by public transport. Don't think the second one's going to be all that popular...

Comment Re:Why not Bussard's fusion reactor? (Score 1) 387

Calling the designs "failed" is a bit harsh considering the enormous progress that has been made since the '50s. Currently operating tokamaks and stellarators were never meant to produce significant fusion power (otherwise they'd run with D-T, rather than D-D). They are purely research devices intended to understand the physics of magnetic confinement: it was found that as soon as plasmas became hot enough for significant fusion (~10 keV, 100 million degrees C) then a whole new range of energy loss mechanisms appeared. Understanding these and optimising the designs to the point where a large scale reactor (ITER) can be built has taken a huge effort. The measure of reactor performance, the achieved triple product (density)*(temperature)*(confinement time) in tokamaks has doubled around every 12-14 months historically, hardly slow progress. Whilst Polywells are an intriguing design, they are far from being proven: from the wikipedia article "Bussard had reported a fusion rate of 109 per second running D-D fusion reactions at only 12.5 kV (based on detecting a total of nine neutrons in five tests...". I submit that 9 neutrons in 5 tests is hardly strong evidence to base a large scale reactor on. There will be many problems to overcome in turning this into an actual reactor. Off the top of my head:
  1. Scaling up will almost certainly lead to additional loss mechanisms. Hotter plasmas have more free energy, and tend to have more violent instabilities which need to be controlled. Extrapolating too far from existing machines is a dangerous game, as ITER is finding in some ways.
  2. Bussard seems to claim that the thermalising Coulomb collision rate is small, and so Bremsstrahlung losses will be small. If you want high fusion rates then high density is needed, at which point I'm not sure I believe this one
  3. Neutron shielding the magnets and electrodes. If you have a power plant producing lots of neutrons then these do terrible things to conductors (turn them into insulators, structurally weaken, expand) and to superconductors (stop superconducting). In ITER and any tokamak power plant, all the magnets have to be behind lots of shielding blankets. How this could be done for electrodes I'm not sure. Not saying it's impossible, just that it needs to be shown.

In short, yes Polywells are an interesting design along with many other alternative fusion reactor designs (stellarators being most advanced, but also spheromaks, gas dynamic traps etc.). They're worth investigating, but as yet the only devices which have demonstrated long operation (minutes to hours in Tore-Supra) at fusion-relevant temperatures (10s of keV) and significant fusion power output are tokamaks. Hence why this remains the main direction of research.

Comment Re:How about glass (Score 1) 321

I think the GP's point is that although the percentage isn't useful when deciding between glass and aluminium, it is useful when deciding whether to recycle the glass. If the saving is only 5%, then it may not be worthwhile to recycle glass once the additional work involved in collection is taken into account. Can't comment on whether this is the case or not though...

Comment Re:No thanks! (Score 4, Interesting) 110

Agreed. Especially for small laptops / netbooks, I find trackpads extremely annoying to use and far prefer to use Trackpoints. As your hands are already resting on the keyboard, it's a tiny movement to get to the mouse, and it doesn't feel so cramped. The main annoyance of trackpads though is that when typing it's extremely easy to accidentally hit the trackpad, shifting the cursor or focus (yes on some laptops you can disable the mouse when typing, but I don't find it a very good solution). I can see that trackpoints are no use at all for games, but neither are netbooks and generally when I'm at a computer I'm typing.

Unfortunately we seem to be in a minority, and finding laptops with trackpoints is really hard. Impressed with the sturdiness of Lenovo laptops (still using an IBM-branded X41 from 2006), but you do pay through the nose for them...

In summary: Bring back Trackpoint (and get off my lawn)!

Comment National labs (Score 1) 211

I work a fair bit at a US national lab which will remain nameless, but as a Foreign National I'm not allowed to use most of the machines. Instead there's a handful of *old* Sun boxes running CDE and Netscape Communicator 4.0. I shit you not. I half expect to hear the familiar warble of a modem, and browsing the half of the internet which isn't blocked by the filter becomes nearly impossible. Does mean I get a surprisingly large amount of work done though.

Comment Re:Surprise move? (Score 2) 1505

The electricity was also initially private in the UK... and was a complete mess. Different providers pushed different voltages, plugs etc. all completely incompatible. It was not until a mass government programme to create the national grid that this was fixed. Sometimes standardisation by diktat is a necessary thing, even if makes people uncomfortable.

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