Stellarator presentation at PPPL

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jcoady
Posts: 141
Joined: Fri Jul 15, 2011 4:36 pm

Stellarator presentation at PPPL

Postby jcoady » Thu Jan 22, 2015 5:01 pm

Here is a presentation about the Stellarator given as part of the Science on Saturday Lecture series at PPPL for high school students.

http://www.pppl.gov/events/stellarators ... t-old-idea

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Re: Stellarator presentation at PPPL

Postby D Tibbets » Sat Jan 24, 2015 1:50 am

I managed to watch the entire video. It is interesting. Some ideas are narrow in the presentation, though obviously a more in depth discussion would resolve this. An example is mention of the helium ash needing to be removed before it cools the plasma and that it is simply a waste product. It is the neutrons (D-T fusion) that provides the output heating that drives electricity production. The ommitted information though is that the helium- alphas, are what heats the plasma in an ignition machine. It is not so much an issue of removing the helium as it is removing the helium at the right time-after thermalization with the fuel, but before continued cooling of the plasma through the heliums contribution to Bremsstruhlung, and diluting the available fuel percentage. The importance of diverters and the early status of their development is mentioned. Of course this is a distinct difference compared to Polywell- no alpha heating and natural escape of the helium"ash" before it can cool the plasma. It is one of those things that should be considered in a system cost- risk analysis.

Stellarators may be able to operate at densities ~ 100 times greater than Tokamaks. This may be significant. If both work, the stellarator may make a much more economical solution for producing economical grid electricity. This would bias the cost risk calculation in its favor, much like the Polywell or FRC.

This cost- risk relationship is mentioned briefly, though only in the context of stellarator versus tokamack. A broad based analyses and priority setting would seem appropriate. Too bad such is not done.

The answer and question portion is also interesting as he goes somewhat into the difficulties and pitfalls of computer modeling.

In response to a question, he replies on the three methods of fueling a reactor. The gas puff is attractive, a neutral beam injector is useful but adds complexity. And pellet injection is another option. This is somewhat in line with what Dr Parks did with the Mini-B reactor. The "pellet" was a sheet of plastic, which was blasted into the reaction space, being ionized along the way. Not an elegant solution and possibly not a useful one for an actual production machine. But it is useful for some experimental situations. The problem with ion and/ or electron injection, is that if the charged particle confinement is good , the barrier to injection is also good. Some methods of overcoming these opposing tendencies need to be resolved. This seems to be a major consideration for Polywell at this stage.

Dan Tibbets
To error is human... and I'm very human.

Robthebob
Posts: 383
Joined: Mon Jun 23, 2008 11:12 pm
Location: Auburn, Alabama

Re: Stellarator presentation at PPPL

Postby Robthebob » Sat Jan 24, 2015 7:58 am

stellarators have literally always been better than toks in principle. There was the dark ages when they couldnt machine the vacuum vessel properly; there was the time when everyone bitched about how making stellarators were hard to do; etc.

Every advantage toks have can be implemented into stellarators. There are some issues about working reactors and the complex nature of the stellarator fields not easily applied due to distance from the core of the reactor... that may be the biggest advantage toks have over stellarators.
Throwing my life away for this whole Fusion mess.


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