stupid tokomak question

kunkmiester · Post by **kunkmiester** » Sat Sep 12, 2009 10:00 pm

Most of the trouble with containment in the tokomak is the neutrality of the plasma, right? This requires the massive magnets and stuff.

How reasonable would it be to try to pull electrons out of the mix as you heat it up? With a sufficiently positive charge, I get the impression the plasma would be easier to contain.

Or would this not work?

hanelyp · Post by **hanelyp** » Sat Sep 12, 2009 11:57 pm

One of the difficulties with the tokomak is regions of the magnetic field where as the plasma pushes the field is stretched out and becomes weaker. One advantage of the polywell is a magnetic field on all sides of the central plasma that is squeezed between the plasma and the magnets, so the plasma pressing harder concentrates the magnetic field, at least up to the point where a cusp blows out. Adjusting the net charge of the plasma does nothing to alter this difference.

To the best of my knowledge none of the instabilities plaguing the tokomak would be helped by changing the plasma charge.

Positive ions are harder to contain with a magnetic field on account of mass/charge ratio.

Skipjack · Post by **Skipjack** » Sun Sep 13, 2009 12:54 am

I thought the biggest challenges for ITER were in the material sciences department. A big machine with a complex shape which makes it harder to replace parts, constant neutron bombardment (because of the DT- reaction) and the need to breed tritium.
From what I remember these are the biggest challenges at the moment.

MSimon · Post by **MSimon** » Sun Sep 13, 2009 1:01 am

Skipjack wrote:I thought the biggest challenges for ITER were in the material sciences department. A big machine with a complex shape which makes it harder to replace parts, constant neutron bombardment (because of the DT- reaction) and the need to breed tritium.
From what I remember these are the biggest challenges at the moment.

They also have a problem with low frequency (Hz) instabilities that are not yet solved.

Skipjack · Post by **Skipjack** » Sun Sep 13, 2009 1:08 am

They also have a problem with low frequency (Hz) instabilities that are not yet solved.

I honestly have not been keeping to up to date with ITER, as I have- quite frankly- written it off as anything other than a nice experiment in plasma physics, without any practical use in power generation and aerospace. Plus I kinda have the feeling that I wont live to see it do anything ever. So I am not surprised about there being other problems that I dont know about. Do you have a link with more information about this issue Msimon?

MSimon · Post by **MSimon** » Sun Sep 13, 2009 1:16 am

Skipjack wrote:
They also have a problem with low frequency (Hz) instabilities that are not yet solved.
I honestly have not been keeping to up to date with ITER, as I have- quite frankly- written it off as anything other than a nice experiment in plasma physics, without any practical use in power generation and aerospace. Plus I kinda have the feeling that I wont live to see it do anything ever. So I am not surprised about there being other problems that I dont know about. Do you have a link with more information about this issue Msimon?

Here is one.

http://www.iop.org/EJ/abstract/0029-5515/48/11/115008

Look up edge-localized modes (ELMs) for others.

TallDave · Post by **TallDave** » Sun Sep 13, 2009 1:34 am

What hanelyp said.

MHD stability is a big problem in that setup, much bigger than anyone anticipated thirty years ago.

Robthebob · Post by **Robthebob** » Sun Sep 13, 2009 2:44 am

I actually did some research, for a school paper.... but nevertheless.

Tokamaks have various challenges that they have to overcome. It's pretty clear, at least to most of the physics community, many not the tokamak community, that tokamaks will never ever be the design to be a power plant. ITER can not be a power plant, it's just not designed that way. But to answer your question, no tokamaks can not pull out of the electrons, because tokamaks rely on electrons to heat up. Maybe they should learn2microwave heating, but I'm just saying. That's what's called Ohmic heating. The electrons run one direction, the ions run the other direction, they collide and heat up. But there's problems with the fact that when things move really fast, they have no time to interact, so the hotter the plasma gets, the slower the plasma gets heat up.

Really, I'm not kidding, learn2microwave heating. But here's the few challenges.

1. not a steady state machine, meaning it cant run continuously, therefore, it can not be a powerplant.

2. Thermonuclear machines of the toroidal magnetic confinement schemes, if you want to go over break even, generates a huge amount of radiation. Currently there are no materials that can withstand the huge amount of power density. (They dont have the materials to build ITER, lol)

3. Plasma instabilities, they can blow up and destroy the machine. That's what you get for running a current to confine your plasma, god darn, learn to build Stellarators.

4. Huge machines, the physics say so.

And a couple others I dont know about. These are the reason why I have no faith in ITER and tokamaks, the so call most recognized and progressed scheme in doing nuclear fusion.

MSimon · Post by **MSimon** » Sun Sep 13, 2009 5:14 am

A comment I got:

How much have we spent/will spend on Polywell research? 10 million? And they claim that they will know if the technology is viable in two years? I just read that ITER is looking like 5 BILLION EUROS and won't produce power until 2026.

My greatest confidence in Polywell is the fact that the guys doing it are confident enough in their work that they aren't trying to turn it into an indefinite taxpayer funded jobs program.

http://www.classicalvalues.com/archives ... ets_t.html

Skipjack · Post by **Skipjack** » Sun Sep 13, 2009 10:05 am

Here is one.

http://www.iop.org/EJ/abstract/0029-5515/48/11/115008

Look up edge-localized modes (ELMs) for others.

Thanks Msimon. I am getting an error message at the moment "service currently not available". So I will try again later.
Thanks anyway.

2. Thermonuclear machines of the toroidal magnetic confinement schemes, if you want to go over break even, generates a huge amount of radiation. Currently there are no materials that can withstand the huge amount of power density. (They dont have the materials to build ITER, lol)

Yeah that is what I meant earlier. I remember that they had that problem already almost 20 years ago. They still have not fully resolved it yet. For a huge machine with a complex shape this is particularily bad, because it makes replacing parts so much more difficult.

alexjrgreen · Post by **alexjrgreen** » Sun Sep 13, 2009 11:55 am

Robthebob wrote:1. not a steady state machine, meaning it cant run continuously, therefore, it can not be a powerplant.

Internal combustion engine?

Robthebob · Post by **Robthebob** » Sun Sep 13, 2009 2:21 pm

with Internal combustion engine, even tho it's pulsed, it returns to it's starting state, it's very clever.

I dont know how clever we can make tokamaks, but we need a changing current running through the transformer in order to induce the plasma current. You would have to keep raising the power, which is simply impossible to do forever, hell it's not even possible to do for a long period of time.

It's just really tough, even my boss, a professor who's been working on thermonuclear plasma fusion for a very long time understands that tokamaks are nothing but an instrument to allow researchers to do experiment with high plasma tempertures and densities. It's good for the research aspect, no good for making any power.

Edit: I cant spell

Aero · Post by **Aero** » Sun Sep 13, 2009 3:17 pm

Robthebob wrote: Edit: I cant spell

Neither can I. I use the free version of WordWeb which is helpful in a lot of cases.
It is available here. http://wordweb.info/

MSimon · Post by **MSimon** » Sun Sep 13, 2009 4:34 pm

Aero wrote:
Robthebob wrote: Edit: I cant spell
Neither can I. I use the free version of WordWeb which is helpful in a lot of cases.
It is available here. http://wordweb.info/

I use Netscape 9.0.0.5 (yeah I'm a retro guy). Spell checker built in.