'Break Even' with the Tokamak

In summary: PhysicistIt is theoretically possible to produce artificial fusion through the use of a tokamak reactor. ITER has been extensively modeled and has already poured a large amount of funding into research. If ITER has been underway for some time and has already invested a lot of money, it's likely that they would have "crunched the numbers" before building the reactor.
  • #1
user01
16
0
I have tryed to look into ITER and tokamak reactors latest updated information online, and cannot find any real specifics on it's latest progress. Does anyone know of where we are with producing sustained fusion for energy purposes, through currently using the tokamak?

Is it possible to reach 'break-even' with the tokamak design considering it uses very large current, and therefore electric power to produce the sort of conditions (temperature in this case) to create fusion?

Why specifically does the tokamak appear to be the design currently in primary consideration which will produce commercial fusion for energy?
 
Engineering news on Phys.org
  • #2
I usually try to stay up to date with this website:
http://fire.pppl.gov/
Also, you can try looking at the journal subscriptions of your library; they may have one that deals with the latest research going on in the world.

ITER is being built to determine if breakeven is possible.

To produce a lot of energy, many reactions will be needed. The easiest way to do that is through confining a lot of plasma and giving it plenty of opportunity to fuse with something else. Inertial confinement could produce a lot of energy, but it would be all at once. Dealing with a tokamak, where you have some control over the reaction rate, would be easier.
 
  • #3
theCandyman said:
To produce a lot of energy, many reactions will be needed. The easiest way to do that is through confining a lot of plasma and giving it plenty of opportunity to fuse with something else. Inertial confinement could produce a lot of energy, but it would be all at once. Dealing with a tokamak, where you have some control over the reaction rate, would be easier.
Candyman,

You have control with inertial confinement too.

A single ICF capsule or pellet is only going to put out a given amount of energy.
As long as you can absorb one pellet's worth of energy at a time - there's no
problem with control.

Dr. Gregory Greenman
Physicist
 
  • #4
I was thinking that if ITER has been underway for sometime, and that they have already poured a large amount of funding (financial), research and time into the project - that producing artificial fusion is a theoretical possibility. I am sure that they would have 'crunched the numbers' before building the reactor.

Im not really sure whether the tokamak's design, using large current to heat the plasma, is the best way to achieve 'break-even'. I was just looking at a few other sites online which claim that at the moment, more energy has to be put into the system - then what they are able to get out of it. This raises questions, at least in my mind, about the overall approach and design of the tokamak reactor.
 
  • #5
user01 said:
I was thinking that if ITER has been underway for sometime, and that they have already poured a large amount of funding (financial), research and time into the project - that producing artificial fusion is a theoretical possibility. I am sure that they would have 'crunched the numbers' before building the reactor.

Im not really sure whether the tokamak's design, using large current to heat the plasma, is the best way to achieve 'break-even'. I was just looking at a few other sites online which claim that at the moment, more energy has to be put into the system - then what they are able to get out of it. This raises questions, at least in my mind, about the overall approach and design of the tokamak reactor.
user01,

You can be sure that ITER has been extensively modeled using computer simulation.
You don't embark on a project like ITER without "crunching the numbers" as you put it.

There are basically two methods under consideration for fusion - and they are at
opposite limits of what I call the "Lawson spectrum". As you may know, there is a rule
of thumb as to what conditions are necessary for break-even fusion; called the Lawson
crierion.

The Lawson criterion states that the product of the particle density and the confinement
time has to be greater than some threshold. For a given product, there are two extremes.
In the low density limit, one can have a low density plasma, and confine it for a relatively
long time. That is the regime that magnetic fusion operates in.

At the other limit, the high density limit; one can have a highly dense plasma but very
short confinement time. That is the regime that inertial confinement fusion lives in.

Within the inertial confinement limit; there are two schemes, laser fusion and fusion using
pulsed power techniques. Laser fusion is being explored at Lawrence Livermore National
Laboratory:

http://www.llnl.gov/nif/

and the Laboratory for Laser Energetics at the University of Rochester:

http://www.lle.rochester.edu/

Pulsed power techniques are being researched by Sandia National Laboratory:

http://zpinch.sandia.gov/ [Broken]
http://www.sandia.gov/media/z290.htm

"Arcs and Sparks" close-up:
http://zpinch.sandia.gov/Z/Images/z.jpg [Broken]

Dr. Gregory Greenman
Physicist
 
Last edited by a moderator:
  • #6
According to the torodial tube, closed ended geometry of the tokamak, it appears as if the plasma is desired to be contained for a long period of time, giving low densities. This would then suggest that the large currents (in the millions of amperes) employed by both fields (torodial & poloidial) for confinement and heating would be required to be operational for a significant amount of time. This also adds problems to trying to achieve break-even.
 
  • #7
user01 said:
According to the torodial tube, closed ended geometry of the tokamak, it appears as if the plasma is desired to be contained for a long period of time, giving low densities. This would then suggest that the large currents (in the millions of amperes) employed by both fields (torodial & poloidial) for confinement and heating would be required to be operational for a significant amount of time. This also adds problems to trying to achieve break-even.

Note: Perhaps only in the millions of amperes with the heating field, I am not sure about the confinement. But regardless, they use large amounts of electrical power.
 
  • #8
I think heating the plasma to the range of tens of keV (I do not know what current would be required), you will have a characteristic confinement time of about five seconds. After that the plasma will hopefully create its own heat from the reactions.
 
  • #9
I think that they have already achieved fusion reactions inside the reactor - but for only a very short period of time. Obviously there has been no net gain of energy from the plasma (no breakeven, as far as I am aware) but they have nevertheless been able to obtain energy from fusion reactions.

This site at the ITER claims the "JET has produced 16 MW for 1-2 s, heating injected plasma at 24 MW." http://www.iter.org/a/index_faq.htm" [Broken] According to this link, this is the closest that anyone has acheived to breakeven.

But the problem of keeping the pressure on the plasma (electromagnetically) so that they are able to achieve the required density, as well as continual confinement and perhaps if needed, additional heating, would appear to stand in the way of breakeven.
 
Last edited by a moderator:
  • #10
user01 said:
But the problem of keeping the pressure on the plasma (electromagnetically) so that they are able to achieve the required density, as well as continual confinement and perhaps if needed, additional heating, would appear to stand in the way of breakeven.
That is the problem in a nutshell - maintaining pressure and temperature of the plasma, which affects the reaction rate, and keeping it stable. Beyond breakeven, the goal is to produce excess energy efficiently and be able to extract for a useful purpose, e.g. electricity.
 
  • #11
I'm quite intriguided as to why exactly ITER has decided to use the tokamak design as the basis to "demonstrate the technical feasibility of fusion power", especially when it has several countries involved as partners, and a large amount of joint funding and time has been, and is to be, invested in the project.

The difficulty for me is that heating plasma by using very large currents seems like an un-viable approach, especially to achieving 'break-even'. - I just need some clarification on this from others who may have a clear understanding in this area of nuclear engineering.

Note: Quote taken from http://www.iter.org/" [Broken]
 
Last edited by a moderator:
  • #12
The nuclear aspects (fusion) are relatively straightforward. The main problem is achieving uniform heating and confinement conditions which is a challenge in plasma physics. Large currents perhaps provide the most uniform (circumferentially that is) for heating the plasma since microwaves and neutral beams must enter the plasma locally at the outer surface and are then attenuated.

Then there is the matter of extracting the energy produced by fusion - e.g. as the plasma expands.
 
  • #13
user01 said:
I'm quite intriguided as to why exactly ITER has decided to use the tokamak design as the basis to "demonstrate the technical feasibility of fusion power"

As opposed to what? Are you asking why stellarators or inertial confinment with lasers was not chosen as the ITER basis?
 
  • #14
theCandyman said:
As opposed to what? Are you asking why stellarators or inertial confinment with lasers was not chosen as the ITER basis?

Sort of - in a way.
Perhaps the problem of the continual confinement of fusion - at least in the nature as proposed by the tokamak is an unrealistic expectation.

The problem I see is that natural fusion reactors, as for instance the sun, are able to confine and sustain continual plasma reactions through their gargantuan mass, and therefore inherently powerful gravitational fields. But to try and artificially reproduce this, using specifically the tokamak's approach of a closed torodial geometry, appears to create problems, at least to achieving 'break-even. An extended period of applied pressure (to continuously achieve a "uniformly" required density) as well as confinement requires large currents to be operational extensively. This leads to even more "energy being put into the system", as opposed to the amount extracted.

Also sustaining the plasma for extended periods of time seems to provide more problems. Many website sources mention that a large proportion of instability within the plasma appears to occur during longer confinement times. Altought this appears to be a theoretical and not practical observation, as current reactors have only achieved fusion for a few seconds, this would however validate the idea of plasma instability increasing with time.

There are some links through the ITER website which show this to be the case http://www.iter.org/paramchoice.htm" [Broken]
 
Last edited by a moderator:
  • #15
user01 said:
An extended period of applied pressure (to continuously achieve a "uniformly" required density) as well as confinement requires large currents to be operational extensively. This leads to even more "energy being put into the system", as opposed to the amount extracted.

Yes, but look at the energy required on the atomic scale. The energy put in is on the order of KeV and what you get out is MeV. Instabilities arise during the time when the plasma starts to heat itself from its own reaction. I believe once this stage is passed, heating the plasa won't require as much energy. I don't know how much energy is required for the magnets, though.
 
  • #16
Well, speaking of alternatives to Tokamaks, how many of you remember the old MFTFB architecture?

http://www.psfc.mit.edu/library1/catalog/reports/1980/83rr/83rr021/83rr021_full.pdf [Broken]

Basically it was a straight tube with reflecting magnets at the ends. I got to see it in construction at Lawrence Livermore Labs many years ago. It was completed on time and on budget, and then mothballed by the Regan administration. Rats. Those reflecting magnets on the ends were way cool to see in person.

Hey Morbius -- wicked picture!
Morbius said:
"Arcs and Sparks" close-up:
http://zpinch.sandia.gov/Z/Images/z.jpg [Broken]
 
Last edited by a moderator:
  • #17
The energy put in is on the order of KeV and what you get out is MeV.
I mentioned in a previous post that the JET fusion reactor, "the world's largest nuclear fusion research facility" http://www.jet.efda.org/" [Broken].

According to http://www.engnetglobal.com/tips/convert.asp?catid=12", 1 MW-H is equivelant to 2.25*10^28 eV.

It is diffucult to find the total input power into a torus, either by JET or ITER, however, ITER have claimed that a heating power alone of 110 MW is attainable ("through radio frequency, ion cyclotron, electron cyclotron, 1 MeV negative ions" ect.) http://www.iter.org/Heating.htm" [Broken]. This information is sketchy since it is efficiently limited and summarised, but I believe that the confinement (control) phase is included in this input estimate.

It appears true that the primary source of instability of the plasma is caused by it undergoing fusion and as so releasing large quantities of thermal energy in nuetrons, gamma rays and also the more stable nuclei products. However, confining this product plasma for extensive periods would, by my observations, add more problems to trying to achieve 'break-even'. Although this appears to be more a theoretical observation rather than a practical one, since fusion reactors have only been able to sustain fusion for a few seconds (according to my understanding), this would however validate the idea of plasma instability increasing with longer confinement periods.

Perhaps this extended confinement period (on the product plasma) should be removed since significant instabilities arise causing noticeable degradation to the integritiy of the fusion cycle in the reactor (i.e. it's ability to sustain and control subsequent fusion reactions and remain operational). I agree with initiating, and then controlling and sustaining the reaction whilst fusion is occurring, however not in the manner as suggested by the design of the tokamak. Other methods within inertial confinement appear promising to initiate fusion, and so perhaps should be combined with magnetic confiment methods to control it.

However, subsequently releasing the products from the system once the thermal energy has been extracted may have more desireable results than trying to produce a uniformly stable and self-sustaining closed ended reactor.
 
Last edited by a moderator:
  • #18
Morbius said:
user01,

The Lawson criterion states that the product of the particle density and the confinement
time has to be greater than some threshold. For a given product, there are two extremes.
In the low density limit, one can have a low density plasma, and confine it for a relatively
long time. That is the regime that magnetic fusion operates in.

At the other limit, the high density limit; one can have a highly dense plasma but very
short confinement time. That is the regime that inertial confinement fusion lives in.

...
Dr. Gregory Greenman
Physicist


Please help me confirm my understanding of Lawson here: it applies to the case where one is trying to 'ignite' the plasma, that is you want it do generate enough energy under pressure and time conditions such that it can sustain itself without the application of additional energy to the system. So then the Lawson criterion does not apply to driven fusion concepts such as the old Hirsch-Farnswirth fusor idea of the colliding beam ideas, that is plasmas not in thermal equilibrium. In these cases the plasma is never intended to ignite, rather power is obtained purely in terms of some power out = density of ion species * ion cross section - energy; this is true independent of time of operation.
 

1. What is a tokamak and how does it relate to 'break even'?

A tokamak is a device used in fusion research to confine plasma at high temperatures and densities in order to initiate a fusion reaction. The concept of 'break even' refers to the point at which the energy produced by the fusion reaction is equal to the energy required to sustain it.

2. Is 'break even' achievable with current tokamak technology?

No, 'break even' has not yet been achieved with current tokamak technology. While significant progress has been made, the energy output of current tokamaks is still not equal to the input energy required to sustain the reaction.

3. What are the major challenges in achieving 'break even' with a tokamak?

The main challenges in achieving 'break even' with a tokamak include the need for extremely high temperatures and pressures to initiate and sustain the fusion reaction, as well as the difficulty in confining and controlling the plasma within the tokamak.

4. Are there any alternative methods for achieving 'break even' besides a tokamak?

Yes, there are several alternative methods being researched for achieving 'break even' in fusion reactions. These include laser fusion, inertial confinement fusion, and magnetic mirror machines.

5. What are the potential benefits of achieving 'break even' with a tokamak?

If 'break even' can be achieved with a tokamak, it would be a major milestone in fusion energy research. It could lead to a nearly limitless supply of clean, safe, and abundant energy, without the production of greenhouse gases or long-lived radioactive waste.

Similar threads

  • Nuclear Engineering
Replies
5
Views
2K
  • Nuclear Engineering
Replies
7
Views
2K
  • Nuclear Engineering
Replies
9
Views
2K
  • Nuclear Engineering
3
Replies
70
Views
8K
  • Nuclear Engineering
Replies
0
Views
223
Replies
2
Views
2K
  • Nuclear Engineering
Replies
19
Views
2K
  • Nuclear Engineering
2
Replies
40
Views
5K
Replies
1
Views
6K
  • Nuclear Engineering
Replies
1
Views
1K
Back
Top