Why can't fusion be accomplished using high energy density electric fields?
I think we call the generators of high density electric fields, Lasers.
But the laser fields vary sinusoidically with time. I am talking about a static field which sort of pushes +ions together. What are the practical difficulties in generating those high energy density fields?
And what device do you think can generate such a thing? Google on the largest static field we have achieved so far.
You will notice that the highest electric field gradients that we can achieved in an accelerating structure of a particle accelerator is via using standing wave cavity of an oscillating EM field. It is prohibitively expensive, and technically unfeasable to construct a static accelerating field of the same magnitude. This is where you are going to be using up more power than you generate, so then what's the point in achieving fusion?
.. and I haven't even mentioned the materials aspect yet that can withstand such high fields without serious breakdown.
Thank you for the reply.
What are the methods used for generating high electric fields? Do know a website which can tell me about the methods?
For high voltage potential differences, the good old Van der Graaff machine comes to mind - http://members.aol.com/_ht_a/lyonelb/sis.html
Then there is the Cockcroft-Walton accelerator.
I am not sure of the specific voltage per stage. I have seen numbers in the 100's kV range.
Are static electric forces stronger that magnetic ?
How much voltage are we talking about ?
In order to overcome the coulomb force between two protons you would need an electro static force greater than:
[tex]F = kq^2/r^2 = 9e9*(1.602e-19)^2/e-30 = 230N[/tex] per proton. A proton's cross sectional area is on the order of e-30 m. or less, so you would need a force/area of 2.3e32 N/m^2. Try to achieve that!
The real reason you could never achieve that kind of force with an electro-static field is because coulomb force has to come from electrons or protons. If you think about it, their static field can't produce a force/unit area greater than the force that you are trying to overcome.
Actually electric fields and magnetic fields are the same thing.
Magnetic fields are caused by the motion of electic fields.
Relativistic effects make the electric field look like a magnetic field.
Although it is frequently taught that Einstein developed Relativity to
explain the null result of the Michaelson-Morley experiment; Einstein's
true motivation was due to Maxwell's equations of electrodynamics.
The influence of the M-M experiment was rather indirect.
"The influence of the crucial Michelson-Morley experiment on my own
efforts has been rather indirect. I learned of it through H.A. Lorentz's
decisive investigations of the electrodynamics of moving bodies (1895)
with which I was acquainted before developing the special theory of
relativity . . . What led me more or less directly to the special theory of
relativity was the conviction that the electromotive force acting on a
body moving in a magnetic field was nothing else than an electric field."
Dr. Gregory Greenman
Thanks for the enlightenment sir. Thats going to help us very much in the future.
Magnetic (we've already gotten past the EMF = movement of E fields part) confinement is most difficult because the various reactor designs all have faults that lead to less than optimal Lawson criterion.
Magnetic confinement fusion is like trying to squeeze jello with a cargo net. You need a very dense, indefinitely sustainable confinement field arrangement that can maintain the plasma at the necessary temperatures. Right now the biggest barriers in this regard are costs of materials to build large enough reactors, thermal and shielding limites of materials, and associated changes in magnetic properties.
It's a challenge that requires more resources (time, money, and man/brain-power) than are currently allotted (worldwide) to accomplish this any time in the forseeable future.
Is there any other way in which fusion can be achived ? ( except cold fusion )
When magnetic forces are used to confine the plasma - it's called magnetic
However, the link above describes the process of "inertial confinement
fusion". One uses lasers, like at LLNL; to implode a small target of fusion
fuel. There's no attempt to contain the plasma - the plasma is contained
due to its own inertia for the brief period of time needed for the reactions
to take place.
The latest fusion laser at LLNL is the NIF - the National Ignition Facility.
This laser, as big as a sports arena; should be powerful enough to actually
achieve fusion ignition:
One can also do what LLNL does with lasers with big pulsed power
machines like at Sandia. The "Z Pinch" machine in action:
This machine puts very large currents into a series of wires. The current
and the magnetic field interact and implode the wire assembly and
compress a fusion target, similar to the way the LLNL lasers do.
Dr. Gregory Greenman
Hydrogen bombs achieve fusion just fine, they just aren't terribly useful for generating power for peaceful ends.
Fusion CAN be achieved with magnetic confinement, it's just not as easy as one might think when considering the initial ideas. The problems with magnetic confinement right now come down to what I said before: money and materials needed for a proper scale reactor.
Other methods of achieving fusion are inertial confinement (lasers), and inertial electrostatic, which is sort of hard to describe, but the device is small and makes an excellent table-top neutron generator. Unfortunately, we can't yet get a power gain out of any designs.
The Pons/Fleischmann experiements for cold fusion back in the late 80s were just bad science. My fusion prof back in school became visibly angered if you ever brought them up in class. The most promising idea for room-temperature devices for achieving fusion had something to do with imploding bubbles in acetone, but I don't know what progress (if any) was ever made on that one.
I don't think we can say that "Fusion CAN be achieved with magnetic
confinement.." quite yet. We do not as yet have a proof of principle for
fusion ignition via magnetic confinement.
As we have built larger and larger machines - like the family of tokamaks
at the Princeton Plasma Physics Lab; PLT [ Princeton Large Torus ] and
TFTR [ Tokamak Fusion Test Reactor ]; to name the latest two in the
series - we've seen more and more varied plasma instabilities that have
circumvented our quest for magnetic fusion.
Hopefully, the latest machine - the ITER - will be more successful.
The progress in inertial fusion has been more sustained. Inertial fusion
ignition has been accomplished in the aforemention hydrogen bombs -
but also the progress has been more sustained in the laser fusion arena.
The main problem facing laser fusion was to be able to drive a target
that was big enough - so that it could capture the product alpha particles
and achieve ignition. Calculations indicate that the new LLNL laser -
the NIF [ National Ignition Facility ] will be large enough and powerful
enough to achieve ignition [ hence the name ].
Dr. Gregory Greenman
Sure you can achieve fusion within current magnetic confinement devices. Whether or not you can achieve breakeven with any current device is a different story. ITER is (and forever will be, at this pace) slated to be the first magnetic confinement device to do that.
If all you want is fusion reactions - then you don't need any containment
system - magnetic. inertial, or otherwise. You just hit your tritiated target
with a beam of deuterons out of a cyclotron.
Implicit in these discussions about the feasibility of fusion is that we are
talking about breakeven or better!
Otherwise, it's a moot, trivial point.
Dr. Gregory Greenman
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