Control Fusion Reaction: Difficulties & Possibilities

[ahsan999]

why it is so difficult for scientist to control the fusion reaction
why they not make a lage room with heat resistance walls and make a explosion to start the fusion reaction and add appropiate amount of hydogen by some hole
if small quantity of hydrogen is entered in such room so the energy produced will be contol able
if this is not possible try to conveince me as early as possible

 

[Astronuc]

The problem is one of containing the plasma in a stable form such that the fusion reaction can progress at controlled rate.

An explosion is essentially a pressure wave, so it would be difficult to feed hydrogen into and explosion. Chemical explosions are very low temperature compared to plasma temperatures.

I think one means implosion, which would compress a plasma. But then what goes in (inward) generally comes back out, and if energy is generated within the imploded mass, the outward pressure would be much greater than the inward pressure and that would put a lot of stress on the magnetic confinement system.

In the case of inertial confinement, it's practicality has yet to be demonstrated. That involves a sequence of microimplosios/microexplosions of fusion targets, with hopefully more energy (thermal energy) generated by the explosion than went into the implosion.

Based on the statement, "if small quantity of hydrogen is entered in such room so the energy produced will be contol able," it is apparent that one does not understand the physics of fusion or plasma confinement.

 

[phyzguy]

why they not make a lage room with heat resistance walls and make a explosion to start the fusion reaction

The temperature needed to generate sufficient energy by nuclear fusion is so high that no walls made of matter can withstand it. Any "heat resistant walls" would be vaporized by the high temperatures.

 

[Astronuc]

The temperature needed to generate sufficient energy by nuclear fusion is so high that no walls made of matter can withstand it. Any "heat resistant walls" would be vaporized by the high temperatures.

That's part of it.

Fusion takes place at temperatures (kinetic energies) of 50-200 keV, and 1 keV = 11605000K. So that's 500 million K to 2 billion K.

The other part is the density of the plasma, and the fact that P = nkT. Even if the plasma is confined magnetically from any material wall, one has to balance that with the enormous pressures.

Terrestrial fusion plasmas confined in a magnetic field operate in essentially a vacuum with particle densities on the order of 10¹⁴ cm^-3. Inertial confinement targets can achieve higher densities than 10²² cm^-3, but the confinment time is on the order of microseconds.

 

[phyzguy]

That's part of it.

The other part is the density of the plasma, and the fact that P = nkT. Even if the plasma is confined magnetically from any material wall, one has to balance that with the enormous pressures.

Terrestrial fusion plasmas confined in a magnetic field operate in essentially a vacuum with particle densities on the order of 10¹⁴ cm^-3.

But the pressure in and of itself isn't really a big problem. For n=10^14 cm^-3, T=200 keV, we would have a pressure of about 30 atmospheres, which would be easily confined by a steel pressure vessel. Bear in mind that with magnetic confinement fusion the pressure of the plasma ultimately needs to be borne by a mechanical structure anyway. If it weren't for the fact that the steel pressure vessel would vaporize, fusion would be easy. You could just fill a steel vessel with a D-T gas and pump heat into it until it ignited.

 

[Astronuc]

Without a magnetic confinement, the steel vessel would quench the plasma. There is not enough mass in a plasma to melt the steel. The problem of the plasma pressure is the push back on the magnetic field, as well as the magnetic field strength, B, required to confine the plasma, which determines the current necessary to produce the magnetic field.

Did the pressure calculation also include the electron pressure in addition to the nuclei? The 10¹⁴ is just an order of magnitude. Double the value, double pressure; quadruple the number, quadruple the pressure; . . .

It's matter of balancing power density, pressure, and other system requirements.

If it was so easy, we would have had a viable commercial fusion plant 20+ years ago.

 

[Drakkith]

Read more on: http://en.wikipedia.org/wiki/Nuclear_fusion