Nuclear Fusion 500 Terawatt Laser At The National Ignition Facility

Canada Weekly November 24, 2017

The world’s most powerful laser system at the National Ignition Facility at Lawrence Livermore Labs can deliver an ultrashort laser pulse, 5×10^-11 seconds long, which delivers more than 500 trillion watts (terawatts or TW) of peak power and 1.85 megajoules (MJ) of ultraviolet laser light to its target.

In context, 500 terawatts is 1,000 times more power than the United States uses at any instant in time, and 1.85 megajoules of energy is about 100 times what any other laser regularly produces today.

The shot validated NIF’s most challenging laser performance specifications set in the late 1990s when scientists were planning the world’s most energetic laser facility. Combining extreme levels of energy and peak power on a target in the NIF is a critical requirement for achieving one of physics’ grand challenges — igniting hydrogen fusion fuel in the laboratory and producing more energy than that supplied to the target.

The first step in achieving an experimental fusion reaction is to induce inertial confinement of a mixture of Deuterium and Tritium (isotopes of hydrogen) at high enough densities so that their is a self-sustaining reaction. such a reaction requires a large cross-section of individual nuclei which can only occur in a high density plasma.

Various methods of achieving this have included using the Z-Pinch Process to create high energy X-rays to induce the confinement in fuel pellets,a so-called Z-Machine. Another fusion method involves using a uniform plasma confined in a collapsing magnetic field, called a Tokamak or a Toroidal Nuclear Fusion Reactor.

A lot of experimental results have come from using high energy laser facilities such as The National Ignition Facility, not only for fusion physics but also in the test of nuclear weapons eliminating the need for ground or sea tests of thermonuclear weapons; all the tests can be done in a laser ignition facility creating minimum effects to the environment.

For commercial Nuclear Fusion, the Tokamak Design is the best design for achieving a self-sustaining fusion reaction by having the toroidal field create a “bottle” of fusion plasma. Such a reactor would have to be very large to achieve critical mass for self-sustaining fusion and by far the International Experimental Reactor (ITER) in France is the best facility for testing the viability of an energy generating reactor.

Extracting the energy from the reaction is a different matter and probably will involve the invention of a high temperature superconducting heat exchanger or confined superfluid technology to become an efficient source of power.

So far the best method of heat extraction from a proposed Nuclear Fusion Reactor Core would be an oxide alloy of a metal with a high cross-section for gamma rays and a high melting point for absorbed infrared; hence an alloy of Tungsten dipped into the fusion reactor plasma is the best form of fusion heat exchanger available with current technology.

The exploration of other fusion reactions which utilise fuels easier to access is also another major problem in developing an efficient fusion reaction, reactions with Helium-3 and even a man-made Carbon-Nitrogen-Oxygen, CNO, cycle have been proposed.
Even the use of low-energy muons to catalyse the reaction have been proposed, though will be probably a long way off until an cost-efficient muon generator is developed.

In NIF’s laser fusion, the lasers fired within a few trillionths of a second of each other onto a 2-millimeter-diameter target. The total energy matched the amount requested by shot managers to within better than 1 percent.

The interesting thing about laser fusion is that, if you make the laser pulses short enough – on the order of a few hundred attoseconds say, you could in principle make a laser that would skip electronic transitions and just manipulate the nuclei of the atoms. This would mean there would be no blast from the laser itself, just from the nuclear reactions. This would give the highest efficiency possible of inducing fusion and the highest level of control, since all of the radiation emitted would be from the laser pulse.

1999 Nobel Prize in Chemistry was warded for using femtosecond lasers to observe and control chemical reactions of individual molecules. Imagine what progress could be done using even shorter laser pulses to control the nuclear reactions. In the future it may even be possible to perform subatomic physics with lasers and go beyond the Schwinger Limit and create any high energy particle we want from the vacuum. This would replace large accelerators for particle physics and could allow mass production of some unstable particles for scientific use.