Earlier this month, Lawrence Livermore National Laboratory (LLNL) announced to the world that they had achieved Record production of 1.3 MJ From their National Ignition Facility (NIF) fusion experiment. However, what exactly does this mean? As their press release points out, the main developments in these results will be used in the US nuclear weapons arsenal.
This particularly concerns the nuclear fusion weapons of the United States, where LLNL and Los Alamos National Laboratory (LANL) and other facilities are involved in research and maintenance.This can be traced back to the roots of NIF in the 1990s, when Inventory management The plan was established to replace nuclear weapons testing. Much of this research involves examining how today’s nuclear weapons have degraded over time and methods for modernizing existing arsenals.
In view of this, one might want to know that the impact of these NIF’s experimental results is not just to ensure the principle crazy Intact. To answer this question, we must look at inertial confinement fusion (ICF), which is the core technology of the NIF experiment.
Laser makes everything better
International Finance Federation It is one of the two main branches of fusion research, and the other is magnetic confinement fusion (IF), including today’s tokamak and star simulators. Just as the initial optimism of MCF and the desperate disappointment of Z-pinch integration proved to be unworkable, ICF also has its own disappointments. Although it was initially thought of as a practical method of generating energy from fusion, it soon became apparent that the energy requirements for initiating (igniting) fusion were much higher than estimated and far from easy to achieve.
MCF discovered the second life in the form of tokamak and star simulator studies. These studies are more complex, but are expected to solve the Z-contraction problem, especially the plasma instability. ICF restarted with the invention of a powerful laser, which may be enough to heat fuel and initiate fusion. The process involves making the fuel ball evenly directly subjected to laser energy (direct drive) or indirectly (indirect drive).
LLNL has been involved in ICF since the 1950s, but it was only in the 1970s, with the advent of more powerful lasers, that the first high-power experiments could be carried out.These include Shiva Laser 1978 and Nova Laser Since 1984. Both of these laser systems failed to achieve ignition and only achieved moderate results, mainly due to changes in laser beam irradiation.
Despite the tight funding for fusion research in the 1980s, the results of these experiments eventually helped LLNL establish NIF, which can be regarded as the successor to the Shiva and Nova laser projects. Although the construction time of NIF is much longer than the original plan, it has received financial support through its main goal of conducting research for the US nuclear management program.
Similar to NIF is Z pulse power facility (Also known as the Z machine) at Sandia National Laboratory in New Mexico. The facility uses the Z-pinch principle, making it an MCF system. Although the Z-pinch-based MCF has been abandoned as a way to generate electricity, it can still be used for research purposes, making it an important part of the same nuclear management plan.
See things through
In summary, the fusion phase in ICF involves heating the surface of the fusion target, causing the resulting plasma envelope to expand, thereby compressing the fuel. This compression increases the temperature and density of the fuel to the point where it ignites, which means that the alpha particles produced by fusion are trapped inside the fuel and help heat it.
This in turn will cause more fusion events to occur inside the fuel, triggering a chain reaction, and ideally all fuels will be fused, thereby releasing all potential energy.
In the case of NIF, a 500 TW (pulsed) laser is used to deliver all the energy to the target within a few picoseconds. Due to the tremendous pressure on the laser system, NIF can only be launched hundreds of times a year.The fuel is generally not directly irradiated by the laser, but contained in a HolrumThis is a hollow object with a special shape. When the laser beam enters the cavity (not hitting the fuel pellet), it emits radiation of a specific wavelength. For NIF, this Hohlraum is designed to produce X-rays.This Hohlraum can have two or more entrance holes, for example detailed description Three-axis cavity design Written by Longyu Kuang et al.
These X-rays heat the fuel pellets and start the fusion process. The advantage of using Hohlraum is that it can heat the fuel pellets more directly and uniformly. Even so, the energy requirement for heating the fuel pellets with ICF is huge.The figure below illustrates this in detail Wikipedia entry On NIF:
Powering the laser system requires approximately 422 MJ of energy (total system input), only part of which is converted into laser beam energy and finally reaches the cavity. Most of this energy contributes to the generation of X-rays in the cavity, and only a small part ultimately contributes to the compression of the fuel pellets.
When considering that it takes 422 MJ to get a return of approximately 1.3 MJ from the fuel target, it may not be necessary to broadly explain why this fusion method is unlikely to reach the break-even point, namely Q 1. The notable aspect here is the energy released. It is 70% of the input laser energy, which means that ignition is almost achieved.
No more life
Between 2008 and 2013, LLNL was actually working on laser inertial fusion energy (Life) Efforts to transform NIF’s experience into nuclear fusion power plants, using solid-state semiconductor lasers and mass-produced fuels. However, at the end of the project life cycle, it is clear that power plants using ICF are clearly unrealistic, especially considering that ICF ignition has not yet been achieved.
When one compares the huge challenges faced by ICF in competing with MCF methods, JET and HL-2M Tokamak and Wendelstein-7X Stellar show very promising results in terms of plasma stability and heating, not to mention The Q factor is very close to 1. It should be clear that ICF is not a participant in the future power plant game unless there are some amazing breakthroughs.
However, the contribution of ICF projects like NIF is to increase our understanding of physics, not only nuclear physics, but also knowledge related to extremely powerful laser systems and general energy physics. This in itself makes this almost ignited event on NIF worth cheering.
[Heading image: Preamplifier at the National Ignition Facility by Lawrence Livermore National Laboratory CC-BY-SA 3.0]