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Perhaps this year, the National Ignition Facility (NIF) will become a real name. The $3.5 billion device, located at the Lawrence Livermore National Laboratory in California, produces the world's largest laser beam, used to implode (initially detonate) a hydrogen isotope target, triggering Nuclear fusion will generate much more energy than the input. The managers of NIF believe that in order to reach the tipping point or to "light the reactor," they have worked for two years and now it can be said that victory is in sight. The project manager Ed Moses said: "We are fully capable of achieving success in the fiscal year 2012."
However, this approach still belongs to inertial confinement fusion. Even if the entire project succeeds, it will face an uncertain future. Does the success of the experiment mean that the U.S. Department of Energy will develop it into an economically viable energy source? If so, is the NIF laser triggering nuclear fusion the best solution? On March 7, an interim report submitted by an expert group of the National Academy of Sciences concluded that it is still too early to conclude. The report also suggests that nuclear fusion scientists continue to look for alternative technologies to ignite nuclear fuel.
Glen Wurden, a plasma physicist at the Los Alamos National Laboratory in New Mexico, agreed with the report and argued that scientists studying inertially confined nuclear fusion should not press the laser to trigger lasers. . He believes: "Controlled nuclear fusion technology is completely immature." He pointed out that another kind of nuclear fusion method - magnetic confinement fusion (magnetic confinement fusion) and the landmark project of this approach, a $ 21 billion international hot The nuclear fusion experimental reactor (ITER) also encountered many difficulties, so that research stagnated. The slow progress of ITER and the continuous expansion of research costs are all due to an immature technology, the tokamak (controlled thermonuclear reaction device), which is a bagel-shaped cage in which a powerful electromagnet keeps one closed. Fusion plasma.
Although the scientists were initially confident and computer model simulation was very beneficial, the NIF project also failed to progress as expected. Urdon said: “Scientists think that the 'ignited' reactor is like a probe.†However, NIF's process of heating and pressurizing hydrogen isotopes is troublesome. In a process called an indirect drive, multiple laser beams are injected from two openings in an eraser-sized "hohlraum" (a gold cylinder) to generate X-rays inside. . After that, the nuclear fuel (hydrogen isotope target) inside the radiation cavity is heated and pressed by X-rays to trigger nuclear fusion. However, inside the radiation cavity, an unexpected vortex interaction occurs between the laser and the plasma, absorbing the energy from the laser beam. This will offset a lot of energy, so that the laser energy output of the NIF does not reach the limit threshold necessary to ignite the reactor.
In any case, NIF's research team has entered a stable experimental phase. Eighteen months ago, when scientists began to advance toward the ignition target, the facility only completed 1% of the necessary conditions for the expected ignition. Now, the degree of completion has reached 10%, and the process is accelerating: There were only 57 record bombings in January this year. The research team is also exploring a range of adjustments, including using tantalum or diamond instead of plastic to wrap nuclear fuel, and changing the material or shape of the radiant cavities. Moses stated that they may also raise the NIF's limit energy from 1.8 megajoules (only reaching this energy level to achieve “break-evenâ€) to 2.2 trillion joules.
But as the National Academy of Sciences report pointed out, other methods may provide an easier way to ignite the reactor and eventually become a practical power plant. So who is paying for these developments? Most studies of inertia-restricted reactors in the United States and around the world have been funded by joint ventures involving national security and weapons development. They have studied nuclear fusion for weapons development, not civilian power plants. Now, laser inertial confinement fusion research is regulated by the National Nuclear Safety Administration (NNSA) under the United States Department of Energy. The main responsibility of NNSA is to manage nuclear reserves.
In the Department of Energy's scientific office, there is almost no funding allocated to inertial confinement nuclear fusion research. Most of the funds are used to support magnetic confinement nuclear fusion, and more and more funds have been given to the ITER project. Fusion Power Associates in Gaithersburg, Maryland, a nuclear energy advocacy group, headed by Stephen Dean, believes that even if the final report of the expert group believes that inertia-contained nuclear fusion energy projects are feasible, This study is still difficult to find a place in the science office. Dean said: "I think the Department of Energy will directly ignore it. Clearly they only have a special liking for ITER and are frantically trying to save the project."
If NIF scientists can get their required $460 million in funding in 2013, they can explore other options. For example, the team of plasma physicists at the University of Rochester in the United States intends to tune the NIF lasers so that they can directly condense a hydrogen isotope target without using radiation cavities.
However, NIF scientists did not wait for the emergence of alternative methods. Before the ignition device, they were actively preparing for the next project, a demonstration power plant called Laser Inertial Fusion Energy (LIFE). Civilian power plants must be economical and practical. The energy produced must be more than 50 times more than the energy input by each bombardment target, and must increase the efficiency of reuse, from several bombings per day to 15 per second, but this is no easy task. .
In fact, this porous NIF facility is an enlarged model of LIFE's reaction chamber, and LIFE's reaction chamber is modular, which is small enough to fit into a truck. NIF's design uses thousands of huge strobes to charge glass lasers, and LIFE uses tiny, transistor-charged emitters. Moses refuted the notion that lasers are the driving force for future nuclear fusion power plants. He believes that the market and the public have made a choice by investing in lasers and transistors for consumer electronics. If you look back at the past, then "people will find that transistors and lasers are epoch-making inventions."
Mike Dunne, LIFE's program director, believes that their power plants, which cost about $4 billion apiece, can provide hundreds of millions of watts of electricity to the grid in the early 1920s, compared to what scientists expected, the first magnet. Constrained nuclear fusion power plants have emerged at least 10 years earlier. Recalling a few years ago at an academic conference where the researchers involved in magnetic confinement nuclear fusion introduced the concept of the LIFE project, Moss said: “They reacted quite fiercely and said, 'This is not possible.' They were then the project. The ambitions of their ambition were shocked and they still feel shocked.â€
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