Threshold of Fusion Ignition
Please consider the Threshold of Fusion Ignition.
On Aug. 8, 2021, an experiment at Lawrence Livermore National Laboratory’s (LLNL’s) National Ignition Facility (NIF) made a significant step toward ignition, achieving a yield of more than 1.3 megajoules (MJ). This advancement puts researchers at the threshold of fusion ignition, an important goal of the NIF, and opens access to a new experimental regime.
The experiment was enabled by focusing laser light from NIF — the size of three football fields — onto a target the size of a BB that produces a hot-spot the diameter of a human hair, generating more than 10 quadrillion watts of fusion power for 100 trillionths of a second.
“These extraordinary results from NIF advance the science that NNSA depends on to modernize our nuclear weapons and production as well as open new avenues of research,” said Jill Hruby, DOE under secretary for Nuclear Security and NNSA administrator.
“Gaining experimental access to thermonuclear burn in the laboratory is the culmination of decades of scientific and technological work stretching across nearly 50 years,” said Los Alamos National Laboratory Director Thomas Mason. “This enables experiments that will check theory and simulation in the high energy density regime more rigorously than ever possible before and will enable fundamental achievements in applied science and engineering.”
Fusion vs Fission
Fission produces nuclear waste. Clean energy proponents will have nothing to do with it, no matter how safe it is.
Fusion has been the holy grail for decades. NASA reports the sun does some of each.
Although the energy produced by fission is comparable to what is produced by fusion, the core of the sun is dominated by hydrogen and at temperatures where hydrogen fusion is possible, so that the dominant source of energy per cubic meter is in fusion rather then the fission of very low abundance radioisotopes. Fission is not a significant source of energy so long as the temperatures and densities are high enough for fusion to occur.
Temperature of the Sun
- The surface temperature of the sun is 5,778K.
- Lead melts at 621.5°F.
- Aluminum melts at 1,221°F.
- Copper melts at 1,984°F.
- Tungsten, the highest melting point alloy, melts at 6,170°F.
6,170°F sounds high. But here is the conversion.
(6170°F − 32) × 5/9 + 273.15 = 3683.15°K
How Nuclear Fusion Reactors Work
How Stuff Works explains How Nuclear Fusion Reactors Work.
- Fusion requires temperatures of about 100 million° Kelvin (approximately six times hotter than the sun's core).
- At these temperatures, hydrogen is a plasma, not a gas. Plasma is a high-energy state of matter in which all the electrons are stripped from atoms and move freely about.
- The sun achieves these temperatures by its large mass and the force of gravity compressing this mass in the core. We must use energy from microwaves, lasers and ion particles to achieve these temperatures.
The EuroFusion project repeats the above.
Deuterium-tritium fusion reactions require temperatures in excess of 100 million degrees. To achieve these remarkable temperatures, three separate heating systems are usually used in tokamaks, each capable of delivering well over a million watts of power to the fuel. Together they generate and sustain plasma that is easily hot enough for the high energy collisions required for fusion to occur.
The constituents of a 100 million-degree plasma are moving about really fast, and, if left alone would soon be so far apart as to render collisions extremely unlikely. To keep the density of the plasma high enough to ensure collisions do actually occur, the plasma vessel is surrounded by huge electromagnets. These create magnetic fields 10,000 times stronger than the Earth’s magnetic field and confine the plasma to perpetually circulate within the ring-shaped vessel. However if the plasma gets too dense then collisions of a different kind – between nuclei and electrons – begin to create large amounts of radiation. This radiation, called bremsstrahlung, saps energy from the plasma and prevents fusion from occurring – the optimum density value is around one millionth of the atmosphere.
The International Atomic Energy Agency aggresses some issues in What is Fusion, and Why Is It So Difficult to Achieve?
Simply put, nuclear fusion is the process by which two light atomic nuclei combine to form a single heavier one while releasing massive amounts of energy. Fusion reactions take place in a state of matter called plasma — a hot, charged gas made of positive ions and free-moving electrons that has unique properties distinct from solids, liquids and gases.
To fuse on our sun, nuclei need to collide with each other at very high temperatures, exceeding ten million degrees Celsius, to enable them to overcome their mutual electrical repulsion. Once the nuclei overcome this repulsion and come within a very close range of each other, the attractive nuclear force between them will outweigh the electrical repulsion and allow them to fuse. For this to happen, the nuclei must be confined within a small space to increase the chances of collision. In the sun, the extreme pressure produced by its immense gravity create the conditions for fusion to happen.
The amount of energy produced from fusion is very large — four times as much as nuclear fission reactions — and fusion reactions can be the basis of future fusion power reactors. Plans call for first-generation fusion reactors to use a mixture of deuterium and tritium — heavy types of hydrogen. In theory, with just a few grams of these reactants, it is possible to produce a terajoule of energy, which is approximately the energy one person in a developed country needs over sixty years.
On earth, we need temperatures exceeding 100 million degrees Celsius and intense pressure to make deuterium and tritium fuse, and sufficient confinement to hold the plasma and maintain the fusion reaction long enough for a net power gain, i.e. the ratio of the fusion power produced to the power used to heat the plasma.
Nuclear fusion and plasma physics research are carried out in more than 50 countries, and fusion reactions have been successfully achieved in many experiments, albeit without demonstrating a net fusion power gain. How long it will take to recreate the process of the stars will depend on mobilizing resources through global partnerships and collaboration.
Threshold of What?
I would like to believe we are on the threshold of amazingly clean energy to power all of our need.
More accurately, I would like to see that happen whether anyone believes it or not.
I am amazed at the scientific breakthroughs and temperatures achieved but from a practical standpoint I have to ask the threshold of what?
We have succeeded at producing the temperatures necessary, but for only 100 trillionths of a second and only by putting in more power than we got out.
I do not believe we are on the threshold of usable fusion energy no matter what the headlines suggest.
But given that fusion can theoretically supply all of our energy needs cleanly, I would prefer to be wrong.
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