One year ago, mankind realized the net energy gain of nuclear fusion reaction for the first time. During this year, NIF has been continuously improved and has successfully realized three more ignitions, breaking several records in a row! Recently, the lead scientist of the project was selected as one of Nature's Top 10 People of the Year...
One year ago, mankind realized the net energy gain of nuclear fusion reaction for the first time. In this year, NIF continued to improve, and then successfully realized three ignition, breaking several records! Just recently, the project's chief scientist, but also selected as one of Nature's top ten people of the year.
December 14 last year, Lawrence Livermore National Laboratory (LLNL) for the first time to achieve controlled nuclear fusion ignition success, for all mankind to take off the clean energy "Holy Grail" -
After delivering 2.05 megajoules (MJ) of energy to the target, a fusion energy output of 3.15 MJ was produced with an energy gain of about 1.5.
On July 30, 2023, the Laboratory achieved its first ever output energy of 3.88 MJ, the highest ever.
On October 30, the lab set another record - 2.2 megajoules of input energy was achieved for the first time. Meanwhile, the output energy of 3.4 megajoules ranked second.
In the face of successful 'ignition' again and again, Nature also excitedly published an article saying - laser fusion is about to enter a whole new era.
It is conceivable that when controlled nuclear fusion is finally realized, mankind will have the possibility of obtaining massive amounts of carbon-free clean energy for the first time in history, revolutionizing the energy roadmap for the future.
In other words, by that time, there will be no more greenhouse gases from burning coal and oil, no more dangerous, long-lived radioactive waste - humanity will have access to 'clean energy' in the true sense of the word.
This means that the energy shortages that have plagued mankind since we entered the Electric Age will disappear. Humanity can even realize unprecedented technological breakthroughs in the stellar energy brought by controlled nuclear fusion.
But let's get back to reality first.
The real difficulty in getting the laser to deliver such huge amounts of energy is how to protect the NIF's precious optics from damage by debris.
NIF is the only laser system in the world that can operate above the damage threshold, and that's in part due to the optical recovery cycle developed in the lab.
Enhanced Optics
In June 2023, NIF completed two key enhancements that were critical to achieving the 2.2 megajoules of input energy.
These include the use of fused silica debris shielding on two-thirds of NIF's beamlines and the installation of metal shielding on 32 lower hemisphere beamlines.
These improvements reduced the damage rate caused by debris by a factor of 10 to 100, depending on the beamline. The optics at the lower beamlines received the most debris from the target chamber due to gravity.
Other improvements include a new anti-reflective coating, vapor hexamethyldisiloxane (HMDS) treatment, and an increase in optical recycling cycle capacity. As well as a new 'gray edge blocker' for a problem that scientists have yet to fully define.
More than just an increase in energy
Increased energy alone is not enough to sustain the amazing breakthroughs NIF has made in science - the
Laser pulses last only a few billionths of a second, so extreme precision is required to achieve the desired results.
To achieve this goal, the team recently completed the deployment of a High Fidelity Pulse Shaping (HiFiPS) system.
A multi-year project, HiFiPS enables more precise and accurate pulse shaping, which in turn enables better power balance and symmetry control in implosions.
In addition, the team refurbished the optical fibers in the facility to make them more tolerant of repeated neutron exposure. These fibers are used to accurately measure the laser pulse delivered to the target.
As a direct result of the refurbishment, the signal strength was increased by a factor of 10 to 100, and the researchers were able to continue to accurately 'observe' the laser performance.
However, there is still a long way to go from the current state of the art to realizing the delivery of fusion energy to the grid.
Although NIF has the largest laser in the world today, the system is extremely inefficient, with more than 99% of the energy in each ignition lost before it reaches its target.
And developing a more efficient laser system is a key goal of DOE's newly launched Inertial Fusion Research Program.
The department recently announced that it will invest $42 million over four years to establish three new research centers to work together to achieve this and other scientific advances.
Each of these centers will include national laboratories, university researchers and industry partners.
And one of the central figures in the entire fusion program, physicist Annie Kritcher, has managed to make it into Nature's Top 10 Science People of the Year, as well.
In 2022, Annie Kritcher achieved a goal at the National Ignition Facility (NIF) that had been elusive in laboratories around the world for decades-compressing atoms to such an extreme that their nuclei fused and produced more energy than the reaction itself consumed.
But after reaching this experimental milestone (i.e., ignition), the team was under pressure to repeat the achievement.
High-stakes research rarely goes smoothly: the team conducted its first replication in June, but the results were poor.
Fortunately, the third attempt was a success.
On July 30, the NIF's 192-beam laser fired 2.05 megajoules of energy at small spheres of the hydrogen isotopes deuterium and tritium suspended frozen in a gold cylinder.
The resulting implosion caused the isotopes to release energy as they fused into helium and produced temperatures six times that of the Sun's core.
Ultimately, these created a record-breaking 3.88 megajoules of fusion energy.
Looking around the world, no laboratory had been able to realize a fusion reaction that outputs more energy than it consumes until NIF achieved this feat.
Kritcher and her team then successfully performed two more ignitions in October, bringing the total to four.
Kritcher began researching fusion energy when she was a summer intern at Livermore in 2004. She soon set her sights on NIF - one of the few places in the world where fusion reactions can be studied.
Since then, she has led a team that analyzes experimental data and uses computer models to design experiments - by adjusting parameters such as the size and configuration of the target and the energy and timing of the various laser beams - to achieve and increase fusion yields. Once her team completes the design, the experimental team takes over firing the lasers and collecting data.
The process has shown Kritcher to be exceptional, and that led to her becoming one of the lead designers at NIF in 2016.
Over the next few years, Kritcher and her team have been number crunching and tweaking the design of NIF's main experimental program. While making various changes to the target, the team also utilized various improvements to increase the overall energy of the laser. The result is that nuclear fusion is being realized, more and more frequently.
With the success of 'Ignition', Kritcher began a new series of experiments - increasing the yield again by delivering more laser energy to a thicker target capsule.
And this represents another step toward achieving tens of terajoules or even higher yields at NIF.
Controlled Fusion, the Holy Grail of Clean Energy
Simply put, nuclear fusion is the process by which two light atomic nuclei combine to form a heavier nucleus and release a huge amount of energy.
Two hydrogen atoms collide and polymerize to form a helium atom, which has a slightly smaller mass than the original hydrogen atom. According to Einstein's iconic E=mc² mass-energy equation, this mass difference is converted into a burst of energy.
At the core of the sun, fusion of 620 million tons of hydrogen is occurring every second. The energy produced is the source of all life on Earth.
But one of the big challenges in utilizing nuclear fusion is how to make the energy released from the fusion reaction greater than the energy input and make the process sustainable.
The NIF Ignition Principle
In the 1960s, a group of pioneering scientists at LLNL hypothesized that lasers could be used to induce nuclear fusion in a laboratory setting.
This revolutionary idea then evolved into inertial confinement fusion under the leadership of physicist John Nuckolls.
To realize this concept, LLNL built a series of increasingly powerful laser systems, culminating in the world's largest and most energetic NIF.
In the experiment, the lasers mimicked the conditions at the center of the Sun by fusing heavy hydrogen isotopes, deuterium and tritium, into helium.
First, a number of hydrogen pellets were placed into a device the size of a pepper grain, and then a powerful 192-beam laser was used to heat and compress the hydrogen fuel.
The lasers, upon entering the torus, hit the inner walls and cause them to emit X-rays, which can then heat it up to 100 million degrees Celsius - hotter than the center of the sun - and compress it to more than 100 billion times the Earth's atmospheric pressure.
High-energy lasers would plasmaize the surface of the blob, and the rest of the central material, driven by Newton's third law, would eventually collapse toward the center and implode.
At the time of implosion, a chain reaction - or "ignition" - can occur if the right amount of heat and pressure is applied to the fuel pellet, which then releases a large amount of energy.
Engineering marvels
The National Ignition Facility (NIF), which makes all of the above possible, is also a remarkable achievement in engineering and technology.
Materials scientists and laser physicists worked with engineers to design a facility containing 7,500 large optics, 26,000 small optics, and more than 66,000 control points.
These optics and other components are contained in approximately 6,200 complex modular units called Line Replaceable Units (LRUs). They can be quickly replaced when necessary to ensure continuous operation of the facility.
The NIF laser pulse travels one kilometer and takes 4.5 microseconds from the initial pulse formation in the main oscillator chamber to reaching the target. The time difference to reach the center of the target chamber is 30 picoseconds with an accuracy of 50 microns.
Achieving this kind of pointing stability and absolute accuracy on the target is an enormous engineering challenge, requiring rock-solid stability of the optical support system, precise positioning and alignment of the components, and a rigorously accurate computerized timing system.
To meet these challenges, all structures supporting the NIF mirrors and lenses were designed with extreme stability in mind.
The engineering team meticulously calculated the possible effects on the laser components, typically the laser mirrors, for all sources of vibration including pumps, motors and transformers.
Through careful modeling, both vibration (>1Hz) and drift (<1Hz) were designed to be met. Test results show that the prototype beamline can perform at or better than the 50 micron requirement.
In addition, to ensure that the beamline components did not affect the laser headroom, the team used precision measurement techniques, resulting in a rigorous measurement network and controlled physical location of all beamline components. The positions of all beam housings, support systems and target chambers were accurate to a quarter of a millimeter.
This information was then provided to the design team, who designed the structure with both sufficient stiffness and damping so that the structure's response to ground vibration and expected vibration from the construction equipment met the overall stability requirements.
Ensuring that all 192 laser beams arrived within the specified 30 picoseconds was achieved through a precision timing system using a GPS satellite system that constantly updates the internal clock. Integrated software and hardware constantly monitor and update the timing to maintain accuracy.
Each mechanical interface is designed to better than 300 femtoseconds (three trillionths of a second) tolerance, so LRUs can be changed at any time to maintain timing accuracy. In addition, a tightly controlled program maintains system timing for each LRU.
Although, we can't really apply nuclear fusion to power generation with this device yet.
But on a scale of 60 years, mankind has made a major breakthrough.
For the future, we may also be able to hold more imagination.
