1 - Fusion Energy
Bret Kugelmass: Tell me about some of the things going on here at Oak Ridge National Labs.
Phil Ferguson: Phil Ferguson is the director of fusion and materials at Oak Ridge National Labs. The ITER U.S. home is at the Oak Ridge National Labs; it is the next step in fusion energy. At this step, the alpha particles coming off of the fusion reaction heat the plasma so external energy is no longer required to keep the plasma at 100 million degrees. Once it gets to a point in which the plasma heats itself, the energy can be pulled off and it can be made into a viable electricity source. Ferguson started out at Missouri University of Science and Technology where he got his PhD. He went to Los Alamos for a summer which turned into two and a half years when they had an issue with the spallation target system. Spallation happens when a piece of the nucleus is broken off, leaving the nucleus in a very energetic or excited state. It wants to become stable as quickly as possible causing it to throw off particles, including neutrons. This timing can be used to do condensed matter physics. In order to achieve spallation, you need a particle at some significant fraction of the speed of light through the use of an accelerator.
2 - Spallation Neutron Source
Bret Kugelmass: What is thrown at the nucleus in a fusion reaction?
Phil Ferguson: Protons, charged particles that are either H-plus or H-minus, are accelerated and thrown at the nucleus to cause a fusion reaction. Plasma is the most common form of matter in the universe, except on Earth. A plasma is created and charged particles, or protons, can be pulled off from the ion source. Plasma is created by heating a gas or a mixture of particles to a certain temperature so it is no longer atoms but instead a pool of electrons and ions. A series of cavities alternate charge states, one end being positive and one end being negative. As the proton comes out, it gets pulled by the negative end and simultaneously pushed by the positive end. The fields in the mile-long accelerator are then flipped as the proton reaches the end; the timing has to be down to the microseconds or nanoseconds. A neutron-rich target, such as a heavy metal or liquid mercury, is placed at the end to cause spallation. The Spallation Neutron Source (SNS), a 1 GeV accelerator, puts that beam incident on a liquid mercury target and for every proton that goes into the target there are about 23 neutrons from the chain reaction. The low-energy component does not have any directionality, but the high-energy component goes in the forward direction. SNS has hundreds of people that study everything from the ion source, quadrupole magnets, the accelerating cavities, the target itself, and the moderators. Experiments at SNS range from fundamental properties of magnets to how drugs are absorbed in the body.
3 - Material Characterization with Neutrons and Photons
Bret Kugelmass: How are neutrons and photons used for material characterization differently?
Phil Ferguson: Neutrons and photons are complimentary. X-rays provide a very bright, intense beam that cannot be achieved with neutrons. However, neutrons can get penetration deep in the material that cannot be provided with x-rays and can get isotopic tailoring. Photons typically show the electronic structure. Neutrons allow one to look at the difference between its cross-section between hydrogen and deuterium since it is a weakly interacting particle. One scattering experiment looked at corrosion in a steam generator which had very thick steel structures. In order to seem inside the structure without destructive testing, neutrons could be used to penetrate through the thick steel wall to look for residual stress or issues in the welding process. While in grad school, Phil Ferguson worked at Los Alamos where he was exposed to the accelerator and studied there on an existing spallation source after getting his PhD. The U.S. was making a push to regain some leadership in neutron scattering and decided to build a spallation source at Oak Ridge National Labs. Ferguson was one of three who formed the initial neutronics or spallation physics team at the Oak Ridge spallation source. His team focused on the design of the target station, specifically how to get the most neutrons and still remove the heat from the target to run reliably. They decided on a liquid mercury target for the Oak Ridge Spallation Neutron Source (SNS).
4 - Fusion in Industry
Bret Kugelmass: How long did it take from concept to commissioning for the Spallation Neutron Source?
Phil Ferguson: Phil Ferguson arrived at the Spallation Neutron Source (SNS) in 2000. The first beam on target was in 2006. Ferguson helped design and commission the target station and was then promoted to be over the entire target station. He moved into neutron source development, taking various steps in spallation until 2012 or 2013 when he took his current job as the Director of Fusion and Materials for Nuclear Systems at Oak Ridge National Labs. Ferguson wanted to move away from the operational side of the work and back into the source design side. In the 1980’s and 1990’s, industry was involved in fusion and there was a lot of money and effort in the technology. Through various changes, the funding in fusion in the U.S. went down significantly and a lot of the industry left fusion, making it more of a science as opposed to a strong drive towards an energy source. At the time, the decision was made that fusion was not a high priority and the technology was not ready for the rapid advancement thought to lead to a quick power source. ITER is the last big step in the physics chain which looks at how physics will change with self-heated plasma.
5 - The Fuse Cycle
Bret Kugelmass: Tell me about how the energy from one reaction helps perpetuate the next reaction in self-heating plasma.
Phil Ferguson: For fusion to take place, there must be three things: there must be enough atoms, they must be hot enough, and they must be held together long enough to fuse. To start that process requires a lot of energy. The energy to be taken away from fusion is not necessarily the heat that heats the plasma. The helium atom has a very short range and heats the plasma. A 14MeV neutron comes off with a very long range and is captured and used to make another triton. Energy is released in that process and is the majority of the energy to be captured and used for electricity. Fusion is a two-step process. The first step is creating a very intense source of neutrons. The second step is doing what’s required to close the fuse cycle to continue the reaction by fueling it and to extract energy. The boundary layer on the plasma is sometimes not stable and collapses, causing core plasma to reach out and touch the wall. Changing the magnetic field may be used to ensure the fuel does not collapse and reach out and touch the wall.
6 - Fusion Nuclear Science
Bret Kugelmass: How is the pellet system used in a fusion reaction?
Phil Ferguson: Changing the composition and size of the pellet can be combined with different techniques to impact the plasma in different ways, such as releasing energy. The plasma must be fueled, the fuel cycle must be closed, and the neutrons must be slowed to be absorbed in lithium and create tritium. The first wall is where the plasma reaches out and touches. In order to be as efficient as possible and close the fuel cycle, the first wall needs to be integrated with the first wall of the blanket. A structure material needs to be compatible with the plasma, since the wall erodes and part of the material goes into the plasma. Certain materials can poison the plasma over time and terminate the reaction. Just outside the first wall is a material stack that cools the wall and, as soon as possible, the neutrons should be absorbed into material to produce tritium. There is not a blanket concept or material that works. There is no material yet that meets all the specifications in terms of temperature operating windows, internal radiation damage, and the helium generated at these energies to build a tokamak. The Cadarache in the South of France is the ITER site, which is the big international collaboration designed to study burning plasma physics. Tokamaks are needed to optimized on the fusion nuclear science. The Chinese Fusion Engineering Test Reactor (CFETR) is a bit ahead of the U.S. Fusion Nuclear Science Facility (FNSF). The ITER track studying the physics could be combined with fusion science and technology aspects to form a demonstration reactor.
7 - Challenges in Fusion Technology
Bret Kugelmass: What are the challenges in developing fusion along with the national science approach and the challenges the more aggressive private industry faces?
Phil Ferguson: Burning plasma physics is going to be important for everyone involved in fusion. There are large instabilities called destructions; a disruption is a magnetohydrodynamic (MHD) instability in which the entire plasma, 500 MW, is lost in one location. Closing the fuel cycle is another challenge. Because of the existing fission reactors, especially the CANDU reactors, there is a significant supply of tritium but it will dwindle because it decays at 5% per year. Creating the fusion fuel source, tritium, in-house with fission reactors is an economic benefit to fusion. Everyone needs a material from which to build their device. The ones that operate deuterium-tritium (DT) fusion will have the same issues in terms of materials. Some of the private fusion ventures envision using liquid metals which interact with material. Lead lithium interacts with the structural materials, causing embrittlement or corrosion. Lead lithium creates tritium in situ, it flows and can be used as a heat removal device, and acts as a good shield. ITER is a very large, expensive facility; making the device smaller is critical. High temperature superconducting magnets produce a stronger field which increases the density of the atoms. This would allow the tokamak to be smaller while still achieving burning plasma.
8 - Innovating Magnetic Fields
Bret Kugelmass: What temperature do high temperature superconducting magnets operate at?
Phil Ferguson: High temperature superconducting magnets typically operate on hundreds of Kelvin. If liquid helium isn’t needed to cool the magnets, there is a tremendous savings in what needs to be done in cooling. REBCO is a rare-earth material that can be made in a very strong magnetic field into a very thin tape. Those tapes can be used to construct a magnet for a tokamak which could double the field size or more. Radiation can displace atoms from its lattice site and can also generate gas in a material. Fission reactors are very high displacement rate with very low gas. Fast reactors produce 10 times more gas with a high displacement rate. 14 MeV neutrons, or fusion neutrons, produce copious amounts of gas but not as many displacements per atom. The same material scientists like to apply their skills across the field, in light water, fast reactor, and fusion applications. Fusion is important because it creates an energy source that costs almost nothing and that produces a waste which is helium gas. This technology is something that should be strived for.