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The reason I mention this is that one can differentiate between the natural pressure of the plasma and the pressure applied by a magnetic field. The ratio of these two, called beta, is an important parameter in fusion reactors. Essentially, the efficiency of fusion goes up rapidly as beta approaches one, so magnetic compression aims to get beta as close to that level as possible.
Recent experiments on the Lithium Tokamak Experiment (LTX), the first facility to fully surround plasma with liquid lithium, showed that lithium coatings can produce temperatures that stay constant all the way from the hot central core of the plasma to the normally cool outer edge. The findings confirmed predictions that high edge temperatures and constant or nearly constant temperature profiles would result from the ability of lithium to keep stray plasma particles from kicking—or recycling—cold gas from the walls of a tokamak back into the edge of the plasma.
Researchers performed this set of experiments with solid lithium, Boyle explained, but a coating of liquid lithium could produce similar results. Physicists have long used both forms of lithium to coat the walls of LTX. Since flowing liquid lithium could absorb hot particles but wouldn't wear down or crack when struck by them, it also would reduce damage to tokamak walls - another critical challenge for fusion.
China's Experimental Advanced Superconducting Tokamak (EAST) made an important advance by achieving a stable 101.2-second steady-state high confinement plasma, setting a world record in long-pulse H-mode operation on the night of July 3rd.
All the plasma parameters, including recycling, and particle and heat fluxes, reached a truly steady state after 20 seconds—the wall saturation time for the W divertor—and remained stable until the end of the discharge.
The stellarator Wendelstein 7-X has received its first divertor. Just one step closer towards realising plasma pulse lengths of half an hour without breaking the machine
“The higher heat handling capabilities of the divertor allows us to make longer pulses with higher energy input”, says Arturo Alonso, W7-X‘s task force leader. A divertor takes the energy that is split out from the main plasma. It diverts waste particles directly into the trash with the help of magnetic field lines. For the first operational period of Wendelstein 7-X (from 10th December 2015 to 10th March 2016) a limiter had to do the job of the actual divertor, but its performance was quite “limited”.
Now that the divertor is in place and the wall elements made of copper-chromium-zirconium have been covered by graphite tiles, researchers expect extended pulse lengths of about one minute, as the permitted energy input per discharge moves from 4 Megajoule up to 80 Megajoule, a 20 fold increase in terms of renergy input!
The suppressed instability is called a global Alfvén eigenmode (GAE)—a common wave-like disturbance that can cause fusion reactions to fizzle out. Suppression was achieved with a second neutral beam injector recently installed as part of the NSTX-U upgrade. Just a small amount of highly energetic particles from this second injector was able to shut down the GAEs.
The redesigned parts, called pole shields, protect magnets in the injectors from the energetic particles from the beam and will replace units that melted and cracked during previous fusion experiments, resulting in water leaks. The magnets redirect charged [...] ions in the beams to an ion dump inside the injectors, permitting only neutral atoms to enter into the plasma.
The new shields consist of half-inch thick, roughly five-foot long copper plates equipped with inserts of the hard, silvery metal molybdenum in the center of the plates, the area that will absorb the most energy from the beam.
At MIT, researchers have focused their attention on using radio-frequency (RF) heating in magnetic confinement fusion experiments
The new approach [...] uses a fuel composed of three ion species: hydrogen, deuterium, and trace amounts (less than 1 percent) of helium-3. Typically, plasma used for fusion research in the laboratory would be composed of two ion species, deuterium and hydrogen or deuterium and He-3, with deuterium dominating the mixture by up to 95 percent. Researchers focus energy on the minority species, which heats up to much higher energies owing to its smaller fraction of the total density.
The new method has resulted in raising trace amounts of ions to megaelectronvolt (MeV) energies — an order of magnitude greater than previously achieved.
Porkolab suggests that the new approach could be helpful for MIT’s collaboration with the Wendelstein 7-X stellarator at the Max Planck Institute for Plasma Physics in Greifswald, Germany.
Still under peer review as of press time was a paper submitted to the journal Physics of Plasmas, in which Lerner and his coauthors claim to have produced a confined mean ion energy of 200 kiloelectron volts, equivalent to a temperature of over 2 billion kelvins. “As far as we know, that’s a record for any fusion plasma,” Lerner says.
Now on a new crowdfunding campaign to upgrade its DPF reactor, LPPFusion says it hopes to be fusing proton and boron by next year. (The results LPPFusion has obtained to date have involved deuterium plasmas.)
"Helium is an element that we don't usually think of as being harmful," said Dr. Michael Demkowicz, associate professor in the Department of Materials Science and Engineering. "It is not toxic and not a greenhouse gas, which is one reason why fusion power is so attractive."
However, if you force helium inside of a solid material, it bubbles out, much like carbon dioxide bubbles in carbonated water.
"Literally, you get these helium bubbles inside of the metal that stay there forever because the metal is solid," Demkowicz said. "As you accumulate more and more helium, the bubbles start to link up and destroy the entire material."
Fusion energy researchers have discovered that they can rapidly extinguish and cool a magnetically confined fusion plasma hotter than the center of the sun by injecting a large quantity of neon gas to prevent damage to fusion-energy devices when there is a loss of plasma equilibrium.
Although successful, there are a number of problems associated with the nature of the TSMG [Top Seeded Melt Growth] technique, including porosity, sample shrinkage and inhomogeneity in the distribution RE-211 [rare earth yttrium] content throughout the volume of sample, which leads to inefficient flux pinning. As a result, a new process based on top seeded infiltration and growth (TSIG) has been developed relatively recently as an alternative approach for the fabrication of large (RE)BCO single grains. The TSIG technique yields samples that are more dense, more uniform and have potentially better properties than those produced by TSMG. However, it is considerably more challenging to fabricate large-sized samples by this technique due to the relative complexity of the process. We describe the TSIG process and its application to a variety of (RE)BCO bulk superconductors and report the successful fabrication of single grains of up to 37.5 mm in diameter YBCO by a novel, 2-step TSIG process. This process enables a straightforward and very reliable growth process, which has clear practical implications for the manufacture of bulk samples for commercial applications.
In 2015, TAE reported that it was able to keep a high-temperature plasma stable for 5 milliseconds in its C-2U plasma generator, marking a significant advance for the field. Since then, the company has upgraded to an even more capable machine that’s nicknamed Norman — in honor of the company’s late co-founder, Norman Rostoker.
TAE is partnering with Google to optimize Norman’s plasma configuration using artificial intelligence, and this month, Binderbauer announced that the company achieved the colliding and merging of field-reversed configurations [FRC] on the new machine.
“FRCs are a critical component of plasma confinement and stability,” Binderbauer said. “Thanks to our previous insights from C-2U, Norman’s plasma will be both hotter and more stable from the outset.”
H. Neilson visited Japan's National Institute for Fusion Science (NIFS) for a series of discussions on topics for stellarator collaboration. A highlight of the visit was a tour of the Large Helical Device (LHD) pellet injection system, which ingeniously combines a 20-pellet burst system with a continuous repeating pneumatic injector. ... The discussions were held in the context of a collaboration, involving ORNL, NIFS, Germany's Max Planck Institute for Plasma Physics, and PPPL to provide a continuous pellet fueling system for the Wendelstein 7-X (W7-X) stellarator to meet fueling requirements similar to those of LHD