{"id":611040,"date":"2024-06-11T09:09:33","date_gmt":"2024-06-11T13:09:33","guid":{"rendered":"https:\/\/platohealth.ai\/new-plasma-escape-mechanism-could-protect-fusion-vessels-from-excessive\/"},"modified":"2024-06-11T10:00:36","modified_gmt":"2024-06-11T14:00:36","slug":"new-plasma-escape-mechanism-could-protect-fusion-vessels-from-excessive","status":"publish","type":"post","link":"https:\/\/platohealth.ai\/new-plasma-escape-mechanism-could-protect-fusion-vessels-from-excessive\/","title":{"rendered":"New plasma escape mechanism could protect fusion vessels from excessive","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"
<\/div>\n

The furious exhaust heat generated by a fusing plasma<\/u> in a commercial-scale reactor may not be as damaging to the vessel\u2019s innards as once thought, according to researchers at the U.S. Department of Energy<\/u>\u2019s (DOE) Princeton Plasma Physics Laboratory<\/u> (PPPL), Oak Ridge National Laboratory<\/u> and the ITER Organization<\/u> (ITER).<\/p>\n

Credit: Simulation credit: Seung-Hoe Ku \/ Princeton Plasma Physics Laboratory on DOE\u2019s Summit computer at Oak Ridge National Laboratory; Visualization credit: Dave Pugmire and Jong Youl Choi \/ Oak Ridge National Laboratory<\/p>\n

\n

The furious exhaust heat generated by a fusing plasma<\/u> in a commercial-scale reactor may not be as damaging to the vessel\u2019s innards as once thought, according to researchers at the U.S. Department of Energy<\/u>\u2019s (DOE) Princeton Plasma Physics Laboratory<\/u> (PPPL), Oak Ridge National Laboratory<\/u> and the ITER Organization<\/u> (ITER).<\/p>\n

\u201cThis discovery fundamentally changes how we think about the way heat and particles travel between two critically important regions at the edge of a plasma during fusion<\/u>,\u201d said PPPL Managing Principal Research Physicist Choongseok Chang<\/u>, who led the team of researchers behind the discovery. A new paper<\/u> detailing their work was recently published in the journal Nuclear Fusion<\/em>, following previous<\/u> publications<\/u> on the subject. <\/p>\n

To achieve fusion, temperatures inside a tokamak<\/u> \u2014 the doughnut-shaped device that holds the plasma \u2014 must soar higher than 150 million degrees Celsius. That\u2019s 10 times hotter than the center of the sun. Containing something that hot is challenging, even though the plasma is largely held away from the inner surfaces using magnetic fields. Those fields keep most of the plasma confined in a central region known as the core, forming a doughnut-shaped ring. Some particles and heat escape the confined plasma, however, and strike the material facing the plasma. New findings by PPPL researchers suggest that particles escaping the core plasma inside a tokamak collide with a larger area of the tokamak than once thought, greatly reducing the risk of damage.<\/p>\n

Past research based on physics and experimental data from present-day tokamaks suggested exhaust heat would focus on a very narrow band along a part of the tokamak wall known as the divertor plates. Dedicated to removing exhaust heat and particles from the burning plasma, the divertor is critical to a tokamak\u2019s performance. <\/p>\n

\u201cIf all of this heat hits this narrow area, then this part of the divertor plate will be damaged very quickly,\u201d said Chang, who works in the PPPL Theory Department. \u201cIt could mean frequent stretches of downtime. Even if you are just replacing this part of the machine, it\u2019s not going to be quick.\u201d<\/p>\n

The problem hasn\u2019t stopped the operation of existing tokamaks which are not as powerful as those that will be needed for a commercial-scale fusion reactor. However, for the last few decades, there has been significant concern that a commercial-scale device would create plasmas so dense and hot that the divertor plates might be damaged. One proposed plan involved adding impurities to the edge of the plasma to radiate away the energy of the escaping plasma, reducing the intensity of the heat hitting the divertor material, but Chang said this plan was still challenging. <\/p>\n

Simulating the escape route<\/strong><\/p>\n

Chang decided to study how the particles were escaping and where the particles would land on such a device as ITER, the multinational fusion facility under assembly in France. To do so, his group created a plasma simulation using a computer code known as X-Point Included Gyrokinetic Code<\/u> (XGC). This code is one of several developed and maintained by PPPL that are used for fusion plasma research. <\/p>\n

The simulation showed how plasma particles traveled across the magnetic field surface, which was intended to be the boundary separating the confined plasma from the unconfined plasma, including the plasma in the divertor region. This magnetic field surface \u2014 generated by external magnets \u2014 is called the last confinement surface. A couple of decades ago, Chang and his co-workers found that charged particles known as ions were crossing this barrier and hitting the divertor plates. They later discovered these escaping ions were causing the heat load to be focused on a very narrow area of the divertor plates.<\/p>\n

A few years ago, Chang and his co-workers found that the plasma turbulence can allow negatively charged particles called electrons to cross the last confinement surface and widen the heat load by 10 times on the divertor plates in ITER. However, the simulation still assumed the last confinement surface was undisturbed by the plasma turbulence.<\/p>\n

\u201cIn the new paper, we show that the last confinement surface is strongly disturbed by the plasma turbulence during fusion, even when there are no disturbances caused by external coils or abrupt plasma instabilities,\u201d Chang said. \u201cA good last confinement surface does not exist due to the crazy, turbulent magnetic surface disturbance called homoclinic tangles.\u201d<\/p>\n

In fact, Chang said the simulation showed that electrons connect the edge of the main plasma to the divertor plasmas. The path of the electrons as they follow the path of these homoclinic tangles widens the heat strike zone 30% more than the previous width estimate based on turbulence alone. \u201cThis means it is even less likely that the divertor surface will be damaged by the exhaust heat when combined with the radiative cooling of the electrons by impurity injection in the divertor plasma. The research also shows that the turbulent homoclinic tangles can reduce the likelihood of abrupt instabilities at the edge of the plasma, as they weaken their driving force.\u201d<\/p>\n

\u201cThe last confinement surface in a tokamak should not be trusted,\u201d Chang said. \u201cBut ironically, it may raise fusion performance by lowering the chance for divertor surface damage in steady-state operation and eliminating the transient burst of plasma energy to divertor surface from the abrupt edge plasma instabilities, which are two among the most performance-limiting concerns in future commercial tokamak reactors.\u201d<\/p>\n

This research received funding from the DOE\u2019s Fusion Energy Sciences<\/u> and Advanced Scientific Computing Research<\/u> to the SciDAC Partnership Center for High-fidelity Boundary Plasma Simulation<\/u> under the contract DE-AC02-09CH11466.<\/p>\n

PPPL is mastering the art of using plasma \u2014 the fourth state of matter \u2014 to solve some of the world\u2019s toughest science and technology challenges. Nestled on Princeton University\u2019s Forrestal Campus in Plainsboro, New Jersey, our research ignites innovation in a range of applications including fusion energy, nanoscale fabrication, quantum materials and devices, and sustainability science. The University manages the Laboratory for the U.S. Department of Energy\u2019s Office of Science, which is the nation\u2019s single largest supporter of basic research in the physical sciences. Feel the heat at https:\/\/energy.gov\/science and https:\/\/www.pppl.gov.  <\/em><\/p>\n

\n
\n
\n
\n
\n

Journal<\/h4>\n

Nuclear Fusion<\/p>\n<\/div>\n

\n

DOI<\/h4>\n

10.1088\/1741-4326\/ad3b1e <\/i><\/p>\n<\/div>\n

\n

Method of Research<\/h4>\n

Computational simulation\/modeling<\/p>\n<\/div>\n

\n

Article Title<\/h4>\n

Role of turbulent separatrix tangle in the improvement of the integrated pedestal and heat exhaust issue for stationary-operation tokamak fusion reactors<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n