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"D-turn" of the steering news from the Mirage

Scientific researcher Alessandro Marinoni shows that reverse traditional plasma shaping provides greater stability for synthesis reactions.

Transverse sections of the pressure profiles are shown in two different configurations of plasma tomato (the center of the tomato maker donut is to the left of them). Discharges have high core pressure (yellow), which reduces to low pressure (blue) at the edge. Researchers have achieved a significant high pressure reverse D plasma response in the National DIII-D Synthesis Mechanism.

Transverse sections of the pressure profiles are shown in two different configurations of plasma tomato (the center of the tomato maker donut is to the left of them). Discharges have high core pressure (yellow), which reduces to low pressure (blue) at the edge. Researchers have achieved a significant high pressure reverse D plasma response in the National DIII-D Synthesis Mechanism.

Photo: Alessandro Marinoni / MIT PSFC

An attempt to duplicate the power of the sun to produce energy on earth has caused tens of decades of fusion researchers. One time to endless carbon-free energy focuses on heating and limiting plasma fuel in the tokamaks that use magnetic fields to keep the turbulent plasma circulating in a donut-shaped vacuum chamber and away from the walls. Researchers in the field of synthesis have preferred the shaping of these Tokamak plasma formations in triangular or D form, with the curvature of D extending from the center of the donut, allowing the plasma to withstand the intense pressures inside the device better than in the round shape.

Led by scientists from Alessandro Marinoni of the Center for Plasma Science and Synthesis of Massachusetts Institute of Technology (PSFC) and Max Austin of the University of Texas at Austin, researchers from the National Mechanism of Synthesis of the DIII-D found promising evidence that reversing the conventional the form of plasma in the Tokamak chamber can create a more stable environment for fusion even at high pressure. The results were published recently in Physical Review Letters and Physics of Plasmas.

Marinoni first experimented with the reverse form, also known as "negative triangulation," while pursuing his PhD degree in TCV Tokamak at Ecole Polytechnique Fédérale de Lausanne, Switzerland. The TCV team was able to show that negative triangulation helps reduce plasma turbulence, thereby increasing the limitation that is key to maintaining fusion reactions.

"Unfortunately, at that time, TCV was not equipped to work at high plasma pressures, with the temperature of the ion being close to that of electrons," Marinoni notes, "so we can not explore the modes directly related to the conditions of the synthesized plasma. "

Growing out of Milan, Marinoni is interested in synthesis through early passion for astrophysical phenomena trapped in pre-school age by the captivating mysteries of the black holes.

"It was charming because the black holes could catch the light. At that time I was a little child. As such, I could not understand why light can be captured by the gravitational force exerted by black holes, as nothing like that happens on Earth.

As he matures, he joins a local amateur astronomical club, but ultimately decides that the black holes will be a hobby, not a vocation.

"My job will be to try to produce energy through nuclear fission or synthesis; this is the reason why I enrolled in the nuclear engineering program at the Polytechnic University of Milan. "

After surveys in Italy and Switzerland, Marinoni took the opportunity to join the PSFC's DIII-D Tokyo co-operation in San Diego, under the guidance of MIT Physics Professor Miklos Porcolab. As a post-doc, he used a contrast-sensing phase of MIT to measure DIII-D plasma density fluctuations, later working as a PSFC researcher.

Max Austin, having read the results of the negative triangle from TCV, decided to explore the possibility of conducting such experiments on DIII-D tokamak to confirm the stabilizing effect of negative triangle. For the experimental proposal, Austin joined forces with Marinoni and together designed and conducted the experiments.

"The DIII-D research team is working against the assumptions of decades ago," Marinoni said. "Generally, it was thought that negative triangulation plasma could not maintain a high enough plasma pressure that would be important for energy production due to the magnitude-unstability of the magnetic-hydrodynamic (MHD) that would arise and destroy the plasma. MHD is a theory that governs the macrostability of electrically conductive liquids such as plasma. We wanted to show that, under the right conditions, the reverse form of D could support MHD stable plasma at high pressures to be suitable for a fusion power plant, even better than D-shaped in some respects.

While D-Plasma is the standard configuration, they have their own challenges. They are affected by high levels of turbulence, which prevents them from achieving the high levels of pressure required for economic merger. Researchers have solved this problem by creating a narrow layer near the plasma limit where turbulence is suppressed by the large shear flow, thus allowing the inner regions to achieve higher pressure. However, the steady-state pressure gradient develops in the outer plasma layers, making the plasma susceptible to instabilities called extreme localized modes which, if powerful enough, will expel a significant portion of the accumulated plasma energy, thereby damaging the tomato camera.

DIII-D is designed for the challenges of creating D-shaped plasma. Marinoni praises the DIII-D control group for "hard work to find a way to manage this unusual plasma with a reversed form."

The effort is paid off. DIII-D researchers have been able to show that even at higher pressures, the D reverse form is equally effective in lowering the plasma core turbulence than in the low pressure TCV medium. Despite the previous assumptions, DIII-D demonstrates that reverse triangulation plasma can maintain pressure levels suitable for a fusion power station; In addition, they can do this without the need to create a steep pressure gradient near the edge that would lead to machine-damaging edges localized modes.

Marinoni and colleagues are planning future experiments to further demonstrate the potential of this approach in an even larger merger-based magnetic topology based on a "detour" tokamak concept. He tried to interest other international tokamaks in experimenting with the reverse configuration.

"Because of hardware problems, only a few Tokamas can create negative triangular plasma; Tokamaks such as DIII-D, which are not intended to produce plasma in triangular triggers, require considerable effort to produce this form of plasma. However, it is important to engage the world fusion community in order to better understand the database of the benefits of this form. "

Marinoni is eagerly awaiting the place where the study will take over the DIII-D team. He goes back to his introduction to Tokamak, which has become the focus of his research.

– When I first learned about Tokamas, I thought, "Oh, cool! It is important to develop a new, carbon-free energy source.

This study is sponsored by the US Department of Energy's Energy Research Office using their DIII-D National Synthesis Fund.

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