Maps
Webmail
Home > About us > Media > Archived news > 2022 > A competition for the spontaneous rotation of the plasma
A competition for the spontaneous rotation of the plasma
All the versions of this article: [English] [français]
Control of rotation is a major challenge in order to obtain a stable and well-confined plasma in future tokamak fusion reactor. While energetic neutral particle injectors allow partial control of flows in medium-sized tokamaks, the large volume of plasma in ITER will make this control more difficult. However, the flows play a key role in the stability of the plasma and the quality of the confinement.
A fascinating observation is that a tokamak plasma rotates, even in the absence of an external source of momentum. This phenomenon is called "intrinsic rotation". There are two mechanisms leading to intrinsic rotation: the force exerted by turbulence and magnetic braking effects.
The turbulence acts on the rotation via an exchange of momentum between waves and particles, which locally bring a net angular momentum to the plasma. The resulting velocity is called "self-generated velocity". The 3D effects of the magnetic field have the consequence of constraining the trajectories of the particles. These constraints are responsible for collisional magnetic braking which imposes the flow velocity of the plasma. This velocity, called “relaxed velocity”, is finite and depends on the temperature gradient. Each of these effects taken separately is well documented.
However, the competition between these two mechanisms has never been studied before. For this study, the 3D perturbation of the magnetic field considered is the "ripple", i.e. the modulation of this field due to the finite number of coils. The larger the amplitude of this perturbation, the more the plasma velocity will tend to reach its relaxed prediction. Conversely, if this amplitude is low or the turbulent intensity is high, it is towards the self-generated prediction that the plasma flows.
The idea is that there is a critical ripple amplitude at which the velocity is closer to its relaxed prediction than to the self-generated one. From an analytical theoretical model, a simple expression of this threshold has been obtained. Its validity has been proven by means of gyrokinetic simulations with the GYSELA code, which take into account both mechanisms in a self-consistent manner, performed with ripple amplitudes below and above this threshold. As expected, the effect of turbulence is subdominant in the high ripple amplitude case, and vice versa for the low amplitude case. Using the critical ripple expression, first estimates on ITER seem to show that the ripple effect will not be negligible near the plasma edge.
Associated publication: R. Varennes et al, Phys. Rev. Lett. 128, 255002
Contact at LPP: Laure Vermare
Also in this section :
- 2022 Summer School for undergraduate students: From the laboratory to the distant universe, the World of Plasmas
- Henri Decauchy defended his PhD "Physics of cold plasma jets - Fundamental study of guided streamers and applications to oncology"
- Public outreach conference on the Solar Orbiter mission and the Sun’s influence on Earth at the Plaisir Castle park
- Lui Habl defended his PhD "Investigation of DC and RF biased gridded ion thruster plume phenomena"
- Review on physics of plasma jets and interaction with surfaces
- Pascal Chabert receives the Silver Medal from CNRS
- Giulia Cozzani, former Ph.D. student at LPP, has been awarded with the Vincenzo Ferraro Prize 2022
- Audrey Chatain has been awarded the 2021 René Pellat prize from SFP (French Physics Society)
- The first international symposium on CO2 recycling by plasma/catalysis closes the H2020 PIONEER project
- Opening of applications for the Master M2 of Physics of Plasmas and Fusion
- Non Thermal Plasmas for in situ resources utilization (ISRU) in Mars missions
- Science Festival 2022
- Jean-Paul Booth receives the 2019 Plasma Prize Award of the American Vacuum Society
- Océane Blaise defended her PhD "Cold atmospheric plasma improves bactericidal activity and stimulates phagosome maturation of macrophages"
- Robin Varennes defended his PhD "Flow drive in tokamak plasmas: competition and synergies between turbulence and neoclassical effects"
- Benjamin Esteves defended his "Investigation of iodine plasmas for space propulsion applications"
- Jonas August defended his PhD "Etude des effets d’un plasma froid d’air ambiant sur la physiologie des graines d’Arabidopsis"
- Soboh Alqeeq defended his PhD "Energy conversion processes related to dipolarization fronts in the Earth magnetotail"
- Nicolas Aunai defended his HDR «Studying magnetic reconnection via modeling and observations in the Earth magnetosphere »
- Ambipolar electrostatic field in dusty plasma
