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research article

Gyrokinetic transport driven by ubiquitous modes in LTX-like tokamak with ‘flat’ temperature

Choudhary, Sagar
•
Krishna M, Gopal
•
Chowdhury, Jugal
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August 1, 2025
Nuclear Fusion

A global, gyro-kinetic nonlinear study of the ubiquitous mode (UM) for Lithium Tokamak eXperiment (LTX)-like profiles, under flat electron and ion temperature scenarios is conducted using a global gyrokinetic model. Exact MHD equilibria with circular shapes are considered. In contrast to conventional trapped electron modes (TEM), where the mode rotates in the electron diamagnetic drift direction, the collision-less TEM branch associated with UMs exhibits a mode rotation in the direction of ion diamagnetic drift. The dispersion relations and mode structures for both UMs and conventional TEMs are computed through linear analysis, revealing that UMs become unstable for toroidal mode numbers n > 17 ( k θ ρ s > 1.14 ). Nonlinear simulations are performed to study the turbulence driven by UMs. The results show weak zonal flow (ZF) excitation, suggesting that the ZF shearing rate plays a limited role in the saturation mechanism of microturbulence. ZFs are further examined for the effects of temperature gradients ( η i , e < η crit ITG ), however, only an insignificant change is observed. One interesting observation is a natural shift of the dynamics from the UM dominated linear and quasilinear regime to the TEM dominated nonlinear regime, with characteristic high-n to low-n ‘inverse cascade’ typical of the quasi-2D nature of tokamak turbulence. Mode coupling and inverse cascading are identified as the dominant mechanisms driving turbulence saturation.

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Type
research article
DOI
10.1088/1741-4326/ade816
Scopus ID

2-s2.0-105010167622

Author(s)
Choudhary, Sagar

ITER

Krishna M, Gopal

Institute for Plasma Research

Chowdhury, Jugal

Institute for Plasma Research

Singh, Amit K.

Institute for Plasma Research

Mahapatra, Jagannath

Institute for Plasma Research

Hayward-Schneider, Thomas

Max Planck Institute for Plasma Physics

Lanti, Emmanuel  

École Polytechnique Fédérale de Lausanne

Ganesh, Rajaraman

Institute for Plasma Research

Villard, Laurent  

École Polytechnique Fédérale de Lausanne

Date Issued

2025-08-01

Publisher

IOP Publishing Ltd

Published in
Nuclear Fusion
Volume

65

Issue

8

Article Number

086006

Subjects

gyrokinetic

•

LTX

•

orb5

•

tokamak

•

transport

•

turbulence

•

Ubiquitous

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
SPC-TH  
FunderFunding(s)Grant NumberGrant URL

HBNI

SERI

Swiss State Secretariat for Education, Research and Innovation

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Available on Infoscience
July 25, 2025
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/252533
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