Publication

Intrinsic momentum transport driven by almost-rational surfaces in tokamak plasmas

Stephan Brunner
2026

Abstract

We demonstrate that a symmetry of the local gyrokinetic model is broken when the safety factor q is almost (but not exactly) a rational number and magnetic shear is ŝ ≈ 0. Tokamaks with such a q profile will spontaneously rotate due to turbulent momentum transport. Nonlinear gyrokinetic simulations indicate this mechanism is significantly stronger than all other drives of intrinsic rotation. It also intrinsically transports electric current, pulling q towards rational values and potentially aiding non-inductive current drive. This is likely important in the triggering of internal transport barriers.

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https://infoscience.epfl.ch/entities/publication/f747cf36-4b7d-4414-8937-f3bc2c2b438d

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Stephan Brunner
2026

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/f747cf36-4b7d-4414-8937-f3bc2c2b438d

About this result

Related concepts (32)

Rational number

In mathematics, a rational number is a number that can be expressed as the quotient or fraction \tfrac p q of two integers, a numerator p and a non-zero denominator q. For example, \tfrac{-3}{7} is a rational number, as is every integer (e.g., 5 = 5/1). The set of all rational numbers, also referred to as "the rationals", the field of rationals or the field of rational numbers is usually denoted by boldface Q, or blackboard bold \Q. A rational number is a real number.

Rational point

In number theory and algebraic geometry, a rational point of an algebraic variety is a point whose coordinates belong to a given field. If the field is not mentioned, the field of rational numbers is generally understood. If the field is the field of real numbers, a rational point is more commonly called a real point. Understanding rational points is a central goal of number theory and Diophantine geometry. For example, Fermat's Last Theorem may be restated as: for n > 2, the Fermat curve of equation has no other rational points than (1, 0), (0, 1), and, if n is even, (–1, 0) and (0, –1).

Rationality

Rationality is the quality of being guided by or based on reasons. In this regard, a person acts rationally if they have a good reason for what they do or a belief is rational if it is based on strong evidence. This quality can apply to an ability, as in rational animal, to a psychological process, like reasoning, to mental states, such as beliefs and intentions, or to persons who possess these other forms of rationality.

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Intrinsic momentum transport driven by almost-rational surfaces in tokamak plasmas

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