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Development of Bounce-Time-Based Orbit-Following Monte-Carlo Code

Kouji SHINOHARA¹⁾, Keiji TANI²⁾, Nobuhiko HAYASHI³⁾, Shuhei SUMIDA³⁾, Akira EJIRI¹⁾, Naoto TSUJII¹⁾, Masanobu SUZUKI³⁾, Andreas BIERWAGE³⁾, Seiya NISHIMURA³⁾, Yi PENG¹⁾, Yu-Ting LIN¹⁾, Yiming TIAN¹⁾, Fumiya ADACHI¹⁾

1)

The University of Tokyo, Chiba, 277-8561, Japan

2)

Kyoto Fusioneering, Tokyo, 100-0004, Japan

3)

National Institutes for Quantum Science and Technology (QST), Naka Institute for Fusion Science and Technology, Ibaraki 311-0193, Japan

(Received 1 December 2024 / Accepted 18 December 2024 / Published 9 April 2025)

Abstract

We developed a bounce-time (BT)-based orbit-following Monte-Carlo code as an extension of the OFMC code in QST. In the BT-based method, we take a bounce time as a time step of the orbit following. The time step is ~ 100 times longer than the gyro period which is a typical time step for the conventional guiding-center (GC) method. In the BT-based method, an accurate and simple estimation of a poloidal projection of the bounce orbit and a staying time are essential. An expression for the orbit gives us an orbit shape by a small calculation with the difference of less than 1% of the minor radius, compared with the GC method with the same fast ion parameters. And an approximate expression for the staying time also gives us the staying time with a good accuracy for our purpose. We can see a good agreement between calculation results for the BT-based method and those for the GC method in an axisymmetric condition. The BT-based method is 70–140 times faster than the GC method, depending on the slowing-down time.

Copyright (c) 2025 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

fast ion transport, bounce time, finite orbit width, Monte-Carlo code, tokamak

DOI: 10.1585/pfr.20.1403017

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