RESONANCE in radio frequency sheath admittance in nuclear fusion scenarios

Rezazadeh, Mikhail Xerxes

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https://hdl.handle.net/2142/116285 Copy

Description

Title

RESONANCE in radio frequency sheath admittance in nuclear fusion scenarios

Author(s)

Rezazadeh, Mikhail Xerxes

Issue Date

2022-07-21

Director of Research (if dissertation) or Advisor (if thesis)

Curreli, Davide

Committee Member(s)

Sankaran, Mohan

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Radio frequency
• radiofrequency
• fusion
• nuclear
• admittance
• resonance

Abstract

The next generation of tokamaks (SPARC, ARC, FNSF, DEMO) and several current tokamaks (WEST, etc.) will operate with Ion Cyclotron Resonance Heating (ICRH) as their sole auxiliary heating technique because it transfers power directly to the ions, and it involves the cheapest radio frequency (RF) components. During ICRH operation, RF sheaths form on the ICRH antenna itself, as well as on far-field magnetically-connected surfaces. However, RF sheaths are associated with large hot-spot formation and large impurity emissions. This work presents high-resolution numerical experiments on RF sheaths in nuclear fusion scenarios using hPIC2, a GPU-accelerated hybrid fluid-kinetic particle-in-cell code. The combined data from these experiments was obtained using super computing GPU-accelerated hardware which would require hPIC2 over 10 years of run time, were it running in single-core CPU mode. The experiments reveal a new RF sheath phenomenon which occurs when the radio frequency is on-par with ion cyclotron frequency in an oblique magnetic field. Due to the $1/R$ scaling of the magnetic field in a Tokamak, such cases are possible on a surface on-axis near the bottom of the vacuum chamber, with the precise location, whether on the divertor or the vacuum chamber first wall, dependent on the geometry of the tokamak. The combination of RF and cyclotron frequency are analogous to the classical driven, damped harmonic oscillator, where charge density damps ion admittance. This study shows that the resulting resonance can lead to increased ion flux at the wall and material sputtering.

Graduation Semester

2022-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Mikhail Rezazadeh

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