Gyrokinetic simulation of full electromagnetic kinetic ballooning mode in tokamaks
Kinetic ballooning mode (KBM) was simulated and studied numerically by means of a full electromagnetic theory that retains all three gyroscopic fields: $\tilde{\phi}$ , $\tilde{A_{||}}$ and $\tilde{B_{||}}$ . The destabilizing influence of the parallel magnetic field fluctuation $\delta B_{||}$ on t...
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| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | Nuclear Fusion |
| Subjects: | |
| Online Access: | https://doi.org/10.1088/1741-4326/aded22 |
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| Summary: | Kinetic ballooning mode (KBM) was simulated and studied numerically by means of a full electromagnetic theory that retains all three gyroscopic fields: $\tilde{\phi}$ , $\tilde{A_{||}}$ and $\tilde{B_{||}}$ . The destabilizing influence of the parallel magnetic field fluctuation $\delta B_{||}$ on the KBM was reported. When $\delta B_{||}$ is neglected, the maximum growth rate decreases by approximately 5% for the magnetohydrodynamic-like ballooning mode (BM), and the growth rates in the higher β region decrease significantly for KBMs with a moderate safety factor ( q ). These are due to the partial cancellation of the stabilizing component of the $\nabla B$ drift by introduction of $\delta B_{||}$ effect. Here, β is the ratio of the thermal pressure to magnetic pressure, and $\textbf {B}$ is the toroidal magnetic field. The destabilizing effect of $\delta B_{||}$ on KBM is weaker for higher q . Under the influence of toroidal effect, the introduction of the $\delta B_{||}$ results in the expansion of the KBM instability window. Compared to the main body of the KBM instability, the extended instability shows partially different features in both the mode- and spectral-structures. For the case of $\eta_i\unicode{x2A7E} 1$ , the KBM is always unstable in almost the entire region of low shear $\hat {s}$ for a smaller pressure gradient, and the stability boundary in $\hat{s}-\alpha$ plane is much wider than that for the case of $\eta_i = 0$ . Moreover, the stability boundary of the KBM changes slightly in the $\hat{s}-\alpha$ plane when $\delta B_{||}$ is included in the model. All the evidences indicated that β affects KBM through both $\delta A_{||}$ and $\delta B_{||}$ , and the fundamental properties of KBM are determined by the two gyroscopic fields: $\tilde{\phi}$ and $\tilde{A_{||}}$ , while a new $\textbf {B}\times \nabla \delta B_{||}$ ion drift is introduced by including $\delta B_{||}$ to modify the mode characteristics to some extent. |
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| ISSN: | 0029-5515 |