Analysis of damping rate measurements of toroidal Alfvén eigenmodes on JET as a function of n: part I

• Published in: Nuclear fusion 2012-02, Vol.52 (2), p.23013-14
• Main Authors: Panis, T., Fasoli, A., Testa, D.
• Format: Article
• Language: English
• Subjects: Continuums; Damping; Diagnostic systems; Discharge; Magnetohydrodynamics; Plasmas; Tokamak devices
• ISSN: 0029-5515; 1741-4326
• DOI: 10.1088/0029-5515/52/2/023013

The linear stability of Alfvén eigenmodes (AEs) is studied experimentally in the JET tokamak using its active MHD spectroscopy system, the so-called Alfvén Eigenmode Active Diagnostic (AEAD). Following the optimization of the AEAD system, AEs with toroidal mode numbers ( n ) in the low- n and medium- n range were excited systematically. A database was created from the damping rate measurements of toroidal AEs (TAEs), obtained in ohmically heated plasmas with monotonic q -profile. The TAE damping rate measurements were studied as a function of n , focusing on the effects of the edge plasma shape and the q profile and investigating their implications for the importance of the continuum and radiative damping mechanisms. In this paper, the first part of the analysis is presented: a statistical treatment of the damping rate database is performed and the correlations with various plasma parameters and relevant quantities are explored. The analysis shows that medium- n modes tend to be less damped than low- n modes, with the measured damping rates (γ/ω) of modes with n ⩾ 4 ranging from ∼0.3% to 4%. In a follow-up paper (part II), the analysis is carried out using a discharge-following approach, by investigating the damping rate variations that are observed in individual discharges.