Numerical simulations of fast ion loss measurements induced by magnetic islands in the ASDEX Upgrade tokamak

A test particle approach, implemented with the Hamiltonian code ORBIT, is used to simulate measurements of fast ion losses induced by magnetic islands in the ASDEX Upgrade tokamak. In particular, the numerical simulations reproduce the toroidal localization of losses and the lost ions pitch angle and energy distribution experimentally measured with the fast ion losses detector (FILD) in the presence of a neoclassical tearing mode (NTM). The simulated NTM induced losses occurring on time scales longer than 100 µs are composed of mainly trapped or barely passing particles, consistently with the slow decay of the experimental signal from one FILD channel after the beam switch-off. The numerical simulations have been performed by taking into account the D-shaped plasma geometry, the collision mechanisms, the losses due to ripple effects and the rotation of the mode. The radial profile of the magnetic perturbation is adjusted in order to match ECE measurements. While statistical properties of FILD measurements are rather well reproduced, the simulated total amount of losses is found to be significantly affected by edge details of the magnetic perturbation as it determines the loss mechanism.

[1]  Allen H. Boozer,et al.  Monte Carlo evaluation of transport coefficients , 1981 .

[2]  M. S. Chance,et al.  Hamiltonian guiding center drift orbit calculation for plasmas of arbitrary cross section , 1984 .

[3]  S. Zweben.  Pitch angle resolved measurements of escaping charged fusion products in TFTR , 1989 .

[4]  S. P. Hirshman,et al.  Preconditioned descent algorithm for rapid calculations of magnetohydrodynamic equilibria , 1991 .

[5]  W. Heidbrink,et al.  CORRIGENDUM: The behaviour of fast ions in tokamak experiments , 1994 .

[6]  S. Zweben,et al.  Measurement of loss of DT fusion products using scintillator detectors in TFTR (invited) , 1995 .

[7]  S. Murakami,et al.  Escaping fast ion diagnostics in compact helical system heliotron/torsatron , 1999 .

[8]  D. Darrow,et al.  Fast Ion Losses in the W7-AS Stellarator , 2001 .

[9]  Cary Forest,et al.  Simulations of beam ion transport during tearing modes in the DIII-D tokamak , 2002 .

[10]  Albrecht Herrmann,et al.  Chapter 1: ASDEX Upgrade - Introduction and Overview , 2003 .

[11]  R. B. White,et al.  Hamiltonian guiding center equations in toroidal magnetic configurations , 2003 .

[12]  M. Isobe,et al.  Scintillator probe diagnostic for high energy particles escaped from Large Helical Device , 2004 .

[13]  J. Contributors,et al.  Scintillator probe for lost alpha measurements in JET , 2004 .

[14]  J. Contributors,et al.  The role of energetic particles in fusion plasmas , 2004 .

[15]  E. Strumberger,et al.  Fast particle losses due to NTMs and magnetic field ripple , 2007 .

[16]  H. Zohm,et al.  NTM induced fast ion losses in ASDEX Upgrade , 2007 .

[17]  E. Poli,et al.  Observation and modeling of fast trapped ion losses due to neoclassical tearing modes , 2008 .

[18]  J. Fontdecaba,et al.  A flexible luminescent probe to monitor fast ion losses at the edge of the TJ-II stellarator. , 2008, The Review of scientific instruments.

[19]  R. White,et al.  Resonance between passing fast ions and MHD instabilities both in the tokamak and the RFP configurations , 2008 .

[20]  H. Zohm,et al.  Fast-ion losses due to high-frequency MHD perturbations in the ASDEX upgrade Tokamak. , 2008, Physical review letters.

[21]  D. Darrow.  Scintillator based energetic ion loss diagnostic for the National Spherical Torus Experiment. , 2008, The Review of scientific instruments.