1. Chalmers University of Technology Szczecin, 23 March 2006 Meeting with Dr. B. Green Dr. B. Green (Euratom) and Prof. A. Gałkowski (Association Euratom-IPPLM) M. Lisak, P. Sandquist, D. Anderson Swedish Fusion Association Euratom-VR Chalmers University of Technology, Göteborg Yu. Kravtsov, S. Berczyński, P. Berczy ń ski Szczecin University of Technology and Martitime University of Szczecin Selected Collaboration Issues on Energetic Particle Effects in Tokamaks

2. Chalmers University of Technology INTRODUCTION Why we should study fast particle effects in fusion plasmas?  Up to now, fusion research was in a sub-critical zone, nTt E < 8.3x10 20 m -3 keVs, without burn or with small burn (Q=0.61, JET)  Burning plasma - fundamentally new physics. New phenomena to be studied: Alpha particles in a burning plasma with Q>10 (f a >60%) can have an affect on Stability: fishbones, TAEs Transport: particle loss, wall heat loading Heating and current drive Edge physics: transport barriers Burn dynamics: He ash, thermal stability etc

3. Chalmers University of Technology  Perhaps, ITER will be the only opportunity before DEMO to study alphas with confidence at various Q’s.  Hence, there is a need for integrated assessment (simulations, based on first-principle theory) of alpha particle behavior in a burning plasma. ITER oriented physics R&D e. Fast particle physics “Most of the research issues listed above (with the exception of disruption studies) are linked to the presence of a population of fast particles. For the investigation of fast particle effects it is not necessary to work with the Alpha particles generated in DT operation: simulations are possible, e.g. by using ICRH minority heating or negative NBI.”

4. Chalmers University of Technology Investigation of nonlinear dynamics of fast ion driven modes near the instability threshold - generalization of the Berk&Breizman theory to multi-mode scenarios (collaboration with B. Breizman at Texas Univ. in Austin) Effects of supra-thermal electrons and NBI and ICRH - accelerated ions on sawteeth (collaboration with S. Sharapov at JET-EFDA) RESEARCH TOPICS WITHIN COLLABORATION BETWEEN CHALMERS AND THE SZCZECIN CONSORTIUM

5. Chalmers University of Technology Nonlinear dynamics of fast ion driven modes JET 1.6x10 8 2.2x10 6 3.3x10 5 ITER 2.7x10 8 0.8x10 6 0.3x10 5  The determination of fast ion-driven wave instabilities in reactor relevant regimes is a problem to be solved on the way to design and construction of an ignition device  Fast ions are generated by RF and NBI heating and in the fusion reactions (3.5 MeV alpha particles)  Free energy comes from a non-monotonic / anisotropic/ inhomogeneous velocity distribution function of fast particles  Resonant excitation process

6. Chalmers University of Technology Studies of instabilities and confinement of energetic ions on JET serve as a framework for the implementation of innovative fast ion diagnostics in next step burning plasma devices such as ITER. InstabilityFrequency (kHz) Physical mechanismImportant parameters Possible effects Alpha - diven fishbones 10 1 -10 2 Prec. res. of internal m=1 mode Beta alpha, prec. freq. Expulsio n of trapped alphas Alpha – driven Alfvén waves (e.g. TAE`s) 10 3 -10 4 Passing alphas with v>v A v/v A, alpha drift freq., beta gradient Anomal ous alpha loss Alpha-loss cone driven Alfvén waves 10 5 -10 6 Velocity space instabilityTF ripple, alpha density, cycl. freq. Alpha losses

7. Chalmers University of Technology  Linear theory Local WKB analysis estimates the linear growth rate and the instability threshold  Quasi-linear theory Diffusion of the fast particle velocity distribution function anomalous ion relaxation in velocity space, anomalous fast ion losses, outward flux of lower energy ions.  Theory of near-threshold nonlinear regimes (Berk & Breizman theory) Typically, macroscopic plasma parameters evolve slowly compared to the instability growth time scale. Perturbation technique is adequate near the instability threshold.

8. Chalmers University of Technology  Single-mode case ( Phys. Rev. Lett. 76 (1996) 1256; Phys. of Plasmas 4 (1997) 1559) - The mode amplitude evolves according to - Steady-state, oscillating and explosive solutions depending on - Bifurcations at single-mode saturation can be analyzed - Formation of a long-lived coherent nonlinear structure is possible  Multi-mode case – the theory will be developed - Resonance overlap can indicate strong nonlinear regime - Multi-mode scenarios with marginal stability are interesting: Full life-cycle of EPMs, starting from instability threshold: So far, described only the initial phase. Fishbones: Transition from an explosive growth to a slowly growing MHD structure (i.e. island near q=1 surface).

9. Chalmers University of Technology

10. Effects of supra-thermal electrons and NBI and ICRH - accelerated ions on sawteeth General aim of work: Development and experimental evaluation of theoretical models for fast particle effects in MHD phenomena. In particular, effects of supra-thermal electrons and NBI and ICRH- accelerated ions on sawteeth have to be validated against JET data. Participation in upcoming JET experimental campaigns C15-C17 on fast particle experiments is planned (P. Sandquist). Participation in the Integrated Modelling Project 2: Non-Linear MHD and Disruptions, where redistribution of fast ions during sawtooth activity will be studied. Presentation on the subject was given (M. Lisak) at the Sawtooth Workshop at JET on 16-17 February 2006. Sawtooth oscillations are one of the most typical form of MHD activity in a tokamak plasma. They appear in the form of oscillations of X-ray radiation, temperature, density and current in the central plasma region and are shaped like the teeth of a saw. The internal kink-mode is considered to be responsible for the sawtooth oscillations.

11. Chalmers University of Technology The sawtooth oscillation The core of a tokamak is subject to relaxation oscillations when q<1

12. Chalmers University of Technology Fast Electron Bremsstrahlung in Low-Density, Grassy Sawtoothing Plasmas Low density, ICRH-only heated plasmas on JET show transitions to a ’grassy’ sawtooth regime (chaotic sawteeth). At the time of the transition, the electric field on axis is close to the critical electric field for runaway production  supra-thermal electrons might play a role in the transition. (P. Sandquist, S. Sharapov, M. Lisak et al, contribution at EPS 2005)

13. Chalmers University of Technology Tomographic reconstructions of FEB emission of supra-thermal electrons (left), fast ion FEB energies (right) and intermediate energies (middle).

14. Chalmers University of Technology  Analysis for assessing generation and evolution of the suprathermal electron population in plasmas with grassy sawteeth has to be performed using analytical description and numerical (MHD and transport) codes. General kinetic Fokker-Planck theory of relativistic electrons is being developed.  Description of fast ion redistribution during sawtooth oscillations has to be developed for particles with large orbit widths (generalization of the previous work at Chalmers ). Research plans

15. Chalmers University of Technology Thank you !