Szczecin, 23 March 2006 Meeting with Dr. B. Green Dr. B. Green (Euratom) and

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

2. INTRODUCTION Why we should study fast particle effects in fusion plasmas? • Up to now, fusion research was in a sub-critical zone, nTtE< 8.3x1020 m-3 keVs, without burn or with smallburn (Q=0.61, JET) • Burning plasma - fundamentally new physics. New phenomena to be studied: Alpha particles in a burning plasma with Q>10 (fa >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. Perhaps, ITER will be the only opportunity before DEMO to study alphaswith 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. RESEARCH TOPICS WITHIN COLLABORATION BETWEEN CHALMERS AND THE SZCZECIN CONSORTIUM • 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)

5. Nonlinear dynamics of fast ion driven modes • 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. 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.

7. 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. 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).

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

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

14. Research plans • 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).

15. Thank you !