3a 3 Hellsten

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Published on September 14, 2007

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Integrated Modelling of ICRH and AE Dynamics:  Integrated Modelling of ICRH and AE Dynamics T. Hellsten, T. Bergkvist, T. Johnson and M. Laxåback Alfvén Laboratory, Royal Inst. of Technology, SE-100 44 Stockholm, Sweden Association Euratom-VR. Slide2:  ICRH is a versatile heating method that can provide: Heating Enhance fusion reactivity Drive Currents Induce rotation Excite AEs ICRH -90o phasing: trapped 3He ions displaced outwards. emission from turning points of trapped ions at cyclotron resonance:  -90o phasing: trapped 3He ions displaced outwards.  emission from turning points of trapped ions at cyclotron resonance +90o ICRH phasing: trapped 3He orbits pinched, then detrapped to co-current wide passing orbits at the low field side of the center RF-induced pinch and detrapping of the orbits T. Johnsson et al, IAEA Technical Meeting, Gothenburgh, 2001 Tomographic reconstruction of the g-emission profiles from JET Tomegraphic reconstruction by C. Ingesson T. Hellsten et al Phys. Rev. Lett 1995 Co Counter Slide4:  ICRH requires self-consistent modelling of distribution functions and wave field; including effects of finite orbit width effects and RF-induced spatial transport of fast ions for waves with finite nf. Due to the different time scales this can be done by iterations. ICRH Modelling Slide5:  1 LION code L. Villard et al, Computer Physics Reports 4(1986)95 and Nucl. Fusion, 35(1995)1173 Define equilibrium, antenna spectrum, power. Calculate the dielectric tensor and wave field for ICRH (LION code1) Calculate changes in orbit invariants by collisions, and ICRH with the FIDO code. Remove lost ions, add NBI, a-particles and edge source. Create tables for the various interactions used in the Monte Carlo code with an orbit solver. Output The SELFO code calculates the distribution function in the invariant space (W, Pf, L) with the Monte Carlo code FIDO and the ICRH wave field with the LION code. Slide6:  Comparison of the gamma emissitivity in the mid-plane z=0 between tomographic reconstructions (full line) dashed region (confidence interval) and the density of high-energy 3He ions calculated with the SELFO code (boxes) +90-phasing location of the excited TAE modes indicated -90-phasing SELFO code modelling by T. Johnson Slide7:  The excitation of Alfvén eigenmodes is sensitive to the details of the distribution function. AEs excited in JET during ICRH with +90° and -90° phasing of the antennas +90° -90° L.-G. Eriksson, et al Phys Rev. Lett 81 (1998) 1231 M. Mantsinen et al Phys. Rev. Lett. 84(2002). Splitting of the mode frequency:  Splitting of the mode frequency A. Fasoli et al Phys. Rev. Lett. 81(1998)5564 Fast damping when ICRH is switched off The AEs are damped in a time period of about 0.1ms after the ICRH is switched off. K. L. Wong,et al Phys. Plasmas 4 (1997) 393 Typical mode splitting of about 2kHz is seen during ICRH. The spitting is too wide to be due to restoration of the distribution function by Coulomb collisions. Ion interaction with AEs:  Ion interaction with AEs In the absence of Coulomb collisions and ICRH the interactions of a resonant ion with an AE lead to a superadiabatic oscillation in the phase space of the invariants of the equation of motion for the drift orbit along the AE characteristics If the distribution function increases with energy around the resonance, energy will then be transferred from the ions to the mode and vice verse. When the distribution function is flattened along all AE characteristics no net transfer of energy takes place. The mode will then be damped by different background damping mechanisms. Pf W m Slide10:  Decorrelation of the interactions leads to a diffusion of the orbits along the characteristics instead of a superadiabatic oscillation along them. Ion cyclotron interactions and Coulomb collisions will partially restore the distribution function in the resonant regions and result in further transfer of energy from the resonant ions to AEs. The decorrelation of the interactions and local renewal of the distribution function by ICRH increases with energy, whereas they decrease with energy for Coulomb collisions. Decorrelation of AE interactions and renewal of the distribution function Renewal of the distribution function by ICRH:  Renewal of the distribution function by ICRH Distribution function f(w) along a characteristic w AE resonance initial distribution function distribution function flattened by an AE The width of the resonance and the renewal rate increase with ICRH power ICRH creates an inverted distribution function along the AE characteristics High energy ions created by ICRH Low energy ions removed by ICRH The dynamics of the AE excitation depend not only on the growth rate of the AE and background damping, but also of the renewal rate of the distribution function and the decorrelation of the wave particle interactions. Slide12:  1 LION code L. Villard et al, Computer Physics Reports 4(1986)95 and Nucl. Fusion, 35(1995)1173 Define equilibrium, antenna spectrum, power, type of AE mode etc. Calculate the dielectric tensor and wave field for ICRH (LION code1) and amplitude of AEs Calculate changes in orbit invariants by collisions, ICRH and AE with the FIDO code. Remove lost ions, add NBI, a-particles and edge source. Create tables for the various interactions used in the Monte Carlo code with an orbit solver. Output The SELFO code calculates the distribution function in the invariant space (W, Pf, L) with the Monte Carlo code FIDO and the ICRH wave field with the LION code. The AE field can either be calculated with the LION code or from a simplified model. Slide13:  Monte Carlo code FIDO for calculating the distribution function J. Carlson et al, 'Theory of Fusion Plasmas' and#x8;and#x8;Varenna 1996, L.-G. Eriksson and P. Helander Phys. Plasmas (1994), T. Bergkvist et al 'Theory of Fusion Plasmas' and#x8;and#x8;Varenna 2004. MHD interactions a-particle lower ripple sawteething channelling hybrid diffusion TAE Resonance regions:  TAE Resonance regions Amplitude variations of the variance of the energy for interactions with an TAE mode. Note that internal zeros of the variance appear. The dynamics of TAE and frequency splitting:  The dynamics of TAE and frequency splitting Fourier decomposition of the time evolution of the mode amplitude gives a characteristic frequency corresponding to the frequency separation of the side bands seen during ICRH. Mode damping after ICRH switch off:  Mode damping after ICRH switch off The fast damping of the TAE of about 0.1ms as ICRH is switched off is consistent with experiments. Code for self-consistent modelling of heating:  Code for self-consistent modelling of heating AE NBI ICRH LH ECRH Wave field Power deposition Fast ion Fusion reactions Current profile Momentum Power deposition Current profile Distribution function for electrons f(y,W,z) 3D-Finite element Source Ray tracing Ray tracing Wave spectrum Wave spectrum Wave field Distribution function for ions f(W,Pf, L) Monte Carlo method 3D-Finite element MHD Sawteeth Fishbones Equi-librium, Loop voltage Conclusions:  Conclusions Self-consistent computations of wave field and distribution function is important for ICRH, in particular power partition. The effects of finite orbit width and RF-induced spatial transport are important for many phenomena. The dynamics of the AEs are strongly affected by ICRH, which have to be taken into account when simulating AE excitation by thermonuclear alpha particles using ICRH ions. The decorrelation by ICRH increases the width of the resonances and the renewal rate, making the interactions with AE much stronger.

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