A limiting velocity for quarkonium propagation in a strongly coupled plasma via AdS/CFT

We study the dispersion relations of mesons in a particular hot strongly coupled supersymmetric gauge theory plasma. We find that at large momentum k the dispersion relations become omega = v_0 k + a + b/k + ..., where the limiting velocity v_0 is the same for mesons with any quantum numbers and depends only on the ratio of the temperature to the quark mass T/m_q. We compute a and b in terms of the meson quantum numbers and T/m_q. The limiting meson velocity v_0 becomes much smaller than the speed of light at temperatures below but close to T_diss, the temperature above which no meson bound states at rest in the plasma are found. From our result for v_0, we find that the temperature above which no meson bound states with velocity v exist is T_diss(v) \simeq (1-v^2)^(1/4) T_diss, up to few percent corrections.We thus confirm by direct calculation of meson dispersion relations a result inferred indirectly in previous work via analysis of the screening length between a static quark and antiquark in a moving plasma. Although we do not do our calculations in QCD, we argue that the qualitative features of the dispersion relation we compute, including in particular the relation between dissociation temperature and meson velocity, may apply to bottomonium and charmonium mesons propagating in the strongly coupled plasma of QCD. We discuss how our results can contribute to understanding quarkonium physics in heavy ion collisions.Comment: 57 pages, 12 figures; references adde

Double Counting Ambiguities in the Linear Sigma Model

We study the dynamical consequences imposed on effective chiral field theories such as the quark-level SU(2) linear $\sigma$ model (L$\sigma$M) due to the fundamental constraints of massless Goldstone pions, the normalization of the pion decay constant and form factor, and the pion charge radius. We discuss quark-level double counting L$\sigma$M ambiguities in the context of the Salam-Weinberg $Z = 0$ compositeness condition. Then SU(3) extensions to the kaon are briefly considered.Comment: 23 pages To be published in Journal of Physics

Turbulence stabilization due to high beta and fast ions in high-performance plasmas at ASDEX Upgrade and JET

High-performance fusion plasmas are desired to reach high plasma beta. Yet, the dependence of the thermal confinement time on this important parameter is unclear: Dedicated experiments yielded inconclusive results [1] and most theoretical results are obtained in simplified setups (overview e.g. in Ref. [2]). Using high accuracy plasma parameter measurements and realistic geometry for recent H-mode discharges at ASDEX Upgrade and JET (with ITER-like-wall), turbulent transport is studied by means of GENE gyrokinetic simulations in the plasma core. Electromagnetic effects in plasma microturbulence The gyrokinetic simulation code GENE is developed for studying microturbulence in strongly magnetized plasmas, such as fusion plasmas. In this work, we use the local flux-tube version of GENE A pair of ASDEX Upgrade discharges varying β In the ASDEX Upgrade discharges #29197 (case A, β N = 1.67) and #29224 (case B, β N = 2.6), β e varies by a factor of two at mid-radius, while changes in other dimensionless parameters, such as ρ ⋆ and ν ⋆ , as well as magnetic geometry are by far less pronounced 42 nd EPS Conference on Plasma Physics P1.15

Simulations of divertor particle and heat loads in ohmic and L-mode plasmas in DIII-D, AUG, and JET using UEDGE Simulations of divertor particle and heat loads in ohmic and L-mode plasmas in DIII-D, AUG, and JET using UEDGE and the DIII-D and ASDEX Upgrad

Abstract (134 words) Measurements and simulations with the UEDGE code of radiated power, and ion saturation currents and power loads to the target plates have been compared for density scans in ohmic and low confinement mode plasmas in DIII-D, ASDEX Upgrade, and JET. Overall, a significantly better match has been obtained when cross-field drifts are used and elevated chemical sputtering yields of 3-4% are assumed. Using these assumptions the simulations DRAFT 3 2 reproduce the measured currents and powers, and their functional dependence on upstream density to within a factor of 2, with the exception of the ion currents to the low field side target in ASDEX Upgrade and the high field side target in JET. The applicability of using enhanced sputtering yields is discussed by comparing measured and simulated emission from low charge state carbon in the divertor regions

NBI Modulation Experiments to Study Momentum Transport and Magnetic Field Induced Ripple Torque on JET

Abstract. Several parametric scans have been performed to study momentum transport on JET. NBI modulation technique has been applied to separating the diffusive and convective momentum transport terms. The magnitude of the inward momentum pinch depends strongly on the inverse density gradient length, with an experimental scaling for the pinch number being -Rv pinch = 1.2R/L n + 1.4. There is no dependence of the pinch number on collisionality. The Prandtl number was not found to depend either on R/L n , collisionality or on q. The gyrokinetic simulations show qualitatively similar dependence of the pinch number on R/L n , but the dependence is weaker in the simulations. Gyro-kinetic simulations do not find any clear parametric dependence in the Prandtl number, in agreement with experiments, but the experimental values are larger than the simulated ones. The extrapolation of these results to ITER illustrates that at R/L n >2 the pinch number becomes large enough (> 3 4) to make the rotation profile peaked provided that the edge rotation is non-zero. And this rotation peaking can be achieved with small or even with no core torque source. The absolute value of the core rotation is still very challenging to predict partly due to the lack of the present knowledge of the rotation at the plasma edge, partly due to insufficient understanding of 3D effects like braking and partly due to the uncertainties in the extrapolation of the present momentum transport results to a larger device

NBI Modulation Experiments to Study Momentum Transport and Magnetic Field Induced Ripple Torque on JET NBI Modulation Experiments to Study Momentum Transport and Magnetic Field Induced Ripple Torque on JET

AbstrAct Several parametric scans have been performed to study momentum transport on JET. NBI modulation technique has been applied to separating the diffusive and convective momentum transport terms. The magnitude of the inward momentum pinch depends strongly on the inverse density gradient length, with an experimental scaling for the pinch number being -Rv pinch / χφ = 1.2R/L n + 1.4. There is no dependence of the pinch number on collisionality. The Prandtl number was not found to depend either on R/L n , collisionality or on q. The gyro-kinetic simulations show qualitatively similar dependence of the pinch number on R/L n , but the dependence is weaker in the simulations. Gyrokinetic simulations do not find any clear parametric dependence in the Prandtl number, in agreement with experiments, but the experimental values are larger than the simulated ones. The extrapolation of these results to ITER illustrates that at R/L n >2 the pinch number becomes large enough (> 3−4) to make the rotation profile peaked provided that the edge rotation is non-zero. And this rotation peaking can be achieved with small or even with no core torque source. The absolute value of the core rotation is still very challenging to predict partly due to the lack of the present knowledge of the rotation at the plasma edge, partly due to insufficient understanding of 3D effects like braking and partly due to the uncertainties in the extrapolation of the present momentum transport results to a larger device