Coherent electronic and nuclear dynamics in a rhodamine heterodimer-DNA supramolecular complex

Elucidating the role of quantum coherences in energy migration within biological and artificial multichromophoric antenna systems is the subject of an intense debate. It is also a practical matter because of the decisive implications for understanding the biological processes and engineering artificial materials for solar energy harvesting. A supramolecular rhodamine heterodimer on a DNA scaffold was suitably engineered to mimic the basic donor-acceptor unit of light-harvesting antennas. Ultrafast 2D electronic spectroscopic measurements allowed identifying clear features attributable to a coherent superposition of dimer electronic and vibrational states contributing to the coherent electronic charge beating between the donor and the acceptor. The frequency of electronic charge beating is found to be 970 cm-1 (34 fs) and can be observed for 150 fs. Through the support of high level ab initio TD-DFT computations of the entire dimer, we established that the vibrational modes preferentially optically accessed do not drive subsequent coupling between the electronic states on the 600 fs of the experiment. It was thereby possible to characterize the time scales of the early time femtosecond dynamics of the electronic coherence built by the optical excitation in a large rigid supramolecular system at a room temperature in solution. © 2017 the Owner Societies.Multi valued and parallel molecular logi

First observations of confined fast ions in MAST Upgrade with an upgraded neutron camera

Spherical tokamaks are key to the successful design of operating scenarios of future fusion reactors in the areas of divertor physics, neutral beam current drive and fast ion physics. MAST Upgrade, which has successfully concluded its first experimental campaign, was specifically designed to address the role of the radial gradient of the fast ion distribution in driving the excitation of magneto-hydrodynamic (MHD) instabilities, such as toroidal Alfvén eigenmodes, fish-bones and long-lived mode, thanks to its two tangential neutral beam injection systems, one on the equatorial plane and one that is vertically shifted 65 cm above the equatorial plane. To study the fast ion dynamics in the presence of such instabilities, as well as of sawteeth and neo-classical tearing modes, several fast ion diagnostics were upgraded and new ones added. Among them, the MAST prototype neutron camera (NC) has been upgraded to six, equatorial sight-lines. The first observations of the confined fast ion behavior with the upgraded NC in a wide range of plasma scenarios characterized by on-axis and/or off-axis heating and different MHD instabilities are presented here. The observations presented in this study confirm previous results on MAST but with a higher level of detail and highlight new physics observations unique to the MAST Upgrade. The results presented here confirm the improved performance of the NC Upgrade, which thus becomes one of the key elements, in combination with the rich set of fast ion diagnostics available on the MAST Upgrade, for a more constrained modeling of the fast ion dynamics in fusion reactor relevant scenarios

Minority and mode conversion heating in (3He)-H JET plasma

Radio frequency (RF) heating experiments have recently been conducted in JET (He-3)-H plasmas. This type of plasmas will be used in ITER's non-activated operation phase. Whereas a companion paper in this same PPCF issue will discuss the RF heating scenario's at half the nominal magnetic field, this paper documents the heating performance in (He-3)-H plasmas at full field, with fundamental cyclotron heating of He-3 as the only possible ion heating scheme in view of the foreseen ITER antenna frequency bandwidth. Dominant electron heating with global heating efficiencies between 30% and 70% depending on the He-3 concentration were observed and mode conversion (MC) heating proved to be as efficient as He-3 minority heating. The unwanted presence of both He-4 and D in the discharges gave rise to 2 MC layers rather than a single one. This together with the fact that the location of the high-field side fast wave (FW) cutoff is a sensitive function of the parallel wave number and that one of the locations of the wave confluences critically depends on the He-3 concentration made the interpretation of the results, although more complex, very interesting: three regimes could be distinguished as a function of X[He-3]: (i) a regime at low concentration (X[He-3] < 1.8%) at which ion cyclotron resonance frequency (ICRF) heating is efficient, (ii) a regime at intermediate concentrations (1.8 < X[He-3] < 5%) in which the RF performance is degrading and ultimately becoming very poor, and finally (iii) a good heating regime at He-3 concentrations beyond 6%. In this latter regime, the heating efficiency did not critically depend on the actual concentration while at lower concentrations (X[He-3] < 4%) a bigger excursion in heating efficiency is observed and the estimates differ somewhat from shot to shot, also depending on whether local or global signals are chosen for the analysis. The different dynamics at the various concentrations can be traced back to the presence of 2 MC layers and their associated FW cutoffs residing inside the plasma at low He-3 concentration. One of these layers is approaching and crossing the low-field side plasma edge when 1.8 < X[He-3] < 5%. Adopting a minimization procedure to correlate the MC positions with the plasma composition reveals that the different behaviors observed are due to contamination of the plasma. Wave modeling not only supports this interpretation but also shows that moderate concentrations of D-like species significantly alter the overall wave behavior in He-3-H plasmas. Whereas numerical modeling yields quantitative information on the heating efficiency, analytical work gives a good description of the dominant underlying wave interaction physics

Investigating fusion plasma instabilities in the Mega Amp Spherical Tokamak using mega electron volt proton emissions (invited)a)

The proton detector (PD) measures 3 MeV proton yield distributions from deuterium-deuterium fusion reactions within the Mega Amp Spherical Tokamak (MAST). The PD's compact four-channel system of collimated and individually oriented silicon detectors probes different regions of the plasma, detecting protons (with gyro radii large enough to be unconfined) leaving the plasma on curved trajectories during neutral beam injection. From first PD data obtained during plasma operation in 2013, proton production rates (up to several hundred kHz and 1 ms time resolution) during sawtooth events were compared to the corresponding MAST neutron camera data. Fitted proton emission profiles in the poloidal plane demonstrate the capabilities of this new system

The global build-up to intrinsic edge localized mode bursts seen in divertor full flux loops in JET

A global signature of the build-up to an intrinsic edge localized mode (ELM) is found in the temporal analytic phase of signals measured in full flux azimuthal loops in the divertor region of JET. Toroidally integrating, full flux loop signals provide a global measurement proportional to the voltage induced by changes in poloidal magnetic flux; they are electromagnetically induced by the dynamics of spatially integrated current density. We perform direct time-domain analysis of the high time-resolution full flux loop signals VLD2 and VLD3. We analyze plasmas where a steady H-mode is sustained over several seconds during which all the observed ELMs are intrinsic; there is no deliberate intent to pace the ELMing process by external means. ELM occurrence times are determined from the Be II emission at the divertor. We previously [Chapman et al., Phys. Plasmas 21, 062302 (2014); Chapman et al., in 41st EPS Conference on Plasma Physics, Europhysics Conference Abstracts (European Physical Society, 2014), Vol. 38F, ISBN 2-914771-90-8] found that the occurrence times of intrinsic ELMs correlate with specific temporal analytic phases of the VLD2 and VLD3 signals. Here, we investigate how the VLD2 and VLD3 temporal analytic phases vary with time in advance of the ELM occurrence time. We identify a build-up to the ELM in which the VLD2 and VLD3 signals progressively align to the temporal analytic phase at which ELMs preferentially occur, on a ∼2−5ms timescale. At the same time, the VLD2 and VLD3 signals become temporally phase synchronized with each other, consistent with the emergence of coherent global dynamics in the integrated current density. In a plasma that remains close to a global magnetic equilibrium, this can reflect bulk displacement or motion of the plasma. This build-up signature to an intrinsic ELM can be extracted from a time interval of data that does not extend beyond the ELM occurrence time, so that these full flux loop signals could assist in ELM prediction or mitigation