A Set of Synopses of Works Which Are Planned to Report at the KINR Annual Conference-2020
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A set of Synopses of works which are planned to report at the KINR Annual conference-2020 PLASMA PHENOMENA CONNECTED WITH THE TRANSFER OF ENERGY AND MOMENTUM BY EIGENMODES A. V. Tykhyy Institute for Nuclear Research, National Academy of Sciences of Ukraine, Kyiv, Ukraine The phenomenon of SC of energy and momentum is a factor that can affect plasma performance in toroidal devices. It is associated with energetic ions produced by NBI, ICRH, and fusion reactions; but it can occur also in a Maxwellian plasma, being caused by suprathermal ions with energies exceeding the thermal energy by a few times. The latter is true, at least, for stellarators where Alfvén eigenmodes can be destabilized by the ion temperature gradient due to non- axisymmetric resonances. In the steady state, the mode energy flux is directed from the unstable region to the region where damping dominates, i.e., either outwards or inwards. However, when the drive exceeds the damping, so that the mode amplitude grows, the picture of the mode fluxes is more complicated, and both outward and inward wave energy / momentum fluxes in different plasma regions during the same instability may occur. Since SC transfers energy and momentum, it may affect plasma energy confinement (deteriorating or improving it), plasma rotation and concomitant frequency Doppler shift, the heating of the electron and ion components, and features of the eigenmodes themselves. In general, SC plays a considerable role when, first, the region driving the instability is well separated from the damping region Sketch of spatial channeling and, second, the mode amplitudes are not very small. The analysis in this work shows that SC due to high-frequency modes, with frequencies above and around the ion cyclotron frequency, is more likely to affect plasma energy balance for reasonable values of mode amplitudes than low-frequency Alfvén modes. Estimates for a JET-like tokamak with NBI heating power of about 10 MW show that modes with ω ≥ ωBi and ω ωBi (fast magnetoacoustic waves, global Alfvén eigenmodes, and high-frequency Alfvén modes present in stellarators such as Helicity- and Mirror- Induced Alfvén Eigenmodes) may directly affect plasma energy balance when mode amplitudes are -4 reasonable (δB/B ~ 10 ), whereas low-frequency Alfvén modes with ω << ωBi can only affect plasma energy balance for mode amplitudes which seem unrealistic (δB/B 2÷3·10-3). On the other hand, SC of momentum can significantly affect sheared plasma rotation for δB/B ~ 10-4, independently of mode frequency, especially on the plasma periphery. Modification of the structure of Alfvén eigenmodes is considered. A radial dependence of the mode phase and concomitant curving of the wavefront due to SC is predicted by means of a simple qualitative analysis. This supports experimental findings in the DIII-D tokamak and in the NSTX spherical torus. The condition of the mode persistence Structure of TAE mode with m=1/2, n=1 (14) [4] was reformulated to be for weak SC (left) and strong SC (right) convenient for practical application. These qualitative results were checked numerically by considering a low-mode-number TAE mode (with m=1 / 2, n=1) in a tokamak with radially separated destabilizing and stabilizing regions. A model term describing the drive and damping, which enabled observation of the evolution of the mode by varying SC strength, was used. It is found that SC decreases the TAE frequency and makes the mode shape more peaked; when the local drive / damping is sufficiently large, the mode disappears, merging into the Alfvén continuum. These effects, obtained numerically, take place when SC is sufficiently strong, in agreement with the analytically obtained condition. It is not clear whether / how the change of the modes caused by the SC affects the saturation level of the instabilities. Till now, SC has been considered in connection with a limited number of experiments. It seems probable, however, that SC took place, although not recognized, in many experiments where Alfvén modes and fast magnetoacoustic modes were destabilized. This work was supported by the STCU-NASU Project No.~6392 and was partly carried out within the framework of the EUROfusion Consortium, having received funding from the EURATOM research and training programme 2014--2018 and 2019-2020 under grant agreement No.~633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. 1. Kolesnichenko Ya.I., Tykhyy A.V., White R.B., 16th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems – Theory of Plasma Instabilities, Shizuoka, 2019. 2. Kolesnichenko Ya.I., Tykhyy A.V., White R.B., Nucl. Fusion, submitted. 3. Kolesnichenko Ya.I., Tykhyy A.V. 2018 Phys. Lett. A 382 2689 4. Kolesnichenko Ya.I., Lutsenko V.V., Tyshchenko M.H., Weisen H., Yakovenko Yu.V. and the JET team 2018 Nucl. Fusion 58 076012 5. Kolesnichenko Ya.I., Tykhyy A.V. 2018 Phys. Plasmas 25 102507 6. Kolesnichenko Ya.I., Yakovenko Yu.V., Tyshchenko M.H. 2018 Phys. Plasmas 25 122508 7. Kolesnichenko Ya.I., Tykhyy A.V. 2018 Plasma Phys. Control. Fusion 60 125004 1 DEVELOPMENT OF COMPTON CAMERA BASED ON MONOLITHIC SCINTILLATOR FOR PROMPT GAMMA-RAY IMAGING A. Sh. Georgadze Institute for Nuclear Research, National Academy of Sciences of Ukraine, Kyiv, Ukraine We develop a new Compton gamma camera for imaging gamma-rays in the MeV region The detector is based on cylindrical shape monolithic inorganic scintillator read-out on both ends with silicon photomultiplier (SiPM) arrays. GEANT4-based Monte Carlo simulation has been performed in order to evaluate the ability of the proposed camera to perform 3D reconstruction of hit positions in crystal scintillator of high energy gamma rays for gamma sources localization with the target on pulsed fast neutron analysis (PFNA). PFNA utilized microsecond wide fast neutron pulses produced by electronic neutron generator to initiate fast neutron inelastic scattering reactions on nuclei. Characteristic combination of prompt gamma-rays from nitrogen, carbon and oxygen nuclei excitations is an evidence of presence explosive materials. Since the fluorescence decay time of widely used and relatively cheap NaI(Tl), BGO and CsI scintillators can reach 300ч1000 ns pulse pile-up become serious problem that cause resolution degradation, spectral distortion and peak position shift. In this case the choice is to use fast LaBr3(Ce) scintillator with <30 ns decay time. But this scintillator is 10-20 times more expensive and has relatively high intrinsic radiation background. To address these issues cylindrical shape monolithic scintillator Ш2"Ч2" coupled to SiPMs arrays for double side readout were simulated using Geant4 optical transport. The photodetectors are composed of an 2 Ч 2 arrangement of 8 Ч 8 channels 3 Ч 3 mm2 photosensitive area SiPMs arrays of the Ketek PA3325-WB-0808 which have in total 256 channels. Fig. 1. The 3-D visualization by Fig. 2. Reconstructed hit Fig. 3. Scintillation patterns VRML driver of GEANT4 positions of 4.4 MeV gamma-ray observed from the side view of the simulation of Compton camera. source at a distance of 1 m. detector unit for alpha particles. Scintillators simulated in this work were NaI(Tl), BGO and LaBr3(Ce). On Fig. 1. the geometry of simulated Compton camera is presented. According to simulations gamma rays in the range 4ч9 MeV undergo multiple Compton scattering inside the Ш2"Ч2" cylindrical crystal. Interaction processes within the crystal scintillator were estimated by using the three-dimensional extended Anger-type calculation [2]. When multiple interaction occurred in a crystal, optical photons are generated and produce hit patterns on 256 pixels of top and 256 pixels of bottom SiPMs arrays. Center of gravity of these multiple interactions were reconstructed using the signals from both SiPMs arrays and the Anger-type formula: where pi is the signal amplitude of the ith SiPMs channel, and Xi, Yi and Zi are the physical x, y and z coordinates of the ith SiPMs channel. In several percent of events multiple Compton scattering processes form scattering and absorption clusters which are spatially separated. Calculating centers of gravity and amplitudes of scattering and absorption clusters and using Compton scattering kinematics it is possible to 2 estimate location of a gamma-ray source by following the tracks of scattered gamma-rays backward according to without any mechanical collimation. According to preliminary simulation results high energy gamma rays undergo multiple Compton scattering inside the Ш2"Ч2" cylindrical crystal several percent of such events form the scattering and absorption clusters spatially separated. Center of gravity of scattering and absorption clusters can be resolved and used to calculate direction on the gamma-ray source. Fig. 4. Scintillation pattern of Fig. 5. Reconstructed positions of Fig. 6. Experimentally detected scattering and absorption clusters. single Compton scattering event in clusters of Compton scattering Ш1"Ч1" NaI(Tl) scintillator. event. Cluster analysis on event-by-event basis allow to separate Compton scattering events from alpha particle absorption events which are the main source of intrinsic background of LaBr3(Ce) scintillator thus improving its detection sensitivity. In case of two gamma quanta hitting the crystal simultaneously cluster analysis can reconstruct 3D positions of interaction events of gamma rays with scintillator and part of this events can be recognized as pile-up pulses and thus rejected. This will allow to use cheap but relatively slow NaI(Tl) and BGO scintillators for imaging gamma sources for the PFNA application as well as to improve performance of systems based on LaBr3(Ce) scintillators by rejecting internal backgrounds. Preliminary measurements have been done with simplified setup using CAEN DT5550W board. The DT5550W is full featured Acquisition System with programmable FPGA which read out 4 Ч PETIROC2A ASICs. Two KETEK matrices (64 channels) are connected to board.