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Dynamic scaling and quenching for heavy quark in the linear expanding medium
No full textWe study the energy loss of the heavy quark and the heavy quark jet propagating through linear expanding quark–gluon plasma (QGP). We show that the concept of scaling is valid for heavy quarks, with the quenching parameter of the equivalent static media being independent from the mass of the quark
Modeling the electrical mismatch caused by potential-induced degradation in crystalline silicon photovoltaic modules and strings
No full textPotential-induced degradation (PID) can not only reduce the output power of a solar cell but also create additional power losses due to non-uniform degradation within a module, string or array, leading to mismatch in the electrical performance of the solar cells in the system. This work models the impact of PID-polarization (increases surface recombination velocity in a solar cell) and PID-shunting (increases recombination in depletion region and shunts the p-n junction of a solar cell) on the current-voltage (I-V) characteristics of a 22 × 8 photovoltaic array and estimates the array level power mismatch losses (the difference between array level power loss and the average power loss of the modules in the array). Each solar cell in the array is represented by a two-diode equivalent circuit model, and PID is introduced in a solar cell by degrading the model parameters including the light generated photocurrent, dark saturation currents, shunt resistance and ideality factor. The module level model is validated with modules that are PID degraded in the laboratory and is used as baseline for creating the array level model: the root-mean square error between simulated and measured I-V curves are within 0.2 A. To generate realistic PID affected I-V characteristics curves, the degradation in solar cells is applied non-uniformly within a module, string and array. For a PV array affected by PID-polarization and PID-shunting, the mismatch losses can increase up to 0.72% and 2.35% which is in addition to the power losses of ∼5.25% and ∼10% caused by PID itself, respectively. The annual energy losses are estimated by increasing the severity of PID in the arrays during a one-year-simulation and it resulted in 4.84% and 10% less in the annual energy production of the arrays, respectively
Electron spectral shape of the third-forbidden
No full textIn recent years, interest in experimental studies of -decay electron spectra – often referred to as spectra – has been growing. This is particularly true for transitions where the electron spectra are sensitive to the effective value of the weak axial coupling, . Such measurements serve as important benchmarks for nuclear physics calculations and can also be used to characterize background in astroparticle physics experiments. In this work, a dedicated experiment has been carried out to investigate the spectral shape of the third-forbidden Rb -decays, with the goal of estimating the effective value for this transition and of deriving the value. This was done by comparing the experimental spectral shape with the estimates from various phenomenological models. The Rb source was embedded directly within the detector material of a new crystal scintillator; the data taking was performed deep underground at Gran Sasso National Laboratory. The obtained experimental half-life value for the studied process is yr; while a value in the range 0.4–0.6 is obtained when accounting for uncertainties and depending on the model adopted as discussed in detail in the text
Comparison of seismic records obtained by distributed acoustic sensing and ocean bottom seismometers
No full textThis work presents an experimental framework for offshore seismic monitoring that combines Distributed Acoustic Sensing (DAS) with ocean-bottom seismometers (OBS). The study was conducted in the Azores region – Faial, where an HDAS interrogator prototype was connected to dark fiber submarine fiber-optic cable, complemented by the installation of two Ocean Bottom Seismometers (OBS) for calibration and validation of DAS technology. The main objective is to demonstrate that seismic observations obtained by DAS from seafloor cables can provide essential information similar to OBS and particularly in areas where land-based monitoring stations are limited
Experimental comparison of millimetre wave power monitor designs
No full textThe ASDEX Upgrade electron cyclotron resonance heating system [1] uses multi-hole waveguide couplers integrated into the matching mirrors ‘M2’ for power monitoring. While the full Gyrotron output power (105 or 140 GHz, typ. 1 MW per unit) is essentially optically reflected at the M2 mirror, a small fraction of the order of several milliwatt is diverted by the coupler and transmitted via fundamental mode waveguide towards a beam lead Schottky diode, which converts the millimetre wave electric field amplitude into a voltage signal. The system is calibrated by a calorimetric measurement, where short pulses of the full Gyrotron power are used to heat water. The calibration of power monitor designs from the years 2009 until 2012 showed variations up to 25% on different experiment days, which is clearly above the uncertainty of the calorimetric calibration procedure. Using the latest power monitor design, these variations seem to be significantly reduced, even on the timescale of eight years, where hardware was unchanged. In this latest design, both the waveguide coupler and the low power transmission and detection scheme including flange interfaces were revised. The improved longevity seems to be mainly caused by improvements in the mechanical precision, stability and rigidity, which is backed by laboratory measurements
Design, Installation, and First Results from the Ion Cyclotron Emission Diagnostic on TCV
No full textTCV is a medium sized tokamak equipped with a large suite of plasma diagnostics, a versatile array of poloidal shaping coils, an electron cyclotron heating system, and a two source neutral beam injection (NBI) system. The NBI system is capable of a simultaneous injection of energetic neutrals in the co-and counter-current directions. The resulting fast ion (FI) populations are used to study a multitude of FI-driven instabilities. While plasma instabilities in the below 1 MHz frequency range can be observed via standard diagnostics such as soft x-ray detectors, magnetics, fast ion loss detectors, and reflectometers, fluctuations in the range of >10 MHz require a specialized diagnostic. For this purpose the TCV tokamak has been equipped with a dedicated ion cyclotron emission (ICE) diagnostic, following a similar approach to AUG [1] and W7-X [2]. The diagnostic consists of a pair of magnetic coils (8 turns, 177 nH, 16 mm long, 7 mm in diameter), oriented orthogonally to each other to detect magnetic field fluctuations in the toroidal and poloidal directions. The coils are housed in a stainless steel electrostatic shield with a slit and are installed on the torus low field side at the midplane location, behind graphite protection tiles. The coil electric outputs are routed to the vacuum feedthroughs via a pair of coaxial cables, at which point one of the outputs is grounded at the feedthrough, from the airside. The second output is then routed to a rectifying radio frequency wave detector and a fast digitizer in the diagnostics rack. The rectifying detector is sensitive to signals in the 10-100 MHz frequency range and can measure the signal amplitude and the phase difference between the two probes, while the frequency information of the signal is lost. The benefit of this detection method is that the output signal can be digitized at a “slow” speed (200 kHz in the case of TCV) with a low cost digitizer and the data volume per plasma discharge is low. The fast digitizer, on the other hand, preserves the frequency information, albeit with a larger data volume. For the case of TCV, a 250 MHz sampling rate digitizer has been temporarily used, while a dedicated 1 GHz digitizer is currently being implemented. First results of high frequency (>10 MHz) instabilities detected in the presence of energetic ions will be presented
Full-wave modeling of arcs within the ITER ICRF antenna for usage in the simulations and design of the RADAR Arc Detection system
No full textThe ITER ICRF antenna [1] has been carefully designed to feature electrical fields below tolerable limits (typically, below 2 or 3 kV/mm depending on the location and orientation) when operating at a maximum voltage of 45 kV. In particular, this allows avoiding arcs. However, as for any high-power RF system, arcs can still occur in the ICRF antenna and its power feeding system, during normal operation and especially during the commissioning. Whenever an arc is detected, the RF power shall be immediately tripped (μs timescale) to avoid strong local energy deposition at the location of the arc. Undetected arcs are forbidden. To this aim, several complementary and redundant Arc Detection (AD) systems are foreseen to protect the ITER ICRF antenna. Among these AD systems is the RADAR Arc Detection (or RAAD [2]) which is currently under evaluation for implementation on the ITER ICRF system To provide a first numerical proof of concept of RAAD, full-wave simulations of the ITER ICRF antenna and its power feeding transmission lines have been performed in the radar bandwidth of operation (up to ~ 350 MHz) with the help of CST Studio Suite and ANSYS HFSS commercial codes. In these simulations, the plasma loading has been approximated by a salty water load (with a relative dielectric permittivity εr = 80 and electrical conductivity σ = 1 S/m), while arcs have been modelled with both perfect electric conductor (PEC) cylinders or lumped element shorts. The obtained S-matrices have been then loaded and processed by the RAAD time-domain circuit simulations and signal processing calculations 2. This paper describes the challenges to simulate the full ITER ICRF antenna with arcs, considering different loading conditions, different materials and different solutions for the arc insertion. It also provides a comparison of the scattering parameters with and without arcs
Initial electron cyclotron heating/current drive scoping study for the SMall Aspect Ratio Tokamak (SMART)
No full textIn this work an initial electron cyclotron heating/current drive (EC H&CD) scoping study is presented for the SMall Aspect Ratio Tokamak (SMART), constructed and operated by the Plasma Science and Fusion Technology (PSFT) Laboratory of the University of Seville. We consider two planned phases of operation with different magnitude of magnetic field (B 0.4, and 1 T). This EC H&CD scoping study is carried out by using the ray tracing code TRAVIS, which allows to quickly perform a series of scans on the main SMART plasma scenarios. A scan in the poloidal and toroidal launching angles is performed for the B 0.4 T plasma scenario assuming three launching locations (mid-plane, off-mid-plane, and top-launcher) and the extraordinary (X-) mode polarization. The absorption occurs at the second harmonic and, overall, the highest power absorption is obtained launching the EC beam from the top of the machine. A numerical analysis of the fundamental X-mode EC H&CD start-up regime for the B 1.0 T plasma scenario with two different wave frequencies (28 and 35 GHz) is presented showing a very high current drive efficiency
Design and analysis of the main passive RF components for the DTT ICRH system
No full textThe Divertor Tokamak Test (DTT) is a new facility designed by Italian DTT Limited Liability Consortium (S.C.ar.l.) [1] aimed at validating an integrated solution for the power exhaust in support of DEMO [2]. The ICRH system, part of the DTT complex of additional heating systems, in its final configuration shall couple to the plasma up to 6 MW in the 60–90 MHz frequency range. All the main radiofrequency passive components of the system have been designed and optimized with the Ansys High Frequency Structures Simulator (HFSS) computer code. In particular 3 dB hybrid couplers, stubs, stretchers and vacuum feedthroughs have been examined. Results of the optimization of these components are presented and discussed in this paper
Progress in the analysis of the cavity resonances in the ITER ICRF antenna port plug
No full textThe ITER ICRF antenna plug [1, 2] can exhibit resonances at specific frequencies, some of them in the relevant range of frequencies for IC heating. These resonances have been identified as eigenmodes of the coaxial cavity, where the array plays the role of inner conductor [3], that can substantially increase the level of electric fields within the cavity as well as the level of RF losses. As no grounding solution is considered, RF probes should be installed to monitor the RF fields in the port plug cavity and additional simulations of a realistic magnetized plasma are required to properly assess the integration (position, orientation) and their effectiveness. Several numerical tools are available and have been extensively used to simulate the ITER ICRF antenna, such as TOPICA [5] or CST Microwave Studio (MWS [6]), but none of these codes allow to combine realistic geometries, realistic magnetized plasma profiles, and lossy materials. In this paper we pursue the effort started in [8] where a method based on a modal analysis in the cavity was introduced to decouple solving the computationally intensive plasma facing front of the launcher from the cavity. The method reproduces the TOPICA electric fields (with gyrotropic plasma effects) obtained in a given vertical reference plane, in a MWS cavity (including lossy materials) using the multimodal scattering matrix of the cavity obtained with MWS. This method is here applied to several realistic ITER plasma profiles. The recently extracted magnetic fields [9] from the TOPICA modeling results, provide an alternate way to compute the excitation spectrum of the cavity and therefore allow to confirm our results. Accurate levels of RF losses can then be obtained from various plasma profiles and excitation of the antenna straps