Examinando por Autor "Pavez, Cristian"
Mostrando 1 - 9 de 9
Resultados por página
Opciones de ordenación
Ítem A model for defect formation in materials exposed to radiation(2021-01-01) Davis, Sergio; González-Cataldo, Felipe; Gutiérrez, Gonzalo; Avaria, Gonzalo; Bora, Biswajit; Jalaj Jain, José; Pavez, Cristian; Soto, LeopoldoA simple model for the stochastic evolution of defects in a material under irradiation is presented. Using the master-equation formalism, we derive an expression for the average number of defects in terms of the power flux and the exposure time. The model reproduces the qualitative behavior of self-healing due to defect recombination, reaching a steady-state concentration of defects that depends on the power flux of the incident radiation and the material temperature, while also suggesting a particular time scale on which the incident energy is most efficient for producing defects, in good agreement with experimental results. Given this model, we discuss the integral damage factor, a descriptor that combines the power flux and the square of the irradiation time. In recent years, the scientific community involved in plasma-facing materials for nuclear fusion reactors has used this parameter to measure the equivalent material damage produced in experiments of various types with different types of radiation and wide ranges of power flux and irradiation time. The integral damage factor is useful in practice but lacks formal theoretical justification. In this simple model, we find that it is directly proportional to the maximum concentration of defects. © 2021 Author(s).Ítem Análisis de la valuación patrimonial de una empresa de acuerdo a los principios contables generalmente aceptados(Universidad Andrés Bello, 1998) León, Alvaro; Morales, Cecilia; Neira, Carlos; Pavez, Cristian; Echaiz Fernández, Iván; Facultad de Ciencias Economicas y Administrativas; Escuela de Contadores AuditoresEl presente estudio centra su atención, en forma inmediata cuestionando la base teórica que sustenta el proceso de valuación contable teniendo como base el principio de costo histórico, al cual se somete la información contable, y que incide en la calidad de la misma, perdiendo con esto objetividad para la toma de decisiones. Por otra parte, se proponen alternativas al actual sistema de valuación contable, de manera que contribuya, en forma teórica, a lograr que se solucione esta debilidad de la contabilidad en el mediano plazo, en lo relacionado a los distintos procesos de decisiones, a través, de la generación de información relevante para los diversos usuarios de la misma.Ítem Design and Stability Analysis of a Digital Automatic Power Control Based on a PI Controller for Laser Drivers(MDPI, 2023-05) Pedreros, Jose; Becerra, Alex; Rojas, Javier; Pavez, Cristian; Diaz, MarcosLaser diodes are widely used in research and industrial applications in areas such as measurements, communications and health. In most of these applications, stability in the emitted light power is required. This can be realized by modifying the internal parameters, such as the current supply, by using an analog automatic power control (APC). This research presents the design and analysis of a feedback laser driver (digital APC system) based on a proportionall–integral (PI) controller. The controller’s theoretical design acting on the supply current in a laser was obtained by algebraically solving the general equations of a PI controller over a laser described as a steady-state system. The required steady-state model can be determined from the lightl–current curve obtained either from the laser data sheet or experimentally. A posterior numerical analysis shows that the proportional gain of the PI controller is only limited numerically by the reciprocal of the slope efficiency of the laser when the characteristic time of the system is greater than the sampling period. Finally, the APC model was tested in an experimental setting using a laser diode ADL-65052TL at several temperatures. The results show that the proposed relations for the proportional gain and the integral time are valid, achieving the desired power stability with a drift of less than (Formula presented.).Ítem Electromagnetic burst measurement system based on low cost UHF dipole antenna(Energies, 2017-09) Escalona, Ismael; Avaria, Gonzalo; Díaz, Marcos; Ardila-Rey, Jorge; Moreno, José; Pavez, Cristian; Soto, LeopoldoNon-linear high-power devices produce electromagnetic noise (EMN) sources of great intensity that can disrupt and damage the surrounding electrical equipment and devices. This radiative phenomenon is very common at facilities where pulsed power generators are required, particularly those that are needed to produce dense transient plasma experiments. These conditions are found at the Chilean Nuclear Energy Commission (CCHEN), due to the presence of pulsed power generators that switch large currents (kA-MA) in short times (10-100 ns). In order to characterize and establish conditions to mitigate the effects of the EMN on nearby devices, a measurement system based on an ultra-high frequency (UHF) dipole antenna was developed. We evaluated the system measuring the EMN emanated from a plasma focus device, the PF-400J. Measurements at the place indicated broadband and intense electric fields that can couple to nearby cables and equipment (10-300 MHz bandwidth, up to 350 V/MHz spectral intensity, 100 V coupled voltage). Based on these measurements a compact and simple protection system was designed, built and tested, capable of effectively mitigating the high levels of EMN. The proper EMN impact mitigation indicates the correct operation of the suggested system. The developed system can be of interest to the energy community by facilitating EMN measurement produced by arc discharges. © 2017 by the authors.Ítem Hard X-Ray Emission Detection Using Deep Learning Analysis of the Radiated UHF Electromagnetic Signal from a Plasma Focus Discharge(Institute of Electrical and Electronics Engineers Inc., 2019) Avaria, Gonzalo; Ardila-Rey, Jorge; Davis, Sergio; Orellana, Luis; Cevallos, Benjamin; Pavez, Cristian; Soto, LeopoldoA method to determine the presence of hard X-ray emission processes from a dense plasma focus (205 J, 22 kV, 6.5 mbar H2) using Ultra High Frequency (UHF) measurements and deep learning techniques is presented. Simultaneously, the electromagnetic UHF radiation emitted from the plasma focus was measured with a Vivaldi UHF antenna, while the hard X-ray emission was measured with a scintillator-photomultiplier system. A classification algorithm based on deep learning methods, using two-dimensional convolutional layers, was implemented to predict the hard X-ray signal standard deviation value using only the antenna signal measurement. Two independent datasets, consisting of 999 and 1761 data pairs each, were used in the analysis. Different realizations of the training/validation process using a deep learning model, obtained overall better results in comparison to other machine learning methods like k-neighbors, decision trees, gradient boost, and random forest. The results of the deep learning algorithm, and even its comparison with other machine learning methods, indicate that a relationship between the electromagnetic UHF radiation and hard X-ray emission can be established, enabling the indirect detection of hard X-ray pulses only using the UHF antenna signal. This indirect detection presents the opportunity to have a simple and low-cost diagnostic, compared to the methods currently used to characterize the pulses of X-rays emitted from plasma focus discharges. © 2013 IEEE.Ítem Kappa distribution from particle correlations in nonequilibrium, steady-state plasmas(American Physical Society, 2023-12) Davis, Sergio; Avaria, Gonzalo; Bora, Biswajit; Jain, Jalaj; Moreno, José; Pavez, Cristian; Soto, LeopoldoKappa-distributed velocities in plasmas are common in a wide variety of settings, from low-density to high-density plasmas. To date, they have been found mainly in space plasmas, but are recently being considered also in the modeling of laboratory plasmas. Despite being routinely employed, the origin of the kappa distribution remains, to this day, unclear. For instance, deviations from the Maxwell-Boltzmann distribution are sometimes regarded as a signature of the nonadditivity of the thermodynamic entropy, although there are alternative frameworks such as superstatistics where such an assumption is not needed. In this work we recover the kappa distribution for particle velocities from the formalism of nonequilibrium steady-states, assuming only a single requirement on the dependence between the kinetic energy of a test particle and that of its immediate environment. Our results go beyond the standard derivation based on superstatistics, as we do not require any assumption about the existence of temperature or its statistical distribution, instead obtaining them from the requirement on kinetic energies. All of this suggests that this family of distributions may be more common than usually assumed, widening its domain of application in particular to the description of plasmas from fusion experiments. Furthermore, we show that a description of kappa-distributed plasma is simpler in terms of features of the superstatistical inverse temperature distribution rather than the traditional parameters κ and the thermal velocity vth.Ítem On the Relationship between the Electromagnetic Burst and Inductive Sensor Measurement of a Pulsed Plasma Accelerator(Institute of Electrical and Electronics Engineers Inc., 2019) Orellana, Luis; Ardila-Rey, Jorge; Diaz, Marcos; Pavez, Cristian; Schurch, Roger; Soto, LeopoldoA remote and non-invasive diagnostic of the plasma focus using antennas is presented in this work. The main motivation is the application of such diagnostic in a miniaturized plasma accelerator, based on the plasma focus architecture, as a cube satellite thruster. The evaluation of this proposal was carried out measuring a hundred of joules plasma focus operation simultaneously with the inductive measurement and antennas. Three different antennas tuned in the ultra high frequency range were tested: a monopole, Vivaldi and helical. The high frequency transients detected with the antennas were time correlated to the known inductive measurement features. The initial dielectric breakdown and later plasma pinch and subsequent disruption (i.e. the source of the propulsion) were identified to be the principal phenomena to be detected. Signal parameter correlations between the inductive sensor and the antennas showed that the pinch phenomena can be correlated with the antenna signals. Good correlation results were obtained with the monopole antenna when using peak value and signal energy parameter from the antenna transient. An improvement in the correlation results, for the helical and Vivaldi antennas, was obtained when calculating the frequency band energy. In this case, the Vivaldi antenna achieved the best results. The results of the monopole antenna make it an alternative remote sensor for plasma focus, but for the application of a miniaturized plasma focus as pulsed plasma thruster, the Vivaldi antenna is a more feasible design to replace the inductive diagnostic due to its compact design in comparison to the monopole. © 2013 IEEE.Ítem Update on the Scientific Status of the Plasma Focus(MDPI, 2021-09) Auluck, Sunil; Kubes, Pavel; Paduch, Marian; Sadowski, Marek J.; Krauz, Vyacheslav I.; Lee, Sing; Soto, Leopoldo; Scholz, Marek; Miklaszewski, Ryszard; Schmidt, Hellmut; Blagoev, Alexander; Samuelli, Maurizio; Seng, Yeow Sing; Springham, Stuart Victor; Talebitaher, Alireza; Pavez, Cristian; Akel, Mohammad; Yap, Seong Ling; Verma, Rishi; Kolacek, Karel; Keat, Paul Lee Choon; Rawat, Rajdeep S.; Abdou, Ali; Zhang, Guixin; Laas, TõnuThis paper is a sequel to the 1998 review paper “Scientific status of the Dense Plasma Focus” with 16 authors belonging to 16 nations, whose initiative led to the establishment of the International Center for Dense Magnetized Plasmas (ICDMP) in the year 2000. Its focus is on understanding the principal defining characteristic features of the plasma focus in the light of the developments that have taken place in the last 20 years, in terms of new facilities, diagnostics, models, and insights. Although it is too soon to proclaim with certainty what the plasma focus phenomenon is, the results available to date conclusively indicate what it is demonstrably not. The review looks at the experimental data, cross-correlated across multiple diagnostics and multiple devices, to delineate the contours of an emerging narrative that is fascinatingly different from the standard narrative, which has guided the consensus in the plasma focus community for several decades, without invalidating it. It raises a question mark over the Fundamental Premise of Controlled Fusion Research, namely, that any fusion reaction having the character of a beam-target process must necessarily be more inefficient than a thermonuclear process with a confined thermal plasma at a suitably high temperature. Open questions that need attention of researchers are highlighted. A future course of action is suggested that individual plasma focus laboratories could adopt in order to positively influence the future growth of research in this field, to the general benefit of not only the controlled fusion research community but also the world at large.Ítem Wire array experiments in a low impedance and low current generator(Institute of Physics Publishing, 2015-03) Cabrini, Nibaldo; Pavez, Cristian; Avaria, Gonzalo; San Martin, Patricio; Veloso, Felipe; Zúñiga, Barbara; Sepúlveda, Adolfo; Soto, LeopoldoIn this work, a preliminary study about the behavior of a low impedance generator on different wire array configurations is reported. The experimental measurements were carried out on a small multi-purpose generator (1.2μF, 345J, 47.5nH, T/4=375 ns and Z=0.2 in short circuit) which produces currents up to 122 kA with 500 ns quarter period, when a charging voltage of 24kV and a wire load are used. Two types of configurations were tested: parallel wires (two and four) and X-pinch configurations. The experiments were carried out on W, Al, and Cu wires with different diameters. The discharge was characterized by means of a set of diagnostics which included: Rogowski coil; filtered PCD detector; filtered PIN diode; gated VUV/soft X-ray pinhole camera, Shadow diagnostic and dark field Schlieren technique. From the set of experimental results, the following observations can be established: (i) The generator is highly sensitive to the changes of load impedance due to its low impedance design. (ii) Every shot shows a dip in the current derivative signal shortly after the discharge onset time (from 6 to 40 ns), which is inversely related to the load resistance. (iii) Both configurations show a similar dynamic to those observed in experiments of higher current and shorter quarter period. (iv) At the X-pinch experiments, two or more hard X-ray bursts are detected, around 200 ns from the current onset time. These X-ray bursts are correlated with the dips observed in the current derivative signal.