Exploring the extreme Universe with a new generation of telescopes
丘政倫 博士(清華大學天文研究所)
<專題討論>2018/3/20(二)13:10綜合大樓2樓48218教室演講
摘要:
Experimental high energy astrophysics probes the most energetic and exotic objects and locations in our Universe by using a variety of X-ray, gamma-ray, and cosmic-ray instruments. These high-energy sources span many orders of magnitude in size and energetics, from cosmic gamma-ray bursts and supermassive black holes to supernovae and compact objects in our Galaxy. The underlying physical processes in these sources are often similar and usually inaccessible in a laboratory. But at the same time, many of the observations have important implications for fundamental physics. Therefore, a key to these studies is to develop and utilize novel instruments with excellent sensitivity and resolution. A current generation, NuSTAR, and a next generation telescope, COSI, which are and will be revolutionizing the observation of high-energy astrophysics phenomena, will be introduced here.
(1) The Compton Spectrometer and Imager (COSI) is a balloon-borne soft gamma-ray (0.2-5 MeV) telescope designed to study astrophysical sources of nuclear-line emission and gamma-ray polarization. COSI employs a compact Compton telescope design, imaging gamma-rays through their scattering history in novel 3D-tracking Germanium detectors. As a balloon payload, this telescope performs sensitive observations of positron annihilation, nucleosynthesis, compact objects, GRBs, and AGN. (2) The Nuclear Spectroscopic Telescope Array (NuSTAR) is the first focusing high energy X-ray satellite in orbit (launched in June 2012), providing more than two orders of magnitude improvement in sensitivity compared to previous high energy missions. NuSTAR's primary science goals include conducting a survey of black holes, mapping young supernovae explosions, studying cosmic accelerators, and identifying high energy sources in our Galaxy.
In this talk, I will present our current achievements with both instruments and future research plans based on these efforts.
| 附件: 20180320 丘政倫博士.pdf
Generation of light beams by electron beam excited surface plasmons
藍永強 教授(成功大學光電系)
<專題討論>2018/3/15(四)14:10綜合大樓2樓48218教室演講
摘要:
When the electron beam moves along or normally onto the plasmonic nanostructures (PNs), it can excite the surface plasmons (SPs) on PNs along with the transition radiation (TR). In the former case, the SPs have specific frequencies determined by the intersection of dispersion curves of electron beam and SPs. In the latter case, conversely, the SPs have a wide frequency band [1]. Furthermore, SPs can be transferred into light emission (SP emission) by the surface structures of PNs. In this work, we will consider three types of light beam generation by electron beam excited SPs. First, we will investigate SP-manipulated and localized SP (LSP)-manipulated Smith-Purcell radiation (SPR) on metallic periodic gratings and disk arrays, respectively [2]. The SPR can be enhanced by exciting SPs and LSPs if their frequencies are within the emission bands of SPRs. Second, the generation of convergent beam by electron-excited SPs is examined. Here the mechanism of SPR on metallic chirped gratings is proposed to generate the convergent light beam. Finally, the SP-manipulated TR and SP emission from the electron beam normally incident PNs with designed slit structures are studied [3]. This work offers potential applications in the fields of optical imaging, holography, cryptography and tunable visible light source, etc.
| 附件: 20180315 藍永強教授.pdf
Facile Synthesis of Single-Elemental Two-Dimensional Materials via Plasma and/or Implantation Assisted Process
蔡勖升 博士(清華大學核子工程與科學研究所)
<專題討論>2018/3/13(二)13:10綜合大樓2樓48218教室演講
摘要:
Synthesis and growth of two-dimensional (2D) materials have been extensively investigated in order to achieve high quality, scalability, and reduce the complexity of process in recent years. Mechanical exfoliation is a quite unpractical method owing to the scale limitation while chemical vapor deposition (CVD) on metal substrates must be combined with the manual transfer step, which seriously damages the materials for device applications. Ultrahigh vacuum (UHV) growth cannot accomplish the high production and reduce the cost of process. The conditions of some particular syntheses are quite difficult to be performed, thus they do not have potential for commercialization. This study announces that a facile synthesis method, so called plasma and/or implantation assisted process, has been successfully utilized to synthesize several single-elemental 2D materials. The process divided into plasma and/or implantation and thermal treatment almost solves all of the issues mentioned above. In addition to demonstrate the feasibility of plasma and/or implantation assisted process for synthesis of the single-elemental 2D materials, superior properties of these 2D materials were measured for seeking real applications.
| 附件: 20180313 蔡勖升博士.pdf
The polar cap magnetic activity (PC) index as an indicator of the solar wind energy incoming into the magnetosphere.
Prof. O. A. Troshichev(Arctic and Antarctic Research Institute, St/Petersburg, Russia)
<專題討論>2018/3/8(四)14:10綜合大樓2樓48218教室演講
摘要:
The polar cap (PC) magnetic activity index was approved by the International Association of Geomagnetism and Aeronomy (IAGA) in 2013 as a new international index assigned to monitor the energy that enters into the magnetosphere under the solar wind-magnetosphere coupling. The following experimental data form the basis for this statement: (1) the PC index strongly follows the time evolution of interplanetary electric field (EKL) reduced to the magnetopause, (2) delay time ΔT in response of PC index to EKL variations is controlled by the EKL field growth rate (dEKL/dt), (3) magnetic storms and substorms are always preceded and accompanied by a growth in РС index, (4) substorms and magnetic storms start to develop as soon as the PC index exceeds the threshold level of 1.5 mV/m, (5) the substorm sudden onsets are commonly associated with a sharp increase in the PC (and EKL) growth rate, (6) the solar wind drivers (ICMEs or SIRs) determine the type of magnetic storm, such as “classic” storm, related to ICME impact, with well-defined PC maximum and clearly expressed one maximum of depression, “pulsed” storm, related to SIR impact, with periodically repeating oscillations in PC and geomagnetic field depression, and “combined storms”, which are regarded as effect of simultaneous ICME and SIR action, (7) maximal depression of magnetic field responds to maximal PC value with a delay of ~1 hour, the storm intensity (Dstmin) being linearly depending on PCmax value. In ~10% of the substorm events the correlation between EKL and PC was practically absent, in spite of the PC index rise before the substorm onset, which means that solar wind, measured in the Lagrange point, passes by the magnetosphere in these cases. Therefore the РС index can be used also to verify whether or not the solar wind measured in Lagrange point L1 is in contact with the magnetosphere.
All these statistically justified relationships testify that the PC index is an indicator of the solar wind energy incoming into the magnetosphere. In this context, the PC index can be successfully used as a new reliable ground-based technique for exploration of short-term changes in space weather and magnetosphere state.
Implementation of a 10 kJ pulsed-power generator
張博宇 助理教授 ( 成大電漿所 )
<專題討論>2017/12/14(四)14:10綜合大樓2樓48218教室演講
A 10 kJ pulsed-power generator as a platform is being built to study plasma jets in space, nuclear fusion, specifically on inertial-confinement fusion (ICF), and to generate neutrons, soft-x rays, and extreme ultraviolet (EUV). The system will be built using an architecture called parallel plate capacitor bank (PPCB). In PPCB, all capacitors are connected in parallel and the current from all capacitors are delivered to the load through a parallel plate transmission line due to its low inductance and simple system configuration. Twenty 1 µF capacitors which can be charged up to 40 kV are used. The total discharge energy can be up to 16 kJ and the expected output current will be more than 100 kA with a rise time of ∼ 1 µs, i.e., an output power of ∼ 10 GW.
Any loads will be heated and ionized by the high current. The generated plasma can potentially be used for following purposes: (1) generating plasma jets to study interactions between plasma flows and unmagnetized/magnetized obstacles analogous to the interactions between solar winds and planetary magnetic fields or unmagnetized planets; (2) generating soft x-ray/EUV using gas- puff z pinches for bio-medical research or EUV lithography; (3) generating soft x-ray lasers using capillary discharge; and (4) studying the pinch in a dense plasma focus device as a high efficient neutron source for Neutron capture therapy of cancer. The pulsed-power generator is being built by students in the lab from scratch and is expected to be finished by next Summer. The preliminary design and some testing results of each hand-made component will be given.
| 附件: 20171214 張博宇助理教授.pdf
Status and vision of the KSTAR program to resolve critical issues of the steady-state high beta operation in ITER and K-DEMO operation
Dr. Yeong-Kook Oh / KSTAR research center, National Fusion Research Institute (NFRI), Daejeon, Korea )
<專題討論>2021/3/25(四)14:10綜合大樓2樓48218教室演講
Developing energy resources that are environmentally friendly and free from high-level radioactive waste is especially important for next generation, particularly in Korea where underground resources are lacking. Fusion energy development is of great significance pursuing one of the alternatives that is less dependent on fossil resources.
The fusion energy development in Korea is based on the Fusion Energy Development Promotion Law, and the KSTAR project plays a very important role in resolving the critical issues required for future fusion reactor development and in raising the human resources capable of the research. The KSTAR project has several unique features (extremely low error field, versatile in-vessel control coils, 2D advanced imaging diagnostics, and high efficient long pulse capable heating system) to achieve a high performance steady-state operation research vision. The KSTAR
The KSTAR project started in 1995, achieving the first plasma in 2008, and has shown a lot of remarkable results for 10 years’ operation. In particular, KSTAR achieved the long pulse (over 70s) H-mode discharge with confinement equivalent to ITER (betaN ~ 1.8) and suppressed Edge Localized Mode (ELM) crash robustly up to 34 s using n=1 Resonance magnetic Perturbation (RMP). In addition, progress in fundamental physics interpretation on the turbulence and instability due to advanced diagnostics system and modeling studies.
In order to explore the plasma confinement and instability at higher confinement (betaN > 3.0), heating systems are under upgrade (NBI heating 5.5.MW à 12 MW, ECCD system 1 MW à 6 MW), and Divertor and current driving system will be upgraded also around in 2021 to develop a steady-state scenario for K-DEMO.
We acknowledge the contribution and collaboration to KSTAR from national and international collaborators. This work is supported by Ministry of Science and ICT (MSIC) of Korea under KSTAR project.
Two types of asymmetries of field –aligned currents distribution in polar ionosphere and of magnetosphere –ionosphere feedbacks during the substorm expansion phase
Prof. Vladimir Mishin / Institute of Solar-Terrestrial Physics, Irkutsk, Russia )
<演講公告>2017/12/4(一)11:00綜合大樓2樓48218教室演講
We use original magnetogram inversion technique created by Vilen Mishin, A.
Bazarzhapov and G. Shpynev in Irkutsk more than 40 years ago. This method uses data of world net of ground-based magnetometers. It was also then developed in parallel in Russia in IZMIRAN (Feldshtein, Levitin, Belov, Papitashvili) and abroad by Kamide et all. Recently, this method is already very few people engaged in, all use the expensive data of multi-satellite projects such as AMPERE. However, our inexpensive method allows, with a 1 min resolution, to build maps of the distribution of field-aligned currents (FACs) and fields and to reveal fine structures in their zones–mesoscale cells, which is inaccessible for other methods. The report deals with two types of FAC distribution in the mesoscale cells of night auroral ionosphere. Also, two types of feedback in the magnetosphere-ionosphere system are investigated: of the intensity of field-aligned currents (FACs) with the ionosphere conductivity (type 1), and with the electric field (type 2). Explosive development of FACs during the substorm expansion phase in the nighttime mesoscale cells of the three Iijima and Potemra (I-P) regions connected by meridional currents, is described.
BCS-type second-order phase transition of classical Langmuir wave system
河森榮一郎 教授 ( 成大電漿所 )
<專題討論>2017/11/30(四)14:10綜合大樓2樓48218教室演講
The BCS-type second-order phase transition of a classical Langmuir wave system is identified theoretically and numerically. The transition takes place between two states: Langmuir wave turbulence (LWT) and Langmuir wave supercontinuum (LWSC), the latter of which exhibits broad power spectra with significant spatiotemporal coherence when a certain number of plasmons (plasma wave quanta) are excited in the system. In the LWT-LWSC transition, the modulational instability and resulting creation of plasmon pairs are the classical counterparts of the Cooper instability and creation of Cooper pairs in superconducting states. The Bose–Einstein condensation of Cooper pairs in superconducting states is replaced by the Kuramoto oscillator-entrainment of plasmon pairs in a LWSC. The order parameter of the LWSC state, which is defined as the mean field of the plasmon pairs, takes on a significant value, which clearly indicates that a macroscopic number of plasmon pairs occupy a single momentum state with an identical phase in the LWSC. The emergence of spatiotemporal coherence and the decrease in the phase randomization are considered as development of long-range order and spontaneous symmetry breaking, respectively, indicating that the LWT-LWSC transition is a second order phase transition phenomenon. By this transition, U(1) symmetry of LWT is broken. The LWSC is, in terms of plasma physics, a so-called Bernstein–Greene–Kruskal mode characterized by its undamped nature.
| 附件: 20171130 河森榮一郎教授.pdf
Micro Power System and its Application / 微動力系統與其應用
李約亨 助理教授 /( 成大航太系 )
<專題討論>2017/11/23(四)14:10綜合大樓2樓48218教室演講
The application of micro power system is prevailing. This talk would introduce the concept, design and demonstration of micro-thermophotovoltaic (micro-TPV) power system. However, the overall efficiency of micro-TPV is strongly associated with radiant efficiency and quantum efficiency. How to improve the overall efficiency of micro-TPV power system during the miniaturization process is a quintessential question to researchers. The talk would point out the inherent deficiency of a small combustion system, and propose some promising strategies to overcome these defaults. Ultimately, the combination of TPV power system and Stirling Engine fueling with (bio-) syngas is demonstrated and discussed.
| 附件: 20171123 李約亨助理教授.pdf
We live in a world of mathematical models
許瑞麟 教授 ( 成大數學系 )
<專題討論>2017/11/16(四)14:10綜合大樓2樓48218教室演講
We are so used to many daily lives that we mistakenly think they are natural. They are not. For example, the calendar is not nature. It is just a model for us to explain the nature. In the calendar (model), we use the term "year" to call, roughly, a full round of a revolution of the earth around the sun; and then divide a year into seasons and months; and into the dates and the time. The calendar is certainly not the nature itself though. Models are subject to change whenever they become inaccurate or whenever we change the way we understand the world. As such, some radical mathematicians claim that " Every model is wrong." In this talk, I will first give some general senses about the mathematical models for the hope that we can properly use models, rather than believe in models. Then, we will see as many concrete examples as possible, subject to the time limitation, that the models help/abuse us.
| 附件: 20171116 許瑞麟教授.pdf