0000000000189813
AUTHOR
C. S. Chang
showing 10 related works from this author
γ-RAY AND PARSEC-SCALE JET PROPERTIES OF A COMPLETE SAMPLE OF BLAZARS FROM THE MOJAVE PROGRAM
2011
著者人数: 145名
Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating
2017
We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed ‘three-ion’ scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of 3He ions to high energies in dedicated hydrogen–deuterium mixtures.…
Novel method for determination of tritium depth profiles in metallic samples
2019
Tritium accumulation in fusion reactor materials is considered a serious radiological issue, therefore a lot of effort has been concentrated on the development of radiometric techniques. A novel method, based on gradual dissolution, for the determination of the total tritium content and its depth profiles in metallic samples is demonstrated. This method allows for the measurement of tritium in metallic samples after their exposure to a hydrogen and tritium mixture, tritium containing plasma or after irradiation with neutrons resulting in tritium formation. In this method, successive layers of metal are removed using an appropriate etching agent in the controlled regime and the amount of evo…
Overview of the JET results
2015
Since the installation of an ITER-like wall, the JET programme has focused on the consolidation of ITER design choices and the preparation for ITER operation, with a specific emphasis given to the bulk tungsten melt experiment, which has been crucial for the final decision on the material choice for the day-one tungsten divertor in ITER. Integrated scenarios have been progressed with the re-establishment of long-pulse, high-confinement H-modes by optimizing the magnetic configuration and the use of ICRH to avoid tungsten impurity accumulation. Stationary discharges with detached divertor conditions and small edge localized modes have been demonstrated by nitrogen seeding. The differences in…
Comparison of the structure of the plasma-facing surface and tritium accumulation in beryllium tiles from JET ILW campaigns 2011-2012 and 2013-2014
2019
In this study, beryllium tiles from Joint European Torus (JET) vacuum vessel wall were analysed and compared regarding their position in the vacuum vessel and differences in the exploitation conditions during two campaigns of ITER-Like-Wall (ILW) in 2011-2012 (ILW1) and 2013-2014 (ILW2) Tritium content in beryllium samples were assessed. Two methods were used to measure tritium content in the samples - dissolution under controlled conditions and tritium thermal desorption. Prior to desorption and dissolution experiments, scanning electron microscopy and energy dispersive x-ray spectroscopy were used to study structure and chemical composition of plasma-facing-surfaces of the beryllium sampl…
The Broadband Spectral Energy Distribution of the MOJAVE Sample
2010
We are constructing the broadband SED catalog of the MOJAVE sample from the radio to the gamma-ray band using MOJAVE, Swift UVOT/XRT/BAT, and Fermi/LAT data, in order to understand the emission mechanism of extragalactic outflows and to investigate the site of high-energy emission in AGN. Since the launch of Fermi gamma-ray Space Telescope in August 2008, two thirds of the MOJAVE sources have been detected by Fermi/LAT. Combining the results of high-resolution VLBI, X-ray, and gamma-ray observations of the jet-dominated AGN sample, we want to pin down the origin of high-energy emission in relativistic jets. Here we present our overall project and preliminary results for 6 selected sources.
VLBI detection of the HST-1 feature in the M87 jet at 2 cm
2010
A bright feature 80 pc away from the core in the powerful jet of M87 shows highly unusual properties. Earlier radio, optical and X-ray observations have shown that this feature, labeled HST-1, is superluminal, and is possibly connected with the TeV flare detected by HESS in 2005. It has been claimed that this feature might have a blazar nature, due to these properties. To examine the possible blazar-like nature of HST-1, we analyzed lambda 2 cm VLBA archival data from dedicated full-track observations and the 2 cm survey/MOJAVE VLBI monitoring programs obtained between 2000 and 2009. Applying VLBI wide-field imaging techniques, the HST-1 region was imaged at milliarcsecond resolution. Here …
Modelling of JET hybrid plasmas with emphasis on performance of combined ICRF and NBI heating
2018
International audience; During the 2015--2016 JET campaigns, many efforts have been devoted to the exploration of high-performance plasma scenarios envisaged for DT operation in JET. In this paper, we review various key recent hybrid discharges and model the combined ICRF NBI heating. These deuterium discharges with deuterium beams had the ICRF antenna frequency tuned to match the cyclotron frequency of minority H at the centre of the tokamak coinciding with the second harmonic cyclotron resonance of D. The modelling takes into account the synergy between ICRF and NBI heating through the second harmonic cyclotron resonance of D beam ions, allowing us to assess its impact on the neutron rate…
A closer look at the flaring feature in the M87 jet
2009
The radio-loud active galactic nucleus in M 87 hosts a powerful jet fueled by a super-massive black hole in its center. A bright feature 80 pc away from the M 87 core has been reported to show superluminal motions, and possibly to be connected with a TeV flare observed around 2005. To complement these studies and to understand the nature of this feature, we analyzed 2 cm VLBI data from 15 observing runs between 2000 and 2009. This feature is successfully detected at the milli-Jansky level from 2003 to 2007. Our detections show that its milli-arcsecond structure appears to be extended with a steep spectrum, and no compact or rapidly moving features are observed. Our results do not favor a bl…
The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004-447 I. The X-ray View
2015
As part of the TANAMI multiwavelength progam, we discuss new X-ray observations of the $\gamma$-ray and radio-loud Narrow Line Seyfert galaxy ($\gamma$-NLS1) PKS 2004-447. The active galaxy is a member of a small sample of radio-loud NLS1s detected in $\gamma$-rays by the Fermi Large Area Telescope. It is the radio-loudest and only southern-hemisphere source in this sample. We present results from our X-ray monitoring program comprised of Swift snapshot observations from 2012 through 2014 and two new X-ray observations with XMM-Newton in 2012. We analyze the X-ray spectrum and variability of this peculiar source using supplementary archival data from 2004 and 2011. The (0.5-10) keV spectrum…