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Maximization of ICRF power by SOL density tailoring with local gas injection
Jacquet, P.,Goniche, M.,Bobkov, V.,Lerche, E.,Pinsker, R.I.,Pitts, R.A.,Zhang, W.,Colas, L.,Hosea, J.,Moriyama, S.,Wang, S.-J.,Wukitch, S.,Zhang, X.,Bilato, R.,Bufferand, H.,Guimarais, L.,Faugel, H.,H IOP 2016 Nuclear fusion Vol.56 No.4
<P>Experiments have been performed under the coordination of the International Tokamak Physics Activity (ITPA) on several tokamaks, including ASDEX Upgrade (AUG), JET and DIII-D, to characterize the increased Ion cyclotron range of frequency (ICRF) antenna loading achieved by optimizing the position of gas injection relative to the RF antennas. On DIII-D, AUG and JET (with the ITER-Like Wall) a 50% increase in the antenna loading was observed when injecting deuterium in ELMy H-mode plasmas using mid-plane inlets close to the powered antennas instead of divertor injection and, with smaller improvement when using gas inlets located at the top of the machine. The gas injection rate required for such improvements (~0.7 × 10<SUP>22</SUP> el s<SUP>−1</SUP> in AUG, ~1.0 × 10<SUP>22</SUP> el s<SUP>−1</SUP> in JET) is compatible with the use of this technique to optimize ICRF heating during the development of plasma scenarios and no degradation of confinement was observed when using the mid-plane or top inlets compared with divertor valves. An increase in the scrape-off layer (SOL) density was measured when switching gas injection from divertor to outer mid-plane or top. On JET and DIII-D, the measured SOL density increase when using main chamber puffing is consistent with the antenna coupling resistance increase provided that the distance between the measurement lines of sight and the injection location is taken into account. Optimized gas injection was also found to be beneficial for reducing tungsten (W) sputtering at the AUG antenna limiters, and also to reduce slightly the W and nickel (Ni) content in JET plasmas. Modeling the specific effects of divertor/top/mid-plane injection on the outer mid-plane density was carried out using both the EDGE2D-EIRENE and EMC3-EIRENE plasma boundary code packages; simulations indeed indicate that outer mid-plane gas injection maximizes the density in the mid-plane close to the injection point with qualitative agreement with the AUG SOL density measurements for EMC3-EIRENE. Field line tracing for ITER in the 15 MA <I>Q</I> <SUB>DT</SUB> = 10 reference scenario indicates that the planned gas injection system could be used to tailor the density in front the antennas. Benchmarking of EMC3-EIRENE against AUG and JET data is planned as a first step towards the ITER SOL modelling required to quantify the effect of gas injection on the SOL density in front of the antennas.</P>
Search for dark matter WIMPs using upward through-going muons in Super-Kamiokande
Desai, S.,Ashie, Y.,Fukuda, S.,Fukuda, Y.,Ishihara, K.,Itow, Y.,Koshio, Y.,Minamino, A.,Miura, M.,Moriyama, S.,Nakahata, M.,Namba, T.,Nambu, R.,Obayashi, Y.,Sakurai, N.,Shiozawa, M.,Suzuki, Y.,Takeuch American Physical Society 2004 PHYSICAL REVIEW D - Vol.70 No.8
Kim, S.H.,Lee, G.C.,Kang, J.Y.,Moriyama, K.,Park, H.S.,Kim, M.H. Pergamon Press ; Elsevier Science Ltd 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.102 No.-
We study a heat flux partitioning analysis of nucleate pool boiling on microstructured surface through infrared visualization technique. A heat flux partitioning analysis of the nucleate pool boiling consists of three kinds of heat flux mechanisms; convective, quenching and evaporative heat flux. It is importance of understanding the dominance among those heat flux mechanisms to fundamental study of the nucleate boiling heat transfer, but it is not clearly figured out. In this study, directly measuring the boiling parameters; bubble departure size, bubble releasing frequency, nucleation site density and bubble growth time through the infrared visualization technique, a nucleate boiling heat flux portioning analysis on pool boiling has been carried out. The experimental results indicate that sum of the three heat flux partitions from the measured boiling parameters shows good agreement with the experimentally given total heat flux. In addition, the quenching heat flux and evaporative heat flux becomes dominant at high heat flux regime by numerous bubble generation and fast bubble growth. On the microstructured surface, the increased heating surface area by the roughness ratio intactly contributes the heat transfer performance enhancement, and the area increase effect have to be reflected on the heat flux partitioning calculation. Although there are still many arguments of the heat flux portioning model analysis on pool boiling heat transfer from literatures and the methodological limitation due to the chaotic boiling phenomena, this study gives good inspiration and understanding of the boiling heat transfer mechanism and the importance of each heat transfer mechanism.
Kang, J.y.,Kim, S.H.,Jo, H.,Park, G.,Ahn, H.S.,Moriyama, K.,Kim, M.H.,Park, H.S. Pergamon Press ; Elsevier Science Ltd 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.93 No.-
The goal of this study is to investigate film boiling heat transfer (FBHT) on a completely wettable surface (CWS) with atmospheric, saturated distilled water (T<SUB>sat</SUB>~97<SUP>o</SUP>C). The CWS was fabricated using anodic oxidation of a zirconium rod, to achieve a contact angle of θ~0<SUP>o</SUP> with liquid-spreading and this was driven by capillary-wicking into the nano-scale, needle-shaped structures on the surface. To consider independently the effects of the maximum height ε<SUB>max</SUB> of the surface roughness, we investigated a roughed zirconium surface (RZS), which was modified by polishing with sandpaper. Quenching experiments were conducted to evaluate the FBHT; the heat transfer coefficient (h<SUB>film</SUB>) during FBHT, minimum heat flux (q''<SUB>min</SUB>) and minimum film boiling temperature (T<SUB>min</SUB>) were all larger with the CWS than with the bare zirconium surface (BZS) or on the RZS. Through high speed visualization, we observed that intermittent wetting during FBHT resulted in an unstable liquid-vapor interface in case of the CWS. Therefore, the remarkable ability of the CWS to supply liquid when in contact with the heat transfer surface resulted in clear enhancement of the FBHT performance (i.e., increases in h<SUB>film</SUB>, q''<SUB>min</SUB> and T<SUB>min</SUB>).
Supernova Relic Neutrino search with neutron tagging at Super-Kamiokande-IV
The Super-Kamiokande Collaboration,Zhang, H.,Abe, K.,Hayato, Y.,Iyogi, K.,Kameda, J.,Kishimoto, Y.,Miura, M.,Moriyama, S.,Nakahata, M.,Nakano, Y.,Nakayama, S.,Sekiya, H.,Shiozawa, M.,Suzuki, Y.,Takeda North-Holland 2015 Astroparticle physics Vol.60 No.-
A search for Supernova Relic Neutrinos ν@?<SUB>e</SUB>'s is first conducted via inverse-beta-decay by tagging neutron capture on hydrogen at Super-Kamiokande-IV. The neutron tagging efficiency is determined to be (17.74+/-0.04<SUB>stat.</SUB>+/-1.05<SUB>sys.</SUB>)%, while the corresponding accidental background probability is (1.06+/-0.01<SUB>stat.</SUB>+/-0.18<SUB>sys.</SUB>)%. Using 960days of data, we obtain 13 inverse-beta-decay candidates in the range of E<SUB>ν@?'e</SUB> between 13.3MeV and 31.3MeV. All of the observed candidates are attributed to background. Upper limits at 90% C.L. are calculated in the absence of a signal.
Search for GUT monopoles at Super-Kamiokande
The Super-Kamiokande Collaboration,Ueno, K.,Abe, K.,Hayato, Y.,Iida, T.,Iyogi, K.,Kameda, J.,Koshio, Y.,Kozuma, Y.,Miura, M.,Moriyama, S.,Nakahata, M.,Nakayama, S.,Obayashi, Y.,Sekiya, H.,Shiozawa, M. North-Holland ; Elsevier Science Ltd 2012 Astroparticle physics Vol.36 No.1
GUT monopoles captured by the Sun's gravitation are expected to catalyze proton decays via the Callan-Rubakov process. In this scenario, protons, which initially decay into pions, will ultimately produce ν<SUB>e</SUB>,ν<SUB>μ</SUB> and ν@?<SUB>μ</SUB>. After undergoing neutrino oscillation, all neutrino species appear when they arrive at the Earth, and can be detected by a 50,000 metric ton Water Cherenkov detector, Super-Kamiokande (SK). A search for low energy neutrinos in the electron total energy range from 19 to 55MeV was carried out with SK and gives a monopole flux limit of F<SUB>M</SUB>(σ<SUB>0</SUB>/1mb)<6.3x10<SUP>-24</SUP>(β<SUB>M</SUB>/10<SUP>-3</SUP>)<SUP>2</SUP>cm<SUP>-2</SUP>s<SUP>-1</SUP>sr<SUP>-1</SUP> at 90% C.L., where β<SUB>M</SUB> is the monopole velocity in units of the speed of light and σ<SUB>0</SUB> is the catalysis cross section at β<SUB>M</SUB>=1. The obtained limit is several orders of magnitude more stringent than the current best cosmic-ray supermassive monopole flux limit for β<SUB>M</SUB><10<SUP>-2</SUP> and also two orders of magnitude lower than the result of the Kamiokande experiment, which used a similar detection method.
마이크로 구조가 있는 친수성/소수성 표면에서의 젖음성 및 액적 증발 현상에 대한 연구
유동인(D. I. Yu),곽호재(H. J. Kwak),도승우(S. W. Doh),강희찬(H. C. Kang),안호선(H. S. Ahn),박현선(H. S. Park),키요후미 모리야마(K. Moriyama),김무환(M. H. Kim) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
According to the surface condition, the droplet has the contact angle and it is complexly evaporated. Therefore, the evaporation phenomena of the water droplet on the surface should be analyzed on the basis of the wetting phenomena. In this study, it is investigated the wetting and evaporation phenomena of water droplet on the textured hydrophilic / hydrophobic surfaces. On the well-defined surfaces about the surface condition, the apparent contact angle is precisely measured. To compare between experimental data and the previous wetting models, the models are experimentally validated. Subsequently, to study the evaporation phenomena, the contact angle and diameter are measured during droplet evaporation. On the basis of the wetting phenomena, the evaporation performance is analyzed depending on the surface conditions.
Search for dark matter in the form of hidden photons and axion-like particles in the XMASS detector
Abe, K.,Hiraide, K.,Ichimura, K.,Kishimoto, Y.,Kobayashi, K.,Kobayashi, M.,Moriyama, S.,Nakahata, M.,Ogawa, H.,Sato, K.,Sekiya, H.,Suzuki, T.,Takachio, O.,Takeda, A.,Tasaka, S.,Yamashita, M.,Yang, B.S Elsevier 2018 Physics letters: B Vol.787 No.-
<P><B>Abstract</B></P> <P>Hidden photons and axion-like particles are candidates for cold dark matter if they were produced non-thermally in the early universe. We conducted a search for both of these bosons using 800 live-days of data from the XMASS detector with 327 kg of liquid xenon in the fiducial volume. No significant signal was observed, and thus we set constraints on the <SUP> α ′ </SUP> / α parameter related to kinetic mixing of hidden photons and the coupling constant <SUB> g A e </SUB> of axion-like particles in the mass range from 40 to 120 keV/ <SUP> c 2 </SUP> , resulting in <SUP> α ′ </SUP> / α < 6 × <SUP> 10 − 26 </SUP> and <SUB> g A e </SUB> < 4 × <SUP> 10 − 13 </SUP> . These limits are the most stringent over this mass range derived from both direct and indirect searches to date.</P>
Abe, K.,Hiraide, K.,Ichimura, K.,Kishimoto, Y.,Kobayashi, K.,Kobayashi, M.,Moriyama, S.,Nakahata, M.,Norita, T.,Ogawa, H.,Sato, K.,Sekiya, H.,Takachio, O.,Takeda, A.,Tasaka, S.,Yamashita, M.,Yang, B.S Elsevier 2018 Nuclear Instruments & Methods in Physics Research. Vol.884 No.-
<P><B>Abstract</B></P> <P>We established a method to assay <SUP>210</SUP>Pb and <SUP>210</SUP>Po contaminations in the bulk of copper samples using a low-background alpha particle counter. The achieved sensitivity for the <SUP>210</SUP>Pb and <SUP>210</SUP>Po contaminations reaches a few mBq/kg. Due to this high sensitivity, the <SUP>210</SUP>Pb and <SUP>210</SUP>Po contaminations in oxygen free copper bulk were identified and measured for the first time. The <SUP>210</SUP>Pb contaminations of our oxygen free copper samples were 17–40 mBq/kg. Based on our investigation of copper samples in each production step, the <SUP>210</SUP>Pb in oxygen free copper was understood to be a small residual of an electrolysis process. This method to measure bulk contaminations of <SUP>210</SUP>Pb and <SUP>210</SUP>Po could be applied to other materials.</P>
Search for sub-GeV dark matter by annual modulation using XMASS-I detector
Kobayashi, M.,Abe, K.,Hiraide, K.,Ichimura, K.,Kishimoto, Y.,Kobayashi, K.,Moriyama, S.,Nakahata, M.,Ogawa, H.,Sato, K.,Sekiya, H.,Suzuki, T.,Takeda, A.,Tasaka, S.,Yamashita, M.,Yang, B.S.,Kim, N.Y.,K North-Holland Pub. Co 2019 Physics letters. Section B Vol.795 No.-
<P><B>Abstract</B></P> <P>A search for dark matter (DM) with mass in the sub-GeV region (0.32–1 GeV) was conducted by looking for an annual modulation signal in XMASS, a single-phase liquid xenon detector. Inelastic nuclear scattering accompanied by bremsstrahlung emission was used to search down to an electron equivalent energy of 1 keV. The data used had a live time of 2.8 years (3.5 years in calendar time), resulting in a total exposure of 2.38 ton-years. No significant modulation signal was observed and 90% confidence level upper limits of 1.6 × <SUP> 10 − 33 </SUP> cm<SUP>2</SUP> at 0.5 GeV was set for the DM-nucleon cross section. This is the first experimental result of a search for DM mediated by the bremsstrahlung effect. In addition, a search for DM with mass in the multi-GeV region (4–20 GeV) was conducted with a lower energy threshold than previous analysis of XMASS. Elastic nuclear scattering was used to search down to a nuclear recoil equivalent energy of 2.3 keV, and upper limits of 2.9 × <SUP> 10 − 42 </SUP> cm<SUP>2</SUP> at 8 GeV was obtained.</P>