Plasma-facing materials (PFMs) undergo constant erosion and redeposition that lead to film growth in the form of redeposited or reconstituted films. These films can be <inline-formula> <tex-math ...notation="LaTeX">\mu</tex-math> </inline-formula>m to mm thick, are often porous, and are comprised of a mix of impurities and the first wall material (e.g., W, B, C, O, and N). The properties of these films (i.e., sputtering and retention) can differ significantly from their pure polycrystalline precursors, which could have important implications for the PFM lifetime. Multi-beam optical stress sensor (MOSS) is an optical technique that can measure the surface stress of a material in situ in real time. Surface stress is affected by a variety of factors, including material deposition, substrate temperature, or defects in the substrate. In this study, this technique is used for the first time to study fusion-relevant thin films. Thin (1. nm) tungsten films were deposited on the surface of polycrystalline tungsten substrates to mimic redeposited films. These artificial films contained 2.% oxygen and were irradiated using low-energy (3. eV) deuterium ions for a total fluence of 4. <inline-formula> <tex-math notation="LaTeX">\times </tex-math> </inline-formula> <inline-formula> <tex-math notation="LaTeX">10^{20} \textrm{ m}^{-2}</tex-math> </inline-formula>. MOSS data acquired during the ion irradiations indicates that thin tungsten films underwent an irreversible change in surface stress as a result of the deuterium ion irradiation. This result suggests that deuterium retention could be responsible for the change observed, which can open the door to using MOSS as a technique to monitor PFMs in real time.
•Recrystallization and grain growth study of W alloyed with TiC, TaC, or ZrC; Pure W recrystallizes at ~1400 C•Addition of second phase particles increases the recrystallization temperature; Addition ...of 10wt.% second phase results in surface oxide formation and growth
Tungsten is the material of choice for the divertor region of future nuclear fusion reactors, an environment that will expose plasma-facing components (e.g. divertor, etc...) to high temperatures and transient high heat flux events. Under these conditions, recrystallization and grain growth of tungsten can occur, leading to undesirable microstructural and mechanical property changes. Therefore, there is a need to raise the recrystallization temperature of tungsten and limit the kinetics of the recrystallization and grain growth processes. In this work, we examine the effect of different types (TiC vs. TaC vs. ZrC) and different concentrations (1.1 vs. 5 vs. 10 wt.%) of dispersed second phase particles in a tungsten matrix on the high temperature performance. The addition of second-phase particles effectively increases the temperature of and time for recrystallization and slow grain growth; however, the addition of a high weight fraction of particles alters the surface chemistry, which may impact subsequent plasma-surface interactions. These results show that the addition of small concentrations of dispersed particles can be effectively employed in tungsten to raise the upper operating temperature limit for tungsten in a fusion reactor.
Tungsten is the material of choice for the divertor region of future nuclear fusion reactors, an environment that will expose plasma-facing components (e.g. divertor, etc...) to high temperatures and ...transient high heat flux events. Under these conditions, recrystallization and grain growth of tungsten can occur, leading to undesirable microstructural and mechanical property changes. Therefore, there is a need to raise the recrystallization temperature of tungsten and limit the kinetics of the recrystallization and grain growth processes. In this work, we examine the effect of different types (TiC vs. TaC vs. ZrC) and different concentrations (1.1 vs. 5 vs. 10 wt.%) of dispersed second phase particles in a tungsten matrix on the high temperature performance. Additionally, the addition of second-phase particles effectively increases the temperature of and time for recrystallization and slow grain growth; however, the addition of a high weight fraction of particles alters the surface chemistry, which may impact subsequent plasma-surface interactions. These results show that the addition of small concentrations of dispersed particles can be effectively employed in tungsten to raise the upper operating temperature limit for tungsten in a fusion reactor.
The upgrade for the data acquisition system of the KOTO detector Tecchio, M.; Beechert, J.; Campbell, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2016, Volume:
824, Issue:
C
Journal Article
Peer reviewed
Open access
A major upgrade to the KOTO detector data acquisition system based on the ATCA standard is being considered. The ATCA standard provides a natural solution to the current KOTO constraints, including ...communication between boards and higher input and output bandwidth.
A search for the rare decay KL → π0νν¯ was performed. With the data collected in 2015, corresponding to 2.2 × 1019 protons on target, a single event sensitivity of (1.30 ± 0.01stat ± 0.14syst) × 10–9 ...was achieved and no candidate events were observed. We set an upper limit of 3.0 × 10–9 for the branching fraction of KL → π0νν¯ at the 90% confidence level (C.L.), which improved the previous limit by almost an order of magnitude. An upper limit for KL → π0X0 was also set as 2.4 × 10–9 at the 90% C.L., where X0 is an invisible boson with a mass of 135 MeV /c2.
For much of the discipline of economics, a closed economy is seen as the result of efforts of distributional coalitions and rent seekers to maintain sector-specific protections. Accordingly, economic ...liberalization is explained by the policy consistency of uncompromising reform elites. Students of the politics of economic adjustment in the developing world, in turn, have argued that reform programs concentrate costs in the present and disperse benefits in the future. Hence, losers are prepared to engage in collective action, whereas prospective winners, facing uncertainty about payoffs, remain disorganized. They thus posit the cohesiveness and insularity of policymakers as the main variable for explaining successful reform. Both economists and political scientists, therefore, adopt a collective action approach that overlooks how groups organize in support of liberalization. In the recent Latin American experience, however, these reforms have preserved market reserves for firms that provided vital political support to, and often colluded with, policymaking elites. This setting has thus reproduced incentives for rent-seeking behavior, even in the presence of comprehensive liberalization. This evidence supports two interrelated theoretical claims. First, distributional coalitions may proliferate when the state withdraws from the economy, not only when it intervenes. Second, interest-based variables retain explanatory power in political economy—which state autonomy arguments disregard—irrespective of whether the economy is closed or open—which neoclassical perspectives overlook. To highlight the centrality of interest groups favoring marketization, therefore, the article suggests modifications to the dominant theories of collective action and the literature on the politics of economic adjustment.
A search for the rare decay K_{L}→π^{0}ννover ¯ was performed. With the data collected in 2015, corresponding to 2.2×10^{19} protons on target, a single event sensitivity of ...(1.30±0.01_{stat}±0.14_{syst})×10^{-9} was achieved and no candidate events were observed. We set an upper limit of 3.0×10^{-9} for the branching fraction of K_{L}→π^{0}ννover ¯ at the 90% confidence level (C.L.), which improved the previous limit by almost an order of magnitude. An upper limit for K_{L}→π^{0}X^{0} was also set as 2.4×10^{-9} at the 90% C.L., where X^{0} is an invisible boson with a mass of 135 MeV/c^{2}.
South American and Latin American military regimes of the 1960s and 1970s are compared for changes in the bureaucratic-authoritarian style of government and the rise of anti-Keynesian neoconservative ...authoritarianism.
PDF
