• Energy Research

The influence of the residence time for the active species and of the helium addition to the plasma in the ammonia formation in N2H2(He) Glow Discharge plasmas has been studied using differential pumped mass spectrometry. Three different residence times for the N2 molecule were studied: 25, 50 and 100ms. Other experiments scanning the helium plasma content (0–8%) were performed with a residence time of 100ms. While no difference in the ammonia formation yields was found between the cases of 25ms and 50ms, the ammonia yields were increased by a 25% in the case of 100ms. Additionally, an increasing helium plasma content enhances the ammonia formation yields up to 45%. Three different effects induced by the presence of helium in the plasma were analyzed: effects in mass spectrometry measurements, changes in the electron temperature and modification of the surface chemistry. The analyzes pointed out to an improved NH recombination on tungsten walls induced by helium presence as the key factor that could explain the higher ammonia yields experimentally found for the highest helium content in the plasma. Keywords: Nitrogen seeding, Ammonia, Tungsten, Helium, Residence time, Electron temperature

Zinc oxide (ZnO) films have been grown on gold (111) by electrodeposition using two different OH− sources, nitrate and peroxide, in order to obtain a comparative study between them. The morphology, structural and optical characterization of the films were investigated depending on the solution used (nitrate and peroxide) and the applied potential. Scanning electron microscopy pictures show different morphologies in each case. X-ray diffraction confirms that the films are pure ZnO oriented along the (0002) direction. ZnO films have been studied by photoluminescence to identify the emission of defects in the visible range. A consistent model that explains the emissions for the different electrodeposited ZnO films is proposed. We have associated the green and yellow emissions to a transition from the donor OH− to the acceptor zinc vacancies (VZn−) and to interstitial oxygen (Oi0), respectively. The orange-red emission is probably due to transitions from the conducting band to Oi− and OZn0 defects and the infrared emission to transition from these Oi−/2− and OZn0/− defects to the valence band.

Nuclear materials and energy 38, 101615 - (2024). doi:10.1016/j.nme.2024.101615 Published by Elsevier, Amsterdam [u.a.]

AbstractThe physisorption of ammonia molecules (sticking) on the walls of a stainless steel pipe (AISI 304L) has been studied at different wall temperatures (323-473K). The total amount of ammonia that is retained on the walls, once equilibrium is reached, has been measured by differentially-pumped mass spectrometry in gas exposure laboratory experiments. The results show ammonia retentions in the range of μg/cm2 resulting in a multilayer adsorption with lower amounts of stuck ammonia at higher temperatures of the stainless steel surface. The sticking coefficient follows an exponential decay evolution with time. The activation energy of the process has been estimated by an Arrhenius fit, assuming that the characteristic time for this decay is inversely proportional to the kinetic adsorption constant. A value of 0.15eV per ammonia molecule has been obtained, being in agreement with nominal values for the physisorption of small molecules or atoms (CO, N2, Ar…) that can be found in the specialized literature. The implication of these results in the possible extrapolation to the ITER vacuum system under nitrogen seeded plasma operation is also addressed.

Abstract The JET 2019–2020 scientific and technological programme exploited the results of years of concerted scientific and engineering work, including the ITER-like wall (ILW: Be wall and W divertor) installed in 2010, improved diagnostic capabilities now fully available, a major neutral beam injection upgrade providing record power in 2019–2020, and tested the technical and procedural preparation for safe operation with tritium. Research along three complementary axes yielded a wealth of new results. Firstly, the JET plasma programme delivered scenarios suitable for high fusion power and alpha particle (α) physics in the coming D–T campaign (DTE2), with record sustained neutron rates, as well as plasmas for clarifying the impact of isotope mass on plasma core, edge and plasma-wall interactions, and for ITER pre-fusion power operation. The efficacy of the newly installed shattered pellet injector for mitigating disruption forces and runaway electrons was demonstrated. Secondly, research on the consequences of long-term exposure to JET-ILW plasma was completed, with emphasis on wall damage and fuel retention, and with analyses of wall materials and dust particles that will help validate assumptions and codes for design and operation of ITER and DEMO. Thirdly, the nuclear technology programme aiming to deliver maximum technological return from operations in D, T and D–T benefited from the highest D–D neutron yield in years, securing results for validating radiation transport and activation codes, and nuclear data for ITER.