2,607 research outputs found
Spin-Exchange Interaction in ZnO-based Quantum Wells
Wurtzitic ZnO/(Zn,Mg)O quantum wells grown along the (0001) direction permit
unprecedented tunability of the short-range spin exchange interaction. In the
context of large exciton binding energies and electron-hole exchange
interaction in ZnO, this tunability results from the competition between
quantum confinement and giant quantum confined Stark effect. By using
time-resolved photoluminescence we identify, for well widths under 3 nm, the
redistribution of oscillator strengths between the A and B excitonic
transitions, due to the enhancement of the exchange interaction. Conversely,
for wider wells, the redistribution is cancelled by the dominant effect of
internal electric fields, which dramatically reduce the exchange energy.Comment: 14 pages, 3 figure
Immunolocalization of a Unique Form of Maize Kernel Glutamine Synthetase Using a Monoclonal Antibody
Development and first operation of a Cavity Ring Down Spectroscopy diagnostic in the negative ion source SPIDER
The Neutral Beam Injectors of the ITER experiment will rely on negative ion
sources to produce 16.7 MW beams of H/D particles accelerated at 1 MeV. The
prototype of these sources was built and is currently operated in the SPIDER
experiment (Source for the Production of Ions o Deuterium Extracted from an RF
plasma), part of the Neutral Beam Test Facility of Consorzio RFX, Padua. In
SPIDER, the H-/D- ion source is coupled to a three grids 100 kV acceleration
system. One of the main targets of the experimentation in SPIDER is to
uniformly maximize the extracted current density; to achieve this it is
important to study the density of negative ions available in proximity of the
ion acceleration system. In SPIDER, line-integrated measurements of negative
ion density are performed by a Cavity Ring Down Spectroscopy (CRDS) diagnostic.
Its principle of operation is based on the absorption of the photons of a laser
beam pulse by H-/D- photo-detachment; the absorption detection is enhanced by
trapping the laser pulse in an optical cavity, containing the absorbing medium
(i.e. negative ions). The paper presents and discusses the CRDS diagnostic
setup in SPIDER, including the first measurements of negative ion density,
correlated to the main source parameters.Comment: 5 pages, 7 figures. Contributer paper for the HTPD 2020 conference.
Accepted manuscrip
Electromagnetic filaments and edge modifications induced by electrode biasing in the RFX-mod tokamak
Comparative Analysis of EPICS IOC and MARTe for the Development of a Hard Real-Time Control Application
Start of SPIDER operation towards ITER neutral beams
Heating Neutral Beam (HNB) Injectors will constitute the main plasma heating and current drive tool both in ITER and JT60-SA, which are the next major experimental steps for demonstrating nuclear fusion as viable energy source. In ITER, in order to achieve the required thermonuclear fusion power gain Q=10 for short pulse operation and Q=5 for long pulse operation (up to 3600s), two HNB injectors will be needed [1], each delivering a total power of about 16.5 MW into the magnetically-confined plasma, by means of neutral hydrogen or deuterium particles having a specific energy of about 1 MeV. Since only negatively charged particles can be efficiently neutralized at such energy, the ITER HNB injectors [2] will be based on negative ions, generated by caesium-catalysed surface conversion of atoms in a radio-frequency driven plasma source. A negative deuterium ion current of more than 40 A will be extracted, accelerated and focused in a multi-aperture, multi-stage electrostatic accelerator, having 1280 apertures (~ 14 mm diam.) and 5 acceleration stages (~200 kV each) [3]. After passing through a narrow gas-cell neutralizer, the residual ions will be deflected and discarded, whereas the neutralized particles will continue their trajectory through a duct into the tokamak vessels to deliver the required heating power to the ITER plasma for a pulse duration of about 3600 s. Although the operating principles and the implementation of the most critical parts of the injector have been tested in different experiments, the ITER NBI requirements have never been simultaneously attained. In order to reduce the risks and to optimize the design and operating procedures of the HNB for ITER, a dedicated Neutral Beam Test Facility (NBTF) [4] has been promoted by the ITER Organization with the contribution of the European Union\u2019s Joint Undertaking for ITER and of the Italian Government, with the participation of the Japanese and Indian Domestic Agencies (JADA and INDA) and of several European laboratories, such as IPP-Garching, KIT-Karlsruhe, CCFE-Culham, CEA-Cadarache. The NBTF, nicknamed PRIMA, has been set up at Consorzio RFX in Padova, Italy [5]. The planned experiments will verify continuous HNB operation for one hour, under stringent requirements for beam divergence (< 7 mrad) and aiming (within 2 mrad). To study and optimise HNB performances, the NBTF includes two experiments: MITICA, full-scale NBI prototype with 1 MeV particle energy and SPIDER, with 100 keV particle energy and 40 A current, aiming at testing and optimizing the full-scale ion source. SPIDER will focus on source uniformity, negative ion current density and beam optics. In June 2018 the experimental operation of SPIDER has started
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