43 Search Results

The most efficient and promising operational regime for the International Thermonuclear Experimental Reactor tokamak is the high-confinement mode. In this regime, however, periodic relaxations of the plasma edge can occur. These edge-localized modes pose a threat to the integrity of the fusion device. Here we reveal the strong impact of energetic ions on the spatio-temporal structure of edge-localized modes in tokamaks using nonlinear hybrid kinetic–magnetohydrodynamic simulations. A resonant interaction between the fast ions at the plasma edge and the electromagnetic perturbations from the edge-localized mode leads to an energy and momentum exchange. Energetic ions modify, for example, the amplitude, frequency spectrum and crash timing of edge-localized modes. The simulations reproduce some observations that feature abrupt and large edge-localized mode crashes. The results indicate that, in the International Thermonuclear Experimental Reactor, a strong interaction between the fusion-born alpha particles and ions from neutral beam injection, a main heating and fast particle source, is expected with predicted edge-localized mode perturbations. This work advances the understanding of the physics underlying edge-localized mode crashes in the presence of energetic particles and highlights the importance of including energetic ion kinetic effects in the optimization of edge-localized mode control techniques and regimes that are free of such modes.

Abstract The impact of plasma shaping on the properties of high density H-mode scrape-off layer (SOL) profiles and transport at the outer midplane has been investigated on Tokamakà configuration variable. The experimental dataset has been acquired by evolving the upper triangularity while keeping the other parameters constant. The scan comprises ${\delta }_{\mathrm{u}\mathrm{p}}$ values between 0.0 and 0.6, excluding negative triangularity scenarios. Within this study, a transition from type-I edge localised modes to the quasi-continuous exhaust regime takes place from low to high ${\delta }_{\mathrm{u}\mathrm{p}}$ . The modification of the upstream SOL profiles has been assessed, in terms of separatrix quantities, within the ${\alpha }_{\mathrm{t}}$ turbulence control parameter theoretical framework (Eich et al 2020 Nucl. Fusion   60 056016). The target parallel heat load and the upstream near-SOL density profiles have been shown to broaden significantly for increasing ${\alpha }_{\mathrm{t}}$ . Correspondingly, in the far SOL a density shoulder formation is observed when moving from low to high ${\delta }_{\mathrm{u}\mathrm{p}}$ . These behaviours have been correlated with an enhancement of the SOL fluctuation level, as registered by wall-mounted Langmuir probes as well as the thermal helium beam diagnostic. Specifically, both the background and the filamentary-induced fluctuating parts of the first wall ion saturation current signal are larger at higher ${\delta }_{\mathrm{u}\mathrm{p}}$ , with filaments being ejected more frequently into the SOL. Comparison of two pulses at the extremes of the ${\delta }_{\mathrm{u}\mathrm{p}}$ scan range, but with otherwise same input parameters, shows that the midplane neutral pressure does not change much during the H-mode phase of the discharge. This indicates that indirect effects of the change in geometry, linked to first wall recycling sources, should not play a significant role. The total core radiation increases at high ${\delta }_{\mathrm{u}\mathrm{p}}$ , on account of a stronger plasma–wall interaction and resulting larger carbon impurity intake from the first wall. This is likely associated to the enhanced first wall fluctuations, as well as a smaller outer gap and the close-to-double-null magnetic topology at high shaping.

We report on searches for neutrinos and antineutrinos from astrophysical sources performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso in Italy. Electron antineutrinos ( $$\bar{ν}_e$$ ) are detected in an organic liquid scintillator through the inverse β -decay reaction. In the present work we set model-independent upper limits in the energy range 1.8-16.8 MeV on neutrino fluxes from unknown sources that improve our previous results, on average, by a factor 2.5. Using the same data set, we first obtain experimental constraints on the diffuse supernova $$\bar{ν}_e$$ fluxes in the previously unexplored region below 8 MeV. A search for $$\bar{ν}_e$$ in the solar neutrino flux is also presented: the presence of $$\bar{ν}_e$$ would be a manifestation of a non-zero anomalous magnetic moment of the neutrino, making possible its conversion to antineutrinos in the strong magnetic field of the Sun. We obtain a limit for a solar $$\bar{ν}_e$$ flux of 384 cm -2 s -1 (90% C.L.), assuming an undistorted solar 8 B neutrinos energy spectrum, that corresponds to a transition probability pνe→$$\bar{ν}_e$$< 7.2 ×10-5 (90% C.L.) for E $$\bar{ν}_e$$ > 1.8 MeV.At lower energies, by investigating the spectral shape of elastic scattering events, we obtain a new limit on solar 7 Be- ν e conversion into $$\bar{ν}_e$$ of pνe→$$\bar{ν}_e$$< 0.14 (90% C.L.) at 0.862 MeV. Last, we investigate solar flares as possible neutrino sources and obtain the strongest up-to-date limits on the fluence of neutrinos of all flavor neutrino below 3–7 MeV. Assuming the neutrino flux to be proportional to the flare’s intensity, we exclude an intense solar flare as the cause of the observed excess of events in run 117 of the Cl-Ar Homestake experiment.

Here we report on searches for neutrinos and antineutrinos from astrophysical sources performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso in Italy. Electron antineutrinos ($$\bar{ν}_e$$) are detected in an organic liquid scintillator through the inverse β-decay reaction. In the present work we set model-independent upper limits in the energy range 1.8-16.8 MeV on neutrino fluxes from unknown sources that improve our previous results, on average, by a factor 2.5. Using the same data set, we first obtain experimental constraints on the diffuse supernova $$\bar{ν}_e$$ fluxes in the previously unexplored region below 8 MeV. A search for $$\bar{ν}_e$$ in the solar neutrino flux is also presented: the presence of $$\bar{ν}_e$$ would be a manifestation of a non-zero anomalous magnetic moment of the neutrino, making possible its conversion to antineutrinos in the strong magnetic field of the Sun. We obtain a limit for a solar $$\bar{ν}_e$$ flux of 384 cm^-2s^-1 (90% C.L.), assuming an undistorted solar 8B neutrinos energy spectrum, that corresponds to a transition probability $$p_{ν_{e}→\bar{ν}_e}$$< 7.2×10-5 (90% C.L.) for $$E_{\bar{ν}_e}$$ > 1.8 MeV. At lower energies, by investigating the spectral shape of elastic scattering events, we obtain a new limit on solar ⁷Be-ν_e conversion into $$\bar{ν}_e$$ of $$p_{ν_{e}→\bar{ν}_e}$$< 0.14 (90% C.L.) at 0.862 keV. Last, we investigate solar flares as possible neutrino sources and obtain the strongest up-to-date limits on the fluence of neutrinos of all flavor neutrino below 3-7 ,MeV. Assuming the neutrino flux to be proportional to the flare's intensity, we exclude an intense solar flare as the cause of the observed excess of events in run 117 of the Cl-Ar Homestake experiment.

The Borexino detector measures solar neutrino fluxes via neutrino-electron elastic scattering. Observed spectra are determined by the solar-$$\nu_{e}$$ survival probability $$P_{ee}(E)$$, and the chiral couplings of the neutrino and electron. Some theories of physics beyond the Standard Model postulate the existence of Non-Standard Interactions (NSI's) which modify the chiral couplings and $$P_{ee}(E)$$. In this paper, we search for such NSI's, in particularly neutral-current-like interactions that modify the $$\nu_e - e$$ and $$\nu_\tau - e$$ couplings, using Borexino Phase II data. Standard Solar Model predictions of the solar neutrino fluxes for both high- and low-metallicity assumptions are considered. No indication of new physics is found at the level of sensitivity of the detector and constraints on the parameters of the NSI's are placed. In addition, with the same dataset the value of $$\sin^2\theta_W$$ is obtained with a precision comparable to that achieved in reactor antineutrino experiments.

Borexino is a 300 ton sub-MeV liquid scintillator solar neutrino detector which has been running at the Laboratori Nazionali del Gran Sasso (Italy) since 2007. Thanks to its unprecedented radio-purity, it was able to measure the flux of ⁷Be, ⁸B, pp, and pep solar neutrinos and to detect geo-neutrinos. A reliable simulation of the detector is an invaluable tool for all Borexino physics analyses. The simulation accounts for the energy loss of particles in all the detector components, the generation of the scintillation photons, their propagation within the liquid scintillator volume, and a detailed simulation of the electronics chain. A novel efficient method for simulating the external background which survives the Borexino passive shield was developed. This technique allows to reliably predict the effect of the contamination in the peripheral construction materials. The techniques developed to simulate the Borexino detector and their level of refinement are of possible interest to the neutrino and dark matter communities, especially for current and future large-volume liquid scintillator experiments.

This paper presents a comprehensive geoneutrino measurement using the Borexino detector, located at Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The analysis is the result of 3262.74 days of data between December 2007 and April 2019. The paper describes improved analysis techniques and optimized data selection, which includes enlarged fiducial volume and sophisticated cosmogenic veto. The reported exposure of $(1.29\pm 0.05)\times {10}^{32}\mathrm{protons}\times \mathrm{year}$ represents an increase by a factor of two over a previous Borexino analysis reported in 2015. By observing ${52.6}_{-8.6}^{+9.4}\left(\mathrm{stat}{)}_{-2.1}^{+2.7}\right(\mathrm{sys})$ geoneutrinos (68% interval) from ${}_{238}\mathrm{U}$ and ${}_{232}\mathrm{Th}$, a geoneutrino signal of ${47.0}_{-7.7}^{+8.4}\left({\text{stat})}_{-1.9}^{+2.4}\right(\mathrm{sys})$ TNU with ${}_{-17.2}^{+18.3}\%$ total precision was obtained. This result assumes the same Th/U mass ratio as found in chondritic CI meteorites but compatible results were found when contributions from ${}_{238}\mathrm{U}$ and ${}_{232}\mathrm{Th}$ were both fit as free parameters. Antineutrino background from reactors is fit unconstrained and found compatible with the expectations. The null-hypothesis of observing a geoneutrino signal from the mantle is excluded at a 99.0% C.L. when exploiting detailed knowledge of the local crust near the experimental site. Measured mantle signal of ${21.2}_{-9.0}^{+9.5}\left(\mathrm{stat}{)}_{-0.9}^{+1.1}\right(\mathrm{sys})$ TNU corresponds to the production of a radiogenic heat of ${24.6}_{-10.4}^{+11.1}\mathrm{TW}$ (68% interval) from ${}_{238}\mathrm{U}$ and ${}_{232}\mathrm{Th}$ in the mantle. Assuming 18% contribution of ${}_{40}\mathrm{K}$ in the mantle and ${8.1}_{-1.4}^{+1.9}\mathrm{TW}$ of total radiogenic heat of the lithosphere, the Borexino estimate of the total radiogenic heat of the Earth is ${38.2}_{-12.7}^{+13.6}\mathrm{TW}$, which corresponds to the convective Urey ratio of ${0.78}_{-0.28}^{+0.41}$. These values are compatible with different geological predictions, however there is a $~2.4\sigma$ tension with those Earth models which predict the lowest concentration of heat-producing elements in the mantle. In addition, by constraining the number of expected reactor antineutrino events, the existence of a hypothetical georeactor at the center of the Earth having power greater than 2.4 TW is excluded at 95% C.L. Particular attention is given to the description of all analysis details which should be of interest for the next generation of geoneutrino measurements using liquid scintillator detectors.

A detailed cross-device investigation on the role of filamentary dynamics in high-density regimes has been performed within the EUROfusion framework, comparing the ASDEX Upgrade (AUG) and TCV tokamaks. Both devices run density ramp experiments at different levels of plasma current, keeping the toroidal field or q₉₅ constant in order to disentangle the role of the parallel connection length and the current. During the scan at a constant toroidal field, in both devices the scrape-off layer (SOL) profiles tend to develop a clear SOL density shoulder at a lower edge density whenever the current is reduced. Different current behaviour is substantially reconciled in terms of the edge density normalized to the Greenwald fraction. During the scan at constant q₉₅ AUG exhibits similar behaviour, whereas in TCV no upstream profile modification signature has been observed at lower current levels. The latter behaviour has been ascribed to the lack of target density rollover. In this work, the relation between the upstream density profile modification and detachment condition has been investigated. For both devices the relation between blob size and the SOL density e-folding length is found independent of the plasma current, with the observation of a clear increase in blob size and the edge density normalized to a Greenwald fraction. ASDEX Upgrade has also explored filamentary behaviour in the H-mode. The experiments in AUG have focused on the role of neutrals, performing discharges with and without cryogenic pumps, highlighting how high neutral pressure, not only in the divertor but also at the midplane, is needed in order to develop an H-mode SOL profile shoulder in AUG.

We have measured the flux of cosmic muons in the Laboratori Nazionali del Gran Sasso at 3800\,m\,w.e. to be (3.432±0.003)∙10^-4m^-2s^-1 based on ten years of Borexino data acquired between May 2007 and May 2017. A seasonal modulation with a period of (366.3±0.6)d and a relative amplitude of (1.36±0.04)% is observed. The phase is measured to be (181.7±0.4)d, corresponding to a maximum at the 1st of July. Using data inferred from global atmospheric models, we show the muon flux to be positively correlated with the atmospheric temperature and measure the effective temperature coefficient α_T=0.90±0.02. The origin of cosmic muons from pion and kaon decays in the atmosphere allows to interpret the effective temperature coefficient as an indirect measurement of the atmospheric kaon-to-pion production ratio rK/π=0.11^+0.11_-0.07 for primary energies above 18TeV. We find evidence for a long-term modulation of the muon flux with a period of ~3000d and a maximum in June 2012 that is not present in the atmospheric temperature data. A possible correlation between this modulation and the solar activity is investigated. The cosmogenic neutron production rate is found to show a seasonal modulation in phase with the cosmic muon flux but with an increased amplitude of (2.6±0.4)%.

Borexino is continuing to take data and presenting the new results. The most recent Borexino results are discussed and plans for the nearest future are presented.