796 research outputs found
Synthetic diagnostic for the JET scintillator probe lost alpha measurements
No full textA synthetic diagnostic has been developed for the JET lost alpha scintillator probe, based on the ASCOT fast ion orbit following code and the AFSI fusion source code. The synthetic diagnostic models the velocity space distribution of lost fusion products in the scintillator probe. Validation with experimental measurements is presented, where the synthetic diagnostic is shown to predict the gyroradius and pitch angle of lost DD protons and tritons. Additionally, the synthetic diagnostic reproduces relative differences in total loss rates in multiple phases of the discharge, which can be used as a basis for total loss rate predictions
Synthetic neutron camera and spectrometer in JET based on AFSI-ASCOT simulations
No full textThe ASCOT Fusion Source Integrator (AFSI) has been used to calculate neutron production rates and spectra corresponding to the JET 19-channel neutron camera (KN3) and the time-of-flight spectrometer (TOFOR) as ideal diagnostics, without detector-related effects. AFSI calculates fusion product distributions in 4D, based on Monte Carlo integration from arbitrary reactant distribution functions. The distribution functions were calculated by the ASCOT Monte Carlo particle orbit following code for thermal, NBI and ICRH particle reactions. Fusion cross-sections were defined based on the Bosch-Hale model and both DD and DT reactions have been included. Neutrons generated by AFSI-ASCOT simulations have already been applied as a neutron source of the Serpent neutron transport code in ITER studies. Additionally, AFSI has been selected to be a main tool as the fusion product generator in the complete analysis calculation chain: ASCOT - AFSI - SERPENT (neutron and gamma transport Monte Carlo code) - APROS (system and power plant modelling code), which encompasses the plasma as an energy source, heat deposition in plant structures as well as cooling and balance-of-plant in DEMO applications and other reactor relevant analyses. This conference paper presents the first results and validation of the AFSI DD fusion model for different auxiliary heating scenarios (NBI, ICRH) with very different fast particle distribution functions. Both calculated quantities (production rates and spectra) have been compared with experimental data from KN3 and synthetic spectrometer data from ControlRoom code. No unexplained differences have been observed. In future work, AFSI will be extended for synthetic gamma diagnostics and additionally, AFSI will be used as part of the neutron transport calculation chain to model real diagnostics instead of ideal synthetic diagnostics for quantitative benchmarking
Energetic particles in reactor-relevant plasmas: modelling and validation
No full textNuclear fusion is a promising future energy source with few carbon dioxide emissions and nearly limitless source of fuel in heavy isotopes of hydrogen. Energetic particles, such as fusion-born alpha particles and neutral beam injected (NBI) fast ions play a vital role in reactor-relevant fusion plasmas, as they are responsible for heating the plasma, but can simultaneously cause localized heat loads and risk of damage on the plasma facing components. In this work, the Monte Carlo orbit-following code ASCOT has been used to simulate fast ions both to validate simulation results with present-day experiments at the JET tokamak, and to predict fast ion losses in next-generation fusion reactors ITER and DEMO.
For validation of ASCOT predictions against JET plasmas, synthetic diagnostics were used to compare the simulated fast ion distributions with the neutral particle analyser (NPA) and fast ion loss detector (FILD) measurements. The NPA simulations qualitatively reproduced the experimentally measured slowing-down distributions and fast ion isotope fraction for NBI-injected hydrogen and deuterium ions, while the FILD simulations for fusion product losses were within 10 % of the experimentally observed losses.
For predictions in ITER plasmas, simulations with resonant magnetic perturbations showed that including the response of the plasma to the external perturbations is vital, as the response not only affected the magnitude but also the distribution of fast ion losses. For DEMO plasmas, the sensitivity of fast ion losses due to various magnetic perturbations was studied, including the toroidal field ripple and ferritic inserts in various configurations. The design was found to be robust with respect to fast ion confinement and losses.
Finally, over the course of this work, a highly parallelized version of the ASCOT code, called ASCOT5, was developed. The new version substantially increased the performance on modern supercomputer hardware as well as improving its maintainability and extensibility.Fuusioenergia on lupaava energiantuotantomenetelmä, joka ei tuota merkittävästi hiilidioksidipäästöjä, ja polttoaineena käytettävät vedyn raskaiden isotoopien varannot ovat runsaat. Suurienergiset hiukkaset, kuten fuusioreaktioissa syntyvät alfahiukkaset ja neutraalisuihkuilla injektoidut (NBI) ionit, ovat merkittävässä roolissa reaktorirelevanteissa plasmoissa. Ne kuumentavat plasmaa ja ylläpitävät fuusiopaloa, mutta saattavat myös vahingoittaa reaktorin rakenteita. Tässä työssä nopeiden ionien radanseurantakoodi ASCOT validoitiin ensin mallintamalla JET-tokamakin plasmapurkauksia, jonka jälkeen sitä käytettiin ennustamaan seuraavan sukupolven ITER- ja DEMO-reaktoreiden nopeiden hiukkasten koossapitoa ja häviöitä.
JET-tokamakissa simuloituja nopeiden ionien distribuutioita verrattiin synteettisillä diagnostiikoilla kokeellisiin tuloksiin neutraalihiukkasanalysaattorista (NPA) ja nopeiden hiukkasten häviöitä mittaavasta detektorista (FILD). NPA-simulaatiotulokset toisinsivat kokeellisesti mitatut vety- ja deuterium-ionien hidastumisjakaumat, ja FILD-simulaatiot vastasivat kokeellisesti havaittuja fuusiotuotehäviöitä.ITER-reaktorille tehdyt simulaatiot resonanttien magneettisten häiriöiden kanssa osoittivat, että plasman vasteen huomioiminen on tärkeää, koska se vaikutti niin nopeiden hiukkasten häviöiden määrään kuin jakaumaan reaktorin sisäseinällä. DEMO-reaktorille tutkittiin häviöiden herkkyyttä muun muassa toroidaalisen kentän kelojen ja ferriittisten komponenttien aiheuttamille magneettisille häiriöille. Suunniteltu reaktorigeometria osoittautui kestäväksi nopeiden hiukkasten aiheuttaman tehokuorman kannalta.
Työn aikana kehitettiin myös uusi, rinnakkaislaskentaa tehokkaasti hyödyntävä koodiversio ASCOT5. Uusi versio lisäsi suorituskykyä merkittävästi uusimmilla supertietokoneilla sekä paransi koodin ylläpidettävyyttä ja laajennettavuutta
Synthetic NPA diagnostic for energetic particles in JET plasmas
No full textNeutral particle analysis (NPA) is one of the few methods for diagnosing fast ions inside a plasma by measuring neutral atom fluxes emitted due to charge exchange reactions. The JET tokamak features an NPA diagnostic which measures neutral atom fluxes and energy spectra simultaneously for hydrogen, deuterium and tritium species. A synthetic NPA diagnostic has been developed and used to interpret these measurements to diagnose energetic particles in JET plasmas with neutral beam injection (NBI) heating. The synthetic NPA diagnostic performs a Monte Carlo calculation of the neutral atom fluxes in a realistic geometry. The 4D fast ion distributions, representing NBI ions, were simulated using the Monte Carlo orbit-following code ASCOT. Neutral atom density profiles were calculated using the FRANTIC neutral code in the JINTRAC modelling suite. Additionally, for rapid analysis, a scan of neutral profiles was precalculated with FRANTIC for a range of typical plasma parameters. These were taken from the JETPEAK database, which includes a comprehensive set of data from the flat-top phases of nearly all discharges in recent JET campaigns. The synthetic diagnostic was applied to various JET plasmas in the recent hydrogen campaign where different hydrogen/deuterium mixtures and NBI configurations were used. The simulated neutral fluxes from the fast ion distributions were found to agree with the measured fluxes, reproducing the slowing-down profiles for different beam isotopes and energies and quantitatively estimating the fraction of hydrogen and deuterium fast ions.SP
Optimization-oriented modelling of neutral beam injection for EU pulsed DEMO
No full textNeutral beam injection (NBI) is one of the auxiliary power systems considered for the EU DEMO pulsed plasma ('DEMO1'). In this paper, we discuss the characteristics of optimized NBI in terms of the DEMO1 requirements, relating physics and engineering contexts in a novel parameter range compared to current NBI systems and in a larger plasma volume than ITER. Different injection options are investigated to account for various concepts discussed in the literature. The investigation is carried out using a wide range of sensitivity studies by means of the METIS 0.5D transport code and ASCOT Monte Carlo simulations of injected neutral-beam particles. This investigation has generated a series of recommendations for the NBI design, contributing to the system optimization process. We show how tangential injection aimed at the plasma core, with an energy ≳ 800 keV, is recommended to maintain high fusion power performance and fulfill the requirements for bulk heating. Compliance with engineering constraints on the NBI design, e.g., the least interference with breeding blanket modules or compatibility with solutions for the beamline components, imposes some restrictions when discussing the beam geometry. The minimum density at which an NBI can be safely operated without harmful shine-through losses is investigated for different injection energies and compared to the ITER case. The NBI operational window for DEMO is shown to be significantly extended to transient, low-density phases, also highlighting the importance of NBI systems designed for modular energy and power output. NBI can therefore sustain the plasma during a considerable portion of the transient phases, i.e., the current ramp-up and ramp-down phases. The final decision on the DEMO heating mix will be made on the basis of system operability and performance: the optimized NBI is shown to be a suitable and effective option for the EU DEMO inductive scenario
Synthetic diagnostic for the JET scintillator probe lost alpha measurements
No full textA synthetic diagnostic has been developed for the JET lost alpha scintillator probe, based on the ASCOT fast ion orbit following code and the AFSI fusion source code. The synthetic diagnostic models the velocity space distribution of lost fusion products in the scintillator probe. Validation with experimental measurements is presented, where the synthetic diagnostic is shown to predict the gyroradius and pitch angle of lost DD protons and tritons. Additionally, the synthetic diagnostic reproduces relative differences in total loss rates in multiple phases of the discharge, which can be used as a basis for total loss rate predictions.SPC3rd European Conference on Plasma Diagnostics (ECPD), May 06-10, 2019, Lisbon, PORTUGA
Estimate of 3D power wall loads due to Neutral Beam Injection in EU DEMO ramp-up phase
No full textHeating and current drive systems such as high energy Neutral Beam Injection (NBI) are being considered for pulsed EU DEMO (“DEMO1”) pre-conceptual design. Their aim is to provide auxiliary power, not only during flat-top, but also during transient phases (i.e. plasma current ramp-up and ramp-down). In this work, NBI fast particle power loads on DEMO1 first wall, due to shine-through and orbit losses, are calculated for the diverted plasma ramp-up phase. Numerical simulations are performed using BBNBI and ASCOT Monte Carlo codes. The simulations have been done using a complete 3D wall geometry, and implementing the latest DEMO NBI design, which foresees NBI at 800 keV particle energy. Location and power density of NBI-related power loads at different ramp-up time steps are evaluated and compared with the maximum tolerable heat flux taken from ITER case. Since NBI shine-through losses (dominant during low density phases) depend mainly on the beam energy, plasma density and volume, DEMO has a more favourable situation than ITER, enlarging NBI operational window. Using ITER criteria, DEMO NBI at full energy and power could be switched on during ramp-up at ~ 1.3 × 1019 m-3. This increases the appeal of neutral beam injectors as auxiliary power systems for DEMO
Forward modelling of Dα camera view in ST40 informed by experimental data
No full textEmbedding diagnostics in future pilot plants will be a challenging task, because of space- and irradiation-related concerns. Relying on high-fidelity synthetic diagnostics would then be valuable.
The 3D Monte-Carlo ray-tracing code CHERAB allows the development of numerous synthetic spectroscopic diagnostics. Focus of the present work is the introduction of new CHERAB models. The forward modelling of a synthetic Dα camera in ST40, the privately funded, high-field spherical tokamak, owned and operated by Tokamak Energy Ltd, and the comparison against experimental data is chosen as a testbed for quality
assessment. Main output of the study then consists of estimates of the neutral particle densities throughout the chamber, of crucial relevance within edge plasma studies.
Starting from simple analytical models, a 2D Dα source in the poloidal plane is generated. However, the centre column limited plasmas in ST40 display an intrinsically-3D Dα emission, mostly localised around the discrete poloidal limiters on the centre column, not captured by any axisymmetric source model. Hence, a novel methodology is introduced in CHERAB to approximate the 3D non-toroidally-symmetric pattern via a piece-wise emission distribution.
Irrespective of the geometry of the emission and size of the tokamak, the pronounced non-homogeneity in the edge plasma emission requires sub-millimetric (∼ power fall-off length) spatial resolution to guarantee an accurate estimate of the peak emission. Minimising the associated burden via implementation of a non-uniform source sampling algorithm, which is a modification of the standard CHERAB uniform sampling, results in a >10-fold reduction of the computational cost.
The significantly-shortened simulation time also makes the inclusion of more sophisticated models
affordable. Of potential appeal in view of highly-detached divertors, the approximation of optically thin plasma
is dropped, and photon-plasma interactions are accounted for. Brand-new CHERAB models able to take into
account phenomena of photon absorption and scattering are so introduced
Neutral beam injection modelling in JT-60SA axisymmetric equilibria
No full text| openaire: EC/H2020/633053/EU//EUROfusionPeer reviewe
Versatile fusion source integrator AFSI for fast ion and neutron studies in fusion devices
No full textASCOT Fusion Source Integrator AFSI, an efficient tool for calculating fusion reaction rates and characterizing the fusion products, based on arbitrary reactant distributions, has been developed and is reported in this paper. Calculation of reactor-relevant D-D, D-T and D-(3) He fusion reactions has been implemented based on the Bosch-Hale fusion cross sections. The reactions can be calculated between arbitrary particle populations, including Maxwellian thermal particles and minority energetic particles. Reaction rate profiles, energy spectra and full 4D phase space distributions can be calculated for the non-isotropic reaction products. The code is especially suitable for integrated modelling in self-consistent plasma physics simulations as well as in the Serpent neutronics calculation chain. Validation of the model has been performed for neutron measurements at the JET tokamak and the code has been applied to predictive simulations in ITER.SP
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