This paper presents the current state of the global gyrokinetic code Orb5 as an update of the previous reference (Jolliet et al., 2007). The Orb5 code solves the electromagnetic Vlasov–Maxwell system ...of equations using a PIC scheme and also includes collisions and strong flows. The code assumes multiple gyrokinetic ion species at all wavelengths for the polarization density and drift-kinetic electrons. Variants of the physical model can be selected for electrons such as assuming an adiabatic response or a “hybrid” model in which passing electrons are assumed adiabatic and trapped electrons are drift-kinetic. A Fourier filter as well as various control variates and noise reduction techniques enable simulations with good signal-to-noise ratios at a limited numerical cost. They are completed with different momentum and zonal flow-conserving heat sources allowing for temperature-gradient and flux-driven simulations. The code, which runs on both CPUs and GPUs, is well benchmarked against other similar codes and analytical predictions, and shows good scalability up to thousands of nodes.
Determination of the poloidal magnetic field distribution in tokamaks is of prime importance for the successful operation of tokamaks. In this paper, we propose a polarization-sensitive ...reflectometry-based optical fiber sensor for measuring the spatial distribution of the poloidal magnetic field in tokamaks. The measurement method exploits the Rayleigh backscattering and Faraday magneto-optic effect in optical fibers. The former is an intrinsic property of optical fibers and enables distributed polarization measurements, while the latter arises in the presence of a magnetic field parallel to the optical fiber axis and rotates the polarization state of the light. When an optical fiber is looped around a toroidal section of the vacuum vessel, the local polarization rotation of the light is proportional to the local poloidal magnetic field in the tokamak. The proposed method is discussed theoretically and experimentally using the results from JET. The obtained magnetic field measurement shows a good agreement with that of the internal discrete coils. A potential solution to recover the magnetic field data from the noise-affected region of the optical measurement is proposed and is demonstrated through simulations using the JET magnetic field configuration.
We describe a new version of GBS, a 3D global, flux-driven plasma turbulence code to simulate the turbulent dynamics in the tokamak scrape-off layer (SOL), superseding the code presented by Ricci et ...al. (2012) 14. The present work is driven by the objective of studying SOL turbulent dynamics in medium size tokamaks and beyond with a high-fidelity physics model. We emphasize an intertwining framework of improved physics models and the computational improvements that allow them. The model extensions include neutral atom physics, finite ion temperature, the addition of a closed field line region, and a non-Boussinesq treatment of the polarization drift. GBS has been completely refactored with the introduction of a 3-D Cartesian communicator and a scalable parallel multigrid solver. We report dramatically enhanced parallel scalability, with the possibility of treating electromagnetic fluctuations very efficiently. The method of manufactured solutions as a verification process has been carried out for this new code version, demonstrating the correct implementation of the physical model.
This paper summarizes the status of the COMPASS tokamak, its comprehensive diagnostic equipment and plasma scenarios as a baseline for the future studies. The former COMPASS-D tokamak was in ...operation at UKAEA Culham, UK in 1992-2002. Later, the device was transferred to the Institute of Plasma Physics of the Academy of Sciences of the Czech Republic (IPP AS CR), where it was installed during 2006-2011. Since 2012 the device has been in a full operation with Type-I and Type-III ELMy H-modes as a base scenario. This enables together with the ITER-like plasma shape and flexible NBI heating system (two injectors enabling co- or balanced injection) to perform ITER relevant studies in different parameter range to the other tokamaks (ASDEX-Upgrade, DIII-D, JET) and to contribute to the ITER scallings. In addition to the description of the device, current status and the main diagnostic equipment, the paper focuses on the characterization of the Ohmic as well as NBI-assisted H-modes. Moreover, Edge Localized Modes (ELMs) are categorized based on their frequency dependence on power density flowing across separatrix. The filamentary structure of ELMs is studied and the parallel heat flux in individual filaments is measured by probes on the outer mid-plane and in the divertor. The measurements are supported by observation of ELM and inter-ELM filaments by an ultra-fast camera.
Among the peripheral instabilities observed at the Globus-M2 tokamak, two types of edge localized modes (ELMs) are brought into focus: ELMs synchronized and desynchronized with the sawtooth ...oscillations. The desynchronized ELMs appear in regimes that are characterized by high values of pressure in the pedestal,
p
ped
≥ 3 kPa, and they are observed in discharges with the toroidal magnetic field
B
T
> 0.6 T and plasma current
I
P
> 0.3 MA. The desynchronized ELMs belong to the type-III/V with the dominating effect of the peeling mode. The synchronized ELMs were observed in a wider range of discharge parameters, including at
B
T
< 0.6 T and
I
P
< 0.3 MA. Calculations of the stability of the peeling-ballooning (PB) mode showed that at pedestal width ψ
norm
= 0.09 and
p
ped
> 3.5 kPa, destabilization of PB modes is possible without additional influence. Experimental data shows that the microtearing mode plays a dominant role in the pedestal. The microtearing mode does not allow the pedestal at Globus-M2 tokamak to reach the state of the unstable kinetic ballooning mode (KBM), which explains the low predictive power of the EPED model at this tokamak.
The first scintillator-based fast-ion loss detector (FILD) was installed in MAST-U as part of its main upgrade and it was commissioned during the first experimental campaign. FILD works as a magnetic ...spectrometer, directly measuring neutral beam injector (NBI) fast-ion losses using a scintillator plate that emits light when fast ions impinge on it. Yttrium aluminum garnet activated by cerium (YAG:Ce) is used as the scintillator material in MAST-U, which has a decay time in the range of 100 ns. This, in combination with an avalanche photo-diode (APD) camera at sampling rates up to 4 MHz, has made it possible to detect fast-ion loss fluctuations at frequencies up to 2 MHz, an unprecedented measurement for any scintillator-based FILD. The probe is protected from the plasma loads with a cap made of 15-<inline-formula> <tex-math notation="LaTeX">\mu</tex-math> </inline-formula>m grain graphite, similar to the divertor tiles. The probe is installed on an in-vessel rotary and reciprocating system actuated with bellow-based feed-throughs and a pair of stepper motors that make it possible to operate remotely on a shot-to-shot basis. The rotary actuator adapts the probe orientation to the magnetic field pitch and the reciprocating actuator adapts the probe radial distance to the separatrix. An infrared camera monitoring the temperature on the graphite cap showed that the temperature increase during a shot is lower than 20 <inline-formula> <tex-math notation="LaTeX">^\circ</tex-math> </inline-formula>C. The impurities added to the plasma by the FILD probe have been monitored using spectroscopy measurements. The operation of the MAST-U FILD provides a source of lessons learned for the design of future reciprocating diagnostics such as the ITER FILD.
The Divertor Tokamak Test (DTT) facility is a fusion device under construction in Italy. The mission of DTT is to test alternative divertor concepts under integrated physics and technological ...conditions that can reliably be extrapolated to DEMO. Due to the plasma core characteristics with relevant edge and scrape-off layer (SOL) parameters and a wall entirely in tungsten (W), DTT will provide an extensive set of information useful to select the most appropriate strategy for the power exhaust in DEMO. Several divertors, which may differ in design or/and technologies or/and poloidal profile, will be tested during the life of the machine. The first divertor to be installed will have to accommodate a multitude of strike points, located at various positions according to the different magnetic configurations, which will be tested in the first operational phases of the machine with the aim to identify the most promising. The first divertor will not test innovative technological solutions but will mainly take advantage of the technologies already qualified for the ITER divertor production. Thus, the entire divertor plasma-facing surface is designed to be used as targets: it will be made of W monoblocks joined on CuCrZr pipes (plasma-facing units, PFUs) similar to the ITER targets. With the purpose to increase the flexibility in operational scenarios by maximizing the allowable thermal load for the PFUs, the possibility of using monoblocks with a plasma side reduced thickness was investigated. By reducing the thickness of the armor, it is possible to limit plastic deformation of the monoblock and to preserve the characteristics of the plasma-facing surface during the component lifetime. A thickness between 3 and 4 mm is compatible both the erosion estimates in the DTT divertor area and the manufacturing constraints and therefore proposed for the DTT PFUs. Several mock-ups based on monoblock design were in the past tested under thermal fatigue, confirming the reliability of the monoblock design and the manufacturing processes, but with larger armor thicknesses (6-8 mm). The experimental verification of the monoblock performance with the proposed reduced thickness has been verified in the GLADIS facility at IPP Garching with a thermal load of 20 MW/m<inline-formula> <tex-math notation="LaTeX">^{2}</tex-math> </inline-formula> applied for 1000 cycles of 10 s. The results showed the absence of plastic deformation and negligible increase in surface roughness.
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