1,693 research outputs found
An optimal penalty method for a hyperbolic system modeling the edge plasma transport in a tokamak
The penalization method is used to take account of obstacles, such as the
limiter, in a tokamak. Because of the magnetic confinement of the plasma in a
tokamak, the transport occurs essentially in the direction parallel to the
magnetic field lines. We study a 1D nonlinear hyperbolic system as a simplified
model of the plasma transport in the area close to the wall. A penalization
which cuts the flux term of the momentum is studied. We show numerically that
this penalization creates a Dirac measure at the plasma-limiter interface which
prevents us from defining the transport term in the usual distribution sense.
Hence, a new penalty method is proposed for this hyperbolic system. For this
penalty method, an asymptotic expansion and numerical tests give an optimal
rate of convergence without spurious boundary layer. Another two-fields
penalization has also been implemented and the numerical convergence analysis
when the penalization parameter tends to reveals the presence of a boundary
layer
Velocity shear, turbulent saturation, and steep plasma gradients in the scrape-off layer of inner-wall limited tokamaks
The narrow power decay-length (), recently found in the scrape-off
layer (SOL) of inner-wall limited (IWL) discharges in tokamaks, is studied
using 3D, flux-driven, global two-fluid turbulence simulations. The formation
of the steep plasma profiles measured is found to arise due to radially sheared
poloidal flows. A complex interaction between sheared
flows and outflowing plasma currents regulates the turbulent saturation,
determining the transport levels. We quantify the effects of sheared flows,
obtaining theoretical estimates in agreement with our non-linear simulations.
Analytical calculations suggest that the IWL is roughly equal to
the turbulent correlation length.Comment: 5 pages, 5 figure
Impact of ICRF on the scrape-off layer and on plasma wall interactions: From present experiments to fusion reactor
Recent achievements in studies of the effects of ICRF (Ion Cyclotron Range of Frequencies) power on the SOL (Scrape-Off Layer) and PWI (Plasma Wall Interactions) in ASDEX Upgrade (AUG), Alcator C-Mod, and JET-ILW are reviewed. Capabilities to diagnose and model the effect of DC biasing and associated impurity production at active antennas and on magnetic field connections to antennas are described. The experiments show that ICRF near-fields can lead not only to EĂB convection, but also to modifications of the SOL density, which for Alcator C-Mod are limited to a narrow region near antenna. On the other hand, the SOL density distribution along with impurity sources can be tailored using local gas injection in AUG and JET-ILW with a positive effect on reduction of impurity sources. The technique of RF image current cancellation at antenna limiters was successfully applied in AUG using the 3-strap AUG antenna and extended to the 4-strap Alcator C-Mod field-aligned antenna. Multiple observations confirmed the reduction of the impact of ICRF on the SOL and on total impurity production when the ratio of the power of the central straps to the total antenna power is in the range 0.6<P/P<0.8. Near-field calculations indicate that this fairly robust technique can be applied to the ITER ICRF antenna, enabling the mode of operation with reduced PWI. On the contrary, for the A2 antenna in JET-ILW the technique is hindered by RF sheaths excited at the antenna septum. Thus, in order to reduce the effect of ICRF power on PWI in a future fusion reactor, the antenna design has to be optimized along with design of plasmafacing components
First ERO2.0 modeling of Be erosion and non-local transport in JET ITER-like wall
ERO is a Monte-Carlo code for modeling plasma-wall interaction and 3D plasma impurity
transport for applications in fusion research. The code has undergone a significant upgrade
(ERO2.0) which allows increasing the simulation volume in order to cover the entire plasma
edge of a fusion device, allowing a more self-consistent treatment of impurity transport and
comparison with a larger number and variety of experimental diagnostics. In this contribution,
the physics-relevant technical innovations of the new code version are described and discussed.
The new capabilities of the code are demonstrated by modeling of beryllium (Be) erosion of the
main wall during JET limiter discharges. Results for erosion patterns along the limiter surfaces
and global Be transport including incident particle distributions are presented. A novel synthetic
diagnostic, which mimics experimental wide-angle 2D camera images, is presented and used for
validating various aspects of the code, including erosion, magnetic shadowing, non-local
impurity transport, and light emission simulation.EURATOM 63305
Impact of ICRF on the scrape-off layer and on plasma wall interactions : From present experiments to fusion reactor
Recent achievements in studies of the effects of ICRF (Ion Cyclotron Range of Frequencies) power on the SOL (Scrape-Off Layer) and PWI (Plasma Wall Interactions) in ASDEX Upgrade (AUG), Alcator C-Mod, and JET-ILW are reviewed. Capabilities to diagnose and model the effect of DC biasing and associated impurity production at active antennas and on magnetic field connections to antennas are described. The experiments show that ICRF near-fields can lead not only to E x B convection, but also to modifications of the SOL density, which for Alcator C-Mod are limited to a narrow region near antenna. On the other hand, the SOL density distribution along with impurity sources can be tailored using local gas injection in AUG and JET-ILW with a positive effect on reduction of impurity sources. The technique of RF image current cancellation at antenna limiters was successfully applied in AUG using the 3-strap AUG antenna and extended to the 4-strap Alcator C-Mod field-aligned antenna. Multiple observations confirmed the reduction of the impact of ICRF on the SOL and on total impurity production when the ratio of the power of the central straps to the total antenna power is in the range 0.6 <P-cen / P-total <0.8. Near-field calculations indicate that this fairly robust technique can be applied to the ITER ICRF antenna, enabling the mode of operation with reduced PWI. On the contrary, for the A2 antenna in JET-ILW the technique is hindered by RF sheaths excited at the antenna septum. Thus, in order to reduce the effect of ICRF power on PWI in a future fusion reactor, the antenna design has to be optimized along with design of plasmafacing components.Peer reviewe
Impact of ICRF on the scrape-off layer and on plasma wall interactions: From present experiments to fusion reactor
Recent achievements in studies of the effects of ICRF (Ion Cyclotron Range of Frequencies) power on the SOL (Scrape-Off Layer) and PWI (Plasma WallInteractions) in ASDEX Upgrade (AUG),Alcator CMod,and JETIL Ware reviewed. Capabilities to diagnose and model the effect of DCbiasingand associated impurity production atactive antenna sandon magnetic field connections to antennas are described. The experiments show that ICRFnearfields can lead not only to EĂB convection, but also to modifications of the SOL density,which for Alcator CMod are limited to anarrow regionne arantenna. On the other hand, the SOL density distribution along with impurity sources can be tail or edusing localg as injection in AUG and JET-ILW with a positive effect on reduction of impurity sources.The technique of RFimage current cancellation atantennalimiters was successfully applied in AUG using the 3-strap AUG antenna and extended to the 4-strap Alcator C-Mod field-aligned antenna.MultipleobservationsconfirmedthereductionoftheimpactofICRFontheSOLandontotalimpuritypro-ductionwhentheratioofthepowerofthecentralstrapstothetotalantennapowerisintherange0.6<Pcen/Ptotal<0.8.Near-fieldcalculationsindicatethatthisfairlyrobusttechniquecanbeappliedtotheITERICRFantenna,enablingthemodeofoperationwithreducedPWI.Onthecontrary,fortheA2antennainJET-ILWthetechniqueishinderedbyRFsheathsexcitedattheantennaseptum.Thus,inordertoreducetheeffectofICRFpoweronPWIinafuturefusionreactor,theantennadesignhastobeoptimizedalongwithdesignofplasma-facingcomponents.https://doi.org/10.1016/j.nme.2018.11.017Received26July2018;Accepted22November2018âCorrespondingauthor.E-mailaddress:[email protected](V.Bobkov).1Seetheappendixof"A.Kallenbachetal.,2017Nucl.Fusion57102015â.2Seetheauthorlistof"H.Meyeretal.,2017Nucl.Fusion57102014â.3Seetheauthorlistof"X.Litaudonetal.,2017Nucl.Fusion57102001â.Nuclear Materials and Energy 18 (2019) 131â140Available online 20 December 20182352-1791/ © 2018 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).TEURATOM 633053US DoE, Office of Science,Office of Fusion Energy Sciences,User Facility Alcator C-Mod DE-FC02-99ER54512, DE-SC0010720, DE-AC05-00OR227
Simulating radiative shocks in nozzle shock tubes
We use the recently developed Center for Radiative Shock Hydrodynamics
(CRASH) code to numerically simulate laser-driven radiative shock experiments.
These shocks are launched by an ablated beryllium disk and are driven down
xenon-filled plastic tubes. The simulations are initialized by the
two-dimensional version of the Lagrangian Hyades code which is used to evaluate
the laser energy deposition during the first 1.1ns. The later times are
calculated with the CRASH code. This code solves for the multi-material
hydrodynamics with separate electron and ion temperatures on an Eulerian
block-adaptive-mesh and includes a multi-group flux-limited radiation diffusion
and electron thermal heat conduction. The goal of the present paper is to
demonstrate the capability to simulate radiative shocks of essentially
three-dimensional experimental configurations, such as circular and elliptical
nozzles. We show that the compound shock structure of the primary and wall
shock is captured and verify that the shock properties are consistent with
order-of-magnitude estimates. The produced synthetic radiographs can be used
for comparison with future nozzle experiments at high-energy-density laser
facilities.Comment: submitted to High Energy Density Physic
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