“…The Te and ne profiles are mtanh( ) fits [22,23] to an ensemble of measured profiles from the high-resolution Thompson scattering system [24] from the pre-ELM phase of several inter-ELM periods, which are taken from the EUROfusion pedestal database [25]. Both profiles are shifted radially to ensure that Te,sep∼100eV, which is a typical value for JET-ILW [19] and mapped onto the normalized poloidal flux coordinate ψN using a magnetic equilibrium reconstruction from EFIT [26]. Figure 2Pre-ELM averaged (∼80--100normal% of the inter-ELM period) pedestal profiles for two 1.4MA JET-ILW H-mode pulses at low (#84794, blue) and high (#87342, green) rates of D gas fuelling with 16and14MW of heating power, respectively, showing (with error bars): ( a ) electron temperature Te, ( b ) density ne, ( c ) pressure pe, their normalized gradients ( d ) R/LTe, ( e ) R/Lne and ( f ) the parameter …”
Section: Comparison Of Predicted With Measured Pedestal Te Profilesmentioning
confidence: 99%
“…The T e and n e profiles are mtanh( ) fits [22,23] to an ensemble of measured profiles from the high-resolution Thompson scattering system [24] from the pre-ELM phase of several inter-ELM periods, which are taken from the EUROfusion pedestal database [25]. Both profiles are shifted radially to ensure that T e,sep ∼ 100 eV, which is a typical value for JET-ILW [19] and mapped onto the normalized poloidal flux coordinate ψ N using a magnetic equilibrium reconstruction from EFIT [26]. Global linear GENE simulations presented in ref.…”
Section: Comparison Of Predicted With Measured Pedestal T E Profilesmentioning
A predictive model for the electron temperature profile of the H-mode pedestal is described, and its results are compared with the pedestal structure of JET-ILW plasmas. The model is based on a scaling for the gyro-Bohm normalized, turbulent electron heat flux
q
e
/
q
e
,
gB
resulting from electron temperature gradient (ETG) turbulence, derived from results of nonlinear gyrokinetic (GK) calculations for the steep gradient region. By using the local temperature gradient scale length
L
T
e
in the normalization, the dependence of
q
e
/
q
e
,
gB
on the normalized gradients
R
/
L
T
e
and
R
/
L
n
e
can be represented by a unified scaling with the parameter
η
e
=
L
n
e
/
L
T
e
, to which the linear stability of ETG turbulence is sensitive when the density gradient is sufficiently steep. For a prescribed density profile, the value of
R
/
L
T
e
determined from this scaling, required to maintain a constant electron heat flux
q
e
across the pedestal, is used to calculate the temperature profile. Reasonable agreement with measurements is found for different cases, the model providing an explanation of the relative widths and shifts of the
T
e
and
n
e
profiles, as well as highlighting the importance of the separatrix boundary conditions. Other cases showing disagreement indicate conditions where other branches of turbulence might dominate.
This article is part of a discussion meeting issue ‘H-mode transition and pedestal studies in fusion plasmas’.
“…The Te and ne profiles are mtanh( ) fits [22,23] to an ensemble of measured profiles from the high-resolution Thompson scattering system [24] from the pre-ELM phase of several inter-ELM periods, which are taken from the EUROfusion pedestal database [25]. Both profiles are shifted radially to ensure that Te,sep∼100eV, which is a typical value for JET-ILW [19] and mapped onto the normalized poloidal flux coordinate ψN using a magnetic equilibrium reconstruction from EFIT [26]. Figure 2Pre-ELM averaged (∼80--100normal% of the inter-ELM period) pedestal profiles for two 1.4MA JET-ILW H-mode pulses at low (#84794, blue) and high (#87342, green) rates of D gas fuelling with 16and14MW of heating power, respectively, showing (with error bars): ( a ) electron temperature Te, ( b ) density ne, ( c ) pressure pe, their normalized gradients ( d ) R/LTe, ( e ) R/Lne and ( f ) the parameter …”
Section: Comparison Of Predicted With Measured Pedestal Te Profilesmentioning
confidence: 99%
“…The T e and n e profiles are mtanh( ) fits [22,23] to an ensemble of measured profiles from the high-resolution Thompson scattering system [24] from the pre-ELM phase of several inter-ELM periods, which are taken from the EUROfusion pedestal database [25]. Both profiles are shifted radially to ensure that T e,sep ∼ 100 eV, which is a typical value for JET-ILW [19] and mapped onto the normalized poloidal flux coordinate ψ N using a magnetic equilibrium reconstruction from EFIT [26]. Global linear GENE simulations presented in ref.…”
Section: Comparison Of Predicted With Measured Pedestal T E Profilesmentioning
A predictive model for the electron temperature profile of the H-mode pedestal is described, and its results are compared with the pedestal structure of JET-ILW plasmas. The model is based on a scaling for the gyro-Bohm normalized, turbulent electron heat flux
q
e
/
q
e
,
gB
resulting from electron temperature gradient (ETG) turbulence, derived from results of nonlinear gyrokinetic (GK) calculations for the steep gradient region. By using the local temperature gradient scale length
L
T
e
in the normalization, the dependence of
q
e
/
q
e
,
gB
on the normalized gradients
R
/
L
T
e
and
R
/
L
n
e
can be represented by a unified scaling with the parameter
η
e
=
L
n
e
/
L
T
e
, to which the linear stability of ETG turbulence is sensitive when the density gradient is sufficiently steep. For a prescribed density profile, the value of
R
/
L
T
e
determined from this scaling, required to maintain a constant electron heat flux
q
e
across the pedestal, is used to calculate the temperature profile. Reasonable agreement with measurements is found for different cases, the model providing an explanation of the relative widths and shifts of the
T
e
and
n
e
profiles, as well as highlighting the importance of the separatrix boundary conditions. Other cases showing disagreement indicate conditions where other branches of turbulence might dominate.
This article is part of a discussion meeting issue ‘H-mode transition and pedestal studies in fusion plasmas’.
“…T e and n e were measured with high resolution Thomson scattering. Equilibrium reconstruction was carried out with EFIT++ [36][37][38] with kinetic constraints. The initial q-profile applied within integrated modelling was calculated by EFIT++.…”
Section: Characteristics Of Analyzed Discharge and Data Preparationmentioning
Previous studies with first-principle-based integrated modelling suggested that ETG turbulence may lead to an anti-GyroBohm isotope scaling in JET high-performance hybrid H-mode scenarios. A dedicated comparison study against higher-fidelity turbulence modelling invalidates this claim. Ion-scale turbulence with magnetic field perturbations included, can match the power balance fluxes within temperature gradient error margins. Multiscale gyrokinetic simulations from two distinct codes produce no significant ETG heat flux, demonstrating that simple rules-of-thumb are insufficient criteria for its onset.
“…The EFIT code is an equilibrium reconstruction code for tokamak plasmas [15][16][17]. While one particular implementation of the EFIT code with a C++ data flow layer which also incorporates a model of the induced currents [18] as a pre-processing step, called EFIT++ [19,20], has been used for MAST reconstructions in the past, another implementation, previously used for the NSTX [5] and KSTAR devices, is now being used for MAST reconstructions in the present work. Both of these codes will be used for MAST-U operation, as will be discussed in section 6.…”
Reconstructions of plasma equilibria using magnetic sensors were routine during operation of the Mega Ampere Spherical Tokamak (MAST) device, but reconstructions using kinetic profiles were not. These are necessary for stability and disruption analysis of the MAST database, as well as for operation in the upgrade to the device, MAST-U. The three-dimensional (3D) code VALEN is used to determine eddy currents in the 3D vessel structures for vacuum coil test shots, which are then mapped to effective resistances in the two-dimensional vessel groupings in the EFIT equilibrium reconstruction code to be used in conjunction with nearby loop voltage measurements for estimated currents in the structures during reconstruction. Kinetic equilibrium reconstructions with EFIT, using all available magnetic sensors as well as Thomson scattering measurements of electron temperature and density, charge exchange recombination spectroscopy measurements of ion temperature, and internal magnetic field pitch angle measurements from a motional Stark effect (MSE) diagnostic are performed for a large database of MAST discharges. Excellent convergence errors are obtained for the portions of the discharges where the stored energy was not too low, and it is found that reconstructions performed with temperature and density measurements but without MSE data usually already match the pitch angle measurements well. A database of 275 kinetic equilibria is used to test the ideal MHD stability calculation capability for MAST. Finally, the necessary changes to conducting structure in VALEN, and diagnostic setup in EFIT have been completed for the upgrade from MAST to MAST-U, enabling kinetic reconstructions to commence from the first plasma discharges of the upgraded device.
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