Introduction to turbulence and isotope
effect session
Carlos Hidalgo
Laboratorio Nacional de Fusión, CIEMAT, Spain
CWGM, 18 – 20 January 2017
Discard the idea and hope that there may be men so much
more learned than we are who, despite nature, are able to
turn into true what is false
Galileo Galilei / Dialogo sopre i due massimi sistimi del
mondo Tolemaico e Copernicano (1632)
So… what is the true meaning of the isotope effect?
2 / 15
ISOTOPE EFFECT:
TRANSPORT
APPROACH
VALIDATION
EMPIRICAL ACTUATORS
ITPA scaling law
Tokamak vs Stellarators /
Heliotrons (LHD)
ü  Ion mass (H/D)
ü  Magnetic
configuration
Plasma conditions for minimum L-H
power threshold in ITER?
Confinement optimization in
stellarators/Heliotron?
Role of ion mass on local
turbulence
Measurements / simulations consistent
with gyro-Bohm-like scaling.
Interplay neoclassical and
anomalous mechanisms
Role of Er (NC) and interplay with short
scale Er (turbulent flows)
Role of ion mass on Zonal Flow (ZF)
and GAMs and magnetic topology
BASIC UNDERSTANDING
Transport channel
Ion vs electron transport
Stability
Pedestal stability can be affected via a
relative shift of temperature and density
profiles and role of Zeff
Role of atomic physics
Boundary conditions (ionization / CX)
3 / 15
ISOTOPE EFFECT:
TRANSPORT
APPROACH
VALIDATION
EMPIRICAL ACTUATORS
ITPA scaling law
Tokamak vs Stellarators /
Heliotrons (LHD)
ü  Ion mass (H/D)
ü  Magnetic
configuration
Plasma conditions for minimum L-H
power threshold in ITER?
Confinement optimization in
stellarators/Heliotron?
Role of ion mass on local
turbulence
Measurements / simulations consistent
with gyro-Bohm-like scaling.
Interplay neoclassical and
anomalous mechanisms
Role of Er (NC) and interplay with short
scale Er (turbulent flows)
Role of ion mass on Zonal Flow (ZF)
and GAMs and magnetic topology
BASIC UNDERSTANDING
Transport channel
Ion vs electron transport
Stability
Pedestal stability can be affected via a
relative shift of temperature and density
profiles and role of Zeff
Role of atomic physics
Boundary conditions (ionization / CX)
4 / 15
Isotope effects on radial correlation of
fluctuations and ZF/GAMs
Scaling local fluctuations
Scaling macro-structures
Lr versus ρi
Amplitude ZF/GAMs versus ρi
GK simulations
D-IIID / McKee et al NF 2001
YES
TEXTOR / Xu et al., PRL 2013
YES (poloidal correlation)
YES
FT-2 / Gurchenko IAEA-2014
YES
YES
ISTTOK / Liu et al., NF 2016
YES
YES
AUG / Hennequin et al.
EPS-2015
YES
YES
JET / Silva et al., NF 2016
TJ-K Ramisch et al., PoP 2005
TJ-II / Liu et al., NF-2015
Losada et al., PPCF-2016
H-J / Ohshima IAEA-2016
YES
YES
YES
(but dominated by ZF)
NO
Low density ECRH plasmas:
no evidence of significant
isotope effect on confinement
YES
(influence of magnetic topology
5 / 15
The isotope effect and multi-scale physics
Larmor radius (ρs) dependence
of turbulent structures
i.e. size of turbulent structures
increases with ρs
Stronger effect in magnetic
configurations with reduced damping
of zonal flows
Change in the k-spectra of
fluctuations
Zonal flow development and ExB symmetry
breaking mechanisms:
Eventually with
beneficial effects
on transport
I. The relative size of turbulence structures with
respect to Er (Neoclassical) shear scale lengths.
II. Damping of zonal flows (magnetic configuration)
ACTION 1: Influence of magnetic topology in the development of ZF
and confinement
(e.g. LHD inwards vs outwards / W7-X
Supporting experiments in HSX QS vs mirror conf / H-J / TJ-II)
6 / 15
SHORT vs LONG radial scale ER
ER SHORT
RADIAL SCALE
(persistent)
STRUCTURES
Radial electric
fields
ER LONG
RADIAL SCALE
(Neoclassical)
STRUCTURES
Breaking of symmetry
[RS drive]
Particle orbits
[damping of ZF]
ACTION 2: Influence of neoclassical Er in the development
and decay time of ZF events
i.e. Check interplay between Long / Short radial scale Er
[Mishchenko & Kleiber, POP 2012 / Losada et al., PPCF2016]
7 / 15
ISOTOPE EFFECT:
TRANSPORT
APPROACH
VALIDATION
EMPIRICAL ACTUATORS
ITPA scaling law
Tokamak vs Stellarators /
Heliotrons (LHD)
ü  Ion mass (H/D)
ü  Magnetic
configuration
Plasma conditions for minimum L-H
power threshold in ITER?
Confinement optimization in
stellarators/Heliotron?
Role of ion mass on local
turbulence
Measurements / simulations consistent
with gyro-Bohm-like scaling.
Interplay neoclassical and
anomalous mechanisms
Role of Er (NC) and interplay with short
scale Er (turbulent flows)
Role of ion mass on Zonal Flow (ZF)
and GAMs and magnetic topology
BASIC UNDERSTANDING
Transport channel
Ion vs electron transport
Stability
Pedestal stability can be affected via a
relative shift of temperature and density
profiles and role of Zeff
Role of atomic physics
Boundary conditions (ionization / CX)
8 / 15
L-H transition / L-mode and the isotope effect
Transport Ion
transport channel
Ryter NF-2014
Pressure gradients
Long-radial-scale Er
shear [ωEXB ≈ γ]
Isotope effect
The influence of ion-mass
on the L-H threshold would
be related to the larger edge
pressure during the
preceding L-mode
Impact on L-H power
threshold
ACTION 3:
ü  Check consistency between L-mode (isotope effect) and
L-H power threshold (isotope effect)
ü  Role of pressure gradients and ZFs to trigger the L-H
transition
9 / 15
ISOTOPE EFFECT:
TRANSPORT
APPROACH
VALIDATION
EMPIRICAL ACTUATORS
ITPA scaling law
Tokamak vs Stellarators /
Heliotrons (LHD)
ü  Ion mass (H/D)
ü  Magnetic
configuration
Plasma conditions for minimum L-H
power threshold in ITER?
Confinement optimization in
stellarators/Heliotron?
Role of ion mass on local
turbulence
Measurements / simulations consistent
with gyro-Bohm-like scaling.
Interplay neoclassical and
anomalous mechanisms
Role of Er (NC) and interplay with short
scale Er (turbulent flows)
Role of ion mass on Zonal Flow (ZF)
and GAMs and magnetic topology
BASIC UNDERSTANDING
Transport channel
Ion vs electron transport
Stability
Pedestal stability can be affected via a
relative shift of temperature and density
profiles and role of Zeff
Role of atomic physics
Boundary conditions (ionization / CX)
10 / 15
Atomic physics and isotope effect
A long standing open issue:
ü  CX / Mahdavi JNM -1990
ü  Ionization / Hidalgo PPCF-1995
ü  Influence of plasma fluctuations on neutral dynamics / de la
Cal NF-2016
ü  Atomic physics and stability / Dunne PPCF-2017 and EFPWDecember 2016
ACTION 4: Investigate the influence of isotope mass on the
coupling between core / edge and SOL regions
11 / 15
Isotope effect:
Different levels of model validation
Linear
simulations
Non-linear
simulations
ü  Level of fluctuations
ü  Frequency spectra
ü  Non-linear mechanisms: role of Zonal flows
ü  Asymmetries (magnetic shear / curvature)
ü  Turbulence spreading
ü  Interplay Neoclassical (Er) – Turbulent mechanisms
Significant isotope effect is found in TEM dominated
regimes [Nakata et al., GK Workshop, 2016 / PPCF2016]
ACTION 5: Check influence of plasma conditions (ITG vs
TEM; role of collisionality) on isotope effect
Discard the idea and hope that there may be men so much
more learned than we are who, despite nature, are able to
turn into true what is false
Galileo Galilei / Dialogo sopre i due massimi sistimi del
mondo Tolemaico e Copernicano (1632)
So…… what is the true meaning of the isotope effect?
ü  Multiple mechanisms (trues) are feasible and should be
experimentally validated
ü  LHD / WX-7 (supported by mid-size devices) will play a key
role on this fascinating scientific journey
[ACTIONS 1-5]
14 / 15
Isotope effect physics / ACTIONS
Action 1: Influence of magnetic topology in the
development of ZF and confinement
Action 2: Influence of neoclassical Er in the
development and decay time of ZF events
Action 3:
ü  Check consistency between L-mode
(isotope effect) and L-H power threshold
(isotope effect)
ü  Role of pressure gradients and ZFs to
trigger the L-H transition
Action 4: Investigate the influence of isotope
mass on the coupling between core / edge and
SOL regions
Action 5: Check influence of plasma conditions
(ITG vs TEM; role of collisionality) on ZFs and
isotope effect
LHD inward vs
outward conf.
supporting
experiments in
HSX, H-J / TJ-II
different plasma
regimes
(ITG / TEM,
collisionality, Lmode and L-H
transition)
+
GK simulations
15 / 15