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H-mode characterization for dominant ECR heating and comparison to dominant
NBI or ICR heating
F. Sommer
PhD thesis advisor: Dr. Jörg Stober
Academic advisor: Prof. Dr. Hartmut Zohm
Advanced Course of EU PhD Network
29 Sep 2010
Max-Planck-Institut für Plasmaphysik
Boltzmannstr. 2, 85748 Garching, Germany
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 2
Outline
• NBI and ECR heating systems• Heat transport theory• H-mode heat transport characterization
– Te, Ti, profiles
• Further investigations and experiments• Summary and discussion
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 3
NBI – general introduction
• Beam of neutrals (H0, D0, T0, He0 ) injected into plasma with
– high power – up to 2.5 MW
– high (appropriate) energy – Ebeam > Ti,e
– Inside plasma neutrals collide with plasma ions & electrons
• H0 + H+ → H+ + H0 – CX
• H0 + H+ → H+ + H+ + e – Ionisation by ions
• H0 + e → H+ + 2 e – Ionisation by electrons
– exponential decay
Ebeam ~ 100 keV today
1 MeV for ITER
• Resulting fast ions are confined within the plasma by magnetic field
slowed down to thermal energies Coulomb collisions ions & electrons
transfer of beam power to plasma
mnA
E AUGD
e
5.018
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 4
• critical energy: rate of energy loss to ions = rate of energy loss to electrons
• Ecr = 14.8 (kTe) [ (A3/2/Ai) ]2/3
– for pure D – beam: Ecr = 19 Te Ebeam/Ecr ~ 1 – 3
ITER: ENBI = 1MeV
E = 3,5 MeV
NBI – power deposition
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 5
NBI – layout
ASDEX Upgrade
neutraliser
ion dump
magnet
PINIs (4x)
box height:~ 4.5 m
cut through 1st injector – 10 MW at 60 kV
– arc sources pins have to be replaced quite often
– 10 MW at 93 kV– RF sources
simpler, cheaper, less maintenance
- pulse = 10 s
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 6
NBI – layout
• 2 Beamlines, each 4 ion sources
• SO-injector
• 2 radial beams
• 2 tangential beams
• NW-injector
• 2 tangential beams
• 2 off-axis deposition
• Also source of :
• particles edge: 1/10, but deep fuelling (not relevant for ITER)
• driven current
• plasma rotation (by NBI torque)
• CXRS
• efficiency factor of only 40 %
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 7
ECRH – principle
• Electron Cyclotron Maser Instability
• Electron gun: hollow e- beam
• Accelerated to relativistic speeds and focussed
• vII converted to v┴ inside resonant cavity (axial B-field)
• Interaction between e- and em wave
• Phase focus of e-
• Slowing down of e- by E transfer to
HF field
• Vgyrotron = 73 kV
Bgyrotron = 5.3 T
• Efficiency factor of 50 %
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 8
ECRH – layout
• fECRH ~ 140 GHz
• Electron cyclotron frequency fce(B = 2.5 T)= eB / (2me) = 70 GHz
• location determined by
– B 1/R
– fECR
– launching angle (mirror)
• Pold = 4 x 0.5MW for 2 s
• Pnew = 2 x 1 MW for 10 s
• Pfuture = 2 x 1 MW for 10 s
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 9
ECRH – advantages
• Localized (few cm) deposition
• Localized current drive
removal of NTMs by heating inside island structure
• Electron heating simulate reactor conditions
• Fast modulation ( 500 Hz) fast response in plasma
• Central heating enhanced impurity transport
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 10
Heat transport - theory
• Why are we interested in heat transport?
– High E low heat transport
– High central density low particle transport
– Low accumulation of impurities enhancement of impurity transport
• Heat transport is not governed by classical or neoclassical drive, but by micro instabilities and turbulent effects
– ITG, TEM, (ETG)
– Scale length ~ ion gyro radius << a
• qe(r) = - ne(r) · e(r) · Te(r)
• (r) = - D (r) · ne(r) + v · ne(r)
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 11
Heat transport - theory
• Gyro-Bohm scaling law in H-mode.
• Turbulence increases above a critical gradient length:
•
• S, 0, R/LTe, crit adjusted to experiment
stiffness of profiles
• Boundary condition at pol = 0.8 (H-mode pedestal)
GBTT
GBsPBe F
L
R
L
RFq
critee
02/3
,
e
e
T T
TR
L
R
e
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iLeGB T
ReB
TF
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 12
ASTRA
• Automated System for TRansport Analysis in a tokamak
• 2D equilibrium
• 1D (radial) profiles and transport equations
• of transport
• Modular build
– Many implemented models
– Easy inclusion of own models
• Equilibrium + radial profiles (Te, Ti, ne, j, Pheat,, Prad, …) qe,i, e,i, Dn, …
• Equilibrium + radial profiles (ne, j, Pheat ,, Prad, …) + i,e,theory radial profiles (Te, Ti)
DGL
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 13
H-mode characterization
• 4 similar discharges: Ip ~ 600 kA, Btor ~ 2.5 T, ne ~ 5 x 1019, PNBI = 5 MW
– Different heating power (PECRH = 0, 0.5, 1.5 MW)
– Different deposition location: PECRH = 1 MW, pol = 0, 0.3, 0.6
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 14
• Power dependence of Te profiles with varying ECRH:
• 0.6 kA, 2.5 T, central ECRH
• ne = 5x1019
H-mode characterization - T profiles
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 15
• Power dependence of Te profiles with varying ECRH deposition location:
• 0.6 kA, 2.5 T, PECRH = 1.2 MW
• ne = 5x1019
H-mode characterization - T profiles II
R.M.McDermott et al 2010 EPS
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 16
H-mode characterization - e profiles
• Electron and ion heat diffusion coefficients derived with ASTRA
with varying heating power
Transport dominated by ion heat transport (ITG)
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 17
• Increase of ECRH power (6 MW) Replacement of NBI in H-mode
• Higher current values up to Ip ~ 1.2 MA
• Lower density values ne < 5x1019
Increased influence of ECRH on e (TEM) due to decreased *
• Variation of R/LTe by variation of ECRH
• Dependence of ei on energy confinement time E
• Influence of central ECRH on pedestal
Further experiments and investigations
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 18
H-mode characterization – ECRH on edge
• Influence of ECRH power on edge profiles (Te, vtor, ne)
Analysis by Elisabeth Wolfrum
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 19
• Increase of ECRH power (6 MW) Replacement of NBI in H-mode
• Higher current values up to Ip ~ 1.2 MA
• Lower density values ne < 5x1019
Increased influence of ECRH on e (TEM) due to decreased *
• Variation of R/LTe by variation of ECRH
• Dependence of ei on energy confinement time E
• Influence of ECRH on pedestal
• Analysis of ICRH heated plasmas: torque e-/D+ heating
Further experiments and investigations
Advanced Course of EU PhD Network, 29 Sep 2010F. Sommer 20
• Difference between NBI and ECR heating
its influence on transport
• Gyro-Bohm scaling law
• Examples of ECRH influence on heat transport
• Increase of available ECRH power increases the range of accessible parameter space to analyse heat transport.
Thank You
Summary and discussion