h-mode characterization for dominant ecr heating and comparison to dominant nbi or icr heating f....

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


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


• 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


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


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 %


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 %


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


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


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)


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

2/3,e

iLeGB T

ReB

TF


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


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


• Power dependence of Te profiles with varying ECRH:

• 0.6 kA, 2.5 T, central ECRH

• ne = 5x1019

H-mode characterization - T profiles


• 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


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)


• 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


H-mode characterization – ECRH on edge

• Influence of ECRH power on edge profiles (Te, vtor, ne)

Analysis by Elisabeth Wolfrum


• 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


• 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

h-mode characterization for dominant ecr heating and comparison to dominant nbi or icr heating f....

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