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1) H-mode in Helical Devices

M. Hirsch1, T. Akiyama2, T.Estrada3, T. Mizuuchi4, K. Toi2, C. Hidalgo3

1 Max-Planck-Institut für Plasmaphysik, EURATOM-Ass., D-17489 Greifswald, Germany2 National Institute for Fusion Science, Toki 509-5292, Japan

3 Asociación EURATOM/CIEMAT, Av. Complutense 22, 28040, Madrid, Spain4 Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Japan

activity based on the regular Coordinated Working Group Meetings for Stellarator/Heliotron Studies

Max-Planck-Institutfür Plasmaphysik

IAEA FEC 2010 in Daejon, EXC/2-5Ra

2) Construction status and scientific objectivesof the Wendelstein 7-X stellarator

on behalf of H.-S. Bosch and the Wendelstein 7-X Team, EXC/2-5Rb

2M. Hirsch, IAEA-FEC Oct. 2010, Daejon, Korea

1. the classical H-mode and ELMs occur in 3D helical devices with a phenomenology similar to tokamaks indicating generic plasma edge physics

particular elements for 3D devices are

2. strong impact of the magnetic topology at the plasma edgeon H-mode operational range and ELMs

3. mean flow shear (Er<0) is predefined already before the transitionfrom the ambipolarity condition of the neoclassical convective fluxes

=> both elements may constitute preconditions for the spin-up of poloidal flowsand the associated suppression of turbulent transport.

H-mode in helical devices

LHD

time (s)CHS

time (s)

CHS

1.14 1.16 1.18time (s)

1.20

TJ-II

time (s)

W7-ASHeliotron-J

1. LH transitions obtained in all helical devices if operated at relevant parameters

H-alpha traces

3M. Hirsch, IAEA-FEC Oct. 2010, Daejon, Korea

time (s)

50 ms

Heliotron-J

4M. Hirsch, IAEA-FEC Oct. 2010, Daejon, Korea

grad(Er)

grad(Te)

edge fluct.

energy / radiation

The quiescent H-mode (H*) is marked by sudden suppression of turbulence

... order of magnitude in <100μs

grad(ne)

grad(Ti)

Edge gradients in neimmediately

example fromHirsch et alPPCF 50 20080

a strongly sheared negative Er occurs

ΔW/W < 1.65

a=14 cm

reff=12.2 cm=13.8 cm

200 ms

... close to H-mode observations in Tokamaks

the classical LH-transition

-> confirms generic characterof underlying edge physics

W7-AS

particular for W7-AS

and ( Ti, Te ) increase

ΔW/W < 1.2-1.65

2. influence of magnetic configuration: high “reversed” shearLHD

H-alpha

density

density

mag. fluct.

-> relevance of iota=1 surface !?

iota=1

Rax=3.6m, inward shifted Rax=3.9m, outward shifted

quiescent H-modeToi et al. 2010, FST

Toi et al. thisconferencepost deadlinepaper

5M. Hirsch, FEC

H-mode with grassy ELMs

power threshold exceeds ITER scaling by factor 1-3 (CHS: factor 2, -> reminiscence to limiter H-mode in Tokamaks )

(and CHS)

energy

influence of magnetic configuration: low shear

variation of edge rotational transform ι(a)/2π

W7-AS: also ELM phenomenologyand their load to targets

-> option for ELM mitigationby the externally defined magnetic configuration

6M. Hirsch, IAEA-FEC Oct. 2010, Daejon, Korea

no H*no H* no H*

no H*

W7-ASHirsch et al. 2006 PPCF

Heliotron J

Estrada et al. 2010, Contrib. Plasma Phys

Sano_2005_Nucl. Fus.

TJ-II

influence of magnetic configuration: low shear

7M. Hirsch, IAEA-FEC Oct. 2010, Daejon, Korea

TJ-II

Heliotron J

H-mode windowat iota(a)=0.56

explanation could be that driving and damping terms for flows depend on magnetic configuration:

-> radial location of rationalsisland separatrix (Heliotron J , W7-AS):-> x-point to target distance

thus space potenial conditions-> poloidal viscous damping

discussion -> EXC/2-5Ra

existence diagram Hirsch et al. 2006 PPCF

8M. Hirsch, IAEA-FEC Oct. 2010, Daejon, Korea

low shear: operational range

operational range and ELM activity for5/9 island divertor configuration W7-AS

transitions to H* occurat low to moderate heating power as density increases

W7-AS: H-mode signatures (ELMs, short H* phases <10ms) already early in discharge

density limit (Sudo limit)determined by (edge) power balance

Giannone_2003_PPCF

Hirsch et al. 2006 PPCF

9M. Hirsch, IAEA-FEC Oct. 2010, Daejon, Korea

W7-AS

ITER physics basis 2007: 98.074.073.0042.0 SBnPthr ⋅⋅⋅=

-> H* obtained with power significantly below tokamak H-mode threshold= easy spin-up to high rotation state ?

operational range W7-AS and comparison with tokamak power threshold

density limit (Sudo limit)determined by (edge) power balance

Giannone_2003_PPCF

existence diagram

operational range and ELM activity for5/9 island divertor configuration

M. Hirsch, IAEA-FEC Oct. 2010, Daejon, Korea

3. the mean ExB flow shear is predefined by neoclassical fluxes

W7-AS

-> mean ExB flow predefinedby ambipolarity of neocassical fluxes(mostly stable on ion-root conditons with Er<0 realized)

-> in the H-mode the well of negative Er deepens

CHS

H

L

Doppler ReflectometryTJ-IIEstrada et al. 2009 PPCF

11M. Hirsch, IAEA-FEC Oct. 2010, Daejon, Korea

sustained spin-up of mean poloidal ExB flow after the transition

Estrada et al 2009 PPCFTJ-II

0.4 0.5 0.6time / s

E r /

(V/c

m) gra(pi)/(n*e)

Er

Baldzuhn, Hirsch et al

W7-AS

relevant layer=(a- 2cm)

development of ExB rotation: -> before H-mode:

Er is close to neoclassical ion-root predictions(-> already moderate to large negative Er).

-> after the L–H transition:value of Er increases by a factor of up to 2 morethan expected from the increase in pi/(e · n) alone

-> Thus in the radial force balance of the bulk ions,Er = pi/(e · n) − Bθ · v (+ Bφ · vθ)

strong enduring poloidal vxB rotation

moderatediamagnetic term

<-> to many Tokamak observaions

toroidal vxB rotationnegligible

also

M. Hirsch, IAEA-FEC Oct. 2010, Daejon, Korea

dynamic sheared flows and turbulence

TJ-IIDoppler Reflectometry,time intervals, about 20 ms, resolution 4 µs / 13 µs W7-AS

LH

-> dynamic sheared flow oscillations start right at L-H transition

n~

rE′

-> correlated oscillations of and in H- and L-mode branch

ExBv n~( )kHz101−′rE

cmΔr 1=

12

see posterEstrada et al EXC/P3-01

Estrada et al 2009 PPCF

1 ms

during H

( )n~log

ExBv

Hirsch et al 2006 PPCF

summary: H-mode in helical devices

13M. Hirsch, IAEA-FEC Oct. 2010, Daejon, Korea

hypothesis of a configuration biased H-mode : -> In helical devices the spin-up of flows to a high-rotation state may be biased (or damped) by the specific flow conditions in the 3D magnetic configuration

remark:-> The guidelines of quasi-symmetry and drift optimization - such as the minimization of the geodesic crvature are expected to influence the system of flows interacting with turbulence also

possible hints (easy access to H-mode in W7-AS for certain configurations andthe high continued vxB rotation in the H-mode of W7-AS and TJ-II as indications ?)

results: -> H-mode is generic but dependency on the 3D magnetic configuration is obvious. -> mean ExB flows are predefined by the ambipolarity condition of the neoclassical fluxes.-> shear flow investigations in W7-AS and TJ-II support current paradigma:

The classical H-mode is a fast bifurcation of turbulent edge transport based on the decorrelation of turbulent eddies and the associated spin up of by dynamic sheared (zonal) flows on top of (and possibly biased by) the equilibrium mean shear flow conditions.

UnternehmungWendelstein 7-X

14

Construction status and scientific objectives of

the Wendelstein 7-X stellarator

on behalf of H.-S. Bosch and the Wendelstein 7-X Team, EXC/2-5Rb

Max-Planck-Institut für Plasmaphysik, EURATOM-Ass., D-17489 Greifswald, Germany

Wendelstein 7-X

cw-operation by

R= 5.5m, a= 0.5 mVplasma= 33 m3

„fully“ optimized stellarator:

outer diameter: 16 m

Bmod on flux surface

-> drift optimization for thermal and fast ionsand stiff equilibrium by-> reduced Shafranov shift (reduced Pfirsch-Schlüter currents) and-> minimization of the bootstrap current

realized simultaneously by the concept ofisodynamicity (minimization of geodesiccurvature of fieldlines)+ low magnetic shear and island divertor

=> HELIAS concept

superconducting coils,cw-heating, fully cooled in vessel and divertorcomponents, cw-diagnostics and CoDaC

S Bosch, Status and Plans for W7-X, EXC/2-5Rb 15

UnternehmungWendelstein 7-X

16

-> comissioning: vacuum, cool-down, magnetic field + field line tracing, plasma startup

-> 1st operation phase with inertially cooled divertor (identical geometry but more robust), only some in-vessel components cooledthus 10s ECRH @ 8MW or max. 7 MW NBI (H, 55 keV)

-> shut-down (15 months): install HHF divertor, cryopumps, completion cooling and diagnostics

-> 2nd operation phase with steady state divertor, extended heating and diagnostics systemsto approach 30min @ 10MW ECRH + 10s NBI pulses

strategy for first operation

S Bosch, Status and Plans for W7-X, EXC/2-5Rb

UnternehmungWendelstein 7-X

10 MW cw ECRH (140 GHz corresponding 2.5 T)

all wall elements stationary cooled,divertor for 10 MW/m2

0.9 MW für 1800s Gyrotron +25 m transmission line

0 8 16 24 32 40 min.

MW 10.80.60.40.2

0

preparation of steady-state operation

microwave stray radiationtests at MISTRAL

launcher for 3 beams

1 MW cw gyrotron

17S Bosch, Status and Plans for W7-X, EXC/2-5Rb

UnternehmungWendelstein 7-X

18

physics preparation of 1st operation phase

1) verify the stellarator optimization :-> reduced 1/ν transport in a 4 MW ECRH @ X2 discharge scenario-> confinement scaling-> minimization of bootstrap current-> minimization of Shafranov shift-> but ⟨β⟩ too low to prove specified MHD stability limits at 5% and

improved fast particle confinement

inertially cooled divertor, partial cooling of in-vessel components-> 10s ECRH @ 8MW tolerable, max. 10MW NBI (D,60keV)

2) develop an integrated high-density scenarioas baseline for high-power steady-state operation in the 2nd operation phase:configuration control, acceptable low impurity confinement, divertor compatible edge conditions

-> X2 heating and current drive up to the cut-off (1.2 1020m-3), -> O2 heating to high density <2.4 1020 m-3

-> impurity control and high density dischages with NBI (High Density Hmode ?) -> tolerable divertor load (symmetry … )

S Bosch, Status and Plans for W7-X, EXC/2-5Rb

UnternehmungWendelstein 7-X assembly status

-> 3 of 5 modules at machine base on final location-> at the 2 other moduls all coils assembled, cryo piping is conducted-> port assembly started (50 fixed)

-> assembly to be finished in summer 2014(~1/2 year buffers included)

Thank you !

H-mode in helical devices: -> poster EXC/2-5Ra W7-X status and plans : -> poster EXC/2-5Rb

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