IAEA FEC 2018 Ghandinagar

Overview of first high-performance
operation of Wendelstein 7-X withisland divertor
Thomas Klinger
Max-Planck-Institut für Plasmaphysik Greifswald, Germany

on behalf of the Wendelstein 7-X Team author list in R. C. Wolf et al. Nuclear Fusion 57 102020 (2017)

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme
2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

1

Major elements of Wendelstein 7-X
50 non-planar NbTi coils
5 types DC <18 kA

plasma 30 m3

20 planar NbTi coils
2 types DC <16 kA
plasma vessel 80 m3
265 m2 in-vessel components

254 ports 120 shapes

4.5 m machine height
16 m machine diameter
735 t device mass
435 t cold mass 3.4 K

113 NbTi bus bars
14 HTSC current leads
about 1000 helium pipes
10 central support ring elements
26.10.2018

cryostat vessel 420 m3
thermal insulation

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

2

The island divertor concept
10 island divertor modules
X-point@ bean-shaped cross sections

ergodic region
islands
total target area 19 m2
heat flux  10 MW/m2
connection lengths  500 m
incidence angles 2-3°
vertical target
baffle  0

horizontal target

initial setup with un-cooled graphite elements
future setup with water-cooled CFC elements
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

3

Electron cyclotron resonance heating 10 gyrotrons 140 GHz 2nd harmonic O and X polarization
 designed for 1800 s pulse length with output power 0.8 MW avg.
 optical system multi-beam transmission line – total loss  6%
 low-field side quasi-optical steerable launchers

Erckmann et al.
Fusion Science and Technol.
52 (2007) 291-312

one of the twotransmission lines
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

4

Neutral beam injection heatingenergygetterpumps

current
pulse length

positive
ion sources

55 keV in H+(93 keV in D+)
60-80 A 10 s
neutral beams
grids
neutralization chamber
26.10.2018

power
3.5 MW in H+
one injector box with two sources

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

Nocentini et al.
Fusion Engineering and Design
100 (2015) 453-460

5

Wendelstein 7-X device and operation figuresquantityunit

stage 1

plasma volume

m3

30

LCFS volume

major radiusm

5.5

averageminor radiusm

0.5

averagemagnetic inductionT

2.5

rotational transform2

5/6 … 5/4

ECRH power

MW

4.3

NBI power

MW

ICRH powerMW

heating energy

MJ4

typical pulse lengths

26.10.2018

stage 2stage 3stage 43.0

remarkon axis1/q

8.5

1010 (15)1 (1.5) MW gyrotrons

3.5

7/10

14/20

H/D 60 keV  10 s

1.5

3.5

25-38 MHz  10 s

200

1000

18000

max heat loads

1-2

10-100100-200

100-1800 typ-max

operationphase 1.1

operationphase 1.2

operationphase 2.1

operationphase 2.x/3

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

6

Stellarator (physics) optimisation
reduced neoclassical transport@ low-collisionality 1/ -regime

improved fast particle confinement
drift orbits of helically trapped particles

classical stellarator issues

1.
2.
3.
4.
5.

poor confinement at high temperatures
loss of fast (non-thermal) particles
strong Shafranov shift of the magnetic axispressure driven stability limits
lack of divertor concept

good finite equilibrium properties
reduced PS current & Shafranov shift

reduced bootstrap current
stable and robust equilibrium

good modular coil feasibility
acceptable curvature and shear stress26.10.2018

good MHD stability properties
ballooning and Mercier stablenested vacuum magnetic surfaces
low-order natural islands @ edge

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

7

Content of the talk
1. High density stationary discharges
wall conditioning, fuelling, radiative density limit, long discharges, energy confinement

2. Stellarator optimization
equilibrium, stability, global confinement, impurity transport, turbulence

3. Island divertor operation
power deposition, power exhaust, pumping, radiation, detachment

a. Overall performance assessmentb. Conclusions and way forward
Related papers on this conference: P. Aleynikov TH/P4-6, S. A, Bozhenkov EX/P8-8, R. Brakel EX/P8-17,
A. Dinklage EX/P8-30, F. Effenberg EX/9-2, G. Fuchert EX/3-5, O. Grulke EX/P8-9, M. W. Jakubovski EX/P8-16,
C. Killer EX/P8-18, R. Kleiber TH/P2-4, H. P. Laqua EX/P8-28, S. C. Liu EX/P8-15, J. D. Lore EX/P8-19,
J. Ongena EX/P8-27, N. Pablant EX/P8-10, T. S. Pedersen EX/9-1, E. Sanchez EX/P1-11, F. Schluck TH/P1-5
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

8Content of the talk
1. High density stationary discharges
wall conditioning, fuelling, radiative density limit, long discharges, energy confinement

2. Stellarator optimization
equilibrium, stability, global confinement, impurity transport, turbulence

3. Island divertor operation
power deposition, power exhaust, pumping, radiation, detachment

a. Overall performance assessmentb. Conclusions and way forward
Related papers on this conference: P. Aleynikov TH/P4-6, S. A, Bozhenkov EX/P8-8, R. Brakel EX/P8-17,
A. Dinklage EX/P8-30, F. Effenberg EX/9-2, G. Fuchert EX/3-5, O. Grulke EX/P8-9, M. W. Jakubovski EX/P8-16,
C. Killer EX/P8-18, R. Kleiber TH/P2-4, H. P. Laqua EX/P8-28, S. C. Liu EX/P8-15, J. D. Lore EX/P8-19,J. Ongena EX/P8-27, N. Pablant EX/P8-10, T. S. Pedersen EX/9-1, E. Sanchez EX/P1-11, F. Schluck TH/P1-5
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

9

Radiative density limit – role of wall conditioning
0.4𝑛ത 𝑐 ∝ 𝑃0.6 /𝑓𝑖𝑚𝑝

boronization broadens the operation window
critical density for radiation collaps increased by 3

O radiation reduced by 10
C radiation reduced by 5very close to the critical density the energy confinement E deterioates
26.10.2018

R. Brakel EX/P8-17

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

G. Fuchert EX/3-5

10

Electron cyclotron resonance heating above X2 cut-off
only 70% single
beam O2 absorption

20171115.039

X2 start-up
full O2 heating(at 1020 m-3 and 3 keV)
X2 ramp-down

multi-pass absorption/w
reflection at tiles & panel

cut-off limits
ECR X2 heating ne<1.2·1020 m-3
ECR O2 heating ne<2.4·1020 m-3

pellet injectionstart

ECE and TS
ECE 141 GHz in cutoff

stray radiation< 20 kW/m2

module 2
module 3
module 4

OXB mode conversion schemes under development

optimumby courtesy of T. Stange

Aleynikov TH/P4-6
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

H. Laqua EX/P8-28

11

Long pulse high density plasmas
O2 ECR heating with 6 MW powerwith nine gyrotrons operatingradiative power fraction 60 %1.61020 m-2 line-integrated density
10 s flat-top full density control[kJ]

1.8 keV central electron temperature
1.8 keV central ion temperature

26.10.2018reference scenario

20180904.15

800 kJ diamagnetic energy
only 1.5 MW total divertor loadin full detachment
IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

H. Laqua EX/P8-28

12

NBI heated discharges with high density
 pure NBI heating can sustain plasma stabilization of ion heating w/o ECRH

 centrally peaked high density plasma core density peaking can be controlled by additional ECRH
 pure NBI heating with npeak(0)=2·1020 m-3 demonstrated
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

13

Content of the talk
1. High density stationary discharges
wall conditioning, fuelling, radiative density limit, long discharges, energy confinement

2. Stellarator optimization
equilibrium, stability, global confinement, impurity transport, turbulence

3. Island divertor operation
power deposition, power exhaust, pumping, radiation, detachment

a. Overall performance assessmentb. Conclusions and way forward
Related papers on this conference: P. Aleynikov TH/P4-6, S. A, Bozhenkov EX/P8-8, R. Brakel EX/P8-17,
A. Dinklage EX/P8-30, F. Effenberg EX/9-2, G. Fuchert EX/3-5, O. Grulke EX/P8-9, M. W. Jakubovski EX/P8-16,C. Killer EX/P8-18, R. Kleiber TH/P2-4, H. P. Laqua EX/P8-28, S. C. Liu EX/P8-15, J. D. Lore EX/P8-19,
J. Ongena EX/P8-27, N. Pablant EX/P8-10, T. S. Pedersen EX/9-1, E. Sanchez EX/P1-11, F. Schluck TH/P1-5
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X14Toroidal plasma current
Rogowski coil measurement

toroidal current (kA)

15

20180828.030
20171108.040
20171115.013
20171122.014
20171123.021

1d transport modelling
DAM

Wdia=400 kJ
Wdia=400 kJ
Wdia=350 kJ
Wdia=200 kJ
Wdia=220 kJ

10EJM

low iota DAM
standard EIM/EJM
high mirror KKM
high iota FTM

offset  2 kA


EIM

5KKM
FTM

00510

15

2025time (s)by courtesy of Y. Turkin

by courtesy of K. Rahbarnia

bootstrap current
26.10.2018

shielding current

good agreement with transport simulation
but current offset due to ECCD contribution?

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

15

A record high performance plasma
20171207.006

X2 ECRH power doubled
record triple product0.6∙1020 keVs/m3hydrogen pellet injection
into helium target plasma

by courtesy of S. Bozhenkov

thermalization Te=Ti

diamagnetic energy  1 MJ

MHD eventS. Bozhenkov EX/P8-8
O. Grulke EX/P8-9
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

16

Neoclassical transport and plasma equilibrium
the ambipolarity condition in a stellarator
yields multiple roots (electron-, ion-root)

plasma equilibrium obtained with theX-ray tomographic multi camera system
20171207.006

radial electric field measured with XICS
20171207.006

by courtesyof C. Brandt
by courtesy of N. Pablantat Te=Ti the ion root with Er < 0 is established26.10.2018

N. Pablant EX/P8-10

 good agreement with VMEC calculations

 Shafranov shift of only 1-2 cm at <>=1%

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

17

Phase contrast imaging of core turbulence
20180904.027

t1 < t < t2 and t > t4
fluctuation amplitude line integrated density

phase contrast imaging
yields density fluctuations

t2 < t < t3
after pellet injection
turbulence suppression

t3 < t < t4
spectrogram shows
frequency chirpingIR laser beam along unfavourable
magnetic curvature  ITG, TEM

 pellet injection moves density gradient inward and LnLTi density profile in the core flattens t > t3 chirping mode transient

26.10.2018

by courtesy of A. von Stechow

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

O. Grulke EX/P8-9
R. Kleiber TH/P2-4
E. Sanchez EX/P1-1118

Impurity transport studies with laser blow-off
laser blow-off (LBO)
Nd:YAG laser 20 Hz
1064 nm 1J @ 6 ns

forward modelling (fit)based on the STRAHL code
20171108.02
0

Al, C, Fe, Mo, Si, Ti, W
approx. 1016 particles

strong anomalous diffusion> 100  neo-classical value
time evolution ofsuccessive ionization levels

26.10.2018

O. Grulke EX/P8-9

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

B. Geiger et al. submitted (2018)19

Impurity transport in the core and in the edge plasma
TESPEL = tracer-encapsulated solid pellet
R. Bussiahn, N. Tamura et al. Rev. Sci. Instrum. 89, 10K112 (2018)

by courtesy of B. Buttenschön and R. Bussiahn
20180906.038

beam/observation

I. LBOedge plasma
102 msblower gun
40 bar He

II. TESPELcore plasma
115 mspolysterene shell 0.5 – 0.9 mm
metal core Al, V, Fe, Mn, W, …
200 – 500 m/s with 3 min repetition rate

subsequent LBO and TESPEL injection
similar impurity transport times 100 ms

TESPEL and LBO provide complimentary information on impurity transport
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

O. Grulke EX/P8-9
A. Dinklage EX/P8-30
20

Content of the talk
1. High density stationary discharges
wall conditioning, fuelling, radiative density limit, long discharges, energy confinement

2. Stellarator optimization
equilibrium, stability, global confinement, impurity transport, turbulence

3. Island divertor operation
power deposition, power exhaust, pumping, radiation, detachment

a. Overall performance assessmentb. Conclusions and way forward
Related papers on this conference: P. Aleynikov TH/P4-6, S. A, Bozhenkov EX/P8-8, R. Brakel EX/P8-17,
A. Dinklage EX/P8-30, F. Effenberg EX/9-2, G. Fuchert EX/3-5, O. Grulke EX/P8-9, M. W. Jakubovski EX/P8-16,
C. Killer EX/P8-18, R. Kleiber TH/P2-4, H. P. Laqua EX/P8-28, S. C. Liu EX/P8-15, J. D. Lore EX/P8-19,
J. Ongena EX/P8-27, N. Pablant EX/P8-10, T. S. Pedersen EX/9-1, E. Sanchez EX/P1-11, F. Schluck TH/P1-5
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X21

Divertor heat flux
connection length

10 high resolution IR camerasby courtesy of P. Drewelow

thermography

low-iota

standard

asymmetry toroidal  40 / 25% (trim coils)
up/down  10-20%
power fall-off length q= 15 … 30 mm
power wetted area Awet  1.2 m2
26.10.2018

T. S. Pedersen EX/9-1
C. Killer EX/P8-18
F. Schluck TH/P1-5

high-iota

strike line position controllable with coils and ECCD

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

M. Jakubowski EX/P8-16
H. Laqua EX/P8-28

22

Power detachment-2

detachment by pellet injection

before detachment

time evolution of heat flux
2power load drops to  zero

10.3
0.2

02
0

T. S. Pedersen EX/9-1
M. Jakubowski EX/P8-16
26.10.2018

0.4

Q [MW/m2]

location [m]H pellet injection into Hedensity ramp-up
to 4-51019m-2

after detachment

0
IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

1

2
time [s]3423

Radiation during detachment
20171109.045

by courtesy of D. Zhang

verticalbolometer224 channels
tomographicreconstruction
by courtesyof S. Kwaklinesradiationof sight at the separatrix
constant plasma conditions (n, Tei, Wdia, Prad)
Prad/PECRH  95%
E  0.1 s not degraded w.r.t. ISS04
pellet injection
26.10.2018

6EIAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

T. S. Pedersen EX/9-1
F. Effenberg EX/9-2

24

Significant particle exhaust with simultaneous detachment prior to boronization: neutral gas compression  6-8 only with pdiv< 0.005 Pa
high density
 after boronization:neutral gas compression  30 with pdiv=0.1 Pa

high power
reduced power starvation?

20180814.024

upper divertor
lower divertor

10power drop?

detachment szenario
upper divertor
lower divertor

high recycling?
by courtesy of O. Schmitz
U. Wenzel and G. Schlisio

O2 mode ECRH plasma PECRH=6.8MW with a density ramp n = 7 … 121019 m-2
26.10.2018

F. Effenberg EX/9-2

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

T. S. Pedersen EX/9-1

25

Content of the talk
1. High density stationary discharges
wall conditioning, fuelling, radiative density limit, long discharges, energy confinement

2. Stellarator optimization
equilibrium, stability, global confinement, impurity transport, turbulence

3. Island divertor operation
power deposition, power exhaust, pumping, radiation, detachment

a. Overall performance assessmentb. Conclusions and way forward
Related papers on this conference: P. Aleynikov TH/P4-6, S. A, Bozhenkov EX/P8-8, R. Brakel EX/P8-17,
A. Dinklage EX/P8-30, F. Effenberg EX/9-2, G. Fuchert EX/3-5, O. Grulke EX/P8-9, M. W. Jakubovski EX/P8-16,C. Killer EX/P8-18, R. Kleiber TH/P2-4, H. P. Laqua EX/P8-28, S. C. Liu EX/P8-15, J. D. Lore EX/P8-19,J. Ongena EX/P8-27, N. Pablant EX/P8-10, T. S. Pedersen EX/9-1, E. Sanchez EX/P1-11, F. Schluck TH/P1-5
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

26

Ingredients for integrated performance plasma scenarios
wall conditioning
glow discharge cleaning
ECRH pulse trains
wall boronization
control of plasma radiation
reduction of core radiation
no impurity accumulation

plasma profile control
overdense O2 ECR heating
peaked density/temperature
central fueling with pellets
high density plasmas
ion root confinement
E in ISS04 scaling with n0.6
 triple product scaling with n1.6transport reduction
ion root confinement regime
suppression of turbulence

control of heat and particle exhaust
control of power loads by strike line control
detachment with sufficient neutral compression
high recycling (?)
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

27

Fusion triple product and pulse lengthby courtesy of M. Kikuchi
T.S. Pedersen submitted to PPCF
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X28

Summary and conclusions
1. Wall conditioning, in particular boronization gave access to an operation
window with stationary high-power high-density discharges. ECRH has
proven to be a most flexible heating and current drive scheme.
2. Transport seems to be dominated by turbulence and no impurity
accumulation at high densities is observed – confinement times
are within ISS04 and normalized plasma pressure is  1.5%.
3. The island divertor shows power detachment and discharges withcontrolled plasma radiation and high neutral compression rates.
The power load distribution is favourable with acceptable asymmetry.

More heating power and active cooling of in-vessel components are needed.
26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X

29Well done, Wendelstein 7-X team!

26.10.2018

IAEA Fusion Energy Conference 2018 – Overview Wendelstein 7-X30