Initial operation of ASDEX Upgrade with 100 % tungsten PFCs

9th ITPA Meeting on Divertor and SOL Physics, 10/5/07 1

Max-Planck-Institutfür Plasmaphysik

Initial operation of ASDEX Upgrade with 100 % tungsten PFCs

Rudolf Neu

With contributions from: V. Bobkov, R. Dux, A. Kallenbach, T. Pütterich, H. Greuner, Ch. Hopf, C.F. Maggi, H. Maier, M. Mayer, V. Rohde, ASDEX Upgrade Team

9th ITPA Meeting on Div/SOL Physics, 10/5/07 R.Neu 2

Operation with 100 % W PFCs

• Transition to W PFCs in ASDEX Upgrade

• Boundary Conditions for Experimental Campaign

• Arguments on boronisation

• First Results of initial operation


Steps in ASDEX Upgrade towards a full W device

guard/

ICRHlimiter

aux.limiter

hor.plate

lower PSL

roofbaffle

2007

W-coating startingwith campaign

2003/2004

2004/2005

2005/2006

guard/

ICRHlimiter

aux.limiter

hor.plate

lower PSL

roofbaffle

2007

W-coating startingwith campaign

2003/2004

2004/2005

2005/2006

Steady increase of area

of main chamber W PFCs

since 1999

Rationales:- risk minimisation- physics investigations- partitioning of installation

time - production capacity


Optimisation of VPS coatings / HHF tests in GLADIS

200 µm W VPS (Plansee) on SGL R6710

Thermal Screening:• surface temperatures

> 2000°C no macroscopic defects


Optimisation of VPS coatings / HHF tests in GLADIS

Cyclic Loading:

200 pulses @ - 10.5 MW/m²- 3.5 s- Tsurf > 1600°C

coatings qualified for use in the lower divertor


• AUG is operated with the help of three flywheel generators:– EZ2 (1.45 GJ / 167 MVA): toroidal field– EZ3 (500 MJ /144 MVA) + EZ4 (650MJ/220MVA):

OH, pol.field, aux. heating

• Reconfiguration of power supplies

necessary:

less power, less energy available

Ip 1.0 MA,

pulse length 3-4 s, Paux 7.5 MW,

intermediate densities / triangularities (@ 1 MA)

Constraints imposed by damage of EZ4

0

5

10

15

20

New

-EZ

3 (k

A)

0.4 0.6 0.8 1.0 1.2Ip(MA)

EZ3 > 11 kAEZ3 ≤ 11 kA

Limit: 11 kA


Setup of program for 2007 campaign

I. Exploration of W compatibility (discharges in agreement with general boundary conditions)

II. Extension of working space - rad. cooled plasmas - impr. H-Mode (high low density)

III. Other ITER related physics investigations, compatible with above results and requirements

envisaged rel. weight(whole campaign)

priority

30%

20%

50%


Guidelines during initial operation

Boundary conditions set by W-PFCs

(during phase I., to be refined):• density: 7e19/m³ (gas puff rate > 6e21/s)• q-edge: > 3.2• f(ELM): > 60 Hz• dominant central heating (no pure off axis heating)

• Pheat < H-mode threshold or Pheat > 2xH-Mode threshold

• power/energy limits for upper divertor (5 MW 4s, 10MW 1s)• monitoring of limiter (and divertor) glow (restrictions on shape,

power, energy: to be adjusted)• power/energy limits for lower divertor from operation / results

of radiatively cooled plasmas


Research Topics of W-programme at AUG for the upcoming campaign(s)

Investigation will concentrate on:

• transition to C-(low-Z) free machine:

- radiatively cooled (integrated) scenarios by simultaneous use

of noble gas puff, central heating and ELM pacemaking

- optimization of gas species/injection • evolution of hydrogen retention:

- influence on gas balance and D inventory in PFCs • disruption characteristics:

- differences in current decay / run-aways• optimization of ICRF:

- is the simultaneous use of with high-Z PFCs possible


Reminder: Unboronized start-up with W HS successful

H ~ 1, Prad ~ 30 %main


Why Boronisation

• Conditioning- large O getter (even in non plasma exposed areas): easier break down higher density limit facilitates start up

- use of BD6 pre-loading of wall, strong pumping larger D puffing rates easier transition to D:

• Coating of surfaces- suppression of W influx- suppression of other intrinsic metallic impurities


Estimates for B Erosion

Thickness of boron layer Main chamber: 50 nm 3e21/m²Limiter: 50 nm 3e21/m²Divertor: 10 nm 5e20/m²

Particle fluxes / Particle temperatures (energies) /B YieldMain Chamber: 1e21 / (E 100 eV) / 1e-2Limiter: 1e22 / T= 20 eV / 1e-2Divertor: 1e23 / T=5 eV / 5e-4

Live-time of boron layerMain chamber: 300 s (100 disch)Limiter: 30 s (10 disch)Divertor: 10 s (3 disch)


Effect of boronisation

• strong reduction of W influx and concentrations

• for ICRH only, H-Mode threshold increases stronger than for NBI for aged boronisation

• time constants shorter than typical distance between boronisations

• recovery of W influx depends on particle and energy load

800 kA 1.8MW ICRH


Effect of boronisation

• strong reduction of W influx and concentrations

• for ICRH only, H-Mode threshold increases stronger than for NBI for aged boronisation

• time constants shorter than typical distance between boronisations

• recovery of W influx depends on particle and energy load


Benefits of start-up without boronization

• Operation/investigation of W machine without (any)

intrinsic low-Z radiator• Comparison of boronised / un-boronised machine:

maybe able to proof of hypothesis on B influence• D retention ‚without‘ low-Z (C,B) contamination• Comparison of D pumping W wall / boronised W wall

and H-D transition


Aims for the unboronized phase

Milestone:

Steady state H-Mode at intermediate density and heating power

with H~1

Specific Investigations: • Exposure of deposition probes to measure:

evolution B,C,W impurities, D retention• Particle Balance (in co-op. TS)• Influence of ICRH• Documentation of edge plasma parameters / radiative cooling

(if applicable/necessary)


Conditioning by baking - He / He-D glow

• 10 days baking @ 150°C• overnight glow in He

(He+10%D2, 500V, 4x1.8A)

Strong pumping of C and O

(through CO and CO2)


First Results of initial operation

• Re-start since 24/4/07 (5 days of operation)

• Reconfiguration of power supplies for OH/V-coils main issue

• Reliability of break-down not yet satisfactory (low-Z impurities, gas release)

• Divertor configuration succes- fully acchieved

• W contamination not important


Long term evolution of W concentrations

• reduced cW at relevant auxiliary heating power and densities


Classification of proposals

• P prerequiste first few weeks• R related first half of campaign• E extended end of first half of campaign• C compatible first few months (lower

priority)• O orthogonal second half of campaign

Priority within categories by TFs

Initial operation of ASDEX Upgrade with 100 % tungsten PFCs

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