WP PWIE SP B and SP D: Meeting on surface roughness and morphology

Friday 6 May 2022, 09:00 → 13:00 Europe/Berlin

Join Zoom Meeting
https://us02web.zoom.us/j/88561916197?pwd=OXhJdUVrZmZzNGtwR29mV1RBeFl0UT09

Meeting ID: 885 6191 6197
Passcode: 876001
 

09:00 → 09:15 Introduction

Speakers: Andreas Kirschner (FZJ - IEK-4), Antti Hakola (TEKES / VTT)

09:15 → 09:30 VTT contribution to experimental surface-roughness investigations

Speaker: Antti Hakola (TEKES / VTT)

VTT_roughness_experimental_Hakola_060522.pdf

• Mean surface roughness (Ra) vs. impact angle distribution --> latter clearly more relevant for rough surfaces --> action for next year's tasks to take this into account
• Dynamic changes in the impact angles due to plasma exposure: analyses of samples before and after the experiments --> Calls for Fourier transform of surface morphology patterns
• Dynamic changes in roughness call for comparison also with data from linear machines --> next year's task

09:30 → 09:45 Effect of surface roughness on erosion of fusion relevant materials (JSI)

Speaker: Mitja Kelemen (JSI)

Kelemen_presentation.pptx

• Overview of the project of samples with controlled roughness (produced by ENEA) for lab studies
• Sputter yields agree with SDTrimSP-3D predictions generally except for the highest roughnesses
• Discussion:
  • Christian: using AFM as input - how many figures taken? Only one randomly selected --> should one take rather a statistical average over larger set of images (like 10)?
  • Udo: deconvolution of the response function from AFM? This may mean that the angular dependence is not fully caught --> correction factor may be necessary for better match with experiments and SDTrimSP
  • Andreas: even small depressions on the surface impact the sputtering yield via deposition; production of atomistically smooth surfaces however very challenging
  • Smooth surface wrt. collision cascade --> not only length scale but also energy plays a role (typically: < 1 nm)
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09:45 → 10:00 Sputtering from rough surfaces (OEAW)

Speaker: Christian Cupak

PWIE-SPB-RoughnessMeeting_TUW_Cupak.pptx

• Roughness can be inspected on different length scales - all these provide different overviews of the studied surfaces
• Different QCMs used for sputtering experiments --> angular dependence of sputtering yield
  • Roughest samples result in "collimation effect"
  • Data from nano-columnar W surfaces deviates largely from SDTrimSP predictions
• Discussion
  • Sebastijan: PWIE request for off-normal operation (resulting from e.g. melting), possibility for detailed surface characterization of W monoblocks & supplemented by sputtering studies of "simulated samples" (resembling ones resulting from off-normal events)
  • How about measuring the velocity distribution of sputtered particles? Maybe in connection with a reference experiment --> combination of a task for fundamental and practical understanding (is our model sufficient in predicting what would happen during the 2nd discharge of ITER or so); Udo thinks no major deviations would occur (based on MD) but interesting to probe it anyway
  • Udo: how robust is QCM for rough samples? lateral inhomogeneity for deposited material may occur; in the end the question is on making a compromise
  •  

10:00 → 10:15 Role of roughness in sputtering process of W by GyM He plasma (ENEA)

Speaker: Andrea Uccello (ENEA)

Uccello_SPB_SPD_Joint_Meeting_May_2022.pdf

• Relatively fresh results from first exposures in GyM
  • Polished and rough graphite and Si as substrates (locally produced), coatings by HiPIMS
  • AFM data of the surfaces provide the necessary background data --> for modelling
• Exposures made with different He+ energies and fixed fluence
• Also studied angular distribution in lab conditions --> comparison with Christian, Mitja for getting a complete picture
• Discussion
  • Andreas: Purity of the plasma? Not yet fully investigated --> potentially to be considered for next year's activities

10:15 → 10:30 Impact of roughness on spectroscopy data in PSI-2 (FZJ)

Speaker: Oleksandr Marchuk (FZJ)

marchuk.pptx

• Doppler shift used as an indicator for roughness (HRS diagnostics in PSI-2)
• Roughness  before/after plasma operation --> requires specific set of samples --> make use of already existing samples (ENEA, OEAW,...) --> Oleksandr provides us with PSI-2 boundary conditions
• Discussion
  • Udo: Removal of Al oxides may have affected some of the observations? Clearly also Al sputtered --> further investigations needed to prove the "coolness" of the method.

10:30 → 10:45 Discussion

10:45 → 11:00 Study on nano-columnar tungsten under Ar irradiation (VTT)

Speaker: Dr Alvaro Lopez Cazalilla

PWIE_06_05_2022_ALC.pdf

• "Toy model" applied for modelling sputtering from nanocolumnar surfaces
• Lower sputtering with nanocolumns included; modelling (SPRAY) and experiments agree very well
• Discussion:
  • Udo: results for flat surfaces strange? related to fluence? surface orientation wrt. beam? To be further investigated, e.g., validity of the potential
  • Andreas: only isolated columns used? periodic boundary conditions applied

11:00 → 11:15 Surface morphology and structure: Experiments, SDTrim-simulations and Surrogate modelling (MPG)

Speaker: Dr Udo von Toussaint

eurofusion_2022_05_06_toussaint_v02.pdf

• Impact angle good parameter for instantaneous sputter yield estimates but does not take into account fluence --> model extended to impact angle distributions
• Also local atomistic structure should be taken into account --> Crystal-SDTrimSP developed (inclusion of lattice structures) --> explains existing experimental data well (factor of 2-8 dependence between varying crystallographic directions)
• Discussion:
  • Different values in different crystallographic directions may impact experiments as well --> SP B link
  • However, dependence on crystallinity not that strong following multiple erosion-deposition steps --> factor of 2-8 dependence relevant only in the start-up phase; in a tokamak the structure around the OSP may not have been preserved following exposure to high fluences (in a magnetic environment)

11:15 → 11:30 Numerical simulations of surface roughness (OEAW)

Speaker: Prof. Friedrich Aumayr (Fusion@ÖAW. Austria)

PWIE-SPD-2022_RoughnessMeeting_TUW_Cupak.pptx

• SPRAY code developed - based on ray-tracing of sputtered atoms, reflected ions etc.
• Nanocolumns implemented by "SEM imitation"
• Surface roughness characterized by mean inclination angle --> best match with experimental results
• Discussion
  • Udo: intuitive analytical model available? should be no big issue

11:30 → 11:45 Surface roughness and morphology studies with ERO2.0 (ENEA)

Speakers: Gabriele Alberti, Prof. Matteo Passoni (ENEA)

SPB&D meeting on morphology 2022 - Alberti.pdf

• Surface roughness and morphology & their implementation in ERO2.0 --> comparison between ERO results and samples (pyramidal structures, different roughnesses) from GyM exposures
• Input
  • SEM and AFM data of all samples & weight-loss measurements
  • statistical analyses of W thickness variations after exposure
• Obtained up to now
  • implementation of surface mesh
  • studies on the dependence of mesh resolution and surface-evolution model
  • SOLPS-ITER plasma background for GyM cases
• Discussion:
  • Klaus: is triangular-surface model appropriate for modelling surface evolution? smoothing may become an issue; in modelling time step may need to be reduced to diminish smoothing?
  • Sebastijan: evolution should be also assessed based on very-high fluence exposures in MAGNUM-PSI --> calls for comparisons

11:45 → 12:30 Discussion

• Re-deposited layers not yet addressed --> calls for actions, both experiments and modelling
• Which model to be used for modelling re-deposits? either explaining experimental data or building "artificial models" into MD
• Issue with tokamak surfaces in the finest scale --> use surrogate models, mean surface angle etc. --> data for understanding global migration picture in tokamaks
• Which parameters are the most important to be included in the models (that would have the largest impact on the results)? Trends more important than exact details? Roughness decreasing during erosion but also cases where roughness may increase --> all these points to be addressed in the future