Ion beam methods for the study of
plasma-facing materials
Department of Fusion Plasma Physics, School of Electrical Engineering,
Royal Institute of Technology (KTH), Association VR, Stockholm, Sweden.
Petter Ström
Per Petersson, Marek Rubel
Petter Ström, Hefei, July 17, 2016
O U T L I N E
• Background: Material modification by plasma–wall interaction
• Analysis needs
• Methods
• Focus: detector design for ToF-HIERDA
Background
TEXTOR tokamak (1982-2013), Forschungszentrum Jülich New plasma facing components, 2003
Typical condition after experimental campaign
Images: Forschungszentrum Jülich
Petter Ström, Hefei, July 17, 2016 2
Plasma-wall interactions
Surface analysis of atomic content after plasma-exposure gives: • Understanding of material transport mechanisms • Estimation of total amount of retained fuel and its distribution • Assessment of component lifetime
Transport of particles and energy • From plasma to wall
• From wall to plasma
Images: Harry Reimer, Forschungszentrum Jülich
Petter Ström, Hefei, July 17, 2016 3
RBS Rutherford Backscattering Spectrometry
Petter Ström, Hefei, July 17, 2016 4
Medium Energy Ion Scattering (MEIS) • Lower beam energy (typically 40-80 keV for 4He) • Smaller probing depth, but resolution ~ 1 nm
Backscattered ion
θ
2 MeV 4He+ • Measure energy of backscattered ions.
• Energy spectrum → information on atomic composition down to a few μm.
• High sensitivity, 1013 atoms/cm2. • Problems: Mixes
information about mass and depth. Light elements often hard to detect.
Petter Ström, Hefei, July 17, 2016 5
NRA Nuclear Reaction Analysis
θ
Reaction products Few MeV 3He, p
• Set projectile energy to get resonance for nuclear reaction at a specific depth.
• Especially useful in a
fusion context for mapping D, Be and 15N.
• Possibility to scan part of the surface with a
20 μm wide beam → Image mapping the atomic concentration of specific element (microbeam analysis).
3He + D → 4He + p 3He + 12C → 14N + p
3He + 9Be → 11B + p p + 15N → 12C + 4He
Gamma rays
Petter Ström, Hefei, July 17, 2016 6
PIXE Particle-Induced X-ray Emission
Characteristic X-ray
Few MeV p
e-
• Fast analysis, detection of all elements from Na and heavier
• High sensitivity, 1012 atoms/cm2 in the best cases
• Possibility for microbeam analysis, like for NRA • Drawback: No depth information.
ToF-HIERDA
• Detection of recoil ions’ velocity and energy → mass-based identification
• Excellent resolution for light isotopes deposited on smooth surfaces
• Probing depth ≈ 1μm
Time-of-Flight Heavy Ion Elastic Recoil Detection Analysis
Recoil ions
Forward scattered primary ions
θ
30 – 40 MeV Iodine I7+ - I9+
Gold Au7+ - Au10+
Petter Ström, Hefei, July 17, 2016 7
WF6
Applications
Tracer experiment with WF6 and 15N: Deposit on a test limiter from TEXTOR,
Species: W, He, C, 14N, 15N, O, F
First Mirror Test at JET for ITER: Analysis of deposits on test mirrors
Petter Ström, Hefei, July 17, 2016 8
Quartz microbalance
covers from JET
9
Purpose • Measure velocity
and energy of incoming particles.
• Differentiate between particles of different mass and nuclear charge number.
• Provide as good
energy resolution as possible
→ depth resolution.
Petter Ström, Hefei, July 17, 2016
ToF-HIERDA Detector
10 Petter Ström, Hefei, July 17, 2016
ToF-HIERDA Detector ToF foil Si3N4 membrane
Gas ionization chamber
11 Petter Ström, Hefei, July 17, 2016
ToF-HIERDA Spectrum
Acknowledgements
Tandem Accelerator Laboratory, Uppsala University Göran Possnert – Professor, Manager
Rogério Zorro, Jonas Åström – Senior Research Engineers
Software COMSOL Multiphysics
J.F. Ziegler, J.P. Biersack: Stopping and Range of Ions in Matter (SRIM)
Petter Ström, Hefei, July 17, 2016 12
