M. Mayer SEWG Fuel Retention June Sample Analysis for TS, AUG and JET: Depth Profiling of Deuterium M. Mayer Max-Planck-Institut für Plasmaphysik, Euratom Association, Boltzmannstr. 2, Garching, Germany

M. Mayer SEWG Fuel Retention June Depth profiling with ion beams Depth profiling is possible due to energy-loss of ions in the sample But unavoidable energy spread due to Detector effects: - Limited energy resolution - Detector size (geometrical spread) Sample effects: - Energy-loss straggling - Multiple small-angle scattering of incident and outgoing particles Always limited depth resolution due to energy spread 3 He D p,

M. Mayer SEWG Fuel Retention June Depth resolution FWHM Depth resolution d: Distance between 2 layers, so that their energy separation is identical to the energy spread Energy spread is measured in FWHM Depth resolution in FWHM It is not possible to obtain information about the depth profile better than the depth resolution d

M. Mayer SEWG Fuel Retention June Depth resolution (2) d x E S eff : Effective stopping power E : Mean energy in detector x : Depth E : Energy straggling

M. Mayer SEWG Fuel Retention June Depth resolution Only structures larger than depth resolution are meaningful Depth profile is ambiguous for structures smaller than depth resolution Structures with thicknesses below depth resolution are meaningless Never interpret structures which are smaller than the depth resolution Occams razor: The depth profile with the smallest number of assumptions should be used Ambiguity of too small structures Example: RBS from AuSi on Si 2 MeV 4 He Au Si

M. Mayer SEWG Fuel Retention June Measure energy-spectrum of protons from 3 He + D 4 He + p (11.7 – 13.2 MeV) Thick detector > 1.5 mm required Backscattered 3 He particles are filtered with a stopper foil Large solid angles are possible Curved detector slit (conic section) Geometrical spread is minimized Resonant cross-section Resonance depth profiling also possible The D( 3 He,p) reaction Sample Detector Foil Slit 3 17

M. Mayer SEWG Fuel Retention June Bad depth resolution at the surface, but improving with depth Dominated by contribution of geometrical straggling Could be improved by smaller aperture, but at cost of sensitivity Depth resolution for D in carbon

M. Mayer SEWG Fuel Retention June Depth resolution of ~1 µm with 6 energies depth ranges with limited resolution, if smaller number of measurements Improved depth resolution compared to resonance method (requires 12 energies) Depth resolution for D in carbon (2)

M. Mayer SEWG Fuel Retention June Measurements at TS samples with 4 different energies Limited depth resolution from 17 to 25 µm due to gap from 4000 – 6000 keV Improvement by more or optimised energies Depth resolution for D in carbon (3)

M. Mayer SEWG Fuel Retention June Depth resolution for D in tungsten Bad depth resolution close to surface, but improving with depth At surface dominated by geometrical spread Dominated by contribution of multiple small-angle scattering Unavoidable sample effect

M. Mayer SEWG Fuel Retention June Depth resolution for D in tungsten (2) Comparable depth resolution with 6 different energies as resonance method with 12 energies

M. Mayer SEWG Fuel Retention June Depth resolution for D in tungsten (3) Both methods applied for AUG samples

M. Mayer SEWG Fuel Retention June Depth resolution for D in tungsten (4) W-sample from divertor of AUG Absolute SIMS intensity calibrated with NRA Good agreement in profile shape

M. Mayer SEWG Fuel Retention June Depth profiling on rough surfaces ~20 µm for CFC Depth of analysis is parallel to the sample surface

M. Mayer SEWG Fuel Retention June SEM of JET W-marker after exposure Laterally inhomogeneous samples and depth distributions may give identical spectra IBA methods alone may be not sufficient for determining sample structure Depth profiling of laterally inhomogeneous samples W W C W 0.15 C 0.85 C 4 MeV H + 50% W-coverage, thickness 4×10 19 W-at./cm 2 Total: 2×10 19 W-at./cm 2 100% coverage with W 0.15 C 0.85, thickness 13.1×10 19 W-at./cm 2 Total: 2×10 19 W-at./cm 2

M. Mayer SEWG Fuel Retention June IBA methods provide depth profile of elements Laterally homogeneous composition varying with depth Laterally inhomogeneous, roughness homogeneous composition Laterally inhomogeneous, roughness composition varying with depth IBA methods provide roughness distribution IBA methods provide total amounts of elements Depth profiling is demanding and difficult to interpret Depth profiling of laterally inhomogeneous samples (2)

M. Mayer SEWG Fuel Retention June Summary D( 3 He,p) reaction can be used for deep depth profiling of D Resonance method for deep depth profiling was (re-)invented at IPP a few years ago Proton energy spectrum method with multiple energies was developed Provides better resolution with fewer necessary energies for low-Z elements Provides comparable resolution with fewer necessary energies for high-Z elements Depth profiling on rough and porous surfaces is possible Line of analysis parallel to surface Depth profiling on laterally inhomogeneous samples is demanding Total amounts of elements can be measured