Laboratory for fusion research

• Fusion technology
• EUROfusion, ITER physics
• TRANSversal Actions for Tritium
• Detection of defects and hydrogen by ion beam analysis in channelling mode for fusion – DeHydroC
• EUROfusion, Fusion Science - Work program Plasma Wall Interaction and Exhaust (WP PWIE)
• EUROfusion, Fusion Technology - Work program Prospective Research & Development –Integrated Radiation Effects Modelling and Experimental Validation IREMEV (WP PRD-IREMEV)
• IAEA CRP Hydrogen Permeation in Nuclear Materials - Experiments and Modelling of in Situ Uptake, Transport and Release Studies of Hydrogen Isotopes in Irradiated Tungsten
• Detection for Hydrogen Isotopes by NRA, Cross Sections and Best Practices

INSIBA experimental chamber is attached to PIXE-ERD beam line at the 2 MV tandem accelerator at Jožef Stefan Institute (JSI), Slovenia. The set up allows creation of displacement damage by implanting high energy ions at a given sample temperature for simulation of irradiation damage caused by neutrons in fusion reactor. Samples can be simultaneously or sequentially irradiated by high energy ions and exposed to a well-controlled flux of atomic deuterium or to deuterium ions from an electron cyclotron resonance (ECR) ion gun. The sample is mounted on a holder with temperature controlled heater, capable of heating the sample up to 1200 K. The resulting deuterium depth profile is measured by the nuclear reaction analysis (NRA) method utilizing D(3He, α)p nuclear reaction. For one depth profile typically six analysing beam energies are used ranging from 0.7 MeV to 4.3 MeV. The proton detector used for the NRA measurement is mounted at a 160 degree scattering angle. Another detector is mounted at the 165° angle and is used for Rutherford Backscattering Spectroscopy (RBS) technique which determines the irradiation dose and depth profiles of species that are heavier than the probing beam ions.

The set up can be changed also for experiments with ERDA method, where detection of elastically recoiled particles is performed. There a small glancing angle of the probing ion beam with respect to the sample surface is needed as the recoiled particles exiting the target in the forward direction are detected. In our case typically 4.3 MeV beam of Li ions is used and is directed to the target at 15° glancing angle with respect to the sample surface. Li ions were used since they give better depth resolution as compared to the He ion beam due to the higher stopping power and the surface peaks of H and D are further apart.

The set up enables:

• classical NRA, RBS, ERDA material analysis for heavy element analysis and hydrogen isotope depth profiling in materials (20 samples can be mounted at once)
• in situ hydrogen isotope depth profiling in materials during or after sample exposure to hydrogen ions or atoms
• computer controlled sample heating up to 1000 K
• high energy (MeV) ion beam irradiation (W ions, He ions, protons)
• Sample exposure to hydrogen atoms and molecules
• Sample exposure to ions (H, D, He, Ar, O) with energies from 0.1 keV to 5 keV

References:

Markelj, S., Schwarz-Selinger, T., Pečovnik, M., Založnik, A., Kelemen, M., Čadež, I., Bauer, J., Pelicon, P., Chromiński, W., Ciupinski, L., 2019. Displacement damage stabilization by hydrogen presence under simultaneous W ion damage and D ion exposure. Nucl. Fusion 59, 086050. https://doi.org/10.1088/1741-4326/ab2261

Markelj, S., Založnik, A., Schwarz-Selinger, T., Ogorodnikova, O.V., Vavpetič, P., Pelicon, P., Čadež, I., 2016. In situ NRA study of hydrogen isotope exchange in self-ion damaged tungsten exposed to neutral atoms. Journal of Nuclear Materials 469, 133–144. https://doi.org/10.1016/j.jnucmat.2015.11.039

Založnik, A., Pelicon, P., Rupnik, Z., Čadež, I., Markelj, S., 2016. In situ hydrogen isotope detection by ion beam methods ERDA and NRA. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 371, 167–173. https://doi.org/10.1016/j.nimb.2015.11.004

Within our fusion related program we are performing experiments with vibrationally excited H₂ and D₂ molecules. For this purpose, a specialized unique vibrational spectrometer has been built. Its operation is based on the properties of dissociative electron attachment (DEA) of low energy electrons (0-5 eV) in hydrogen. A magnetic field is used in this spectrometer for guiding the electron beam and for extracting and separating H- and D- from heavier ions and electrons. Original ion extraction system based on penetrating electric field was constructed for focusing and detection of low energy ions.

 Studies of vibrational population of hydrogen molecules are performed, which are created by:

• Atom recombination on metal surfaces exposed to the partially dissociated neutral atmosphere,
• Recombination at Pd membrane after hydrogen permeation,
• Effusion from hot tungsten capillary and
• Thermal desorption.

New data are acquired on DEA in H₂ and D₂.

References:

Čadež I., Hall R. I., Landau M., Pichou, F., Winter M., Schermann C., Electron attachment to molecules and its use for molecular spectroscopy. Acta Chim. Slov., 2004, vol. 51, pp. 11-21.

Čadež, I., Markelj, S., Pelicon, P., Rupnik, Z., 2009. Reemission of neutral hydrogen molecules from tungsten. Journal of Nuclear Materials 390–391, 520–523. https://doi.org/10.1016/j.jnucmat.2009.01.074

Markelj, S., Rupnik, Z., Čadež, I., 2008. An extraction system for low-energy hydrogen ions formed by electron impact. International Journal of Mass Spectrometry 275, 64–74. https://doi.org/10.1016/j.ijms.2008.05.020

E. Krishnakumar, S. Denifl, I. Cadez, S. Markelj and N. J. Mason, Dissociative Electron Attachment Cross Sections for H₂ and D₂,Phys. Rev. Lett. 106, 243201 (2011)

Markelj, S., Čadež, I., 2011. Production of vibrationally excited hydrogen molecules by atom recombination on Cu and W materials. The Journal of Chemical Physics 134, 124707. https://doi.org/10.1063/1.3569562

AmTDS - Thermal desorption spectroscopy of Ammonia

Temperature programmed desorption of sample is performed to study ammonia or hydrogen isotope atom surface adsorption on metals. The experimental set up consists of the Hydrogen Atom Beam Source (HABS) (MBE Komponenten GmbH) and the residual gas analyzer (RGA) (Pfeiffer, Prisma Plus quadrupole mass spectrometer, 1–100 amu/e) mounted to a small ultrahigh vacuum chamber pumped by a 500 l/s turbomolecular vacuum pump (Pfeiffer, TMU 521Y P N).

A sample holder is mounted on the flange facing turbo-molecular pump. Sample can be linearly heated up to 1100 K and exposed to hydrogen atom beam from HABS. Ammonia is introduced through a side leak by small stainless steel tube directed to the center of the sample. NH₃, D₂, or a mixture of both is introduced through HABS, and the gas composition in the chamber is monitored by RGA either by recording the entire mass spectra in the 1–100 amu/e range or by recording the time variation of a set of characteristic mass peaks in the spectrum [multiple ion detection (MID) mode].

References:

Markelj, S., Založnik, A., Čadež, I., 2017. Interaction of ammonia and hydrogen with tungsten at elevated temperature studied by gas flow through a capillary. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 35, 061602. https://doi.org/10.1116/1.4995373

Sources available:

• Source of vibrationally hot H₂ and D₂ has been constructed in house for spectroscopic studies in hydrogen plasma.
• A commercial hydrogen atom beam source (HABS) by MBE Komponenten GmbH [K. G. Tschersich, J. P. Fleischhauer, and H. Schuler, J. Appl. Phys. 104, 034908 (2008)] for production of partly dissociated hydrogen gas. Production of H or D atoms depending on the use of gas H₂ or D₂, respectively.
• A commercial electron cyclotron resonance (ECR) ion gun (energy range 25 eV – 5 keV) by Tectra Gen II  http://www.tectra.de/sputter.html. The ion gun is a filamentless ion source based on a microwave plasma discharge.

AES Auger Electron Spectroscopy

Auger Electron Spectroscopy (AES),  Instrument: DESA 100, Producer: STAIB Instrumente GmbH. DESA 100 STAIB is compact instrument with cylindrical mirror analyzer (CMA) geometry, that can be build in into existing vacuum systems. While keeping all the advantages of the CMA, such as unbeatable sensitivity, small size and integrated electron source, the additional new features of DESA 100 are large working distance, uncritical sample positioning and electrically variable energy resolution.

Photos:  Auger electron spectrometer before mounting (left) and as mounted in the UHV system (right).

The spectrometer for Auger electron spectroscopy is intended for the analysis of the surface of various materials, and in particular allows: determination of contamination of samples with hydrocarbons, oxides; analysis of the amount of adsorbed molecules on the studied samples and analytical composition of thin layers.

For access to the instrument for measurements contact dr. Sabina Markelj.

Dr Anže Založnik