Speaker
Description
The primary aim of this WP was to reduce the spectral bandwidth of laser-induced emission in order to reliably detect and separate the hydrogen (Hα) and deuterium (Dα) lines using Laser-Induced Breakdown Spectroscopy (LIBS), with particular relevance to plasma–material interaction studies in fusion research. To achieve this goal, a LIBS laboratory was established from the ground up, including ultrafast lasers, ICCD-based spectrographs, vacuum and discharge systems, and diagnostics, and the methodology was progressively optimized as instrumentation became available.
A semi-qualitative investigation of nanosecond (ns), picosecond (ps), and femtosecond (fs) LIBS parameters demonstrated that spectral resolution is not governed solely by signal intensity but critically by the temporal evolution of the plasma.
The crater study, performed using optical profilometry, was a key component of this work and addressed a gap in the literature where LIBS spectral analysis and crater morphology are rarely studied simultaneously. Crater depth and width evolution on tungsten and molybdenum showed that ultrashort pulses produce well-defined, reproducible craters with minimal melting and redeposition. We have explored depths up to ~16 µm, well beyond the few-micrometer range commonly reported for fuel retention.
The discharge-assisted LIBS study demonstrated that an externally applied electrical discharge can decouple ablation from excitation. The discharge sustained excitation long after the LIBS plume decayed, allowing signal integration over hundreds of microseconds. This approach mitigated signal degradation over multiple laser shots and enabled stable detection even when the LIBS-only signal vanished at long delays.
A dedicated study of discharge characteristics and deuterium loading showed that a low-pressure two-electrode discharge can sputter electrode material and and trap deuterium onto a nearby molybdenum surface, producing laboratory-prepared samples. Electrical characterization confirmed stable discharge operation, and LIBS analysis verified the presence of hydrogen and deuterium emissions.
Finally, the detection and separation of Hα and Dα lines was achieved using optimized fs-LIBS conditions. Time-resolved spectra showed clear separation of the two lines at early delays, with reduced bandwidth compared to ns and ps cases. Overall, this work establishes a complete experimental framework spanning LIBS optimization, crater morphology, discharge assistance, and sample preparation that demonstrates a viable pathway toward high-resolution, depth-resolved detection of hydrogen isotopes relevant to fusion plasma diagnostics.
References
1. Hussain, A., Aceto, D., Ambrico, P. F., & Dilecce, G. (2025). Characteristics of glow-discharge LIBS in a rarefied environment. Plasma Physics and Controlled Fusion, 67(10), 105014. https://doi.org/10.1088/1361-6587/ae0cfe;
2. Cipelli, S., Aceto, D., Ambrico, P. F., Casiraghi, I., Cremona, A., De Pascale, O., Dilecce, G., Hussain, A., Laguardia, L., Pedroni, M., Ricci, D., Ripamonti, D., Scionti, J., & Uccello, A. (2025). Nanosecond laser ablation modeling of silicon and tungsten as support activity for LIBS diagnostic. Journal of Nuclear Materials, 156315. https://doi.org/https://doi.org/10.1016/j.jnucmat.2025.156315
3. Hussain, A, D. Aceto, P. F. Ambrico, G. Dilecce; (2025). Laser Induced Breakdown Spectroscopy from
ns to fs laser pulses for the detection of deuterium in fusion plasma walls[Poster]. International Conference on Phenomena in Ionized Gases 36th Edition; Aix-en-Provence France;
4. Hussain, A, D. Aceto, P. F. Ambrico, G. Dilecce., (2024). Discharge-assisted LIBS for the analysis of hydrogen isotopes content in tungsten samples [Poster]. Low-Temperature Plasma Diagnostic Conference 2024, Czech Republic;
5. Hussain, A, D. Aceto, P. F. Ambrico, G. Dilecce., (2024). Enhanced LIBS signal with small linewidth by electrical discharge assistance for application to hydrogen and deuterium line separation in plasma-surface interaction studies [Poster]. Third Futuro INAREA Symposium 2024, Bari, Italy;
6. Cipelli, S., Aceto, D., Ambrico, P. F., Cremona, A., De Pascale, O., Dilecce, G., Hussain, A., Laguardia, L., Ricci, D., & Uccello, A., (2024). Nanosecond laser ablation modeling using COMSOL Multiphysics as support activity for LIBS diagnostics [Poster]. FuseNet PhD Event 2024, Stuttgart.
7. Hussain, A., (2024). 61st Culham Plasma Physics Summer School, Culham Campus, Abingdon UK; http://www.culhamsummerschool.org.uk. 15/07/2024-25/07/2024.