Impurities removal by laser blow-off from in-vacuum optical surfaces on RFX-mod experiment

Journal Article · Wed Dec 15 00:00:00 EST 2010 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.3511557· OSTI ID:22062218

Alfier, A; Fassina, A; Pasqualotto, R; Cervaro, V; Lotto, L ^[1]; Barison, S; Fiameni, S ^[2]; Giudicotti, L ^[1]

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1. Consorzio RFX, Associazione EURATOM-ENEA sulla Fusione, Corso Stati Uniti 4, 35127 Padova (Italy)
2. Istituto per l'energetica e le interfasi, C.so Stati Uniti 4, 35127 Padova (Italy)

An in situ window cleaning system by laser blow-off through optical fiber has been developed on the basis of a feasibility study previously presented. The beam generated by a Q-switched Nd:YAG laser is launched in a vacuum box into a high damage threshold optical fiber through a lens. The fiber output is focused on the impurities-coated surface of a vacuum window exposed to the plasma of the RFX-mod experiment, and it is remotely controlled with an xy motion system to scan the entire surface. We first investigate the energy density threshold necessary to ablate the deposited impurity substrate on removed dirty windows: above threshold, a single laser pulse recovers {approx}95% of the window transmission before its exposure to the plasma, while below it the efficiency of the cleaning process is too poor. The system so conceived was then used to clean the three collection windows of the Main Thomson scattering diagnostic on RFX-mod. We also present results obtained applying the same technique to the SiO-protected Al mirror used for the Z{sub eff} diagnostic: an energy threshold for efficient impurity removal without mirror damage is first identified, then ablation tests are executed and analyzed in terms of recovered reflectivity. The SIMS technique is used both with windows and mirror to study the composition of surfaces before and after the ablation.

• OSTI ID: 22062218
• Journal Information: Review of Scientific Instruments, Vol. 81, Issue 12; Other Information: (c) 2010 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ABLATION
ALUMINIUM
EFFICIENCY
ENERGY DENSITY
FEASIBILITY STUDIES
ION MICROPROBE ANALYSIS
MASS NUMBER
MASS SPECTROSCOPY
MIRRORS
NEODYMIUM LASERS
OPTICAL FIBERS
PHOTON BEAMS
PLASMA
Q-SWITCHING
REFLECTIVITY
RFX DEVICE
SURFACE CLEANING
SURFACES
THOMSON SCATTERING
TRANSMISSION