NBTF Padua (Consorzio RFX-Italy) – SPIDER, the most powerful hydrogen/deuterium negative ion source, is entering a new operational phase, ready for nominal performance operation after a major upgrade campaign.
This moment represents both a technical and symbolic milestone. With the installation back into the vacuum vessel, SPIDER is once again a complete and fully integrated operation system, ready to resume hydrogen/deuterium plasma generation and acceleration at 100kV, closer than ever to the performance required by ITER.
“Attention now shifts to the next phase of experimental validation.” – says Diego Marcuzzi, NBTF Project Manager – “The closing shutdown has not only been a maintenance period, but a comprehensive upgrade campaign addressing key issues identified during previous experimental operations and improving both performance and reliability”.
Upgrades driven by experience
The upgrade carried out during SPIDER 2025-2026 shutdown was extensive and deeply rooted in operational experience.
A major effort focused on surface conditioning. Deposits, oxidation and burn marks by plasma operation, caesium and beam interactions were removed through mechanical and chemical cleaning. This allows the new campaign to start from controlled and reproducible surface conditions.
Another critical improvement addressed parasitic beamlets, previously generated by outgassing holes and line-of-sight paths in grid components. A redesign of extraction grid cover plates and closure or reduction of critical lines, now, mitigates parasitic beamlets.
Significant work was also carried out on the grid system. A leaking grounded grid segment was replaced with an improved one, with increased electro-deposited layer thickness, and optimized design.
In the RF drivers, the shutdown revealed degradation of molybdenum coating. Components were fully decoated and refurbished and a new solution (molybdenum coating with a chromium interlayer) has been introduced on part of the system to improve adhesion and durability.
A step change in cooling system reliability
“One of the most impactful upgrades concerns the cooling circuits, at least from the engineering point of view”saysMauro Pavei, Head of Thermomechanical Engineering at the NBTF plant in Padua.
“A large number of VCR (threaded) fittings of the Beam Source, identified as a possible source of heat-induced leaks, have been replaced with welds, as in MITICA components, using orbital welding. This modification is expected to significantly improve vacuum integrity and operational reliability, in view of the installation of the Vacuum Enhancement Module, foreseen for next autumn.” Pavei explains.
The cooling system has been further optimized through:
“These changes aim at ensuring stable thermal management under high-power operation” Pavei adds.
More flexibility, better control
New design solutions also introduce greater operational flexibility.
A revised connection between the bias plate and the source body now allows different electrical configurations, including MITICA-like operation modes.
Additional improvements include:
Together these upgrades expand the accessible operational space and improve control over key physical processes.
Back to operation towards nominal parameters
“With SPIDER soon back in vacuum, the focus shifts to experimental validation” – continues Marcuzzi – “the objective remains clear: to demonstrate stable, high-performance operation of a full-scale negative ion source, addressing at 100 kV all critical aspects required for ITER neutral beam injectors”.
This new phase builds directly on the experience of previous campaigns. With with a machine that is more robust and more capable the programme enters a new and key phase where expected performance becomes a concrete experimental target.
