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Laser-welded 1.3 GHz SCRF niobium cavity developed at RRCAT

"The very first laser-welded 1.3 GHz SCRF niobium cavity developed at RRCAT using innovative laser welding technique reached an accelerating gradient (Eacc) of 31.6 MV/m with a quality factor (Q0 ) of 1.0 x 1010 at 2 Kelvin."

            An innovative technique to fabricate superconducting radio-frequency (SCRF) niobium cavities by laser welding has been developed at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, Department of Atomic Energy, India. The first laser-welded 1.3 GHz SCRF cavity developed at RRCAT using this technique was recently tested at Fermilab, USA, and it reached an acceleration gradient (Eacc) of 31.6 MV/m with a quality factor (Q0) of 1.0x1010 at 2 Kelvin. This performance is similar to that of standard cavities fabricated by conventional process involving electron beam welding.

 

The first laser-welded 1.3 GHz SCRF niobium cavity developed at RRCAT and tested at Fermilab, USA showed Eacc of 31.6 MV/m with a Q0 of 1.0x1010 at 2K.

 

Dr. R.K.Sinha, Chairman, Atomic Energy Commission & Secretary, Department of Atomic Energy, Government of India, discussing with Dr. P.D.Gupta, Director RRCAT the laser welding of SCRF niobium cavities.

            Scientists and engineers at RRCAT have developed laser cutting and welding techniques using in-house developed 10 kW fiber-coupled Nd:YAG lasers. These have been successfully deployed in a number of laser cutting and welding operations such as welding of brachytherapy assemblies for cancer treatment, welding of titanium shells for heart pacemakers, remote cutting of bellow-lips during en-masse coolant channels replacement campaign in three pressurized heavy water reactors (PHWRs) resulting in a substantial cost savings and reduction in radiation exposure to the personnel. In the present instance, the laser welding was applied for development of innovative technology for fabrication of superconducting radio-frequency (SCRF) cavities. The idea was conceptualized for the first time and developed at RRCAT. An international patent was earlier filed with title "Niobium based superconducting radio frequency cavities comprising niobium components joined by laser welding, method and apparatus for manufacturing such cavities" (Application no. 09812469.6-2302 PCT / IN20090621). A positive search report from International search authority was received for this patent application.

            In parallel, efforts were launched for practical realization of the above technique. An in-house developed 10 kW fiber-coupled Nd:YAG laser was used for welding and a cavity welding rig was fabricated with the help of Indian industry. The laser welding experiments were carried out on more than 150 samples for parameter optimization, and a single-cell 1.3 GHz SCRF niobium cavity was fabricated. The cavity was processed and tested at Fermilab, USA. The cavity went up to an accelerating gradient of 31.6 MV/m at Q0 of 1.0x1010 at 2K.

10 kW fibre-coupled Nd:YAG laser

Superconducting cavity welding setup

The first laser-welded single-cell
1.3 GHz Nb cavity

            Traditionally, electron beam welding technique is used for fabrication of SCRF niobium cavities where it is necessary to carry out the welding operation in a vacuum environment. The international experts are quite surprised at the high quality factor achieved in our laser-welded cavity, especially as the welding was carried out in an inert gas atmosphere. The advantages of the laser-welding technique are much lower cost, small heat affected zone, no necessity to have vacuum environment for welding, and enhanced rate of production. It is expected that this development will open up an entirely new R&D path which will be greatly followed by scientists and engineers engaged in accelerator programmes using superconducting cavities world over.

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