Superconducting Cavities Development Division


Infrastructure Facilities for development of SRF Cavity Development

RRCAT has taken up a program on R&D activities of 1 GeV, high intensity superconducting proton linac for Indian Facility for Spallation Research (IFSR). The most serious limitation of normal conducting RF cavities is the thermal load for high duty cycle operation. Above a certain limit of such thermal load it is not possible to remove the heat from the cavity walls without losing performance or reliability. Development of SRF cavities is an important accelerator technology to provide efficient, high current and high gradient accelerating structure for nearly all major high duty proton/ H- accelerator projects around the world. Infrastructure facilities have been established in the areas of SRF cavity fabrication, testing and dressing. A dedicated building has been constructed to house the SRF cavity infrastructure facilities. Major facilities setup at RRCAT includes:


Material characterization facility

A material characterization facility has been setup to analyze the issues related to cavity development. The facility includes –

Measurement of “Residual Resistivity Ratio” (RRR) of Niobium

A facility has been developed to measure the “Residual Resistivity Ratio” (RRR) of Niobium. This test is very useful for gross qualification of niobium for bulk resistivity from various sources and also to monitor the variation in RRR during any of the cavity processing stages. An indigenous set up has been designed and developed and is routinely operational. The facility has been calibrated with bench mark samples from FNAL and CERN.
RRR Measurement Setup
RRR Measurement Setup


SRF cavity fabrication facility

The SRF cavities are made using blanks cut from Niobium (Nb) sheets. A detailed quality control is needed for checking the quality of Nb sheets received from the manufacturer for pits, scratches or inclusions of foreign material prior to use in forming cavities. The cavity parts are joined together using Electron Beam Welding (EBW) Machine in high vacuum to minimize contamination during welding. A 15 kW Electron Beam welding machine has been installed and commissioned at SCDD for the purpose.

Major specification of machine

Beam power 15 kW ( 150 kV x 100 mA)
Inner size of chamber 3650 x 1500 x 1950 mm3 ( LxBxH)
Vacuum ready pressure < 4x10-4 mbar in 15 minutes
Ready for welding pressure < 1x10-6 mbar in 30 minutes
Online optics With CCD camera and suitable illumination system
Rotary Manipulator Dual spindle Rotary and Tilt rotary
CNC Control axis 7 axis ( 4 Mechanical + 3 electrical)


15kW Electron Beam Welding Machine
15kW Electron Beam Welding Machine


SRF cavity testing facility

Performance of SCRF cavities is limited by dissipation of power by various loss mechanisms like thermal breakdown, Multipacting, field emission etc. These loss mechanisms present the major problem in achieving high gradient cavities. To understand these performance limiting mechanisms a silicon diode based thermometry system has been designed and developed for detection of hot spot locations on the equator region of SCRF cavities. The thermometry system is operational and is used regularly while testing SCRF cavities in VTS facility at 2K. The thermometry results have shown good correlation with the RF test signals during cold test and microscopic observations performed at room temperature after cold test. A thermal signature observed during cold test of 1.3 GHz single cell SCRF cavity is shown in the following figure.

650 MHz five cell cavity equipped with temperature mapping system at RRCAT VTS Facility
650 MHz five cell cavity equipped with temperature mapping system at RRCAT VTS Facility


(i)Cavity mounted on VTS test insert, (ii)Thermometry system
(i)Cavity mounted on VTS test insert, (ii)Thermometry system


Quench signature recorded during testing at 1.84 K, Eacc = 35.6 MV/m
Quench signature recorded during testing at 1.84 K, Eacc = 35.6 MV/m


SRF Cavity Dressing Infrastructure

Cavity dressing requires an important infrastructure known as environment-controlled welding glove box. The glove box environment produces the best quality TIG welds that meet ASME Boiler and Pressure Vessel Code. (Fig.) shows the glove box of size ~ 3.4 m3 for accommodating dressed cavity assembly for welding. It has 12 glove-ports for welding from various locations of dressed cavity with 6 viewing window. This system can be operated in manual, semi-automatic and automatic mode which can be controlled by a panel as shown in fig. This panel is also equipped for controlling the glove box pressure, regeneration system for Argon gas, Mechanism for rotation of cavity etc. The dedicated large volume welding glove box has been installed, tested and commissioned recently at RRCAT with achieved Oxygen level <10 PPM and relative humidity (RH) level <2%, which are better than the required level of 20 PPM for Oxygen and 15% of RH. This is an important milestone towards the development of dressed SRF cavity.

Controlled environment Welding glove box
Controlled environment Welding glove box


Further a specially designed insertion bench aka ‘medium bertha’. This is crucial for proper alignment of various dressing components before loading in to glove box as shown in figure.

Alignment and assembly fixture- ‘ medium bertha’
Alignment and assembly fixture- ‘ medium bertha’
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