Linac and Vacuum Components Development Section

Superconducting RF Cavity Development

LVCDS is involved in the development of Super conducting RF cavity technology & infra structure development for fabrication, processing, assembly & test stands for SCRF cavities. The section is also involved in development of SCRF cavity technologies in collaboration with Fermi National Accelerator Lab (FNAL) under Indian institution Fermilab collaboration (IIFC). The major activities related to SCRF cavity development are :-

Superconducting RF Cavity technology 

Single Cell SCRF Cavity Development

Under Indian Institution Fermi Lab collaboration (IIFC) LVCDS is developing 1.3 GHz TESLA type cavities. It started with development of Prototype Single cell cavities in aluminum for qualification of process.


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Electron beam welded Prototype 1.3 GHz Single cell cavity in Aluminum

The work is also currently ongoing under IIFC collaboration to develop 1.3 GHz Single cell cavity in Copper for Thin film deposition R & D effort at Fermi lab.


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Electron beam welded Prototype 1.3 GHz Single cell cavity in Copper

Very recently two nos Prototype 1.3 GHz Single cell cavity in Niobium have also been ompleted. All these prototype have been tested and qualified for Mechanical inspection, Frequency control, vacuum leak tightness.


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As part of collaboration these cavities have been shipped to Fermilab, Batavia, USA for their further processing and performance evaluation. The processing stages consist of ‘Electro-Polishing’, ‘Centrifugal Barrel Polishing’, ‘High Pressure Rinsing’, ‘Heat Treatment’ followed by Clean room (Class-10) assembly and testing at 2 K.



Cavity shipment to Fermilab, USA for processing

First Prototype 1.3 GHz Nb cavity after processing has been tested at Fermi Lab during March 2010 at 2 K. The cavity achieved the accelerating Gradient of 21 MV/m at Q > 1.5 E+10.

TE1CAT002_QvsE plot

Vertical Test Stand

Fermilab is upgrading its existing Vertical Test facility with two additional Vertical Test stands. The upgradation will increase the capacity of the testing facility and can test 1.3 GHz single & multi-cell elliptical cavities, 325 MHz single spoke resonators and 325 MHz triple spoke resonators.

The Vertical Test Stand operates at a nominal temperature of 2K with a supply LHe in excess of 20g/sec and provide bath pumping capacity of 200W at 2K. The cryostat consists of a vacuum vessel and LHe vessel, equipped with magnetic shielding to reduce the earth magnetic field to <10mG on SCRF cavity.

RRCAT is also planning to setup a Vertical Test Stand to test the SCRF cavities developed at Indian Accelerator Institutes as one of the items of XI Plan program.

Under Indian Institution Fermi Lab collaboration (IIFC) LVCDS has carried out the engineering design of Vertical Test Stand-2&3 in collaboration with Fermi Lab. RRCAT engineers and scientist will participate in the fabrication and commissioning VTS facility at Fermi lab and also at RRCAT jointly with engineers and scientist from Fermilab.

LVCDS has carried out design of the following components of the Vertical Test Stand by ASME Boiler & Pressure Vessel Code:

  • Liquid Helium Vessel Shell
  • Liquid Helium Vessel Top Flange
  • Vacuum Vessel Shell
  • Vacuum Vessel Flange
  • Top Insert Plate

and verified the design of following by Analysis –

  • Assembly of LHe Vessel Top Flange + Weld Rim
  • Top Insert Plate
  • Assembly of Vacuum Vessel Flange + LHe Vessel Flange + Top Plate + Support Pads
  • Magnetic Shield design – 300K & 2K using Opera 3-D software

LVCDS has also designed the 80K shield, suggested the piping layout for liquid helium, prepared 3-D model of the complete VTS-2 assembly & prepared set of drawings for the various parts & assemblies of VTS-2.

The major dimensions of the vessels are :

1.

Vacuum Vessel

Inner Diameter
Outer Diameter
Wall Thickness
Overall Length

ø 53.00 inch
ø 54.00 inch
½ inch
211.375 inch

2.

Liquid Helium Vessel

Inner Diameter
Outer Diameter
Wall Thickness
Overall Length

ø 36.32 inch
ø 36.50 inch
0.09 inch
191.35 inch

3

80K Shield

Inner Diameter
Outer Diameter
Wall Thickness
Overall Length

ø 49.75 inch
ø 49.50 inch
0.125 inch
186.74 inch

 

Scissors Tuner (Co-axial tuner)

The concept to construction of the Scissors tuner mechanism is being developed at LCDSL of LVCDS. A prototype made in SS and the mechanism is tested at LN2 temperature for the desired force and movement.

Lever Tuner: (Mounted at the end of the cavity)

A first fist prototype is made in mild steel and the mechanism is tested for the desired force and movement at room temperature.

Design and development of stepper motor for cryo temperature application:-

For the operation of mechanisms like tuner, stepper motors of various torque rating operable at liquid helium temperature and high vacuum is required. These motors and very costly and are not available for such applications in large number. LCDSL is also involved in development of such stepper motors. These motors have been successfully tested at LN2 temperature for large number of cycles.

Slide1
Stepper motor for LN2 temperature testing and

Infrastructure for SCRF cavity

Deep Drawing Facility

A 120 Ton capacity Deep Drawing press has been installed in LVCDS for drawing of SCRF cavities. The press is capable of handling jobs up to a size of 900mm x 900mm and has a maximum stroke of 400mm. The machine has a die cushioning of 40 Tons. The drawn half cells are trimmed & Electron beam welded to form dumb-bells/ end cells which are then electron beam welded to form multi cell cavities.
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120 Ton Hydraulic Press

 

Frequency Measurement Setup for half cell & Dumb-Bells

A pneumatically operated Frequency measurement setup has been developed to measure resonant frequencies of half cells & dumb-bells before & after electron beam welding. The measurement provides necessary input for trimming/ tuning of the cavities.

Bead Pull Measurement Setup

A test bench for bead-pull perturbation has been designed and developed for measuring frequency & field distribution at various stages of fabrication of single cell and multi-cell cavities. The motorized setup is designed to test the cavities in vertical position. This reduces the possibility of sagging of guiding thread and cavities. A computer based DAQ has been designed for measuring the field distribution in a single cell and multi-cell cavities.

Electropolishing Setup

• A horizontal electro-polishing setup for single cell to Nine cell 1.3 GHz SCRF cavity has been developed. A hollow aluminum cathode is placed along the cavity beam axis. The electrolyte is a mixture of hydrofluoric (HF) and sulfuric acid (H2SO4), which flows in the cavity through the hollow cathode and returns through overflow ports. The cavity is rotated at 2-10 rpm. Carbon brushes are used to connect power supply to the cavity(anode) during electropolishing. The current density during polishing is 50-100 mA/cm2 for a material removal rate of 0.5 μm/min. Special Acid pumps, valves & plumbing will be used for Sulphuric & Hydroflouric acid.


Horizontal Electropolishing Setup

 

A mechanical set-up has been developed for high pressure rinsing of superconducting radio frequency cavities made of niobium material. High pressure jets of ultrapure water are used to remove contaminants from internal surfaces of the cavity to achieve high electric fields. The set-up comprises of a linear motion system which moves the 1.2 meter long cavity up and down at low speed of 60 mm per minute and a rotary mechanism to rotate the water jets at 2 to 10 rpm coming out from fine nozzle tips. A piston pump is used to produce water jets at 100 bar pressure.

High pressure Rinsing Set up in Clean enclousure (Class 100)

Ultrapure Water Treatment Unit

An ultrapure water treatment unit has been installed which is capable of delivering Ultra pure water with resistivity of 18 M-ohm-cm at a flow rate of 10-12 litre per minute. The ultra pure water will be used for high pressure rinsing of processed SCRF cavities.


Ultra Pure Water Plant

SCRF Cavity Processing Building

Cavity Processing Building

The building is under construction to house clean rooms, Electron Beam welding machine. High Vacuum Annealing Furnace, Electro-polishing setup, Centrifugal barrel polishing machine etc. for cavity fabrication, processing and assembly.

SCRF Lab Building

The building will house Cavity forming facility, machining facilities, CMM, SIMS, material testing facility etc.

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

The CJQL lab is also involved in developing the facility 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. Sample preparation for RRR measurement is done by a precision sectioning low speed saw machine capable to cut samples of length upto 120mm and thickness 0.2mm by using precision diamond wafering blades driven by a fractional hp DC motor with variable speed from 0-300 rpm with a facility of built in micrometer for cross feed arrangement.

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RRR measurement facility procedure qualification
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RRR sample preparation machine qualification Niobium
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