Vertical cryostats for cavity tests

Vertical cryostat CV1

Context

Low power RF characterization tests of superconducting cavities at low temperature down to T = 1.8 K.

Two buried vertical cryostats (CV1 and CV2) shielded against earth magnetic field allow one to measure accelerating gradient and surface resistance of superconducting cavities. They can accommodate cavities up to Φ = 0.45 m diameter and l = 1 m long in CV1, and Φ = 0.7 m diameter and l = 1.9 m long in CV2.

 

 

 

 


 

 

Elliptical cavity on insert

 

 

 

 

Technical means

  • Liquid Helium cooling: a refrigerator unit producing 140 l/h and 2000 l buffer tanks for each vertical cryostat, allowing one to provide helium at 4.2 K or 1.8 K by pumping on the helium bath. 500 l liquid helium are consumed for a typical cavity test in CV1, and 1500 l in CV2.
  • RF sources with adjustable frequency and power (80-90 MHz 50 W; 170-180 MHz 500 W; 700-1500 MHz 200 W; 704 MHz 1 kW), controlled via PLL based closed circuit loop.
  • Measurement of incident, transmitted and reflected RF power; estimation of heat losses via helium consumption (level drop or flowmeter).
 

Vertical cryostat CV1 and CV2 bunkers

 

 

Achievements, related projects

  • Single cell cavities to prototype new cavity preparation methods (etching, rinsing, heating, doping, ….),
  • XFEL, SPL, ESS elliptical cavity prototypes,
  • 12 Spiral2 quarter-wave cavities qualification,
  • IFMIF half-wave cavities qualification.
 

ESS 5 cell high beta cavity

 

 

Technical steps, expertise

  • Mounting of the cavity on vertical insert, vacuum leak tests, installation of thermal probes,
  • Positioning of the insert into the cryostat, connection to pumping lines and RF coax lines,
  • Leak checks and low power RF checks at room temperature,
  • Cooling down to 4.2 and / or 1.8 K, with fast ramps (3 K / min) from 150 to 50 K,
  • Control of the cavity frequency, the field ramp in the cavity by injecting increasing RF power and concurrent measurement of quality factor deduced from Pi, Pt, Pref.
 

Contact: 

 

Last update : 08/07 2017 (3995)

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