Vertical cryostats for cavity tests
Vertical cryostat CV1
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
- 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.
Last update : 08/07 2017 (3995)