Effect of the cavity cooldown on the quality-factor Vitaliy FREIA, - PowerPoint PPT Presentation

Effect of the cavity cooldown on the quality-factor Vitaliy FREIA, Uppsala 2016-02-08

Paradigm of slow cooling 2 Vitaliy Goryashko

Thermal currents Normal cooldown Cycling, slow cooldown 3 Vitaliy Goryashko

Thermal currents: cont’d Temperature along the cavity at the onset of the SC phase transition ( Δ� ) and residual resistance for the cooldown and thermal cycles. 4 Vitaliy Goryashko

The effect of thermal cycling 5 Vitaliy Goryashko

The conclusion of this and similar studies was that the cavity cooldown should be as slow as possible in the vicinity of the transition temperature in order to avoid thermocurrents and associated with them trapping of magnetic fluxes. That was also the recommendation of SRF2013. But a year later the Fermilab group made a discovery… 6 Vitaliy Goryashko

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Expulsion effect 9 Vitaliy Goryashko

Nucleation of SC phase The propagating phase boundary sweeps out the magnetic flux. 10 Vitaliy Goryashko

Temperature gradient for a one-cell cavity 11 Vitaliy Goryashko

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Cooling in the presence of a strong magnetic field 13 Vitaliy Goryashko

Cooling rate and thermal gradient The temperature The cooldown rate is difference at the phase not the key parameter front is the main factor. The gradient along the cavity surface must be more than 0.1 K/cm. 14 Vitaliy Goryashko

Summary There is still a lot of room in this field of research and it might be of interest for us to look into this effect. 15 Vitaliy Goryashko