I'm working on the Q-drop phenomenon in high gradient SRF cavities.
Superconducting rf resonating cavities made of niobium (Nb) are the essential parts of future accelerators such as
the International Linear Collider (ILC) and Energy Recovery Linac (ERL) due to the fact that they can be operated
at high gradient, high current and continuous wave conditions. Their benefits arise because of small dissipation in
the cavity walls compared with normal conducting rf cavities. The performance of a superconducting rf cavity can
be evaluated by measuring the Q factor at the accelerating field Eacc. Ideally the stored energy is proportional to the
square of accelerating field, and the Q(Eacc) curve is flat under at all field levels. But experimental results from cavity RF tests have shown that there are anomalous losses depending on the surface magnetic field levels Hs which correspond to accelerating gradients
Eacc. That is called Q-drop phenomenon.
