Speaker
Description
The heat treatment of SRF cavities at medium temperature ($250°\text{C}$ to $350°\text{C}$), also known as “mid-T heat treatment”, is one of the R&D activities at DESY towards a high-duty-cycle (HDC) upgrade of the European XFEL.
Such treated cavities exhibit an improvement in the quality factor $Q_0$ ($3\cdot10^{10}$ to $5\cdot10^{10}$) at a moderate accelerating electric field strength $E_{acc}$ ($10~\text{MV/m}$ to $20~\text{MV/m}$) compared to EuXFEL cavities. In fact, cavities treated in this way do experience quenching at $E_{acc}$ in the range of $20–30 ~\text{MV/m}$, i.e. they cannot be operated at gradients above $30 ~\text{MV/m}$.
However, in this work, we have found that a heat treatment consisting of a combination of mid-T and low-T not only favorable high $Q_0$-values were measured, but additionally high gradients of up to $40 ~\text{MV/m}$ could be achieved. This offers great potential for upgrading modern LINACs with new high usable performance.
The results of 1.3 GHz TESLA-type single- and nine-cell cavities as well as the influence of the effective oxygen diffusion length l will be presented. Further insights into the surface of Nb are provided by supporting sample analyses.
