Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
For CW applications of superconducting cavities, obtaining a high quality factor is an important issue, since the required cryogenic power drops inversely proportional to Q0. Q0 is limited by BCS-losses and static losses, i.e. impurities and trapped magnetic flux. With sufficient magnetic shielding for TESLA type cavities, typical values of 2*1010 are being achieved at 1.8K operating temperature. The flux trapping was monitored by cooling the cavity at different ambient magnetic fields. In another experiment we have observed a significant increase in the Q0 value of up to 50% when subjecting the cavity to an additional cryogenic cooling cycle. Quantitative results are being presented and possible explanations for the effects are being discussed.
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
BESSY GmbH, Berlin
Most proposals of fourth generation light sources are based on cw operated sc liancs used in a FEL or ERL. The required RF power is strongly amplitude modulated due to the fact, that microphonics in the sc cavities plays an importand role. The requirements for the stability of the RF field in the cavities are better than 0.1 deg phase and better than 0.1% amplitude. At the HZB a modular RF transmitter was developed with FUG, that can be used for IOT tubes for different power levels and frequencies. Special attention was taken to the stability in the case of AM modulation.
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
The TTF-III input coupler was designed for pulsed operation at average power levels up to 5 kW. For CW-applications, higher power levels are desirable. Previous investigations have identified the connection between 4K and 78K section as the bottleneck for maximum usable power level. We have modified this section of the coupler by including a gas cooling. This setup was tested in a coupler-test-stand at room temperature. We have achieved stable operation at power levels up to 10kW which is sufficient for the field levels that are to be reached in the BerlinPro ERL. The results can be regarded as a worst case scenario, since the heat conductivity of all involved materials is rising significantly upon cooling to operating temperatures.