DESY, Hamburg
The 9-cell TESLA type superconducting cavity based accelerating module is one of the key elements of the successfully operating FLASH linear accelerator at DESY as well as of the XFEL. The next FLASH 1.2 GeV upgrade modules and new XFEL prototype module have been assembled and tested on Cryo Module Test Bench (CMTB) at DESY. Results of these tests are presented and discussed.
DESY, Hamburg
The CW test of the 9 cell TESLA-type cavity in liquid helium bath at 2 K gives the cavity performance data for the cavity acceptance. The excitation of parasitic modes of the operating pass band is an error source for the cavity gradient and quality factor determination. The excitation of the parasitic modes in the operating pass band has been observed in 81 CW cold tests out of 170 and in 41 cavities under test out of 65 since 2006. The ramp up time of the parasitic mode depends strongly on the Qload of the input antenna. Some modes are exited in the combination with electron emission but others (7/9 Pi) have large amplitude without any attribute of field emission (x-ray or e- current at pick up). The growing up function of parasitic modes is different from the cavity response on the outside excitation but it describes a positive feed-back system. The relation of this effect to the field emission as well as to other test parameters has been investigated and is described in this paper.
DESY, Hamburg
The main RF-Couplers for 1.3GHz TESLA-Type cavities in the FLASH linac need several preparation and processing steps. The RF processing is usually done on coupler test stands (2 couplers pairwise), on a single coupler together with a superconducting cavity in the horizontal cavity test stand, on the module test stand (up to 8 cavities) or finally in FLASH. In FLASH one or more modules are connected to one klystron and conditioned together. Therefore the software was forked several times and merged during the last FLASH shutdown into one version. This is flexible enough to handle all these different test setups, without additional programming for IO hardware or data handling. The system is based on LabView, DOOCS and Linux operating system. The working principle is shown, including a possible outlook for the XFEL cavity production and operation.
DESY, Hamburg
For the series production of XFEL cryo modules, it is planned to test all complete modules prior the installation in the XFEL tunnel. For the test stands in the Accelerator Module Test Facility (AMTF), we have developed a new technical interlock. The interlock allows the observation of 8 individual analog signals per device (like temperature, pressure, light, free electrons) and can be fully remote controlled. Each channel has its own upper and lower remote controlled thresholds. The channels will be customized with sensor specific module cards, which adapt the power needs and signal conditioning to the specifications of the different sensors. The local display is used as user interface and the little space requirement makes the device quite suitable. An overview of functionality, internal features, connectivity and extendability of the device is given.
DESY, Hamburg
Radio frequency measurements on parts and subassemblies of superconducting cavities during its fabrication are a proper method of quality management and quality assurance. During the fabrication of 1.3 GHz cavities for FLASH, a simple device was used for measuring the half cells, dumb bells and endgroups. Because of the long test duration the device is not applicable for massproduction of 800 cavities. A semiautomated RF measurement machine was designed and built. This machine performs an easy load of the parts, consistent RF contacts, automated RF measurements and documentation. We describe the functionality of the RF-measurement machine and performance of the prototype during fabrication of 40 cavities for FLASH.
DESY, Hamburg
Fermilab, Batavia
A semi-automatic cavity tuning machine is used at DESY since 15 years to tune the field flatness and concentricity of the TESLA shape 9 cell cavities for FLASH. Based on this experience a further development work was done in a collaboration effort among FNAL, DESY and KEK to support the high throughput cavity fabrication necessary for the European XFEL and other SRF based future projects. Two of the four machines will be delivered to and operated by the cavity vendors for the tuning of the XFEL cavities. We describe the mechanical design and functionality of these machines and discuss the safety aspects for the operation at the industry.