Fermilab, Batavia
DESY, Hamburg
A 4-cavity 3.9 GHz cryomodule has been constructed at Fermilab and delivered to DESY. Its intended use is to linearize the non-linear beam energy-time profile produced by the 1.3 GHz accelerating gradient and thus improve the operating characteristics of FLASH for its users. First cold testing of the module is expected in the near future prior to its installation. We will report on the performance of the cavities, assembly and transport of the module as well as anticipated testing, installation, and commissioning plans.
DESY, Hamburg
Temperature mapping systems are used since many years to locate performance limiting defects on superconducting cavities during the RF measurements. In order to investigate the nature of such defects non-destructive optical inspection systems are in use. Due to better quality control of the niobium material and welds as well as the preparation steps the limitations could be pushed up to gradients higher than 30MV/m. According to the higher gradients and therefore smaller defects new methods of detecting and visual inspection are developed in the recent past. This paper gives an overview of the recent developments of such systems and findings on the RF surfaces of superconducting cavities.
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
TESLA 9-cell cavity was designed a decade ago for pulse operation at duty factor of a few percents. Recently, numerous coherent and synchrotron light sources projects base their driving superconducting linacs on this design assuming operation in a continuous wave (CW) mode at rather high gradients. We have performed CW tests of a standard 9-cell TESLA cavities installed in helium vessel and fully equipped with the standard TESLA-TTF auxiliaries, main coupler and both Higher Order Mode (HOM) couplers in the horizontal test cryostat to find out a limit in the CW operation. Tests details and results are presented and discussed.
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.