HOM Characterization for Beam Diagnostics at the European XFEL

HOM-based diagnostics in SC accelerating cavitiesPrincipleExperience at FLASHThe European XFELSpectra of 1.3 GHz cavities in the E-XFELBeam measurements in 1.3 GHz cavities in the E-XFEL injectorSummar

Overview of HOM-based Diagnostics at FLASH and the European XFEL

Principle, benefitsHOMBPMs for 1.3 GHz cavitiesFLASHE-XFELHOMBPMs for 3.9 GHz cavitiesFLASHE-XFELHOM-based beam phaseMeasurement of cavity alignment at FLASHSummar

First Tests of a Micro-TCA-Based Downconverter Electronic for 5GHz Higher Order Modes in Third Harmonic Accelerating Cavities at the XFEL

Beam excited higher order modes (HOM) in 3.9GHz accelerating cavities at the European XFEL are planned to be used for beam position monitoring. The specifications of the monitors have been defined during an extensive study on the 3.9GHz module at FLASH. Selected HOMs for precision measurement are located around 5440MHz and 9040MHz. An electronics developed by FNAL has been recently installed at FLASH and provides a basis for the XFEL electronics. The paper will present the design and first test of the hardware for the Micro TCA standard used for the XFEL. The hardware consists of three different Rear Transition Modules (RTM), two four channel down converter RTMs (5GHz and 9GHz) and a third RTM with two phase locked loop synthesizers on board for LO generation. Presently the 5GHz and the PLL RTMs are under construction. The first measurements with these cards will be presented

Cavity Tilt Measurement in a 1.3 GHz Superconducting Cryo-Module at FLASH

TESLA superconducting (SC) cavities are used for theacceleration of electron bunches at FLASH. The HigherOrder Modes (HOMs) excited by the beam in these cavitiesmay cause emittance growth. The misalignment of thecavities in a cryo-module is one of the essential factorswhich enhance the coupling of the HOMs to the beam.The cavity offset and tilt are the two most relevant misalignments.These can be measured by help of dipolemodes, based on their linear dependence on the beamoffset. The cavity offset has been measured before inseveral modules at FLASH. However, the cavity tilt hasso far proved to be difficult to be measured, because theangular dependence of the dipole mode is much weaker.By carefully targeting the beam through the middle of acavity, the strong offset contribution to the dipole fieldscould be reduced. Careful data analysis based on a fittingmethod enabled us then to extract the information on thecavity tilt. This measurement has been implemented in thecavities in one cryo-module at FLASH. First results of theongoing measurements from several cavities are presentedin this paper. It is for the first time that the cavity tilt inseveral cavities has been measured

Simulations and Measurements of Beam Pipe Modes excited in 9-cell Superconducting Cavities

Higher order modes (HOM) excited in 9-cell superconducting cavities have been studied to detect cavity alignment. Dipole modes have been monitored, since their magnitude is proportional to beam offsets from their electrical centers. Detection of cavity alignment is important for the ILC to confirm alignment accuracy and furthermore possible source of emittance growth. We are particularly interested in beam pipe modes because they are localized in both ends of the cavity. We measured beam-induced HOM in the STF accelerator at KEK in 2012 â 2013. From the results of the measurement, we found some modes whose behaviors are like dipole mode at around 2.1 GHz instead of 2.28 GHz as calculated by R. Wanzenberg for an ideal cavity [TESLA 2001-33, September 2001]. We also measured beam induced HOM in the TESLA superconducting cavities in FLASH at DESY. In order to identify beam pipe modes and to compare the measurement with the calculation, we calculate beam pipe modes of 9-cell superconducting cavity by CST MICROWAVE STUDIO 2012 and HFSS 12. We will discuss about these calculations and the measurement