Manchester University Christmas talk 04/01/2010 HOM experiments and electromagnetic simulations using the Generalised Scattering Matrix Manchester University Christmas talk 04/01/2010 Dr Ian Shinton The University of Manchester; Cockcroft Institute, Daresbury, UK Manchester Christmas talk, I.R.R.Shinton, The University of Manchester, 4/1/2010

LARGE SCALE SIMULATIONS USING GSM PERTURBATION SIMULATIONS USING GSM The GSM technique is very accurate and requires little in the way of computational resources – see 3cell benchmark example to left: Large scale simulations (of multi module structures) beyond the currently available computational resources of a purely numerical approach is possible – see far left full scale simulation of FLASH PERTURBATION SIMULATIONS USING GSM The GSM technique allows cavity perturbations to be included in an efficient manner (unlike FD or FEM techniques). Effects on HOM’s can quickly be ascertained and their R/Q’s. A dented perturbation study confirmed that due to their bandwidths the alternative designs of the Ichiro and Re-entrant were more sensitive to fabrication errors than the baseline TESLA design – results were confirmed using Slater's theorem Manchester Christmas talk, I.R.R.Shinton, The University of Manchester, 4/1/2010

RAPID CAVITY PROTOTYPING USING GSM AND MODE MATCHING It is analytically possible to calculate the Scattering matrix for a sharp transition, and by using a mode matching technique the fields can also be analytically obtained. Combining this with a GSM technique allows rapid, accurate cavity prototyping with a minimum of resources – see picture to the right – which can be described by a simple equation for the dispersion curve The technique can be further extended to curved surfaces by considering then a a series of conjoined sharp transitions – see far right R/Q calculation of an elliptical cavity REALISTIC CAVITY SIMUTLATIONS USING GSM AND MODE MATCHING All these combined techniques can be used to rapidly search for cavity field profiles/trapped modes (see below and middle) – here third nearest neighbor coupling is required for the circuit model. Accurately determine the R/Q’s and kick factors of any given cavity design see middle where R/Q are obtained using mode matching from Impedance calculation of FERMI 3.9GHz bunch shaping cavity. Determine the RMS of any given cavity design – see far right RMS of a 3.9GHz bunch shaping cavity simulation – showing the cavity sensitivity Mode matching field at resonance Manchester Christmas talk, I.R.R.Shinton, The University of Manchester, 4/1/2010

The WP10.5.2 work package for the 3.9GHz bunch shaping cavity Working as part of the EUCARD WP10.5.2 task HOM cavity diagnostics and simulations for the 3.9GHz bunch shaping cavity at DESY being installed at FLASH with implications for XFEL. This is a collaboration with: DESY, FNAL, University of Manchester (UK) and the University of Rostock (Germany). Deliverables: Develop HOM sub-structure alignment algorithm Perform detailed sub-structure and cavity alignment via HOM’s Report on HOM experimental method and code Manchester Christmas talk, I.R.R.Shinton, The University of Manchester, 4/1/2010

WP10.5.2: HOMCD Acknowledgements WP10.5.2: HOMCD Future work Developed a dipole circuit model for this structure Sensitivity studies of the Dipole and HOM’s in this structure Full analysis of both the “warm un-tuned” and “cold tuned” DESY data and comparing it to the theoretical results – including phase calculations by considering a complex Lorentzian fits to the data Include couplers in the theoretical calculations Wakefield analysis Taking part in the upcoming beam and non-beam based tests at DESY on mode characterisation Will also be taking part in HOM diagnostics, which overlaps with WP 10.5.1 in order to get the diagnostics working. WP10.5.2: HOMCD Acknowledgements Main contributors from CI and UMAN B. Szczesny: UMAN (3.9GHz monopole circuit model) N.Juntong: CI/UMAN (initial 3.9GHz dipole circuit model) Collaborators: N.Baboi and G.Kreps: DESY H.W. Glock, T. Flisgen, U. Rienen: University of Rostock N. Eddy, T.N. Khabiboulline: FNAL Manchester Christmas talk, I.R.R.Shinton, The University of Manchester, 4/1/2010