Sub-Task HOM-BPM HOM based Beam Position Monitors – Planned and Extant Measurements N. Baboi, DESY, Hamburg EuCARD WP 10: SRF, Annual Review Meeting Cockcroft Institute, Apr. 8, 2010

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Contents Overview Object: 3 rd harmonic SC cavities built in module ACC39 for FLASH Task: minimize wakefields and build HOM-BPMs Work made so far Previous work on 1.3 GHz cavities Spectrum measurements on ACC39 etc Resources Costs and man power Future plans

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Object: 3.9 GHz cavities TESLA cavity (1.3 GHz) 3 rd harmonic cavity (3.9 GHz) photo courtesy E. Vogel & DESY

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM The FLASH Facility at DESY user facility of VUV SASE-FEL radiation test facility: for the XFEL and the ILC drawing courtesy E. Vogel ACC39

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM 3.9 GHz Cryo-Modules TESLA cryo-module (ACC1) 8 x 9-cell 1.3 GHz cavities ACC39 cryo-module 4 x 9-cell 3.9 GHz cavities photo & drawing courtesy E. Vogel & FNAL

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Role of 3.9 GHz cavities Bunch compression bunch accelerated off-crest in ACC1 slow head of bunch takes longer path through magnetic chicane (aka bunch compressor) than fast tail  shorter bunch length Problem non-linearity of RF fields in 1.3 GHz cavities Solution linearize RF fields with 3 rd harmonics cavities

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Bunch compression bunch accelerated off-crest in ACC1 slow head of bunch takes longer path through magnetic chicane (aka bunch compressor) than fast tail  shorter bunch length Problem non-linearity of RF fields in 1.3 GHz cavities Solution linearize RF fields with 3 rd harmonics cavities Role of 3.9 GHz cavities ACC1 ACC39 bunch compr. e-e-

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Idea Issue: wakefields much stronger in 3.9 than in 1.3 GHz cavities Idea use HOMs (Higher Order Modes) − to reduce wakefields by beam alignment − for beam diagnostics  HOM-BPMs (HOM Beam Position Monitors) Note: can also be used for measuring beam charge, phase etc.

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM HOM-couplers (pick-ups) Task of Sub-Task Task: develop, build, test electronics for 3.9 GHz cavities interpret signals and integrate in control system measure cavity alignment HOM-couplers one at each cavity end enable monitoring the HOMs excited by beam drawing for TESLA cavity (similar for 3.9 GHz cavity)

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Previous work: HOM-BPMs at the TESLA Cavities in FLASH HOM-BPMs at 1.3GHz cav. use dipole mode at 1.7 GHz installed in 5 accelerating modules (40 cavities) calibration: with SVD technique −problem: unstable in time Beam alignment in modules routinely used in FLASH Other studies cavity alignment in cryo-module beam phase measurement with monopole modes at ~2.4GHz XFEL: plan to install in some 1.3 GHz and in all 3.9 GHz cavities

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Work made so far for this sub-task Spectra measurements at CMTB (Cryo-Module Test Bench) Sep. – Oct together with other sub-tasks and Fermilab first measurements in cold cryo-module previously: measurements in individual cold cavities at Fermilab

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM ACC39 in CMTB Manchester University/ Cockcroft Institute Rostock University Fermilab DESY courtesy E. Vogel

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Spectra Measured in CMTB data courtesy T. Khabibouline

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Spectra Measured in CMTB: Fundamental Monopole Band accelerating (actually decelerating) mode

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Spectra Measured in CMTB: Dipole (and Other) Band For comparison: dipole band in TESLA cavity

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM 3.9 GHz vs 1.3 GHz Cavities Higher fundamental frequency  higher mode density than in TESLA cavities (see prev. single cavity spectra) Larger beam pipe diameter  low cut-off frequency (~4.2 GHz)  most HOMs propagate in all cavities TESLA cavity: −first 2 dipole bands are below beam pipe cut-off

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Comparison to Single Cavity Fermilab (same plot with various freq. range) data courtesy T. Khabibouline

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Other work Prepare measurements at FLASH prepare hardware and software synchronization of data taking Documentation Previous work made at Fermilab Information about cavities, power coupler, HOM couplers (two types), rotation angles etc. −not trivial to find exact information about cavities designed and built elsewhere...

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Resources Direct costs Electronic components: real-time spectrum analyzer ~80k€ → DESY Travel:410 € → EuCARD Other costs:85 € → EuCARD Man power DESY: P. Zhang (PhD student, full time), N. Baboi, B. Lorbeer Rostock University: H.-W. Glock, T. Flisgen University of Manchester / Cockcroft Institute: I. Shinton, R. Jones Collaboration with Fermilab −Work made by Fermilab −Beam studies and possibly electronics design

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Future Plans FLASH is about to start commissioning after shutdown first beam through module ACC39 Measure spectra at FLASH (w and w/o beam) next few months participate in accelerator commissioning −alignment of beam in ACC39 → reduce wakefield effects parasitic studies Analyze spectra studies from other two sub-tasks essential for understanding Design and build electronics this and next year Beam studies understand mode behavior, compare modes etc. time depends on FLASH overall schedule

N. Baboi, DESY EuCARD WP 10 SRF Annual Review, 8 Apr Sub-task HOM-BPM Summary 3.9 GHz cavities installed at FLASH (and XFEL) monitoring essential due to strong wakefields Spectra measured so far and planned to be measured in the next few months initial data analysis comparisons with single cavity data Future plans some parasitic measurements expected to be made in the next few months design electronics detailed beam studies depend on FLASH schedule