Undulator BPM Diagnostics R&D Plans

1. Breakout Session SC3 – Undulator Undulator BPM Diagnostics R&D Plans P. Krejcik

2. Requirements • Single-pulse readback at up to 120 Hz • Resolution of 1 mm or better • Over a bunch charge range of 0.1 to 1 nC Cavity BPM chosen over striplines • Inherently better resolution • Less prone to systematic offsets

3. Cavity Beam Position Monitors • Frequency choice • Cavity Iris should be masked from SR • Vacuum chamber dimensions for the undulator are now chosen • 10 mm aperture • is larger than 8 mm diameter inside quadrupole • X-band chosen to maximize resolution and minimize length. • Issues • BPM location with respect to quadrupoles • Resolution in combination with beam-based alignment with EM quads • Signal processing 5 mm 10 mm

4. X-Band Cavity BPM Zenghai Li feedthrough Ri = 5 mm 18 mm • Resolution exceeds LCLS requirements • Sensitivity of 1.6 mV/nC/mm • 20 nm demonstrated at KEK/SLAC experiments – S. Smith et al • Systematic offsets are of greater concern

5. Sources of offset in the cavity BPM lid body • Calculate effects from errors in • Concentricity of 3 surfaces • Coupler offsets and tilts Concentric surfaces Parallel surfaces 5 um machining tolerances achievable - C. Pearson

6. Cavity Electric Center Sensitivity

7. Tolerance on Coupling Slots

8. Undulator Cavity BPM locations with respect to quadrupoles • Quadrupole and BPM mounted adjacent on the undulator support cradle to ensure 1 um beam based alignment resolution • Also need to keep the distance between the electron beam and the undulator segment axis to less than 70 microns rms • Considering beam position measurement options at downstream end as well QuadBPM assemblies Optional wire monitors, Train-linked undulator sections – see H.-D. Nuhn presentation

9. Cavity BPM Signal Processing • X - Y cavity at each undulator short gap plus 1 phase reference cavity per girder at each long gap • High-frequency x-band signal is attenuated in a short distance • Incorporate a local mixer to IF at the cavity • Only a simple passive device in the tunnel • Temperature stable • Relatively low radiation loss environment • Distribution of reference x-band oscillator signal in the tunnel • Choose intermediate frequency to match into the RF front end used for stripline

10. Cavity BPM Signal Processing Upstairs RF receiver RF in IF IF Amp IF ~50 MHz BP filter Dw~10 MHz ~300 MHz BP filter Dw~5 MHz Common Local Oscillator RF Amp • In-tunnel X-band heterodyne receiver Digital processing ADC 14 bit e.g Echotek Control system IF 300 MHz Local Oscillator 11.1 GHz Calibration Pulse 11.42 GHz 119 MHz Clock 24th harmonic

11. Digital BPM Signal Processing • Use same RF front end for stripline BPMs and output from first mixer for cavity BPMs • Initial desire to use a commercially produced BPM processing module (Libera) • We obtained a try out Libera module • Integration into the control system not proceeding fast enough, e.g. could not access raw data in the module. • Present design solution • Commercial VME 8 channel digitizer • RF front end from discrete, commercial components • See T. Straumann presentation

12. Cavity BPM Prototyping and Test Plan • Components for prototyping and testing can be divided into: • Cavities • Feed-throughs and waveguide • RF receiver electronics and reference oscillator • Digitizer electronics • EPICS integration and application programs • Bench tests • Beam tests

13. Cavity BPM Prototyping and Test Plan • Cavities • Fabrication of 4 X-band BPM cavities and 2 reference cavities in SLAC’s Klystron Engineering Department • Use their experience in machining and brazing X-band structures for linear collider research • Brazing and cold RF testing of waveguide to coaxial feed-through assembly

14. Cavity BPM Prototyping and Test Plan • RF receiver electronics and reference oscillator • Prototype heterodyne receiver assembled from connectorized parts using standard filters, mixers and amplifiers • Similar to assembly for SLAC/KEK cavity BPM tests • Reference oscillator signal derived from SLAC LLRF distribution • Opportunity to test other receivers: AM/PM

15. Cavity BPM Prototyping and Test Plan • Digitizer electronics • We have acquired an Echotek 14-bit 125 MHz 8-channel VME card • Clocked at the 119 MHz SLAC reference harmonic • Over-clocked version of current version of this module • Presently bench testing the card with a low-noise oscillator

16. Cavity BPM Prototyping and Test Plan • Bench tests • RF cold testing will evaluate feed-through and cavity combination • Verify frequency, Q, coupling • Antennae tests on a precision x-y stage to measure the electrical center with respect to the mechanical center

17. Cavity BPM Prototyping and Test Plan • Beam tests • On the SLAC FFTB line • Mount 3 cavities plus a reference cavity on a ~1 m long rigid girder • Check cavity+electronics calibration procedure by moving beam ±1 mm • Correlate the position readings from all 3 cavities for small position changes (beam jitter) and determine system resolution and offsets

18. Draft R&D Schedule

19. Draft R&D Schedule