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

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

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

X-Band Cavity BPM Resolution exceeds LCLS requirements 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

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

Cavity Electric Center Sensitivity

Tolerance on Coupling Slots

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 Quad BPM assemblies Optional wire monitors, Train-linked undulator sections – see H.-D. Nuhn presentation

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

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

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

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

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

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

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

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

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

Draft R&D Schedule

Draft R&D Schedule