Beam Instrumentation for Orbit Stability

I. Pinayev

Complement of Storage Ring Diagnostics/Beam Instrumentation

Monitor Quantity Function4-button pick-ups 226 Beam position, dispersion, response matrix,

turn-by-turn dynamicsStripline pick-up 1 Longitudinal and transverse frequency

componentsTune monitor 1 Betatron tunes measurement, impedanceLoss monitors 10 Beam losses monitoring Fluorescent flags 4 Position and profile of injected beam Transverse feedback 2 Suppress beam instabilitiesStreak-camera 1 Bunch length measurementDCCT 2 Beam current measurementFCT 2 Filling pattern monitoringBeam scrapers 4 Machine studies (beam size, energy aperture),

haloFireWire camera 1 Transverse beam characteristicsEmittance monitor 1 Transverse beam sizesUndulator radiation 1 Energy spread, beam divergence, momentum

compaction factorPinhole camera 1 Horizontal emittance (using undulator radiation)Counter 1 RF frequency monitorPhoton BPMs 10 Photon beam angle and position

RF BPMs

• Design similar to one adopted at RHIC• 5-mm radius buttons• Stray capacitance 1-4 pF

(2π×500MHz×50Ω×3pF≈0.5)• Signal level -1.1 dBm for 500 mA at 500

MHz• Dependence of vacuum chamber

shape/size and button capacitance (and hence sensitivity) on fill pattern and circulating current can be significant

• Switch to strip-line geometry?• Electronics front-end overload• Monitors of the vacuum chamber position

can be affected by the EM noise• Other factors?

Processing Units

• Utilized at Elettra, NSSRC, Diamond, Soleil, PLS • Fast acquisition 10 kHz sampling rate, 2 kHz BW• Slow acquisition: 10 Hz sampling rate, ~4 Hz BW• 32 bit data• RMS uncertainty (for 10 mm scale in 1 kHz BW) -90.5dB

→0.3µm @ Pin = -20 dBm • 8-hour stability (ΔT=±1°C) -80dB→1µm • Temperature drift (T=10–35°C) -94dB/°C → 0.2µm/°C • MTBF ≥ 100,000 hours• For 270 units failure rate will be one unit in 17 days

• Can filtering improve RMS uncertainty to required level?

• Spares?• In-situ calibrators?• Other receivers?

Photon Beam Position Monitors

• Will provide information on photon beam position and angle (to account for errors in the wiggler field)

• Use of photon BPMs will allow sub-microradian pointing stability

• Contamination with dipole radiation can be of less concern due to reduced magnetic field in the bending magnet

• Can be used for orbit feedback and/or control of users optics

• 2D translation stages will precisely locate the photon BPM

• Should withstand high power density• Response time?• Noise susceptibility?• Other sensors: CVD diamond photoresistors,

bolometers, etc?

Photon Beam Intensities for Dipole and Undulator

• E=3 GeV• ρ=25 m• B= 0.4 T

• εc=2.4 keV

• λc=0.52 nm• ψ=1/γ=0.17 mrad

• Ptot=143 kW (@ 0.5 A)

• U19: λU=19 mm

• K=1

• LU=3 m (NU=158)

• λU=0.4 nm

• εU=3.1 keV

• σr′≈(λU/LU)½=11.5 μrad

• Ptot=2.7 kW (@ 0.5 A)

213.0mrad

kW

d

dP

Low dipole field – do we need Decker distortion?

220mrad

MW

d

dP

Back-Fluorescent Hard X-ray BPMs

• Hard X-rays hit Cu target which re-radiates 8.05 keV photons

• Insensitive to dipole radiation• High level signals• 12 keV photons are presently

tested• A lot of R&D still required• Can we extend range down to

softer X-rays?

Presented by G. Decker at BIW’06

Diagnostics with Synchrotron Radiation

• FireWire Camera eliminates need for frame-grabber– Exposure from 20 μs– Trigger jitter ±10 ns– 120 fps (full resolution)– 463 fps (100×100 ROI)

• Position sensitive diodes provide signal proportional to the displacement of center of gravity– 0.3 μs response time– 0.6 μ position sensitivity– Can be used to monitor beam

motion in the dipole

Auxiliary Equipment

• Two DCCT for monitoring of circulating current• Two fast current transformer for monitoring filling

pattern• What other beam parameters we need to

monitor to insure high stability?

Fast Orbit Stabilization System (FOSS)

• BW ultimately limited by corrector magnets (<500Hz)

• Basic building blocks– Libera Electron– Fast private communication

system– Computational engines– PS interfaces and corrector

magnets• What is optimal configuration?

– reliability– cost– flexibility

Characteristics for FOSS Components

• Available data: amplitudes, positions, status• FPGA communication module is user specific• Synchronization to external clock• Fast network

– 270 Liberas * 72 bytes * 10 kHz = 194 MB/s

• Latency– 1Gb/s: 40 μs on one cable– Processing latency 350 usec

• Reliability of GB switch is a must• Different computational engines are available

Following Tomaž Karčnik from I-Tech