Beam position monitors

LCABD Plenary meetingBristol, 24th March 2009

A. Aryshev, S. T. Boogert, G. Boorman, S. Molloy, N. Joshi

JAI at Royal HollowayA. Lyapin

University College London

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Outline•Commissioning ATF2 beam line (corner

stone of next 2 years work)

• Software systems

• 40+ high performance BPMs

• S-Band BPM electronics

• Just completed electronics installation

• Commissioning in April 2009

• Diamond BPM work

• Low cost high precision BPM for light sources

• CLIC drive beam RF diagnostics

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Spectrometry•Key knowledge from spectrometer tests

• Stability of BPM systems most important

• ESA test beam problems with BPM stability on time scales ~12 hours

• Beam stabilisation at ATF2 requires 50 nm for time scales ~ 1 operation week, 120 hours

• ATF2 design goals same for energy spectrometer

•Environmental monitoring

• Thermal

• Low level RF systems (locking, calibration signals)

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ATF2 beam line (BPM centric)Last dipole

of EXT

FF

S-band system

C-band system

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Example ATF2 Quad/BPM/Mover package

•C-band cavity integrated into quad

•Calibration by moving quad and BPM

Mixer electronics

Quad suppor

t

Quad

Quad mover

C-band BPM

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ATF2 beam line commissioning

•Challenging task

• 37 dipole cavities

• 33 C-band (small aperture, normal beam transport applications)

• Based on experience and designs of LCABD

• 4 S-band (large aperture, FF large beta function)

• Closely linked to energy spectrometer design

• 5 reference cavities

• 4 C-band

• 1 S-band

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BPM processing software•Real time processing of mixed cavity output

signals

•Convert amplitude and phase of signal to position for the ATF2 control system

• Required for

• Orbit control (Beam based alignment etc)

• Dispersion and coupling correction

• Beam orbit for other experiments (Interaction point beam size monitor, laser-wire)

•EPICS based soft input output (IOC) controller system

•Simple to use for large, novice user group

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BPM processing algorithms•Mix RF with local oscillator

• Always obtain IF at ~20 MHz

• Filter 2w frequency (gaussian filter)

• Identify point to measure amplitude and phase

• Calculate In-phase and quadrature components

•20 MHz IF is further mixed digitally to baseband

• 88 Channels of 120 MHz digitizers

• Digital mixing, filtering and calibration

• Transmit to ATF2 control system

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Software design

•Complete robust EPICS design

• No crashes since December 2008

• Multiple user control and diagnostics system

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BPM control and readout software

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Tuning cavity readout

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Tuning cavity readout

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Calibration of BPMs•Typical calibration

over +- 100 micron

•Move BPM/Quad package (also kick beam)

• Clear IQ rotation

• Position dependence

•Currently signals have 20 dB attenuation

• Jitter dominated by beam jitter

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Trigger/phase problems•Low level RF

and trigger distribution at ATF quite obfuscated

• race conditions

• phase drifts

•Result large position shifts

• Must resolve in order to have stable system

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Dynamic range example•Example

large distance calibration

• +-1mm

• IQ rotation clear

• BPM response very linear

• Some x-y coupling at large x

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S-band system•S-band electronics complete (LCABD

responsibility)

• Reference cavity (being delivered next week)

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Future work •Developing three major strands to post-

LCABD work

• RF diagnostics for future light sources

• Beam position monitors (beam alignment w.r.t. undulators)

• Installation at Diamond light source (3 C-band cavities + 1 reference)

• CLIC drive beam

• BPMs and RF phase detection

• Industrialised BPM systems

• Collaboration developing with FMB-Oxford

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Diamond BPM system•Use already proven technology

• Turn key operation is being developed at KEK

• Develop BPM for FEL based light sources. C-band system

>>>

Booster-Diamond transfer line

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Future BPM work (AL, TIPP09 conf)

•Thinking about future design

• Continue lineage of current designs (single slot, is example)

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Summary•ATF2 seen significant progress

• Complete installation of final focus system

• Calibration and operation of C-band system

• Near turn key RF cavity BPM processing system

• Complete software implementation

•Started new projects on advanced BPM systems

• Is LCABD correct avenue to discuss general continuation of diagnostics work

•Energy spectrometry developed into package for BDS BPMs as well as specialist systems