StaFF: Motion Stabilization with Nano-Meter Precision

• Proposed experiment conducted within framework of StaFF (Stabilization of Final Focus for ILC).

• Funded by EuroTEV.• Development of active feedback systems to monitor

and stabilize for example final focus quadrupoles or beam position monitors in the energy chicane. – Develop laser interferometric methods to monitor

relative position of two objects at • Nanometer scale resolution.• For separations of order 10m.• Frequency range 100Hz – 0.01 Hz

– Develop and implement algorithms for active stabilization.

• StaFF at KEK: Stabilize Nano-BPM systems relative to each other.

KEK: Integrated

spectrum of vertical motion

Why StaFF at KEK

• Benefits for StaFF– Test of distance meters in accelerator environment.– Measurement of 6-D coordinates trough intermediate object (triangle),

similar method is needed to project out position and orientation of accelerator component at ILC.

– Related objects are BPMs: Allows cross check of achieved resolutions.• Benefits for nano-BPM

– Unfold nano-BPM resolution and broadening caused by mechanical relative motion between the two BPM setups.

– Each setup uses 3 BPM’s also establishing beam angles. Two sets can in principle measure relative displacements

• Each beam bunch differs in position and angle → over-constrained system needed.

• 2-platform stability important for energy chicane– BPMs measure beam position, proposed experiment measure relative

position motion.

Measurement of Relative Motion

• Typical situation:

– Need straightness monitor to measure relative motion.

(Leave for development later).

– Need distance meter to project out. (Develop first).

Quadrupole Quadrupole~10m

Reference Structure Reference

Structure

Vertical & angular position measurement of ref. structure

Straightness monitor to measure relative vertical movement between ref. structures

A Straightness Monitor Made from Distance Meters

• Accuracy few tens of nanometer for vertical displacement between KEK and SLAC BPM.

KEK BPM

SLAC BPM

Floor node

A Straightness Monitor Made from Distance Meters

• Project 6-D coordinates from one BPM via middle triangle to the other BPM.

KEK BPM

SLAC BPM

Floor node

A Straightness Monitor Made from Distance Meters

KEK BPM

SLAC BPM

Floor node

• Red lines: Michelson interferometer displacement meter nm resolution.• Multilateration requires absolute distance meter with m resolution: FSI.• Both systems with same setup!

Spider web Design with Opto-Geometrical Simulation: Simulgeo

• Resolution of distancemeter: 1nm

• Mount precision of distancemeter: 1nm

• Angle precision of distancemeter holder: 10 rad.

SLAC BPM: referenceKEK BPM variable (6D):

Position: x:32 y:19 z:2 nmAngle: x:0.01 y:0.01 z:0.1 rad

~1m absolute distance resolution needed to determine constants required to solve geometry.

Stabilization• Actively stabilize setup using input from interferometers:

– Both Nano-BPM setups are mounted on actuators.– Use movers on SLAC setup for coarse angle adjustment.– Use piezo movers on KEK setup for small adjustments.

• We measure the relative motion of the two reference frames of the SLAC and KEK BPM’s– Closed loop feedback system relates the KEK reference bar to the KEK

nano-BPM’s.– Closed loop feedback system relates the SLAC carbon fibre frame to

the SLAC nano-BPM’s.– Overall feedback loop has to integrate 3 measurements!

• 100-0.01Hz (or preferably even slower) is unusual frequency range for feedback system and might require some fundamental study.

• Collaboration with EuroTEV partners developing closed loop feedback circuits expected.