Stabilization of Focus at ATF2
David Urner
University of Oxford
ATF2 Meeting May 2006 2
StaFF→MonALiSA
Dr. David Urner Dr. Paul Cole Dr. Armin Reichold
Stephanie Yang(mechanical engineering)
Tony Handford(workshop)
Roy Wastie(electrical engineering)
StaFF Stabilization of theFinal Focus
→
MonALiSAMonitoring of Alignment
and Stabilization with high Accuracy
ATF2 Meeting May 2006 3
Interferometric Monitoring
• Develop 2 instruments:– Distance meter with nm resolution over 10m– Straightness monitor with nm resolution over
10m
Michelson mode: 1nm resolution relative distances
FSI mode: 1m resolution absolute distances
Distance meter:0.3 0.4 0.5
0
5
10
15
Am
plitu
de /
Arb
uni
ts
Length / m
ATF2 Meeting May 2006 4
= 7m
FSI Performance
=4m
• Using 5m conventional Michelson interferometer in air as reference.
• Running at small tuning speed• Tuning over small fraction of tuning range
ATF2 Meeting May 2006 5
Attaching Vacuum System Force-Free
Here attach vacuum tube for interferometerAttached to BPM.
Holds retro reflector.
Firmconnection
Strain Gauge• Needs bellow to allow motion of BPM– Vacuum causes a force
order of 100N!
• Develop small force vacuum mount using double bellow system.
• Allows small motion (~1 mm) of BPM-system
• Test stand to measure remaining (perpendicular) force on BPM frame. -1mm-3mm 1mm 3mm
1N
2N
-1N
0N
-2N
-3N
-3N
Force exerted on carbon frame (BPM)±1mm: < 0.5N/mm±3mm: < 0.8N/mm
Force exerted by perpendicular motion
ATF2 Meeting May 2006 6
A Straightness Monitor Made from Distance Meters
• Red lines: Distance meter. • Multilateration measure 6D coord. of A with respect to B.
A
B
ATF2 Meeting May 2006 7
A Straightness Monitor Made from Distance Meters
• Information related via central triangle
Floor node
A
B
Ceiling node 1Ceiling node 1
~2.5m
ATF2 Meeting May 2006 8
Compact Straightness Monitor
• Too big in perpendicular direction!• Develop compact version
– Need 2 devices to separate rotation from vertical translation. + length measurement
– Next step: Test different ideas
Pointsource
Retro
Mirror
Collimator
Fibre launchand readout
Long arm
Use reflection from fibreend as short arm
Distancemeter
ATF2 Meeting May 2006 9
Compact Straightness Monitor
• Too big in perpendicular direction!• Develop compact version
– Test different ideas
• Aspect ratio A/B is relevant• A 5m: B somewhere at 20cm – 50cm for 1nm
resolutions
BA
ATF2 Meeting May 2006 10
ATF2: Stabilization
• General strategy:– Use one active feedback system only, which can combine inputs
from several measurements• Difficult if active feedback system compete!
– Test of a system with several input measurements using StaFF setup that will be installed at ATF.
– Big question is where to locate the actuators to get best response
• Should consider a system moving beam with kicker rather than move Shintake monitor.– This is a feed forward system, which is easier to control than an
active feedback system.– Additional cost?– Do we introduce jitter by such a kicker, and how much?
ATF2 Meeting May 2006 11
Placement of MonALiSA monitoring system at ATF2
• Easiest if we have direct line of sight between FF quadrupole and Shintake monitor.– Which is the crucial element of Shintake monitor do
we have to monitor. • Are there several parts to monitor • Can we get optical access to the crucial element(s)
• We need room (30-50cm) above either the Shintake monitor or above the FF magnet– Probably easier to get above magnet.
ATF2 Meeting May 2006 12
Funding and Timeline
• We are currently preparing bids to get funding in the framework of LC-ABD – 1 postdoc 2007-2010– ½ DAQ expert– Resources in electronics engineering and
construction, mechanical design and workshop– Funds to develop prototype and final system for ATF2
• We expect to have a first system ready early 2009.– Any reason why we urgently should be ready earlier?
ATF2 Meeting May 2006 13
ATF2 Meeting May 2006 14
Distance meter simulation
• Simulation done with Zemax
• Use non-sequential mode– Take into account
polarisation → correct interference pattern
– Allows stray light analysis
• Allow analysis of chromatic aberrations
ATF2 Meeting May 2006 15
Simulated Interference Patters
ATF2 Meeting May 2006 16
Piezzo Driven Monitor
Detector
Detector
PZT
MovingMirror
Mirror
Mirror
Mirror
Splitter
Splitter
Splitter
Tuning laser
SinglePointmeasurement
980 1000 1020 1040 1060 1080
-4
-3
-2
-1
0
1
2
3
4
Phase stepping cycle
Laser is tuning continuously
Pha
se
/rad
ian
s
(Derive phases modulo 2from intensity data)
Moving mirror: Measure Intensity pattern
ATF2 Meeting May 2006 17
3–D mechanical model, detector side removed for clarity
ATF2 Meeting May 2006 180 10 20 30 40
-5
0
5
10
15
0 10 20 30 40-2
0
2
Te
mp
era
ture
ch
an
ge
/ m
K
Time / s
Re
f V
/ m
V
Time / s
Reference channels Thermometer channels
First Temperature Measurements