Luminosity Optimisation Overview
Philip Burrows
(QMUL)
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•
•
•
•
•
Introduction
Tools
Active component stabilisation
Beam-based feedback
Beam parameter diagnostics
Summary
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
1. Introduction
Relative component displacement ->
emittance blowup (linac, BDS)
mis-steering (FF), esp. final quads
IP
• ‘static’ effects:
misalignments …
• diffusive effects:
settling, hydrology …
• ‘seismic’ motion:
earthquakes, ocean waves …
• cultural/facilities noise:
traffic, pumps, water flow…
• slow drifts:
temperature, pressure …
Philip Burrows
Luminosity
vs. beam offset
50nm: ~ 80% lost
MDI Workshop, SLAC 6-8/01/05
Available solutions
• Optimise site choice + civil/mech. engineering:
minimise (relative) component motion
• Active component stabilisation:
compensate via (inertial/optical) feedback
• Beam-based feedback/scans:
move beam(s) position/angle via feedback
• Integrated system:
some/all of the above working in harmony
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Issues for machine-detector Interface
• Stabilisation of final doublets
• Intra-train and pulse-pulse beam feedback
• Beam parameter diagnostics
Terse summary/overview: hopefully raise issues for
discussion
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
2. Tools
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•
•
•
•
Ground motion data/models
Facilities noise models
Linac -> IP beam transport
PLACET+MERLIN
DIMAD+LIAR
integrated Matlab environment: MatMERLIN, MatLIAR
Beam-beam interaction: luminosity, backgrounds
CAIN
GUINEAPIG
Materials/detector simulations: shower tracking
GEANT3 -> GEANT4
EGS
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Site studies + ground motion
CDR/TDR: more studies to bound problem?
(Seryi)
studies of specific sites?
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Facilities Noise
Not difficult
to find noisy
environments!
Example:
noise at SLD
TDR: need to model
for real engineered
MDI design?
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Engineering approach (Asiri)
Select a Location
(Representative Site)
Good Geology and Quiet
Geotechnical Studies
(Soil/Rock
Classification)
Select and Locate
Near-Field
(Cryo/compressors, pumps)
Far-Field Excitation
(Ambient Ground Motion
Measurement)
Attenuation
Characteristics of
Soil/Rock
Estimate Near-Field
Excitation
(At Their Footings)
Estimate Vibration @
Invert of Beam Housing
( Response to Near and
Far Fields Sources)
Done O(1) for few sites
Revisit for cold ILC
Reestablish for cold ILC
Adopt as a Concept
Design Requirement
Philip Burrows
Yes
Acceptanc
e Criteria
No
MDI Workshop, SLAC 6-8/01/05
2. Tools
•
•
•
•
•
Ground motion data/models
Facilities noise models
Linac -> IP beam transport
PLACET+MERLIN
DIMAD+LIAR
integrated Matlab environment: MatMERLIN, MatLIAR
Beam-beam interaction: luminosity, backgrounds
CAIN
GUINEAPIG
Materials/detector simulations: shower tracking
GEANT3 -> GEANT4
EGS
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Codes Database Page
http://hepwww.ph.qmul.ac.uk/~white/accodes/codedeb.htm
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Example: GUINEA PIG Page
http://hepwww.ph.qmul.ac.uk/~white/accodes/guinea.htm
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
QMUL High Throughput Cluster (HTC)
•
174 x 2 GHz cpus
•
40 TB attached storage
•
GBit ethernet
•
Peak capacity:
50k cpu-hours/week
•
400k cpu-hours used for
LC simulations (9 mos.)
•
Another 2-300 ‘boxes’
by Spring 06
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Linac to IP Simulation Results Repository
http://hepwww.ph.qmul.ac.uk/lcdata/
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Output files
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
3. Final quadrupole stabilisation
IP
Passive:
‘cushioned’ magnet supports
support tube connecting opposite sides of IR
Active:
inertial stabilisation
optical anchoring schemes
NB: details linked to final doublet technology
(Parker et al), crossing angle …
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Final doublet stabilisation: inertial
(SLAC, CERN/CLIC …)
SLAC: mockup of final quad girder:
Non-magnetic inertial sensor
CERN: stabilisation of CLIC quad:
Sub-nm achieved > few Hz
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Final doublet stabilisation: optical
(UBC, SLAC, CERN, KEK …)
Optical anchor concept
UBC prototype
10kg mass:
90 -> 5 nm (ground)
4.5 -> 1.5 nm (isolated)
Optical anchor system in
development:
NanoBPM project (ATF)
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
‘Nano’ Project at KEK ATF
System test: aim for optical-anchor stabilisation of pair of
BPM triplets at nm level, with intra-train beam FB/FF
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Possible ATF optical anchor scheme (Oxford):
simulations in progress
Philip Burrows
Urner
MDI Workshop, SLAC 6-8/01/05
4. Beam-based feedback
• ‘slow’ upstream orbit feedbacks
• IP pulse-pulse feedback (5 Hz)
• IP intra-train (bunch-bunch) feedback: 3 MHz
Position and angle corrections:
most critical in vertical dimension
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Beam-beam deflection
GUINEAPIG simulations (White)
Deflection curve depends on: Q, sigma-x, sigma-y, sigma-z …
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Intra-train Beam-based Feedback Concept
(same hardware for pulse-pulse FB)
Intra-train beam feedback
is last line of defence
against relative beam
misalignment
Key components:
Beam position monitor
(BPM)
Signal processor
Fast driver amplifier
E.M. kicker
Fast FB circuit
TESLA TDR: principal IR
beam-misalignment correction
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Zero-degree crossing angle (TESLA TDR)
FB BPM
Upstream
kicker(s)
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
‘Large’ crossing angle (NLC)
kicker
Philip Burrows
FB BPM
MDI Workshop, SLAC 6-8/01/05
Angle feedback: upstream in BDS
30
y (m)
25
20
~450 m
BPM 2
~158 m
15
BPM 1
10
Kicker
R
5
300
400
500
600
700
800
900
1000
Distance from IP (m)
Place kicker at point with IP phase.
BPM at phase 90 degree downstream from kicker.
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Angle feedback: locally near IP – crab cavity
(IR with crossing angle)
Fast phase adjust
using a second klystron
and fast phase
difference.
Needs
careful
integration
into MDI
design!
Diagram by J. Frisch
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
IP Feedback model
Linearise Beam-Beam
Kick Curve Response
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Feedback Algorithm
•Proportional-Integral (PI) Controller:
k 1
uPI (k )  uP (k )  uI (k )  K Pe(k )  K I  e( j )
j 0
•Subtract uPI(k-1) to get recursive algorithm:
uPI (k )  uPI (k  1)  K P  e(k )  e(k  1)   K I e(k  1)
•2 free parameters: gains KP and KI :
•KP provides fast response to error signal.
•KI cancels steady-state error.
•Iterate simulation to obtain optimum parameters to give fast
correction and maintain collisions at 0.1y level.
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Illustration of Intra-train feedback performance
(White/QMUL) (TESLA TDR)
3
x 10
34
Luminosity / cm-2s-1
OPTIMAL
LUMINOSITY
y angle scan
2
y position scan:
optimise signal
in pair monitor (+4%)
1
starting point:
need to add
y position FB:
restore collisions
within 100 bunches
1 seed:
post-BBA
Excellent
0
+ GM
0
100
200
further
‘reality’ …
300
Bunch #
400
500
600
+ wakes
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Intra-train beam feedback prototypes and
beam tests (QMUL, Oxford, DL, SLAC, KEK …)
FONT1 and FONT2 prototype intra-train FB
systems tested with beam at SLAC/NLCTA.
FONT3/FEATHER
beam tests at KEK/ATF
summer 2005:
micron-level stability
of 1.3 GeV ATF beam
(model of nm- level
stability of ILC beam)
Full delay-loop feedback on:
Cold ILC:
robustness,
Latency 53ns
Philip Burrows
algorithmic control
MDI Workshop, SLAC 6-8/01/05
Continuing feedback hardware development
Short-term: FONT3 at ATF: aim for micron-level stability of 1 GeV beam
Long-term:
demonstrate robust intra-train FB system for ILC, based on digital
signal processing, and ideally test with beam:
requires long bunchtrain with 337 ns bunch spacing
2005-6: 3 (or 4) bunches x 100 ns at ATF would allow first tests:
stabilise last bunch at 100 nm level as part of Nano project
also feed-forward studies ring -> extraction line?
> 2006: 20 bunches x 337ns at ATF/ATF2 would allow FB algorithm
development
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Backgrounds (QMUL)
Feedback system incorporated into GEANT IR model
Need to ensure: FB system performance OK,
FB material does not cause additional backgrounds in detector.
Considering experimental background tests at SLAC/ESA
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Pulse-pulse IP beam deflection feedback
(Hendricksen)
Input GM models
Linac->IP tracking
A, B, C:
+ 5 Hz FB (TESLA)
<Luminosity>
Need for
intra-train FB
Need to integrate simulation of FBs:
upstream slow, active stabilisation, 5Hz, intra-train …
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
SLC optimised ‘dither’ feedback at IP
(Phinney)
Deflection scans: 5 knobs/beam : x/y waist, x/y dispersion, coupling
Old method: scan of
New method: optimise lumi
beam size vs. single knob:
w. dither FB on each knob
Poor resolution, lumi loss
Philip Burrows
Increased lumi, eased ops.
MDI Workshop, SLAC 6-8/01/05
5. IP beam parameter diagnostics
Sigma x
Sigma y
Sigma z
What do you want to know?!
Sigma x'
Sigma y'
x offset
y offset
x' offset
y' offset
x-waist shift
y-waist shift
Bunch rotation
N particles/bunch
Banana shape
……
Luminosity
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Available diagnostics
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Transverse emittance: sigma x, sigma y, sigma x’, sigma y’
laserwire etc. beam size monitors (probably upstream)
Bunch length: sigma z
electro-optic, ODR, Smith-Purcell etc. monitors
Bunch charge:
toroids
Beam position/angle offsets:
beam-beam deflections
Luminosity
Pair/beamstrahlung monitors
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Beam diagnostics possibilities in IR limited
Lumi mon.
(Bhabhas)
Forward
BSR mon.
IP BPM (beam
deflections)
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Beam parameters from beamstrahlung?
(Stahl, White)
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Observables/Beam Params List
•Sigma x
E_tot
r moment
1/r moment
Thrust Direction
Thrust Value
Angular Spread
E_out/E_in
L-R Asymmetry
T-B Asymmetry
Diagonal Asymmetry
N/E_tot
Forward + backward
calorimeters
Philip Burrows
•Sigma y
•Sigma z
•Sigma x'
•Sigma y'
Each variable where
appropriate exists for the
mean of e- + e+ bunch and
difference in obs/par
between them.
•E
•E spread
•x Offset
•x' offset
•y offset
•y'' offset
•x-waist shift
•y-waist shift
• Bunch rotation
• N particles/bunch
• Amount of y+y’ type-1 banana
• Amount of y+y’ type-2 banana
• Amount of y+y’ type-3 banana
MDI Workshop, SLAC 6-8/01/05
Parameter Reconstruction
x  [ x1 , x 2 ,....x n ]'
x *  x Design
f n ( x)  observable n for x vect or
f n ( x * )  observable n for x * design vec tor
1
* ~
f ( x)  f ( x )  ( x  x )' div.[ f ( x )]  ( x  x )' A( x  x * )  ...
2
 2 f
2 f
2 f 
•Compute Taylor matrices through
.


multiple GP runs varying beam
2

x

x

x

x

x
1
2
1
n 
params-> use Grid computing at QM
 21
to do in finite time (have to stick to

f


~
.
.
.
2nd order calculations realistically).


A  x x
•For parameter reconstruction:
 2 1

.
.
. 
Solve x for given f(x) using multi 2.
2
parameter fit. Prob. no unique
 f 
  f
.
.
solution- choice of fit technique
2 
 x n x1
x n 
likely to be important.
n
n
Philip Burrows
*
*
n
*
MDI Workshop, SLAC 6-8/01/05
Single-parameter analysis: sanity check
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Initial results (Gaussian beams) (Stahl)
Seems to be promising; MUCH more study needed …
Philip Burrows
MDI Workshop, SLAC 6-8/01/05
Summary of collision optimisation/MDI issues
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•
•
•
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Active position stabilisation of final quads?
-> properly engineered design incl. laser tubes etc.
(through detector)
IP beam deflection feedback essential: intra-train and 5Hz
-> FB BPM, kicker, cables … need integrating into MDI design
-> understand background environment better
Crab cavity could be used for angle feedback?
-> needs integrating into real MDI design
Fast bunch-by-bunch lumi measurement vital input to FB
-> develop realistic prototypes of fast BSR/pair monitor
BSR/pair monitor offers potential for beam parameter determination
-> more simulation work needed
Need to develop integrated FB + scanning strategy:
-> intra-train + 5 Hz + dither + upstream slow + feedforward …
Philip Burrows
MDI Workshop, SLAC 6-8/01/05