luminosity optimisation overview

Philip Burrows MDI Workshop, SLAC 6-8/01/05

Luminosity Optimisation Overview

Philip Burrows (QMUL)

• Introduction• Tools• Active component stabilisation• Beam-based feedback• Beam parameter diagnostics• Summary


1. Introduction

Relative component displacement -> emittance blowup (linac, BDS) mis-steering (FF), esp. final quads

• ‘static’ effects: misalignments …• diffusive effects: settling, hydrology …• ‘seismic’ motion: earthquakes, ocean waves …• cultural/facilities noise: traffic, pumps, water flow…• slow drifts: temperature, pressure …

IP

Luminosity

vs. beam offset

50nm: ~ 80% lost


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


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


2. Tools

• Ground motion data/models• Facilities noise models • Linac -> IP beam transport

PLACET+MERLINDIMAD+LIARintegrated Matlab environment: MatMERLIN,

MatLIAR• Beam-beam interaction: luminosity, backgrounds

CAINGUINEAPIG

• Materials/detector simulations: shower tracking GEANT3 -> GEANT4

EGS


Site studies + ground motion

CDR/TDR: more studies to bound problem?

studies of specific sites?

(Seryi)


Facilities Noise

Example:

noise at SLD

Not difficult

to find noisy

environments!

TDR: need to model

for real engineered

MDI design?


Engineering approach (Asiri)

Far-Field Excitation(Ambient Ground Motion

Measurement)

Acceptance Criteria

Select a Location(Representative Site)

Good Geology and Quiet

Estimate Near-Field Excitation

(At Their Footings)

Geotechnical Studies(Soil/Rock

Classification)

Attenuation Characteristics of

Soil/Rock

Adopt as a Concept Design Requirement

Estimate Vibration @ Invert of Beam Housing( Response to Near and

Far Fields Sources)

Select and LocateNear-Field

(Cryo/compressors, pumps)

NoYes

Done O(1) for few sites

Revisit for cold ILC

Reestablish for cold ILC


2. Tools

• Ground motion data/models• Facilities noise models • Linac -> IP beam transport

PLACET+MERLINDIMAD+LIARintegrated Matlab environment: MatMERLIN,

MatLIAR• Beam-beam interaction: luminosity, backgrounds

CAINGUINEAPIG

• Materials/detector simulations: shower tracking GEANT3 -> GEANT4

EGS


Codes Database Pagehttp://hepwww.ph.qmul.ac.uk/~white/accodes/codedeb.htm


Example: GUINEA PIG Pagehttp://hepwww.ph.qmul.ac.uk/~white/accodes/guinea.htm


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


Linac to IP Simulation Results Repositoryhttp://hepwww.ph.qmul.ac.uk/lcdata/


Output files


3. Final quadrupole stabilisation

Passive:‘cushioned’ magnet supportssupport tube connecting opposite sides of IR

Active:inertial stabilisationoptical anchoring schemes

NB: details linked to final doublet technology (Parker et al), crossing angle …

IP


Final doublet stabilisation: inertial(SLAC, CERN/CLIC …)

Sub-nm achieved > few Hz

SLAC: mockup of final quad girder: Non-magnetic inertial sensor

CERN: stabilisation of CLIC quad:


Final doublet stabilisation: optical(UBC, SLAC, CERN, KEK …)

UBC prototype 10kg mass:

90 -> 5 nm (ground)

4.5 -> 1.5 nm (isolated)

Optical anchor system in

development:

NanoBPM project (ATF)

Optical anchor concept


‘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


Possible ATF optical anchor scheme (Oxford):simulations in progress

Urner


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


Beam-beam deflection

GUINEAPIG simulations (White)

Deflection curve depends on: Q, sigma-x, sigma-y, sigma-z …


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 circuitTESLA TDR: principal IR

beam-misalignment correction


Zero-degree crossing angle (TESLA TDR)

FB BPM

Upstream

kicker(s)


‘Large’ crossing angle (NLC)

FB BPMkicker


Angle feedback: upstream in BDS

300 400 500 600 700 800 900 1000

5

10

15

20

25

30

BPM 2

KickerR

~450 m

BPM 1

~158 m

Distance from IP (m)

y ( m

)

Place kicker at point with IP phase.

BPM at phase 90 degree downstream from kicker.


Angle feedback: locally near IP – crab cavity(IR with crossing angle)

Fast phase adjust using a second klystron and fast phase difference.

Diagram by J. Frisch

Needs

careful

integration

into MDI

design!


IP Feedback modelIP Feedback model

Linearise Beam-Beam Kick Curve Response


Feedback AlgorithmFeedback Algorithm

1

0( ) ( ) ( ) ( ) ( )

k

PI P I P Ij

u k u k u k K e k K e j

•Subtract uPI(k-1) to get recursive algorithm:

( ) ( 1) ( ) ( 1) ( 1)PI PI P Iu k u k K e k e k K e k

•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 0.1y level.

•Proportional-Integral (PI) Controller:


Illustration of Intra-train feedback performance (White/QMUL) (TESLA TDR)

0 100 200 300 400 500 6000

1

2

3x 10

34

Bunch #

Lu

min

os

ity

/ c

m-2s

-1

y position FB:

restore collisions

within 100 bunches1 seed:

post-BBA

+ GM

+ wakes

y position scan:

optimise signal

in pair monitor (+4%)

y angle scan

OPTIMAL

LUMINOSITY

Excellent

starting point:

need to add

further

‘reality’ …


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.

Latency 53ns

Full delay-loop feedback on:

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)

Cold ILC:

robustness,

algorithmic control


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


Backgrounds (QMUL)

Need to ensure: FB system performance OK,

FB material does not cause additional backgrounds in detector.

Considering experimental background tests at SLAC/ESA

Feedback system incorporated into GEANT IR model


Pulse-pulse IP beam deflection feedback(Hendricksen)

Input GM models

A, B, C:

Linac->IP tracking

+ 5 Hz FB (TESLA)

<Luminosity>

Need for

intra-train FB

Need to integrate simulation of FBs:

upstream slow, active stabilisation, 5Hz, intra-train …


SLC optimised ‘dither’ feedback at IP(Phinney)

Deflection scans: 5 knobs/beam : x/y waist, x/y dispersion, coupling

Old method: scan of

beam size vs. single knob:

Poor resolution, lumi loss

New method: optimise lumi

w. dither FB on each knob

Increased lumi, eased ops.


5. IP beam parameter diagnostics

Sigma xSigma ySigma z

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

What do you want to know?!


Available diagnostics

• 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


Beam diagnostics possibilities in IR limited

Lumi mon.

(Bhabhas)

IP BPM (beam

deflections)

Forward

BSR mon.


Beam parameters from beamstrahlung?(Stahl, White)


Observables/Beam Params List

E_totr moment 1/r moment Thrust DirectionThrust ValueAngular SpreadE_out/E_inL-R AsymmetryT-B AsymmetryDiagonal Asymmetry N/E_tot

Forward + backwardcalorimeters

•Sigma x

•Sigma y

•Sigma z

•Sigma x'

•Sigma y'

•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

Each variable where appropriate exists for the mean of e- + e+ bunch and difference in obs/par between them.


Parameter Reconstruction

•Compute Taylor matrices through multiple GP runs varying beam params-> use Grid computing at QM to do in finite time (have to stick to 2nd order calculations realistically).

•For parameter reconstruction: Solve x for given f(x) using multi-parameter fit. Prob. no unique solution- choice of fit technique likely to be important.


Single-parameter analysis: sanity check


Initial results (Gaussian beams) (Stahl)

Seems to be promising; MUCH more study needed …


Summary of collision optimisation/MDI issues

• 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 …

luminosity optimisation overview

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