Online Models for PEP-II Status

PEP-II MAC December 2004 Mark Woodley (ILC) 1

Online Models for PEP-IIStatus

• brief review of PEP modeling• fully coupled “normal form” optics representation• Orbit Response Matrix (ORM) model calibration:

“fudge factors” for quadrupole strengths• continuing work


PEP Online Modeling: Procedure

• prepare input files for MAD

–read reference input files–set magnets to configuration file values–apply ORM-derived fudge factors to quadrupole strengths

• run MAD

–use XCORs and YCORs to steer to measured absolute orbit–compute “effective” transfer matrices (RMATs)

• generate model files for MCC

–extract coupled lattice functions from RMATs


PEP Online Modeling: ProcessMCC (VMS) pepoptics (linux)

Database

SCP

LERmodelHERmodel

Matlab

MADinput

ReferenceFiles

MAD

AT

LEGO

AT

InputFiles

Magnets,Orbit,

Fudges

ConfigurationFiles

Magnets,Orbit,

Fudges

ConfigurationFiles

RMATs,Twiss,nij

Model Files

SCP,SSH

11

1

2

3

4

5

6

78

9

10

DIMADnot usedanymore

MADupdated tov 8.51/15

RMATs,Twiss,nij

Model Files


Lattice parameters in highly coupled systems

• MAD (v 8.51/15-SLAC) has been modified to output “effective” transfer matrices (first order expansion about the closed orbit; includes “feed down” effects from sextupoles)

• Andy Wolski’s normal form analysis1 is used to extract coupled lattice parameters from the transfer matrices

• 10 coupled lattice parameters (μ, β, α, η, η΄ for modes 1 & 2) and 8 elements of the normalizing transformation (n13, n14, n23, n24, n31, n32, n41, n42) at each element are returned to be loaded into the MCC database

1See http://www-library.lbl.gov/docs/LBNL/547/74/PDF/LBNL-54774.pdf

http://www-library.lbl.gov/docs/LBNL/547/74/PDF/LBNL-54774.pdf


ORM analysis: LER• ORM analysis begins with the “config” lattice (actual magnet strengths,

steered to the measured absolute orbit)

• only quadrupole strength errors are fitted (no sextupole strength errors)

• errors are assigned to quadrupole families (power supplies)

• sextupole “feed down” effects are not explicitly fitted (even though they are important for LER) … the assumption is that the BPMs are correct (BBA) and that steering to the measured orbit is sufficient to model the feed down effects

• “fudge factors” are computed by comparing the fitted quadrupole strengths with their config values; normal quadrupole fudge factors are multiplicative; skew quadrupole fudge factors are additive (since most skew quads should nominally be at or near zero)

• the actual ORM analysis for LER is performed by Cristoph Steier (LBNL) using the Matlab-based version of the LOCO program

See PT’s presentation on Recent ORM Results for further details …


ORM-derived fudge factors: LER (1)

•normal quadrupoles

•skew quadrupoles

1

1

1ORM

config

Kf

K

1 1ORM configf K K

QDBM6L

ORM data taken on December 11, 2003


( )( )calcxmodelx

fudgedunfudged


fudgedunfudged

( ) ( )meas modelx x


( )

( )

calcymodely

fudged

unfudged


fudged

unfudged

( ) ( )meas modely y




ORM-derived fudge factors: HER (1)

•normal quadrupoles

•skew quadrupoles

1

1

1ORM

config

Kf

K

1 1ORM configf K K

ORM data taken on June 10, 2004


( )( )calcxmodelx

fudgedunfudged


fudged

unfudged

( ) ( )meas modelx x


( )

( )

calcymodely

fudgedunfudged


fudgedunfudged

( ) ( )meas modely y




Continuing work• steering to absolute orbits when generating the model in order to properly

account for sextupole feed down effects requires accurate knowledge of BPM offsets → BBA1; many offsets for both HER and LER have been measured and are being routinely used to correct measured orbits; LER BBA is ongoing (more on this in a minute …)

• continue to fine tune the ORM analysis setup to avoid degeneracy in the variables

• fudge factors for individual magnets (?)

• develop more robust steering algorithms for model generation to take into account bad BPMs (especially for LER)

• create “fudged” design configs … move toward design optics in both rings

• participate in the ILC design1See Tonee Smith’s presentation on New BBA Hardware for further details …


BBA at PEP-IIStatus

• large unexplained LER BPM offsets from BBA → uncoupled analysis of orbits in a highly coupled machine

• new analysis algorithm• BPM offsets revisited


Unexplained large (~1 cm) LER BPM offsets from BBA

… from Marc Ross’ summary at April MAC …


• orbit fitting lies at the heart of our BBA analysis algorithm

• move the beam in a quadrupole (using a closed bump), change the strength of the quadrupole, and look at the orbit change

• if the orbit doesn’t change when the quadrupole strength is changed, the beam is passing through the center of the quadrupole; the reading on a nearby BPM under these conditions is the “BPM offset”

• if you’re moving the beam in X, you look at the change in the X orbit, which should be proportional to the distance (in X) between the beam and the quadrupole center … in an uncoupled ring

• if you’re moving the beam in X, and the beam happens to be offset in Y to begin with, the previous statement remains true … in an uncoupled ring

• if you’re moving the beam in X, and the beam happens to be offset in Y, and your ring is highly coupled, you have to pay attention to what’s happening in both planes simultaneously (well duh)

BBA Analysis


QDBM3 simulated X data-10 mm Y offset

uncoupled orbit fit

Δx

(mm

)

blue – o = MADred - - = orbit fit



BBA Analysis


Change in closed orbit (Δxco,Δyco) due to a change in strength (K→K(1)) of a

misaligned quadrupole (xbq,ybq):

†A. Wolski and F. Zimmerman, “Closed Orbit Response to Quadrupole Strength Variation”,

http://www-library.lbl.gov/docs/LBNL/543/60/PDF/LBNL-54360.pdf

bq

bq

co

co

y

xssCKssCKssCK

sy

x 1

0000)1()1( ;1;;

quadrupoleskew

quadrupolenormal

,

,

;

;1;;

3234

1214

3432

1412

0

10000

CC

CC

CC

CC

ssC

ssRssRssC

includes closed orbit effects of ΔK (both kick and position shift) includes optics effects of ΔK (change in closed orbit response matrix) fits both planes simultaneously, including any known coupling

Coupled BBA Analysis Algorithm


Δx

(mm

)Δ

y (m

m)

QDBM3 simulated X data-10 mm Y offsetcoupled orbit fit


LER BPM X Offsets: Then and Now


LER BPM Y Offsets: Then and Now


Acknowledgements & thanks!

Andy Wolski, Christoph Steier

James Safranek, Andrei Terebilo

Yuri Nosochkov, Yunhai Cai, Yiton Yan

Uli Wienands, Jim Turner, Martin Donald, Gerry Yocky

Peter Tenenbaum, Marc Ross, Janice Nelson, Tonee Smith

Documents

Online Models for PEP-II Status