How the Magnetic Measurements and the

Reference Magnet System (RMS) will be used for commissioning ?

presented by L. Bottura

Workshop CERNmonix XIV

Thursday, January 20th, 2005

RMS forever !

Hasta la victoria, SIEMPRE

Special thanks to JPK for his fervor, persistence, and faith in

reference magnets

Outline

Summary of information available on day-1 from magnetic measurements at: warm cold

Injection setting and ramp generation (currents) in: main circuits (MB, MQ) corrector circuits (MCS)

The RMS conceptual design and results of the review RMS concept proposal work in progress

Open issues and conclusions

Available data warm measurements on the

production: all (superconducting) MB, MQ,

MQM, MQY: main field integral strength higher order geometric harmonics

all (superconducting) MBX, MBRx, MQXx

warm measurement on MQTL so far at CERN

most (superconducting) lattice corrector and spool pieces (about 90% of data available)

all (warm) MQW a sample (5 to 10) of other warm

insertion magnets (MBXW, … measured at the manufacturer before delivery)

at the present rate, cold measurements on: ≈ 20 % of MB and ≈ 20 % of MQ

in standard conditions special tests (injection decay and

snap-back, effect of long storage) on 15…20 MB

a sample of MQM and MQY (10 % SM-18, 30 % B4)

≈ 75 % of MBX, MBRx 100 % of MQXx (Q1, Q2, Q3) 2 MQTL cold tested (plan for

series TBD(*)) a limited sample of lattice

correctors and spool pieces (about 120 tests over 7000 magnets, plan for the series TBD(*))

(*) see the next talk, by W. Venturini

magneti

zati

on

deca

y

satu

rati

on

W/C CM offset

W/C CC offset

geometric

What data is stored ?example of integral dipole and sextupole field in an LHC dipole

a break-down in different components is necessary to accurately model the data

cold data

The field model general decomposition in error sources, with given

functional dependency on t, I, dI/dt, I(-t) (see appendix) geometric Cn

geom

DC magnetization from persistent currents CnMDC

iron saturation Cnsaturation

decay at injection Cndecay

snap-back at acceleration CnSB

coil deformation at high field Cndef

coupling currents CnMAC

residual magnetization Cnresidual

linear composition of contributions:

smaller valuessmaller variability

smaller uncertainty

higher valueshigher variability

higher uncertainty

The burning question…

If we keep going as we do today, by end 2006 we will have

≈ 3.5 million measurementsand 35 GB of accumulated data

in the databases…

… what are we going to do with them ?

Use of data The data will be used to:

1. set injection values2. generate ramps3. forecast corrections (in practice only for MB’s or IR quads)

on a magnet family basis Families are magnet groups powered in series, i.e.

for which an integral transfer function (and, possibly, integral harmonics) information is needed. Example: the MB’s V1 line in a sector (154 magnets)

The concept is best explained by practical examples MB injection settings sextupole correction forecast from MB data

MB injection settings - 1/5 Determine the current I in the MB to obtain a given

integrated field B dl over the sector (as specified by LHC control system). Algorithm:

retrieve warm transfer function TFWM for each

magnet in the sector apply warm-cold scaling fTF and offset TF(I) and

obtain the cold transfer function TFCM

TFCM(I) = fTF TFW

M + TF(I)

integrate the TFCM over the sector

TFC(I) = ∑M TFCM(I)

compute the current by inversion of the (non-linear) TFC

I = (TFC(I))-1 B dl

only if cold data is missing

MB Injection settings - 2/5 Warm and cold magnetic data is

stored in an Oracle databases (today in 3 different databases) containing separate entries for: warm data cold data

injection flat-top

warm/cold offsets injection flat-top

components in cold conditions geometric persistent currents decay and snap-back saturation

MB injection settings - 3/5

warm/cold correlation based on production accumulated so far.

computed in July 2004 on approximately 100 magnets

offsets are stable, standard deviation acceptable and comparable with expected measurement accuracy

fTF = 1.00 (-)

TF = 5.5(6) (mT m/kA)

MB injection settings - 4/5

The magnet installation sequence is determined at the Magnet Evaluation Board (MEB), based on constraints on:

geometry field quality other (quench, non-conformities, …)

The information is collected in an installation map, recorded in the Manufacturing and Test Folder (MTF)

We know which magnet is where

we can build integral field information

MB injection settings - 5/5 average transfer function at injection for sector 78 (extrapolated

from 109/154 magnets allocated) warm/cold extrapolation for 44/109 magnets (65 cold measured)

TF1 = 10.117(5) (T m/kA)

TF2 = 10.117(1) (T m/kA)

current in sector 78 for an injection at 450 GeV from SPS (1189.2 T m)

I = 763.2(5) A

Note down this number for sector test with beam !

Modelling functions for harmonics (see appendix for details)

geometric multipole

persistent currents

decay

saturation

€

cngeom=γn

€

cnMDC=μn

IIinj

⎛ ⎝ ⎜ ⎜

⎞ ⎠ ⎟ ⎟

2−α Ic−IIc−Iinj

⎛ ⎝ ⎜ ⎜

⎞ ⎠ ⎟ ⎟

β

€

cndecay=δn

Δt,tinj,τ,aΔ( )Δtinj

std,tinj,τ,aΔ( )

€

cnsaturation=σn

ΣI,I1σ,ΔI1σ,I2σ,ΔI2σ,aσ( )ΣInom,I1σ,ΔI1σ,I2σ,ΔI2σ,aσ( )

from cold measurements

from fit of a sample of cold measured magnets

Sextupole forecast - 1/2 compute integral of cold components over a sector as:

derived from measurements taken on each magnet, or extrapolated from the average over magnets of the same family, e.g.

scale the function that describes the behavior of the component by the integrated value of the component in the sector, e.g.:

add all contributions

send the forecast to the LHC control system for correction (MCS and/or MS)

€

cnMDC=μ n I

Iinj

⎛ ⎝ ⎜ ⎜

⎞ ⎠ ⎟ ⎟

2−α Ic−IIc−Iinj

⎛ ⎝ ⎜ ⎜

⎞ ⎠ ⎟ ⎟

β€

μ n=1M μn

mm=1

M∑

Sextupole forecast - 2/2

error ≈ 0.2 units during the energy ramp

Reference Magnet System (RMS) conceptual design review

Objectives: provide settings and trims in the main

magnets (MB, MQ, …) and in the corrector circuits to prepare the LHC for injection, correct for decay and snap-back, program the ramp

provide a display of the magnetic state in the main magnets (MB, MQ)

play/replay machine cycles to prepare for a change of operating mode

Review of the conceptual design (July 2004)

MARIC presentation by R. Ostojic (August 2004).

LTC presentation by L. Bottura (August 2004)

MAC presentation by L. Bottura (December 2004)

Options for a partial/staged implementation

Option 1 (RHIC Paradigm) Static magnetic field model

Option 2 (Tevatron Paradigm) Parametric magnetic field

model Off-line reference magnet

measurements Off-line correction of model

predictions Option 3 (HERA+Tevatron

Paradigms) Parametric magnetic field

model On-line reference magnet

measurements On-line correction of model

predictions

Status as of November 2004 Given the present priorities (production, testing, installation) it is not

foreseen to realize a system as complex as the “option 3” of the proposed RMS

However, the test benches will be kept alive after end of the series tests for special measurements/re-measurements of magnets

Work on models and instrumentation proceeds aside main tasks (staffed by PJAS, DOCT, TECH) on: model specification for MB’s, development for MQ’s special tests on injection behavior digital integrator for faster (3 Hz) magnetic measurements fast (10 Hz), Hall-plate based sextupole measurements during snap-

back

On day-1 we will have a system with minimum capability (option 1 …)

augmented by off-line measurements (… and 1/2)

Some open issues Make order in the data collected (3 databases used today)

homogenize (formats, units, reference frames) centralize (database views) secure data for > 15 years of operation

Define a common interface for beam tracking calculations as well as for LHC operation the two tasks have similar requirements, but different time scales work will foster discussion with users on needs and solutions

Provide validated models for the magnet behaviours MB’s (on-going, to be completed) MQ’s (little done so far) other magnet types (to be done from scratch). A sample of specific

issues: hysteresis in the transfer function of correctors field errors generated in correctors operation of MQM at low field IR magnets

A starting point for the conceptual design of the LHC magnetic model

warmcorrector

data

warmMB/MQdata

coldmagnetic

data

machinetopologydatabase

LHC magnetic reference tables

warm-coldextrapolation

engine

conversion ofslot ID tomagnet ID

s

m

queryengine

Magnet selection

t, I, …

Response: cn

Query: magnet at slot s at time t, current I,…

normalised modelfunctions

€

fMDC=IIinj ⎛ ⎝ ⎜ ⎜ ⎞

⎠ ⎟ ⎟2−α Ic−IIc−Iinj

⎛ ⎝ ⎜ ⎜ ⎞

⎠ ⎟ ⎟β

scaling

€

cnMDC=μnfMDC

fieldcomponents

€

μn

Parameter file for the description ofthe magnetic properties of the LHC Model

Conclusions - 1/2 Warm and cold measurements can be used integrally for the

commissioning and initial operation of the LHC. No measurement goes in the trash bin.

Magnet setting and correction forecast is a non-linear problem. Feasible, but requires today: cross-calibration between measurements to decrease the error

margins on settings (e.g. transfer function for quads and higher order correctors)

special measurements to have a sufficient sample for interpolation and extrapolation of field errors (e.g. b3 at injection and ramp)

studies to establish a physical description of field and errors to provide a robust model for control (e.g. corrector hysteresis)

i.e. bench time and manpower

Conclusions - 2/2 There is a need to unify data, aiming at making practical

forecast easily available to users (AB-ABP, AB-OP) start activity aiming at a LHC magnetic model for

tracking studies (first priority) and LHC control (later) The work on instrumentation is pursued as basic technology

development within the core activity of the AT department. The schedule is not necessarily tied to LHC start-up initial measurements, on demand of LHC-OP, may be done with the

series test system, at reduced rate, and will require considerable processing (weeks) to perform re-calibration of the machine model

the off-line measurement system presently designed will not be suitable for on-line operation in real-time (the scope of the development has been limited).

On-line reference magnets, as in HERA, are ruled out for the commissioning of LHC

Appendix - The field model Field and field errors are assumed to have different origins

(components) that have clearly identified physical origin (e.g. geometric, persistent, saturation, …)

General functions for each component are obtained fitting cold data as a function of current or time, using functional dependencies that are “epexcted” from theory, or “practical” in describing data

Scaling parameters are applied to the general functions to model single magnets

The scaling parameters are either measured (injection, mid-field, flat-top), or extrapolated from warm conditions (geometric), or extrapolated from averages measured (persistent currents for the

same cable combination). The field and field errors are obtained from the linear

superposition of all components

Geometric multipoles important at all field levels absolute field is linear in current, normalised field is

constant

measured in warm conditions (can be extrapolated from industry data)

€

Tgeom=γm

€

cngeom=γn

€

Tcold=fTTwarm+ΔT

€

cncold=fcncn

warm+Δcn

Persistent currents mostly important at low field (but present throughout) proportional to the magnetization M proportional to Jc

assume that the Jc(B) scaling is maintained, geometry and B distribution effects are condensed in fitting exponents and

€

M∝JcD

€

Jc∝1B

BBc

⎛ ⎝ ⎜ ⎞

⎠ ⎟α1−B

Bc

⎛ ⎝ ⎜ ⎞

⎠ ⎟β

€

TMDC=μmIinjI2

IIinj

⎛ ⎝ ⎜ ⎜

⎞ ⎠ ⎟ ⎟

α Ic−IIc−Iinj

⎛ ⎝ ⎜ ⎜

⎞ ⎠ ⎟ ⎟

β

€

cnMDC=μn

IIinj

⎛ ⎝ ⎜ ⎜

⎞ ⎠ ⎟ ⎟

2−α Ic−IIc−Iinj

⎛ ⎝ ⎜ ⎜

⎞ ⎠ ⎟ ⎟

β

aditional T-dependence of Jc to be added

Iron saturation important at high field only associated with details of iron geometry (shape of inner

contour, slits, holes, …) no “theoretical” expression available, apart for the general

shape of the saturation curve (sigmoid) that provides a convenient fit to experimental data

€

ΣI,I1σ,ΔI1σ,I2σ,ΔI2σ,aσ( )=aσSI,I1σ,ΔI1σ( )+1−aσ( )SI,I2σ,ΔI2σ( )[ ]

€

SI,Iσ,ΔIσ( )=1πarctanI-Iσ

ΔIσ ⎛ ⎝ ⎜ ⎞

⎠ ⎟+π2

⎡ ⎣ ⎢ ⎤

⎦ ⎥

€

Tsaturation=σmΣI,I1σ,ΔI1σ,I2σ,ΔI2σ,aσ( )

ΣInom,I1σ,ΔI1σ,I2σ,ΔI2σ,aσ( )

€

cnsaturation=σn

ΣI,I1σ,ΔI1σ,I2σ,ΔI2σ,aσ( )ΣInom,I1σ,ΔI1σ,I2σ,ΔI2σ,aσ( )

Decay appears during constant current excitation associated with current redistribution in the

superconducting cables result of a complex interaction:

current redistribution local field magnetization bore field assume that the dynamics follows that of current diffusion

€

t,tinj,τ,aΔ( )=aΔ1−e−t−tinjτ

⎛ ⎝ ⎜ ⎜

⎞ ⎠ ⎟ ⎟+1−aΔ( )1−e−

t−tinj9τ

⎛ ⎝ ⎜ ⎜

⎞ ⎠ ⎟ ⎟

⎡ ⎣ ⎢ ⎢

⎤ ⎦ ⎥ ⎥

€

Tdecay=δmI

Δt,tinj,τ,aΔ( )Δtinj

std,tinj,τ,aΔ( )

€

cndecay=δn

Δt,tinj,τ,aΔ( )Δtinj

std,tinj,τ,aΔ( )

Powering history effects average effect of powering history has an uncertainty due

to limited sampling (2 % of production ?)

2 magnets3 magnets

Powering history dependence main parameters:

flat-top current flat-top duration preparation time before injection (injection duration)

tFT

tinjection

tpreparation

IFT

I

t

€

δn=δnstdIFT

IFTstd ⎛ ⎝ ⎜ ⎞

⎠ ⎟A−Be−tFTτ

A−Be−tFTstd

τ

⎛

⎝ ⎜ ⎜ ⎜

⎞

⎠ ⎟ ⎟ ⎟C+De−

tpreparationτ

C+De−tpreparationstd

τ

⎛

⎝ ⎜ ⎜ ⎜

⎞

⎠ ⎟ ⎟ ⎟

Snap-back first few tens of mT in the acceleration ramp, after injection pendant to decay: magnetization changes are swept away by

background field result of a complex interaction:

current ramp background field magnetization bore field

b1 and cn obtained from the decay scaling at end of injection I obtained from magnet family invariant (found by serendipity)

€

I=Δcnξn

€

Tsnap−back=Δb1e−I t()−Iinjection

ΔI

€

cnsnap−back=Δcn

decaye−I t()−Iinjection

ΔI

Look at the data the right way…

fit of the b3 hysteresis baseline

hysteresis baseline subtracted

b3 snap-back singled out

exponential fit

Same magnet, different cycles

b3 and I change for different cycles…

… and they correlate !

An invariant for snap-back !?!

the correlation plot holds for many magnets of the same family

Magnetic Reference System (RMS) conceptual design

magneticreferencedatabase

machinetopologydatabase

LHC operating conditions I, T

Referencemagnets

DAQ systemsDAP systems

non-linear field modelCn[t,I,dI/dt,T,I(-t)]

scaling laws

data fusion

router

Measurement time base adjustmentMeasurement recombination

LHC timing

Lynx-OS

DIM

CMWLynx-OS

CMW

Measurement dataanalysis system

Field modellingsystem

Digital, reducedmeasured harmonicsCn,RC(tRC,I,dI/dt,T)Cn,FC(tFC,I,dI/dt,T)Cn,HP(tHP,I,dI/dt,T)Cn,NMR(tNMR,I,dI/dt,T)

predicted field strength (Bm) andharmonics (cn) by sector

Synchronisedmeasured harmonics

Cn(tLHC,I,dI/dt,T)

Analog and digital signalsDigital I/O to instrument controllers

LHC controls

ramptrims

CMW

baselineramp

linearfield modelCn(t,I,dI/dt)

transferfunctions

TF-1(I)

opticsmodel …

RMS options Option 1 (RHIC Paradigm)

Static magnetic field model

Option 2 (Tevatron Paradigm) Parametric magnetic field model Off-line reference magnet measurements Off-line correction of model predictions

Option 3 (HERA+Tevatron Paradigms) Parametric magnetic field model On-line reference magnet measurements On-line correction of model predictions

magneticreferencedatabase

machinetopologydatabase

LHC operating conditions I, T

Referencemagnets

DAQ systemsDAP systems

non-linear field modelCn[t,I,dI/dt,T,I(-t)]

scaling laws

data fusion

router

Measurement time base adjustmentMeasurement recombination

LHC timing

Lynx-OS

DIM

CMWLynx-OS

CMW

Measurement dataanalysis system

Field modellingsystem

Digital, reducedmeasured harmonicsCn,RC(tRC,I,dI/dt,T)Cn,FC(tFC,I,dI/dt,T)Cn,HP(tHP,I,dI/dt,T)Cn,NMR(tNMR,I,dI/dt,T)

predicted field strength (Bm) andharmonics (cn) by sector

Synchronisedmeasured harmonics

Cn(tLHC,I,dI/dt,T)

Analog and digital signalsDigital I/O to instrument controllers

LHC controls

ramptrims

CMW

baselineramp

linearfield modelCn(t,I,dI/dt )

transferfunctions

TF-1(I)

opticsmodel …

magneticreferencedatabase

machinetopologydatabase

LHC operating conditions I, T

Referencemagnets

DAQ systemsDAP systems

non-linear field modelCn[t,I,dI/dt,T,I(-t)]

scaling laws

data fusion

router

Measurement time base adjustmentMeasurement recombination

LHC timing

Lynx-OS

DIM

CMWLynx-OS

CMW

Measurement dataanalysis system

Field modellingsystem

Digital, reducedmeasured harmonicsCn,RC(tRC,I,dI/dt,T)Cn,FC(tFC,I,dI/dt,T)Cn,HP(tHP,I,dI/dt,T)Cn,NMR(tNMR,I,dI/dt,T)

predicted field strength (Bm) andharmonics (cn) by sector

Synchronisedmeasured harmonics

Cn(tLHC,I,dI/dt,T)

Analog and digital signalsDigital I/O to instrument controllers

LHC controls

ramptrims

CMW

baselineramp

linearfield modelCn(t,I,dI/dt )

transferfunctions

TF-1(I)

opticsmodel …

magneticreferencedatabase

machinetopologydatabase

LHC operating conditions I, T

Referencemagnets

DAQ systemsDAP systems

non-linear field modelCn[t,I ,dI/dt,T,I(-t)]

scaling laws

data fusion

router

Measurement time base adjustmentMeasurement recombination

LHC timing

Lynx-OS

DIM

CMWLynx-OS

CMW

Measurement dataanalysis system

Field modellingsystem

Digital, reducedmeasured harmonicsCn,RC(tRC,I,dI/dt,T)Cn,FC(tFC,I,dI/dt,T)Cn,HP(tHP,I,dI/dt,T)Cn,NMR(tNMR,I,dI/dt,T)

predicted field strength (Bm) andharmonics (cn) by sector

Synchronisedmeasured harmonics

Cn(tLHC,I,dI/dt,T)

Analog and digital signalsDigital I/O to instrument controllers

LHC controls

ramptrims

CMW

baselineramp

linearfield modelCn(t,I,dI/dt )

transferfunctions

TF-1(I)

opticsmodel …