Magnetic requirements for the commissioning

E. Todesco

Accelerator Technology DepartmentMagnet and Superconductors Group

Acknowledgements: the speakers, S. Ramberger, J. P. Koutchouk

CERN, 10th February 2006

Chamonix summing up

February 10 2006 E. Todesco AT-MAS-MA 2

Magnetic requirements for commissioning

85% of the main dipole coils and 100% of the main quadrupole coils have been wound and assembled

What has been done is done …

Activities related to magnet performances and field quality are shifting

from the follow-up of the production, and corrective actionsto gather all the knowledge that could be useful for the commissioning

Introduction

-2

0

2

4

6

8

10

0 100 200 300 400 500 600 700

Aperture progressive number

b6 in

tegr

al w

ith n

omin

al µ

r (u

nits

)

upper target systematicsystematic

AT-MAS

lower target systematic

cross-section 1 cross-section 2

Main quadrupoles

-15

-10

-5

0

5

10

0 100 200 300 400 500 600 700 800 900 1000Collared coil progressive number

b3 in

tegr

al (

units

)

Firm 1

Firm 2

Firm 3

Collared coil

upper limit for systematic

lower limit for systematic

X-section 3

AT-MAS & MTM

X-section 2

Main dipoles

February 10 2006 E. Todesco AT-MAS-MA 3

Magnetic requirements for commissioning

Behavior of magnets for operationOrbit, tune and chromatic correctors (R. Steinhagen, W. Venturini)Dynamic effects for the field model (M. Lamont)

Estimating quantities relevant for commissioningBeta-beating (S. Sanfilippo)Quench level without beam (P. Pugnat)

OtherMEB activities (L. Bottura)Parasitic fields estimates (A. Devred)

Structure of the session

February 10 2006 E. Todesco AT-MAS-MA 4

Magnetic requirements for commissioning

With a pre-cycle 0A – 55A – 0 AThe remenant field corresponds to a kick of 0.560.05 rad

Both systematic and random effects are within tolerances

No need of a degaussing cycle to set the systematic to zero

Hysteresis in orbit correctors (R. Steinhagen)

Feedback correctionSmall loops are giving an hysteresis which does not affect the feedback algorithm

Measurements at Block4 by W. Venturini et al.

February 10 2006 E. Todesco AT-MAS-MA 5

Magnetic requirements for commissioning

Tune correctors (MQT)It would be better to operate them at small, non-zero current (1.5% of max corresponds to 0.2 of detuning)Global hysteresis gives a detuning of 0.005Decay of b2 gives 0.01 of detuningA correction with a linear model gives an uncorrected detuning of 0.0015 Hysteresis can be ignored

Hysteresis in tune and chromatic correctors (W. Venturini)

Chromatic correctorsSmall loops are giving an hysteresis which does not affect the feedback algorithm

0.00E+00

1.00E-03

2.00E-03

3.00E-03

4.00E-03

5.00E-03

6.00E-03

7.00E-03

8.00E-03

9.00E-03

1.00E-02

0 1 2 3 4 5 6 7 8Current (A)

Inte

grat

ed B

2 (T

m @

17m

m)

-1.0E-03

-5.0E-04

0.0E+00

5.0E-04

1.0E-03

1.5E-03

-20 -15 -10 -5 0 5 10 15

Current (A)

MC

S B

3 i

nte

gra

l (

Tm

@1

7 m

m)

February 10 2006 E. Todesco AT-MAS-MA 6

Magnetic requirements for commissioning

Field model (FiDeL)Magnetic measurements fitting procedure and extraction of model parameters (by N. Sammut, L. Bottura, J. Micallef)

Slot allocation evaluation of the behavior of magnets connected to the same power supply

DeliverablesSector test

Transfer function of MB, MQ, correctorsDecay predictionCycling prescription

CommissioningEverything for sector test plus snapback

Field model deliverables (M. Lamont et al)

I

ItIsnapback

injection

ebtb

33

Example of snapback fit

February 10 2006 E. Todesco AT-MAS-MA 7

Magnetic requirements for commissioning

Beta-beating:Error in the optic functions due to imperfections (mainly on the quadrupole strength)It reduces the mechanical aperture for the beamThe budget is 21% of maximum beta-beating

Estimates of beta-beating (S. Sanfilippo et al)

Previous experienceBeta-beating in LEP was 200% at the beginning of commissioning

LTC asked for estimates: are imperfections under control ?

Previous workDifferent sources of beta-beating have been identified

Targets/estimates based on the early production have been given

February 10 2006 E. Todesco AT-MAS-MA 8

Magnetic requirements for commissioning

New estimate:Based on measured values, slot allocation, estimated precision of measurement systems (by P. Hagen, J. P. Koutchouk, M. Giovannozzi, T. Risselada)

Effect of cell MQ, of MB, and of individually powered MQ taken into account Feed down due to misalignment still relies on estimates – measurements will be included soon

Results within target

Estimates of beta-beating (S. Sanfilippo et al)

February 10 2006 E. Todesco AT-MAS-MA 9

Magnetic requirements for commissioning

Available data908 main dipoles tested, 115 with a 2nd thermal cycle196 main quadrupoles, 9 with a 2nd thermal cycle

Statistical analysis to guess how many quenches are needed to work at 7 TeV

25-306 quenches per octant in the dipoles (depending on detraining), with a two sigma error86 quenches per octant in the quadrupoles, with a two sigma error

Expected quench level without beam (P. Pugnat)

February 10 2006 E. Todesco AT-MAS-MA 10

Magnetic requirements for commissioning

Magnet Evaluation Board activity is at full speed1/2 of the dipoles and 1/3 of the quadrupoles allocatedMixing of dipole manufacturers in sectors

Small systematic differences in field quality between firms

The same inner cable in the same sector (when possible)

Criteria (S. Fartoukh et al.)

Geometry maximizing mechanical aperture

Field qualityMinimizing σ(b1) in dipoles (avoid eating the orbit correctors budget)Minimizing σ(b2) in quadrupoles (beta-beating, mechanical aperture)Minimizing σ(b3) in dipoles (3rd order resonance, dynamic aperture)

What we gained with sorting (L. Bottura)

February 10 2006 E. Todesco AT-MAS-MA 11

Magnetic requirements for commissioning

Geometry Dipole allocation taking into account the actual beam dimension (worse magnets in mid half-cell positions)Quadrupole installation with tilts and rolls in a few cases to maximize mechanical aperture

What we gained with sorting (L. Bottura)

Field qualityb1 sorting used for the early phase of production (first sector)In the first sector, random b3 was 15% larger than target

sorting allowed to stay within targets (improvement by a factor 3 !)

Sorting still used to further improve random b3 (you never know …)

installation with tilt and roll

What we would get with nominal installation

February 10 2006 E. Todesco AT-MAS-MA 12

Magnetic requirements for commissioning

Beam screenNew analysis of the measurements at block4 (W. Venturini) show agreement with simulations (B. Auchmann)

Smaller effect on b5, b7 can be due to misalignment

Chasing parasitic fields (A. Devred)

Connection cryostatPbSb plates in the connection cryostat can become superconductive and quench

Kick on the beam well above specificationSolution: add a thermal link to keep “warm” the PbSb (above Tc) (A. Poncet et al.)

Effect of bus-bars3d models have been built, (B. Auchmann) field and impact on the beam is being evaluated (C. Vollinger, J. P. Koutchouk)

February 10 2006 E. Todesco AT-MAS-MA 13

Magnetic requirements for commissioning

Future outlookOptimize the magnetic measurements activities to get as much information as possible(Production follow-up is less critical now)

Dynamic components of main quadrupoles

Transfer function of special quadrupoles

Statistics on the dynamic components of dipoles

Characterization of all correctors (cycles, feedback)

Translate the magnetic and geometric measurements into a model of the machine

Including the slot allocation

Start estimating the relevant quantities for the beamTF for MB and MQ, detuning, natural chromaticity, (resonances)

Different TF and corrector settings for octants

Be ready for the first benchmark with the beam