Ion operation and beam losses

H. Braun, R. Bruce, S. Gilardoni, J.Jowett

CERN - AB/ABP

Lead ion nominal scheme parameters

Some operation issues are the same as for protons, however others are related to the fact that an ion is an ensemble of nucleons and charges.

Collimation Issues

Electromagnetic InteractionIon losses Possible magnet quench

Collimation• Ion nuclear physics collimation more complicated

– Isotopes miss secondary collimators, and are lost in downstream SC magnets

• Basically an ion lost can became a source of ions

7476

7880

82

185

190

195

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205

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Hadronic Fragmentation cross sections for 208Pb on 12C

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mba

rn)

7476

7880

82

185

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Electromagnetic Dissociation cross sections for 208Pb on 12C

(

mba

rn)

H. Braun

Heat load in IR7 dispersion suppressor, =12 min

570 580 590 600 610 620 630

0

5

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20

P' (W

/m)

distance from TCP.D6L7.B1 (m)

Fractional heat load in dispersion suppressor, =12min

MQ

.10R

7.B

1

MQ

TL

I.10

R7.

B1

MB

.A11

R7.

B1

MB

.B11

R7.

B1

MQ

.11R

7.B

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MQ

TL

I.11

R7.

B1

Maximum for continous loss,corresponds to local collimation inefficiency of 1.61 10-3m-1

Pb208

Pb207

Pb206

Pb205

Pb204

Pb203

Tl204

Tl203

Tl202

Tl201

Tl200

Tl199

Tl198

Hg201

Hg200

Hg199

H. Braun

HHe

OAr

KrIn Pb

H

EMD

ECPP

tot

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barn

HHe

OAr

KrIn Pb

Interaction cross sections at LHC collision energy

Cross-section for Pb totally dominated by

electromagnetic processes

H EMD ECPP tot

Hydrogen 0.105 0 4.25 1011 0.105

Helium 0.35 0.002 1. 108 0.352Oxygen 1.5 0.13 0.00016 1.63016Argon 3.1 1.7 0.04 4.84Krypton 4.5 15.5 3. 23.Indium 5.5 44.5 18.5 68.5Lead 8 225. 280.756 513.756

ECPPEMDHtot

beam from removalion for section -cross Total

Electromagnetic Interactions of Heavy ions

QED effects in the peripheral collisions of heavy ions Rutherford scattering:

82208822088220882208 PbPbPbPb Copious but harmless

Free pair production:

eePbPbPbPb 82208822088220882208 Copious but harmless

Electron capture by pair production (ECPP)

ePbPbPbPb 81208822088220882208 Electron can be captured to a number of bound states, not only 1s.

Secondary beam out of IP, effectively off-momentum”

Pbfor 012.01

1

Zp

Electromagnetic Dissociation (EMD)

Secondary beam out of IP, effectively off-momentum:

Pbfor 108.41

1 3

Ap

nPb

*)Pb(PbPbPb

82207

82208822088220882208

(Numerous other changes of ion charge and mass state happen at smaller rates.)

82 8 208208 208 82 82 2 8 10 PP Pb Pb ebb

Pb81+ footprint in a dipole

From LHC design report

To interaction point

Pb81+ beam separated from the Pb82+ beam

Pb81+ beam parameters

Energy: 2.75 TeV/ux about few mms = 55 cmIncident angle = 0.5 mradExpected intensity ~ 2.5e5 Pb81+/s

Energy deposition in dipole simulated using FLUKA to evaluate the quenching risk

Dipole geometry model and magnetic field map

Thanks to Fluka collaborators.

¼ of the magnet

Field at nominal collision value of 8.33 TThe simulation of a single Pb ion at 2.75 TeV/u in this geometry and without biasing takes about 10 hours

Energy deposition in a LHC dipole

z(cm) z(cm)

10

m

10

m

phi(rad) x(cm)

Impact point

Energy deposition vs. z

Beam direction

Quench limit as quoted in LHC design report

Energy deposition vs. angle

Quench limit as quoted in LHC design report

Mesh chosen for FLUKA calculationEnergy deposition or power losses quoted in GeV/cm3 or W/cm3. Important to choose the right dimension for the representative volume

Assumptions:

• z binning should be a fraction of the electromagnetic interaction length of the wire materials and comparable to the wire winding length, both about 15 cm

• r, compared to the typical distance to embrace a volume which behave as a single thermal body

z = 5 cm

r = 1.55 cm

= 4

What is missing?

From A. Siemko, Chamonix ‘05

More precise conversion of the energy deposition into temperature

• understand the binning choice

• understand the quench level FOR IONS

FLUKA results can be dominated by a “not too clever” choice of the binning:

• cyan and blue line dominated by statistical fluctuation well above the quench limit

How to validate the Monte-Carlo results

• Compare FLUKA results with other codes

– GEANT4 high energy ions hadronic interaction under development (Thanks to H.P. Wellisch from PH/SFT group)

– preliminary results for thin targets with Pb at 100 GeV/u show no major discrepancies between FLUKA and G4

• Check the approach with past experience in other proton machines

– Fermilab – Extrapolation to ion case not easy– Simulations pretty old (1980-1990):

Monte-Carlo simulation improved consistently

• Investigate existing machine

– RHIC experiment

Comparison with Tevatron dipole geometry

Is the model used for the geometry precise enough to be predictive?

Technical design of FNAL dipole

Geometry implemented for simulation

From FERMILAB-PUB-87/113

Comparisons between data and Monte-Carlo not completely satisfactory but due to hadronic cascade modelling. It was in 1987 andthe Cascade Calculation evolved a lot.

BFPP experiment @ RHIC

RHIC run V : Cu-Cu collisions @ 100 GeV/u (Cu Z=29)

13.32 nb-1 (01/03/05) delivered so far (http://www.agsrhichome.bnl.gov/AP/RHIC2005/)

Possibility to observe BFPP due to larger momentum deviation than for Au-Au run

Experimental setup @ RHIC

•Pin-diode detectors located outside the dipole cryostats

•Most probable locations of losses computed by J. Jowett

•Experiment status: first data yesterday

Photos from Jowett’s visit two weeks ago

Pin-diode

Aims:

•first attempt to measure BFPP cross section

•cross check of Monte Carlo simulation of ion transport in matter

Impact point determination

Calculation from J. Jowett

Circular Beam pipe

Collision pointPredicted impact point @ ~ 137 m

First data from RHIC BFCC experiment

Luminosity measurement

Nice correlation between diode at 141 m and luminosity.

Discrepancy with prediction @137 m due likely to particle shower development

PreliminaryReceived: 02/03/05

Conclusions/Summary

• Pb81+ ions losses may lead to magnet quenching– Possible solution under investigation:

• optics steering to decrease, for example, the beam density

• FLUKA simulation still under way– Validation of results obtained with other codes

• GEANT4 and MARS – Checking that the optics solution really help on the energy deposition

– However would be better to integrate Monte-Carlo calculation with thermodynamic simulation to understand the quench limit in the specific case

• From RHIC data– Check the BFPP cross section– Simulation of RHIC dipole also to validate simulation chain

Thanks to...

• A. Ferrari, G. Smirnov, M. Magistris and all the FLUKA team.

• B. Jeanneret, A. Siemko, M. Giovannozzi for the fruitful discussions

• H.P. Wellisch and V. Grichine for the GEANT4 support

• Angelika Drees, Wolfram Fischer, Spencer Klein and all the RHIC team