ion operation and beam losses h. braun, r. bruce, s. gilardoni, j.jowett cern - ab/abp
TRANSCRIPT
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
200
205
0
50
100
150
200
250
300
Hadronic Fragmentation cross sections for 208Pb on 12C
(
mba
rn)
7476
7880
82
185
190
195
200
205
0
50
100
150
200
250
300
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
10
15
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
1
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
0
200
400
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