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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 Interaction
Ion 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
Electromagnetic Dissociation
cross sections for 208Pb on 12C
300
300
250
250
200
200
 (mbarn)
 (mbarn)
Hadronic Fragmentation
cross sections for 208Pb on 12C
150
100
150
100
50
50
0
0
185
185
Ma 190
ss
Nu 195
mb
er
A
190
Ma
s
sN
200
205
74
76
78
80
N
mic
o
t
A
Z
er
b
um
82
H. Braun
195
um
be
r
200
A
205
74
76
78
N
mic
o
t
A
82
Z
ber
m
u
80
Heat load in IR7 dispersion suppressor, t=12 min
Fractional heat load in dispersion suppressor, t =12min
Pb208
20
Pb207
Pb206
Pb205
Pb204
15
Pb203
Tl204
Tl203
10
Tl201
Tl200
Tl199
Tl198
Hg201
Hg200
5
Hg199
570
580
590
600
distance from TCP.D6L7.B1 (m)
610
620
H. Braun
MQTLI.11R7.B1
MQ.11R7.B1
MB.B11R7.B1
MB.A11R7.B1
MQTLI.10R7.B1
0
MQ.10R7.B1
'
P (W/m)
Tl202
Maximum for continous loss,
corresponds to local collimation
inefficiency of 1.61 10-3m-1
630
Interaction cross sections at
LHC collision energy
Cross-section for Pb totally
dominated by
electromagnetic processes
400
200
barn
Total cross - section for ion removal from beam
tot
ECP P
EMD
H
H
He
O
Ar
Kr
In
Pb0
 tot   H   EMD   ECPP
H
Hydrogen
Helium
Oxygen
Argon
Krypton
Indium
Lead
0.105
0.35
1.5
3.1
4.5
5.5
8
EMD
0
0.002
0.13
1.7
15.5
44.5
225.
ECPP
4.25 10
1. 10 8
0.00016
0.04
3.
18.5
280.756
tot
11
0.105
0.352
1.63016
4.84
23.
68.5
513.756
Electromagnetic Interactions of Heavy ions
QED effects in the peripheral collisions of heavy ions
Rutherford
scattering:
Free pair
production:
Electron
capture by pair
production
(ECPP)
Electromagnetic
Dissociation
(EMD)
208

Pb82  208 Pb82 

208
Copious but harmless
208
Pb82  208 Pb82
208
Pb82  208 Pb82  e   e 

Pb82  208 Pb82 

208

Pb82  208 Pb82 

Pb82  208 Pb81  e 
Electron can be captured to a number of
bound states, not only 1s.
208
208

Pb82  208 Pb82 

208
Pb82  ( 208 Pb82 ) *

207
82
Pb
n
Copious but harmless
Secondary beam out of IP,
effectively off-momentum”
p 
Secondary beam out of IP,
effectively off-momentum:
p  
(Numerous other changes of ion
charge and mass state happen at
smaller rates.)
208
Pb
82 

208
Pb
82 



208
1
 0.012 for Pb
Z 1
Pb82  208 Pb81  e 
1
 4.8  10 3 for Pb
A 1
Pb81+ footprint in a dipole
Pb81+ beam separated from the
Pb82+ beam
Pb81+ beam parameters
Energy: 2.75 TeV/u
x about few mm
s = 55 cm
Incident angle = 0.5 mrad
Expected intensity ~ 2.5e5 Pb81+/s
From LHC design report
Energy deposition in dipole simulated using
FLUKA to evaluate the quenching risk
Dipole geometry model and
magnetic field map
¼ of the magnet
The simulation of a single Pb ion at Field at nominal collision value of 8.33 T
2.75 TeV/u in this geometry and
without biasing takes about 10 hours
Thanks to Fluka collaborators.
Energy deposition in a LHC dipole
x(cm)
phi(rad)
z(cm)
10 m
10 m
z(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 calculation
Energy 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?
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
More precise conversion of the
energy deposition into temperature
• understand the binning choice
• understand the quench level
FOR IONS
From A. Siemko, Chamonix ‘05
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 and
the 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
Pin-diode
•Most probable locations of losses
computed by J. Jowett
•Experiment status: first data yesterday
Photos from Jowett’s visit
two weeks ago
Aims:
•first attempt to measure BFPP
cross section
•cross check of Monte Carlo
simulation of ion transport in
matter
Impact point determination
Collision point
Predicted impact point @ ~ 137 m
Circular Beam pipe
Calculation from J. Jowett
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
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