Challenges and Progress on
the SuperBeam Horn Design
NuFact 08
Valencia-Spain, June 30 - July 5 2008
Marcos DRACOS
IN2P3/CNRS Strasbourg
30 June 2008
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Super-Beam Studies in Europe
• Super Proton Driver at CERN (SPL)
• Target and collector integration
• Hadron Collector
• Pulser
• Conclusion
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Conventional Neutrino Beams
proton
beam
hadrons
p
target
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p
Decay tunnel
hadron collector
(focusing)
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physics
n
Detector
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SPL Super-Beam Project
H- linac 2.2, 3.5 or 5 GeV, 4 MW
Accumulator
ring + bunch
compressor
p
proton driver
Magnetic
horn capture
(collector)
p
Target
hadrons
n, m
decay tunnel
~300 MeV nm beam to far detector
to be studied in EUROn WP2
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Super Proton Linac at CERN
SPL
(http://doc.cern.ch/yellowrep/2006/2006-006/full_document.pdf)
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SPL (CDR2) main characteristics
Ion species
H-
Kinetic energy
3.5
GeV
Mean current during the pulse
40
mA
Mean beam power
4
MW
Pulse repetition rate
50
Hz
Pulse duration
0.57
ms
Bunch frequency
352.2
MHz
Duty cycle during the pulse
62 (5/8)
%
rms transverse emittances
0.4
p mm mrad
Longitudinal rms emittance
0.3
p deg MeV
Length
430
m
butch compressor to go down to 3.2 ms (important
parameter for hadron collector pulsing system)
(possible energy upgrade to 5 GeV could be the subject of a 3rd CDR)
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Proton Target
• 300-1000 J cm-3/pulse
• Severe problems from : sudden heating, stress,
activation
• Safety issues !
• Baseline for Super-Beam is solid target, mercury is
optional (baseline for NF)
– Extremely difficult problem : need to pursue two
approaches :
• Liquid metal target (Merit experiment)
• Solid target (extensive R/D program at CCLRC and BNL)
• Envisage alternative solutions
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Proposed collection system
proton beam
horn
300 kA
8.5°
3.7 cm
4 cm
target
40 cm
16.6 cm
80 cm
taking into account the proton energy and collection
efficiency, the target must be inside the horn
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Proton Target
some ideas
CC target
Horn
Proposed rotating
tantalum target
ring (realistic?)
Helium
cooling of
target
He OUT
He IN
fluidised jet of
particles
cooling is a main issue…
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Liquid Mercury (MERIT)
Work at BNL and RAL
Experience on T2K target (750 kW)
very useful
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Hadron production
Particles coming out of
the target
2.2 GeV protons
pT distribution not
the same for all
targets

the choice of the
target could
influence the hadron
collection system
(horn shape)
pT
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From now on Hg will be considered
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Hadron production uncertainties
2.2 GeV protons
p+ momentum
disagreement between models
(Monte Carlo production,
interaction and transport
codes)
more development is needed
(simulation, measurements)
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Proton Energy and Pion Spectra
• pions per proton on
target.
• Kinetic energy spectrum
– 2.2 GeV:
interesting
region for
SPL SB
Ekine (GeV)
1GeV
2GeV
• <Ek>=300MeV
– 3.5 GeV:
cos q
• <Ek>=378MeV
hadrons boosted forward
-1
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Proposed design for SPL
for pions coming out of the target
500 < pp < 700 MeV/c
p+ angle
p+ momentum
horn region
for a Hg target, 30 cm length, 15 mm (x1016/sec)
relatively better collection
when pproton
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the target must be inside
the horn
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Horn geometry
•
• 2.2 GeV proton beam :
– <pp> = 492 MeV/c
– <qp> = 55°
I = 300 kAmp
r(m)
– <pp> = 405 MeV/c
– <qp> = 60°
r(m)
3.5 GeV proton beam :
B~1/r
I = 300 kAmp
B~1/r
target
30 cm
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B must be 0
4 cm
4 cm
B must be 0
z(m)
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target
30 cm
z(m)
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Proposed design for SPL
600 kA
proton beam
Hg target
reflector
horn
300 kA
3.7 cm
8.5°
4 cm
12.9°
16.6 cm
20.3 cm
4 cm
40 cm
80 cm
70 cm
very high current inducing severe problems
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Focusing Power
p- transverse momentum
p+ transverse momentum
(2.2 GeV option)
p- are deflected
20% more p+ with reflector
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Present Collectors
In operation
(120 GeV)
In operation
(8 GeV)
completed
(12 GeV)
CERN horn prototype for SPL
Super-Beam
(3.5 GeV)
In operation
(400 GeV)
MiniBooNE
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CNGS
K2K
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Decay Tunnel
Flux vs decay
tunnel length
(2.2 GeV option)
short decay tunnel
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More about previous studies
•S. Gilardoni: Horn for Neutrino Factory and comparison with a solenoid
•http://doc.cern.ch/archive/electronic/cern/preprints/thesis/thesis-2004-046.pdf
•http://newbeams.in2p3.fr/talks/gilardoni.ppt
•A. Cazes: Horn for SPL
•http://tel.ccsd.cnrs.fr/tel-00008775/en/
•http://slap.web.cern.ch/slap/NuFact/NuFact/nf142.pdf
•http://slap.web.cern.ch/slap/NuFact/NuFact/nf-138.pdf
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Main Technical Challenges
•
•
•
•
•
•
•
•
Horn : as thin as possible (3 mm) to minimize energy deposition,
Longevity in a high power beam (currently estimated to be 6 weeks!),
50 Hz (vs a few Hz up to now),
Large electromagnetic wave, thermo-mechanical stress, vibrations,
fatigue, radiation damage,
Currents: 300 kA (horn) and 600 kA (reflector)
– design of a high current pulsed power supply (300 kA/100 μs/50
Hz),
cooling system in order to maintain the integrity of the horn despite of
the heat amount generated by the energy deposition of the secondary
particles provided by the impact of the primary proton beam onto the
target,
definition of the radiation tolerance,
integration of the target.
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CERN horn prototype
cooling system
Current of 300 kA
p
Protons
To decay channel
B=0
Hg Target
B1/R
initial design satisfying both, neutrino factory and super-beam
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Energy deposition in the conductors
MARS
48.2 kW
67kW
14.9kW
78.7kW
+8kW from
Joule effect
4MW, 2.2GeV proton beam
(1MeV = 1.82 kW)
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P (kW)
Localization of the energy deposition
target
z (cm)
z (cm)
power deposited in the inner
conductor as a function of z
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z position of the particles coming
out of the target
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Horn prototype
•
For the horn skin AA 6082-T6 /
(AlMgSi1) is an acceptable compromise
between the 4 main characteristics:
– Mechanical properties
– Welding abilities
– Electrical properties
– Resistance to corrosion
– Same for CNGS
…but Al not
compatible with
Mercury!
•tests done with: 30
kA and 1 Hz, pulse
100 ms long
•new tests to be
Electrical and
water connections done with 50 Hz
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Power Supply for horn pulsing
(major issue)
values considered by CERN
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3 Solutions proposed by ABB
schematic versions
at the
capacitors
ends
option 1
at the
capacitors ends
option 2
Switching
device
in the charge
Diode
Load
option 3
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Pulser simulation parameters
• magnetic field with electrical excitation (pulses 100 μs,
50 Hz)
• induced current distributions
• magnetic forces
• temperature and expansion distributions
• mechanical constraints and deformations (static+
dynamical), vibration modes
• non-linear magnetic and thermal effects in the calculation
of mechanical constraints
• fatigue (and constraints from radiations if any)
studies are needed to make the right choice, increase the system
lifetime, reduce the cost
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New ideas
2.5 m
minimize power dissipation and
radiation problems
(pulser problems remain as before)
protons
protons
2.5 m
protons
same decay
tunnel Ø 3 m
protons
to be studied
in EUROn
2 options:
•send at the same time 1 MW per target/horn system
•send 4 MW/system every 50/4 Hz
possibility to use solid
target?
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New (crazy) ideas
use a cryogenic horn (toroidal coil)
superconducting wire (1 mm Ø) in
superfluid He,
DC power supply
blow gas He
to avoid
quenching
problems
•No problem with power supply (pulser no more needed)
•Proton compressor no more needed
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to be studied
in EUROn
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Conclusions
• Proton driver characteristics and target have to be fixed
before horn design.
• Preliminary studies about horn focusing performance for
SPL already exist.
• Collector studies are necessary to increase the system
lifetime.
• Target/horn integration to be considered since the
beginning.
• Multi-physics simulations would be very useful.
• New studies will start soon in the framework of EUROn
FP7 project.
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End
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