Superbeam target work at RAL
Work by:Ottone Caretta, Tristan Davenne , Peter Loveridge,
Chris Densham, Mike Fitton, Matt Rooney (RAL)
EURONu collaborators:C. Bobeth, P. Cupial, M. Dracos, M. Kozien, B. Lepers, A. Longhin, F.
Osswald, B. Skoczen, A. Wroblewski, M. Zito
Presented by Ottone [email protected]
EuroNu Meeting, RALJanuary 2011
Introduction
EUROnu Annual Meeting, January 2011
• EUROnu target-station scheme has 4 targets and 4 horns– Each target exposed to ¼ of the total beam power (1.11e14 protons/pulse, 4.5 GeV, 12.5 Hz
repetition rate)– Reduced Beam induced heating in target by a factor of 4– roughly 50kW of heat deposited in each target– beam sigma 4mm. Target diameter 30mm (around 780mm long)– Target almost entirely inserted in the bore of the horn
2
protonsprotons
protonsprotons
2.5 m
2.5 m
protonsprotons
protonsprotons
Beam Separator4 MW Proton
beam from accumulator
at 50 Hz
4 x 1MW Proton beam each at
12.5 Hz
Decay Volume
Target Station (4 targets, 4 horns)
Marcos Dracos
Ottone Caretta, RAL, January 2011
Target design criteria
Cost
Simplicity
Safety
1. Feasibility
2. Reliability
3. Reliability
4. Reliability
5. Physics performance
Ottone Caretta, RAL, January 2011
Some issues of interest for the engineering of the target
Heat removal beam ~50kW
Joule from current (integrated target&horn) ~20kW
Thermal/mechanical stressesstatic
dynamic
Cooling layout – design & medium water
helium
peripheral vs transversal cooling
Neutron production – heat load/damage of horn (avoid high Z materials)Safety (e.g. Activated mercury vapours)Radiation resistance Reliability! – engineering integration (simple is good!)Pion yield
Ottone Caretta, RAL, January 2011
Heat removal
Beam heating~50kW - substantial!cooling is feasible butthermal stresses are an issue
Joule heating (if considering an integrated target and horn) ~20kW not much but challenging if added to the beam heating
P Loveridge
Steady-State AnalysisBeryllium Target
1 MW Power-on-Target
0
100
200
300
400
500
600
700
0 2,000 4,000 6,000 8,000 10,000 12,000
Heat Transfer Coefficient (W/m2K)
Tem
pera
ture
(°C
)
0
50
100
150
200
250
300
350
Stre
ss (M
Pa)
Tmax coreTmax surfVM-Stress max
Peter Loveridge
Ottone Caretta, RAL, January 2011
Thermal/mechanical stresses
Static stresses (related to steady state dT in material)on centre temperature difference between core and
surface in a rod generates high mechanical stresses largely independent of the rate of cooling
off centre higher stresses and significant deformations are to be expected in a target excited by an off centre beam.
Dynamic inertial stresses by instantaneous heating can play an important role
P Loveridge
Effect of Spill Duration on Peak Dynamic Stress in the EUROnu TargetCantelevered Beryllium Cylinder (Ø30mm L780mm, beam-sigma = 4mm)
1MW beam power (1.11e14 protons/spill @ 4.5 GeV, 12.5 Hz rep-rate )
Radial Oscillation Period
Longitudinal Oscillation Period
Static Stress
0
20
40
60
80
100
1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02
Spill time (seconds)Pe
ak V
on-M
ises
Stre
ss (M
Pa)
Ottone Caretta, RAL, January 2011
Cooling layout & medium
Water
avoid enclosed water in proximity of the beam:1K of (instantaneous) beam induced heating generates approximately 5bar of
pressure rise which may result in water hammer and/or cavitation
Helium
almost beam “neutral” is good also for transversal flow cooling (across the beam footprint) although pressure has to be kept higher (10bar) to obtain a high cooling efficiency. No generation of stress waves in coolant. Low activation of coolant. No corrosion problems
Peripheral vs transversal cooling
peripheral cooling does not appear sufficient to maintain alow dT within the target material.A transversal cooling arrangement may be necessary toprovide cooling at the core of the target.
Ottone Caretta, RAL, January 2011
Radiation damage
Mechanical properties of graphite degrade rapidly with irradiation
1 2 3 (dpa)
400oC
800oC
Thermal conductivity (After/Before)
IG 43 graphite
Nick Simos, BNL
Mike FittonMatt Rooney
Ottone Caretta, RAL, January 2011
Summary of target options
Mercury jethigh-Z (too many neutrons & heat load on horn) not chemically compatible with horn
Graphite rodthermal conductivity degrades with radiation damagemechanical stress depends on dThence short life time
Beryllium rodthermal stress is significantalternative geometries could overcome the problem (still
under investigation)Integrated Be target and horn
extra heat load makes it even more challengingcombined failure modes could reduce the life time
Fluidised powder targetpotential solution for higher heat load
Static pebble bedreduced stresses. Favourable transversal cooling. Good yield
Cylindrical Solid Target
48 (°C) 255 (°C) 0 (MPa) 220 (MPa)
Temperature (left) and and Von-Mises thermal stress (right) corresponding to steady state operationof a peripherally cooled cylindrical beryllium target
Steady-State Temperature Steady-State Stress
• Initial baseline was a solid cylindrical beryllium target. This has since been ruled out– At thermal equilibrium (after a few hundred beam pulses) large temperature variations
develop within the target– The large ΔT between the target surface and core leads to an excessive steady-state
thermal stress– This ΔT depends on the material thermal conductivity and cannot be overcome by more
aggressive surface cooling
HTC = 10kW/m2 K
HTC = 10kW/m2 K
“Pencil Shaped” Solid Target
Temperature (left) and Von-Mises thermal stress (right) corresponding to steady state operationof a peripherally cooled “pencil shaped” beryllium target
68 (°C) 306 (°C) 0 (MPa) 110 (MPa)
Steady-State Temperature Steady-State Stress
• A potential solution may be found by shaping the upstream end of the target such that the cooling fluid is in close proximity to the region of peak energy deposition– Shorter conduction path to coolant– Reduced ΔT between surface and location of Tmax– Thermal stress is reduced to an acceptable level– Able to operate with a factor 2 x less aggressive surface cooling– Pressurised helium gas cooling appears feasible
HTC = 5kW/m2 K
HTC = 5kW/m2 K
Offers high surface to volume ratio for good heat transfer throughout target
Possible to remove dissipated energy without concerning temperatures and stress
Insensitive to off-centre beamNeed pressurised gas for high power depositionBulk density lower than solid density ( use titanium
instead of beryllium )
Packed bed Target Concept for EUROnu
Induction heating may provide an interesting way to test a packed bed
Model of a 12mm radius Titanium alloycannister containing packed bedof 3mm titanium spheres
Ideal Transverse flow configuration
Induction heater testGraydon et al.
1MW beamHelium mass flow = 93grams/sHelium outlet temperature = 109°C
Maximum titanium temperature = 673°C
FLUKA + CFX
Physics performance for titanium spheres looks reasonable
Tristan Davenne
