CERN’s n_TOF neutron spallation target operating experience and future consolidation plans M. Calviani (CERN) 6 th High Power Targetry Workshop Oxford, April

Outline  n_TOF facility and experiment  History of target #1 and target #2  Operational feedback of target #3  Design of target #3 and ongoing R&D 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop2

n_TOF facility  Neutron time-of-flight facility for high accuracy cross-section measurements  Nuclear astrophysics & Nuclear technology EAR1 ~185 m EAR2 ~20 m  Spallation neutrons generated by 20 GeV/c protons on a lead target 20 GeV/c protons 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop3

14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop4 Courtesy: F. Gunsing (CEA)

n_TOF measurements 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop5 Courtesy: F. Gunsing (CEA)

n_TOF neutron flux  Extremely high instantaneous neutron flux  10 6 n/cm 2 /10 ms (EAR2)  Unique for measurement of radioactive isotopes  High resolution in energy (~10 -4 )  resonance studies  Large energy range (~mev to 1 GeV)  Low repetition rate (<0.8 Hz)  no wrap-around 11 orders of magnitude! 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop6 Measurements Courtesy: M. Barbagallo (INFN)

n_TOF facility and requirements  Due to the specific use of the facility, focus is not on average power on target, but to instantaneous flux  8.5*10 12 p+/pulse in 7 ns (27 kJ)  1.5x1.5 cm 2 1   Rep. rate ~4.8 sec  ~5.5 kW average  Instantaneous power  ~4 GW  Important dynamical effects during pulse in target  Target material: since facility conception, focus was on Pb:  Highest neutron yield (!)  Low neutron capture cross-section  improved background conditions 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop7

n_TOF spallation target #1 ( ) 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop8  Facility was conceived in 2000 and operated with a Pb target immersed in a pool with cooling water  Design limitations:  Insufficient cooling and the hot spot (proton/lead impact)  Surface oxidation due to rupture of protective layer when flushing  Mechanical instability  Lack of water chemical stabilisation – pitting corrosion enhancement  Facility stopped in 2004 due to water contamination

n_TOF spallation target #2 (2008-now) 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop9  Cope with limitations of target #2  Target embedded in a pressurized vessel  Monolithic lead core, support and anticreep in AW5083  Water chemistry continuously monitored

Target #2 operational feedback  Target #2 is not optimized for EAR2 (whilst compatible!)  Beam power on target is presently limited by the need to maintain surface temperature low enough to avoid water boiling 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop10 EAR1 EAR2

n_TOF target material results  Dedicated analyses quantified average of 6  m/y (~80  m/y for 10 B circuit) for AW5083-H111  Erosion/corrosion of 99.99% Pb significant  ~900  m/y average (local max 3.2 mm/y)  Severe environment  Pb corrosion products unavoidable, lead dissolved in water or residues  O 2 production by radiolysis  Smooth run since April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop11

Target #2 operational feedback 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop12  Erosion/corrosion generates a significant contamination of the circuit  Long-lived isotopes “coating” the pipes of the cooling water circuits EDMS

Target #2 operational feedback  6 years operation:  Average conductivity <0.15  S/cm  Oxygen content below 80 ppb  Full continuous purification via redundant ion exchangers  Purified N 2 flush via a Liqui-Cel ® membrane 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop LS1

Target #2 operational feedback  In order to reduce photon background in EAR1, the target moderator is filled with 10 B enriched boric acid in saturation (1.28%)  Dedicated circuit to guarantee constant concentration  Conductivity ~60  S/cm 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop14 Courtesy: C. Domingo (IFCV

n_TOF target inspection April 2014  External inspection performed in April 2014  Only surface oxidation stains have been observed, due to humid atmosphere 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop15

Introduction of target #3 design 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop16  Main goal is to reduce circuit contamination by embedding the production core in a corrosion resistant envelope  Dedicated moderator for EAR2  Target structure in low Co SS316L (waste)  Water cooling maintained to guarantee excellent time-to- energy relation 1.Ta-cladded pure W core + PbSb4 multiplicator 2.Ti6Al4V-contained PbSb4 core 3.Back-up: optimised bare PbSb4 core

14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop17 Option 1  Ta-cladded W via HIPing – excellent heat transmission  Al anticreep structure for PbSb4 mass Option 2  Ti6A/Pb contact critical for heat evacuation  Container shall always behave elastically w/o plasticization  Eliminates creep problem

Physics optimisation 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop18  All solutions improve fluxes in EAR2 (up to a factor of 3x)  Small reduction in fluxes for EAR1 (as bare Pb is the absolute best)

Ongoing prototyping works – Ta-cladded W 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop19  Ongoing orders with external companies to validate quality of the surface bonding  Non destructive + destructive tests  Synchrotron x-ray tomography (ESRF)  Possible development in-house at CERN at a later stage

Ongoing prototyping works – Ti6Al-Pb 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop20  Few Ti6A-contained Pb prototypes (1:4 and simplified geometry) are being developed to find the most adapted production method for the best thermal contact  Pb casting into Ti6A cylinder (+metal pressing)  Pb cryogenic shrink fitting into Ti6A cylinder PbSb4 prototype cylinder metrology Al prototype for fitting tests Ø150 mm 100 mm

Foreseen beam tests HiRadMat 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop21  To evaluate the effect of stresses/fatigue on the materials interface (Ta-W, Ti6A-Pb), it is foreseen to perform a beam test at HiRadMat facility during 2017  ~3000 pulses per target, ~1.5*10 11 p/pulse, 10 mm sigma Ta-cladded W Ti6A-contained PbSb4 ~40 cm ~10 cm Tank 440 GeV/c beam See C. Torregrosa’s talk on HRMT-27 (AD-target materials)

Conclusions and perspectives 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop22  Significant experience developed for the operation of bare Pb targets at CERN since 2000 (target #1 and #2)  New generation target (#3) will have a corrosion resistant cladding  Detailed design of target #3 will progress until end of 2017, production in 2018  R&D activities being carry out to validate technical choices

Thanks a lot

Ex. Exchange of ion exchangers  During this winter shutdown we exchanged both cooling circuit ion exchangers  High dose rate ~10 mSv/h  High contamination levels of the circuit (200 kBq/l)  Collective dose ~0.6 mSv  Mixed bed exchangers:  Nuclear grade (Purolite ® NRW3240)  Industrial grade (Amberlite 200C Na and IRA900 Cl) 14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop24

14 April 2016M. Calviani - n_TOF - 6th High Power Targetry Workshop25