Neutrino Factory Targets J R J Bennett roger
Neutrino Factory Targets J. R. J. Bennett roger. bennett@rl. ac. uk Rutherford Appleton Laboratory Chilton, Didcot, Oxon. OX 11 0 QX, UK
The Target • Specification • Current Status • What we would like • Reality FP 6
Specification Proton Beam - Pulsed at 10 -50 Hz • Energy 2 -30 Ge. V • Average Power ~4 MW
Proton Bunch Train • There a number of individual bunches which make up the bunch train, which may be several microsecond long. • RAL design has 4 bunches, CERN design over 100. individual bunches, ~1 ns long pulse train, several ms long
The Target Proton beam Energy 2 -30 Ge. V Current 2 -0. 1 m. A Power 4 MW Target (high z material such as tantalum) Not a stopping target Dimensions 20 cm long (2 interaction lengths), 1 -2 cm diameter Power Dissipation Pulse ~2 ms, Power Density (2 ns substructure) 50 Hz Energy Density 1 -2 cm diameter target cylinder 20 cm ~1 MW (average) ~16 k. W/cm 3 (average) ~320 J/cm 3/pulse
target protons Typical Schematic Arrangement of a Muon Collider Target
1 -2 ns 50 Hz 20 k. J 0. 3 k. J/cm 3 • pulse length • pulse repetition rate • energy dissipated per pulse • energy density 1 -10 MW 1 ms 50 Hz 20 -200 k. J 0. 03 k. J/cm 3 6 k. J/cm 3 • mean power dissipation • pulse length • pulse repetition rate • energy dissipated per pulse • energy density p-bar target at Fermi Lab Spallation Neutron Source Target 1 MW • mean power dissipation Neutrino Target Power Dissipation High Power Pulsed Targets
The Importance of Target Studies • The proton accelerator looks good • The collection and cooling channel is inefficient but will work • The target is the only “Show Stopper” • Know how to design a target for lower power dissipation - ~100 k. W
Design Considerations Need to know Beam current density profile and target geometry Power density distribution within the target Apply thermal calculations Cooling, Stresses including Pulsed Effects, Temperatures Radiation Effects Shielding, Activity, Remote Handling, Beam Dump, Radiation Damage, Maintenance, Target Changes, Disposal Magnetic field, sc magnet (heat and radiation), Forces, Induced Currents
Cooling Mainly a problem of power density 1. Fluid Cooling Water (limited to ~5 -10 k. W/cm 3) Liquid metals Gas 2. Conduction 3. Radiation Limited to ~400 W/cm 2 Increase the Effective Volume Larger target- less dense, larger cross-section, less radiation damage Moving target - rotating wheel, moving band Flowing Target - liquid metal in tube, liquid metal jet, solid powders in fluid - radiation damage no problem
Water Cooled Target 2 cm diameter x 20 cm long water one central water channel 2 mm diameter water channels, taking up 50% of the cross sectional area Insufficient heat transfer across the water boundary Just possible (probably)
Current Status CERN have had considerable success with studies of mercury jets (with BNL), including within solenoidal fields. They are putting forward mercury jet and granular targets. CERN ISOLDE have experience of the problems of radioactivity and of shock waves. They have a laboratory suitable for handling active materials and molten metals - mercury. PSI are building a liquid metal target. They are involved with the US in liquid metal targets for high power spallation sources. RAL has done preliminary tests on shock waves in hot tantalum using electron beams. CERN, PSI (not pulsed) and RAL have facilities providing high power proton beams. Also in the US at Los Alamos, Brookhaven and FNAL.
Programmes under way The USA are building SNS. The Japanese are active as well. LAL/Orsay are developing Horns.
Target Studies Continue with present lines of study 1. Molten Metal Jets 2. Flowing Contained Molten Metal 3. Helium Cooled Solid Spheres 4. Moving Solid Targets or Rotating Band 5. New Ideas?
The ISIS Target
Flowing Metal Target • Problems with Cavitation. • Problem for SNS and ESS Solid Target • Water cooled metal (tantalum) for up to 1 -2 MW • Tantalum is a good material. a. Little radiation damage. b. OK with water.
The basic concept (left) and conceptual design (right) of the MEGAPIE target
The Mercury Jet Proposed for the USA and by CERN • The jet breaks up when the beam hits it, but the beam has interacted with the jet before it has time to break up. So no problem. Tests show that the “next jet” is not prevented from appearing in time. Jet velocity ~30 m/s. • No power limit? • The jet hits the walls and they must take the heat and the effect of the mercury hitting the walls. Not thought to be a problem. • The mercury is condensed and recycled. It can also be distilled so removing some of the radioactive isotopes formed in the jet. • Interaction of the jet with the magnetic field of the solenoid is not a problem. • A mercury pool in the target chamber can serve as the beam dump.
• Handling the mercury is hazardous. If the mercury escapes severe hazard. Messy! • Need windows between the other parts of machine.
Tests at BNL and CERN • Calculations of injecting into a magnetic field showed small perturbations. • The field provides damping of the motion in the jet. Tests at Grenoble (CERN) show this. • Tests with a proton beam at BNL showed that the jet broke up.
Recent schematic of the CERN Target
Solid Metal Spheres in Flowing Coolant P. Sievers, CERN Small spheres (2 mm dia. ) of heavy metal are cooled by the flowing water, liquid metal or helium gas coolant. The small spheres can be shown not to suffer from shock stress (pulses longer than ~3 ms)and therefore be mechanically stable.
A Cu-Ni Rotating Band Target (BNL and FNAL) Radiation Cooled Rotating Toroid, Magnetically Levitated (RAL)
• TOROID OPERATES AT 2000 -2500 K • RADIATION COOLED • ROTATES IN A VACUUM • VACUUM CHAMBER WALLS WATER COOLED • NO WINDOWS • SHOCK? Pbar target OK. Tests using electron beam simulation indicate no problem.
Levitated target bars are projected through the solenoid and guided to and from the holding reservoir where they are allowed to cool. proton beam solenoid collection and cooling reservoir
Pulsed Effects • The thermal shock can exceed the mechanical strength of the material causing it to break. • The “pbar target” at FNAL is OK at 10 times the pulse power density. The pbar target has: 600 -700 J/gm in nickel discs, DT per pulse (1. 6 ms) ~1000 K (compare to 60 J/gm in the neutrino tantalum target) Stack of slowly rotating discs Gas cooling between discs proton beam pbar target
OTHER PROBLEMS Magnet • Target operates in a magnetic field, Forces, Induced Currents • SC magnet (heat and radiation), Radiation • Beam Dump - 1 -4 MW! Spread the beam to make cooling easier. • Radiation Shielding. • Maintenance. Remote handling essential. Target changes. • Disposal • Safety requirement/legislation -formidable.
Conclusions • We have a number of possible solutions. • None have been tested at full beam or lifetime (problem!). • Other problems only partly addressed. • Lots to do!!
Current Status
In-Beam Target Studies For a full-scale test with beam - need: 1. High Power Beam 2. Target Station with Facilities: • Radioactive handling • Chemical and contamination hazards • Disposal • EXPENSIVE!! - £ 100 M +
Note: Even with a full power beam test it is difficult to simulate life time studies in much shorter times.
Reality 1. CERN - no funds 2. ESS (neutrons) - no funds 3. RAL - some reasonably substantal funds over 3 years starting 2004 for accelerator and target R&D 4. Other Europe - no funds (? ) 5. SNS (neutrons, USA) - big effort on the target 6. Japan (neutrons) - likely to have big effort on target
FP 6 1. Network to include target studies 2. Design Study to be considered Will not provide enough money for a Target Station (or a full power proton beam)
FP 6, Network Target Section Collaborators: Helge Ravn (CERN) Roger Bennett (RAL) Jacques Lettry (CERN) Paul Drumm (RAL) Peter Sievers (CERN) Chris Densham (RAL) Bruno Autin (CERN) Dave Rodger (Bristol Univ. ) Francois Meot (CERN) Mohamed Farhat (Lausanne Univ. ) Andre Verdier (CERN) Friedrich Groeschel (PSI) Jean Marie Maugain (CERN) K. Thomsen (PSI) Günter Bauer (Juelich) G. Heidenreich (PSI)
What can be Realistically Achieved? 1. Calculations. 2. Simulated tests using electron beams, lasers etc. 3. Pulsed proton beams of less than ideal intensity from CERN or ISIS or -? 4. Unlikely to be able to do full power in-beam tests prior to building a suitable accelerator.
“EXCITING TIMES” • Challenge • At the edge and beyond present knowledge • New Ideas Required 1. The Liquid Metal (Mercury) Jet 2. Flowing, Contained Mercury 3. Spheres in Flowing Coolant 4. Rotating Band 5. Bars
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