Source Group Bethan Dorman Paul Morris Laura Carroll Anthony Green Miriam Dowle Christopher Beach Sazlin Abdul Ghani Nicholas Torr

Why? A Neutrino Factory yields the highest flux neutrino beams achievable, and the beam parameters are well controlled and understood A Neutrino Factory is the only way to produce equal ratios of electron and muon type neutrinos Thus, the Neutrino Factory and its remote detector will enable precision measurements of all the unknown parameters.

Schematic diagram NOT TO SCALE

4MW Power : Neutrino flux is heavily dependant on the power of the proton beam, by the relation: 10 GeV Energy …compromise of high yield of ‘interesting’ pions and sustainability of target Beam must be bunched, and the bunches separated into pulses … sustainability of target muons are produced with a narrow longitudinal spread to reduce beam loss in the acceleration processes Proton Driver Requirements of a Proton Driver for a Neutrino Factory

Proton Driver Requirements of a Proton Driver for a Neutrino Factory

Key Features of the Proton Driver Proton Driver Penning Hydrogen ion source  Must be able to supply 60mA of current  lifetime of approximately 60 days  duty cycle of between 5 and 10%  NB. Contains Caesium to improve efficiency in production Solenoids  3 Solenoids will act as the Low Energy Beam transport (LEBT)  Focuses and collimates beam from the source to the RFQ  Chosen over Electrostatic Einzel Lens LEBT due to proximity to Caesiated ion source

Key Features of the Proton Driver Proton Driver Linac Structure 1 Radio Frequency Quadrupole (RFQ) RF-Focused Drift Tube (RFD) Combines the efficiency of a DTL and strong focusing of an RFQ Utilises Radio Frequency cavities to gently accelerate, bunch and focus beam Injection energy of 65 KeV, Extraction energy 3 MeV Chopper Removes sections of the beam to create a larger separation between bunches Use of ‘Fast’ and ‘Slow’ Chopper to avoid partially chopped bunches Removes 30% of the beam with a 99.9% efficiency

Key Features of the Proton Driver Proton Driver Linac structure 2 Linac structure 2 based on RAL design  Accelerates and focuses with RF-Cavities ions from 3 MeV to 180 MeV  Drift Tube Linac (DTL) to 90 MeV  Side-Coupled Linac to 180 MeV  Single pass device…not subject to repetitive conditions which can cause destructive resonance Stripping Foil  Converts H- ions to protons by removing both electrons  Carbon foil chosen due to low nuclear charge and a high efficiency at low foil thicknesses, which reduces beam loss  Located before acceleration to higher energies to avoid excessive foil heating

Key Features of the Proton Driver Proton Driver Synchrotron Synchrotron based on RAL design Four rapid cycling synchrotrons (RCS) 2 identical stacked boosters: 2GeV, 50Hz This combats space charge effects, and reduces demand on source by increasing beam intensity These boosters jointly feed the two main synchrotrons in alternate pulse succession Two identical stacked main synchrotrons: 10GeV, 25Hz Used for final acceleration and bunch compression Alternate pulses from each main synchrotron fired at target

Schematic Design of Proton Driver Proton Driver

Target Material Target material – Liquid-Hg. Why? A very good conductor High atomic number, Z = 80. Withstand thermal shock Higher production of pions when bombarded by the protons in the beam. Target limitations: 4 MW power delivered in < 40 μs-long at 1 ns length proton pulses with a repetition rate of 50 Hz.

Target Material Why not solid materials like Carbon, Gold, Tantalum or Tungsten? ISIS found the problems arose for solid target are: Extreme radiation damage in the target itself Thermal shock produced by short pulses of high power proton beam. Ability to cool the target at proton beam power above ≈ 1MW. Eddy current effects

Pion Production Figure 1: Left: Liquid Mercury target Right: Solid Carbon target

Beam dump High powered proton beam still remains after target Liquid mercury Looped in with target

Methods of Capture Solenoid has higher pion capture Horns are essential for the separation of pion signs The shape can be changed Double horn Diagram showing water cooing for a horn

Horn Shape designed to look at one area of the particles produced The polarity of the particles being looked at can easily be changed Water cooled Limited lifetime Replaced as a unit

The ‘Neuffer’ Front End Many different methods but ‘Neuffer’ uses existing technology – more cost effective Allow particles to drift Bunch the beam using RF cavities Phase Rotation Inject into a cooler system

Allows pions to decay to muons. Branching ratio ~99.99%. Decay length L 0 needed, relativity a factor. L 0 = βc x γτ where γ = E/m Probability of decay given by, P = 1 – exp(-L D / L 0 ) The drift channel will be 27m long allowing ~60% of the muons to decay. Effects of premature muon decay will be minimal. To ensure flux of muons per year ~10 14 pions per second needed The channel will be constructed of five, 5m long, 1.25T solenoids with 0.5m gaps between them for beam diagnostic equipment or servicing ports. Drift Section

Phase Rotation Used to reduce the energy spread of muons by a factor of 2. Interesting muons in the energy region 200MeV±100MeV. Phase rotation will modify this to be 200MeV±50MeV. This is achieved by decelerating particles that arrive early with high energy and accelerating those with low energy. This bunches the particles together. This is done by flipping the polarity of a series of RF cavities according to the bunch length of particles entering this section. This section also builds up a correlation between particle energy and position. Values of frequencies required are still undergoing calculation.

Ionization Cooling Beam emittance must be further reduced. When particles travel through a material, they ionize electrons within that material and hence loose momentum. Beam is passed through an absorber (loosing transverse momentum) then re-accelerated longitudinally.

Cooling Channel Design A linear ‘SFOFO’ design. Liquid hydrogen absorbers separated by RF cavities, all surrounded by a focusing solenoid. Total length of 120m. The field will oscillate (~ 201MHz) and increase in strength along the channel. Aim to achieve an emittance of 8.8mm. mrad before entering the FFAG accelerator.

FFAG’s for Muon Acceleration Fixed Field Alternating Gradient accelerators: Muon decays occur too quickly for cycling magnets. Require less RF then Linacs and RLA. FFAG lattice can accept beam over large energy range (5- 20 GeV). And a large momentum acceptance. High repetition rate. Small magnet apertures. Field increases with particle energy but through path variation not time variation. Orbit changes with energy, RF changes slightly. Injection low energy Extraction high energy

Scaling or Non-Scaling Scaling FFAG’s have a constant orbit shape, Which gives constant betaron tune. If Non-Scaling then can lose control of tune so get resonance. However with rapid acceleration betaron doesn’t have time to build up resonances that destroy the beam. Advantages to Non-Scaling FFAG’s: Smaller orbit excursion thus small/cheaper magnets. Higher RF system can be used ~200MHz Linear variation of magnetic field with radius which leads to a large dynamic aperture and transverse acceptance.

The acceleration in FFAG’s occur in RF cavities between the bending magnets. (Just like in synchrotrons) RF Cavities The accelerating field varies sinusoidally with time. For a particle to be accelerated, they must arrive at the cavity at the right time. Example: For a muon (negative charge) to be accelerated it should arrive in the RF cavity at positive and exit at negative voltage. RF Voltage Tim e

To achieve the energy required a linac followed by two FFAGs will be used in the acceleration system. 600 MeV muons from cooling and phase rotation Linac 200 MeV to 5 GeV High energy FFAG (22 to 45 GeV) 45 GeV muons to decay ring Low energy FFAG (5 to 22 GeV) Acceleration System Arrangement The FFAGs will be based on the EMMA accelerator which is currently under construction. As is shown the muons are accelerated to a final energy of 45 GeV then stored in the decay ring.

Muon Storage Rings Where the muons decay to neutrinos. Muon decay length increased as they are at 45GeV Neutrinos follow tangentially the same path as their parent muons Requires decay straights to create a beam

Geometries Three main types: 3.) Triangle 1.) Racetrack 2.) Bow-Tie

Racetrack - For two detectors, need two rings: raises costs - Two ring design offers flexibility of detector locations OR straights inclined with respect to each other: raises costs due to more complicated engineering, and more loss on elongated arcs

Bow-Tie - Can produceandsimultaneously along axis of the decay straights (to two different detector sites), or single polarity to detector sites in front and behind - No spin depolarisation due to geometry - makes calculation of energy spread difficult.

Triangular - Can produceandsimultaneously along axis of the decay straights (to two different detector sites), or single polarity to detector sites in front and behind - More efficient than racetrack configuration (short arc length, long decay straights) - Low neutrino beam divergence due to focussing solenoids

Triangular Triangular design chosen because - High neutrino production efficiency - Cost - Flexible geometry (detector site)

Muon Storage Rings Triangular Two production straights of length Third side houses loss collimators, RF systems, tuning quadrupoles Efficiency

Energy Distribution An important result required to ensure the configuration of the source and detector is the angular energy distribution of the final neutrino beam for both electron and muon neutrinos(antineutrinos). In the muon rest frame this is given by, Where x = E ν /m μ, dΩ = dcosθ l dφ and θ is angle between spin and mom m. To modify this to the lab frame it must be Lorentz boosted i.e. replace E ν /m μ with E ν /E μ. To plot a distribution of the beam on axis we must: – Integrate over the azimuthal angular dependence i.e. multiply by a factor of 2π. – Let cosθ = 1.

Energy Distribution

Summary

Thank you

Design specifications Low energy FFAG (5 to 22 GeV)High energy FFAG (22 to 45 GeV) Radius (m)14095 Number of bending magnets Magnet packing fraction15%18% Min Magnetic field (Tesla) Max Magnetic field (Tesla) Number of RF cavities RF Frequency (MHz) RF Gradient (MVm -1 ) Number of orbits to max energy ~10~20

Muon Storage Rings Triangle Racetrack Efficiencies