Proposal for a High Intensity Chopper Spectrometer at LANSCE Science requiring high sensitivity neutron spectroscopy Limitations of current instrumentation.

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Presentation transcript:

Proposal for a High Intensity Chopper Spectrometer at LANSCE Science requiring high sensitivity neutron spectroscopy Limitations of current instrumentation Optimizing for sensitivity Description of the HELIOS spectrometer Project Cost and Schedule

The HELIOS Team Gabriel AeppliNEC Research Institute Collin BroholmJohns Hopkins University Brent FultzCaltech Bernhard KeimerPrinceton University Sanford KernColorado State University Thom MasonOak Ridge National Lab. Herb MookOak Ridge National Lab. Steve NaglerOak Ridge National Lab Ray OsbornArgonne National Lab. Rob RobinsonLos Alamos National Lab.

Science Requiring High Sensitivity Neutron Spectroscopy 5<h  <500 meV Materials with inherently broad spectra and weak scattering - Phonon Density Of States (DOS) of small powder samples - Magnetic excitations in correlated metals - Impurity Dynamics - Dynamics in disordered systems - Multi-magnon modes in Quantum Magnets Parametric Studies of Dynamics versus P, T, H and composition - Phonon DOS throughout structural phase diagram - Spin dynamics throughout magnetic phase diagram - Initial surveys of novel classes of materials

Coupled magnetic and phonon excitations in SrRuO3 Only small samples are available Several Q and T must be probed

MARI data on pure Y 2 BaNiO 5 Magnetic Scattering from a one dimensional S=1 Antiferromagnet Large crystals were available and we used 20 g

Ca Doping of Y 2 BaNiO 5 Yields Mobile Solitons Double Ridge below 7 meV is structure factor of spin soliton We want to know if solitons persists above the Haldane gap

MARI data on Ca doped Y 2 BaNiO 5 Single crystals of Y 2-x Ca x BaNiO 5 are too small for detailed studies of hole doping in a quantum spin liquid using MARI

Universal Scaling of  ”  at Quantum Critical Point in UCu 4 Pd

Pros and cons of current Instrumentation for this type of experiments Thermal Neutron Triple Axis Spectrometers Conventional Spallation Source Chopper Spectrometers

Neutrons per pulse at sample N =  t 1 dE i /dt 0  t 0  i

Energy Transfer Resolution

Constrained Optimization Given: E i, h ,  h , and secondary spectrometer Optimize: Incident Flight path and pulse width  t 0 Assume: Peak flux  and  t 0 are independent and N=4 guide starting 4 m from source

Flux and Resolution Calculation Flux (n/cm 2 /sec) E i (meV) dE i (meV)

Comparing MARI and HELIOS HELIOS views 12.5x12.5 cm 2 moderator MARI views 10x10 cm 2 moderator (Actual case)

Comparing MARI and HELIOS HELIOS views 12.5x12.5 cm 2 moderator MARI views 12.5x12.5 cm 2 moderator (Optimistic case)

HELIOS Spectrometer Development Team

Summary of HELIOS Proposal Important problems in Materials Science and Condensed Matter Physics require high sensitivity neutron spectroscopy with 5 meV < h  < 500 meV and 5 meV <  h  < 10 meV. Current neutron spectrometers are not optimized for such experiments. HELIOS combines the broad phase sampling of chopper spectrometers with the relatively coarse energy resolution of triple axis spectrometers to address this need. HELIOS will be a unique resource at LANSCE and an important development project for the SNS.