Cold Neutron Spectroscopy on MACS  Virtues and limitations of INS  Enhancing INS at the NCNR  Description of MACS  Science on MACS  Integration of MACS in CHRNS  Summary Collin Broholm Johns Hopkins University and NIST Center for Neutron Research

CHRNS 1/5/05 Neutron Spectroscopy  A central tool in condensed matter physics - Unique information about dynamic correlations - Model independent access to interaction strength - Access microscopic structure of dynamic systems  Limited scope on current instruments - Need cm 3 sized crystals - Need weeks of beam time - Need neutron scattering expert  Increased sensitivity will broaden impact - Comprehensive surveys to test theory - Parametric studies - Smaller samples

CHRNS 1/5/05 Interesting samples come in all sizes Cu 2 (quinox) 2 Cl 4 ZnCr 2 O 4 Cu(C 4 D 4 N 2 )(NO 3 ) 2 Y 2 BaNiO 5 ≈ 40 mm ≈ 10 mm ≈ 4 mm ≈ 0.1 mm Bound spinons in spin-1 chainFree spinons in spin-1/2 chain Frustrated Magnetism Bound spinons in spin-1/2 ladder Need high sensitivity to access physics in small samples

CHRNS 1/5/05  Q and E resolved spectroscopy:  Energy scale J varies more than length scale a Resolution requirements to probe magnets Need range of E resolution at fixed Q resolution

CHRNS 1/5/05 Comparing TOF to TAS Large detector solid angle is possible E-scan without moving parts Can use spallation source peak flux Large detector solid angle is possible E-scan without moving parts Can use spallation source peak flux Can focus neutrons with Bragg optics Freely select range of energy transfer Can use reactor CW flux Can focus neutrons with Bragg optics Freely select range of energy transfer Can use reactor CW flux TAS like TOF like

CHRNS 1/5/05 TOF/TAS complementarity TOF Data from MAPS/ISIS TAS Data from NIST 10% Ca doped Y 2 BaNiO 5 Xu et al science (2000)

CHRNS 1/5/05 Unique Opportunities for INS at the NCNR 10 3  /  0 Brightness through cooling Steradian view of ≈ 250 cm 2 cold source

CHRNS 1/5/05 Characteristics of a TAS at NG0  Wave vector resolution using full beam:  Energy Resolution:  Flux on sample:  Incident Energy Range meV Ideal conditions for probing slowly propagating excitations in hard condensed matter Collin Broholm NIM (1996)

CHRNS 1/5/05 Maximizing the potential for new science  Beam delivery system - Focus full beam onto small sample - High rejection rate for non-E i neutrons - Variable Q and E i resolution  Detection system - Maximize solid angle of detection system - Offer variable resolution - Maximize S/N through shielding and geometry  User interface - Fast, accurate, and safe setup - Data Acquisition Planning Tools - Click for access to all features - Comprehensive visualization and analysis tools

CHRNS 1/5/05 Overview of MACS Shielding Helium Cold Source Shutter Cooled filters Radial Collimators Variable Aperture Focusing monochromator on translation stage Focusing monochromator on translation stage 6.2 m Focusing supermirror Aperture Attenuator Monitor Aperture Attenuator Monitor Sample position 40 channel detection system

CHRNS 1/5/05 MACS beam shutter Four position rotating shutter 1.Closed: 70 mm thick neutron shielding 2.50 mm vertical slit 3.Conical full opening mm vertical slit

CHRNS 1/5/05 Cooled Incident Beam filters Reject non-E i neutrons  E i < 5 meV : 10 cm beryllium  E i <15 meV : 5 cm PG  E i <20 meV : 8 cm Sapphire  Cold filters move in vacuum  Pneumatic actuation in <15 s

CHRNS 1/5/05 The Monochromator Cask Collimators to control E-resolution Doubly focusing monochromator Aperture to control Q-resolution Translation Stage to vary incident energy

CHRNS 1/5/05 Four-position Radial collimator Open 40’ 20’ 60’ Control source size hence   Gd 2 O 3 coated Stainless foils  Two aligned segments: 4 settings  Pneumatic actuation in <15 s

CHRNS 1/5/05 Variable incident beam aperture Control beam envelope hence  Q  Independent control of Q-resolution  Trim beam to match monochromator  Full range actuation in 5 s  10 cm moderating+absorbing shutters B4CB4C High density Polyethylene 10 cm

CHRNS 1/5/05 The MACS monochromator Rotation Stage Translation Stage 10 B:Al shielding 3 × Hollow aluminum posts 357×4 cm 2 PG(002) platelets with adjustable surface normal 357×4 cm 2 PG(002) platelets with adjustable surface normal 45 cm 35 cm

CHRNS 1/5/05 Worlds brightest neutron beam Y. Qiu and Y. Dong (2004)  (10 8 n/cm2/s) ’ 40’ 60’ open IN14

CHRNS 1/5/ Channel MACS detection system Cryo-filters to reduce background Collimators to vary resolution 20 × spectroscopic detectors 20 × double x-tal PG analyzers 20 × double x-tal PG analyzers 20 × diffraction detectors

CHRNS 1/5/05 The Double Crystal Analyzer Unit  Variable energy 2.5 meV<E<15 meV  Vertically focusing “compound lense”  Background suppressing collimator  Motion controlled by a single motor  Patent pending for Tim Pike’s design PG not yet mounted

CHRNS 1/5/05 Multi Analyzer Crystal Spectrometer

CHRNS 1/5/05 Constant energy transfer slice kiki kfkf Q

CHRNS 1/5/05 Assembling slices to probe Q-E volume 2 meV 1 meV 0 meV

CHRNS 1/5/05 Data Acquisition Planning with DAVE  User indicates part of Q-E space to cover - Click and drag graphical input on Q-E space slices  DAVE generates script for optimal settings - Point spacing determined by calculated resolution - With full awareness of limits of motion - Reports actual volume covered  Script is executed by instrument control program  DAVE provides real time images of data

CHRNS 1/5/05  Expand the scope for Inelastic scattering from crystals: —0.5 mm 3 samples —Impurities at the 1% level —Extreme environments: pressure and fields to tune correlated systems —Complete surveys to reveal spin-wave-conduction electron interactions  Probing short range order —Solid ionic conductors, spin glasses, quasi-crystals, ferroelectrics, charge and spin polarons, quantum magnets, frustrated magnets.  Excitations in artificially structured solids —Spin waves in magnetic super-lattices —Magnetic fluctuations in nano-structured materials  Weak broken symmetry phases —Incommensurate charge, lattice, and spin order in correlated electron systems Elements of Scientific Program for MACS Saxena et al. (2000) Schreyer et al (2000) Lee et al. (2002) Matsunada et al. (2002) J. Rodriquez et al (2004)

CHRNS 1/5/05 Funding MACS InstitutionFunds NIST$3.9M NSF-MRI$1.7M JHU$1.3M MACS$6.9M

CHRNS 1/5/05 White Beam Conditioning System (NCNR) Monochromating system (JHU-IDG) Get Lost pipe (NCNR) Monochromatic beam transp. Sample positioning system Detection System Building MACS

CHRNS 1/5/05 Schedule for MACS MilestoneDate Installation of beam line components requiring long shutdownSept First monochromatic beam to sample positionSpring 2005 Instrument ready for commissioning experimentsFall 2005 Instrument ready for general users through CHRNSSummer 2006

CHRNS 1/5/05 Integration of MACS in CHRNS  Broad scientific impact requires CHRNS users - Partial support for 1 senior+2 junior scientists to operate MACS for users - Software development through DAVE - Amplify the MACS educational program through the CHRNS summer school  Partial support of maintenance - Miscellaneous repairs and upgrades - Computer hardware and software  Distribution of beam time - 20% NIST - 20% JHU - 60% CHRNS users

CHRNS 1/5/05 Summary  MACS makes use of unique aspect of the NBSR: large solid angle access to intense cold neutron source  MACS will be a formidable tool to probe nano-scale dynamics in hard condensed matter - Most intense cold neutron beam in the world - Multi-channel low background detection system - seamless access to advanced features through DAVE  Ability to tailor energy range and resolution makes MACS complementary to TOF spectrometers  An active user program through CHRNS is needed to realize the scientific potential of MACS

CHRNS 1/5/05 Contributors to MACS project NIST Center for Neutron Research: G. Baltic, P. C. Brand, C. Brocker, M. English, P. D. Gallagher, C. J. Glinka, P. Kopetka, J. G. LaRock, J. W. Lynn, J. Moyer, N. Maliszewskyj, D. J. Pierce, M. Rowe, J. Rush, and others Johns Hopkins University: R. Barkhouser, C. Broholm, R. Hammond, P. K. Hundertmark, R. Lavender, J. Orndorff, T. D. Pike, G. Scharfstein, S. A. Smee, and others