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1、Conceptual design and performance of high throughput cold spectrometer : MACS,Why MACS Layout and key elements Performance Data collection Scientific program Budget and schedule Conclusion,Collin BroholmJohns Hopkins University and NIST Center for Neutron Research,NSF/NIST 10/19/00,MACS development
2、team,Overall instrument designPaul Brand NISTChristoph Brocker NISTCollin Broholm JHU Jeff Lynn NISTMike Rowe NISTJack Rush NISTYiming Qiu JHU,Focusing MonochromatorSteve Conard JHUJoe Orndorff JHUTim Reeves JHUGregg Scharfstein JHU Stephen Smee UMD,Shielding CalculationsCharles M. Eisenhauer,NSF/NI
3、ST 10/19/00,Why cold neutrons and double focusing,Q and E resolved spectroscopy requires,Energy scale J varies more than length scale a,To probe a range of materials must vary keeping To probe hard matter with low energy scales Reduce Ei. Cold source provides the flux Increase angular divergence bef
4、ore and after sample,NSF/NIST 10/19/00,Kinematic limits for neutron scattering,Efix and 2q range determine accessible Q-E space,NSF/NIST 10/19/00,Comparing TOF to TAS,Larger detector solid angle E-scan with “no” moving parts Can use pulsed spallation source peak flux,Can focus beams with Bragg optic
5、s Can select range of energy transfer Can use reactor CW flux,TAS like,TOF like,NSF/NIST 10/19/00,NCNR Liquid Hydrogen cold source,MACS Beam,New cold source to be installed in 2001 will double flux,Overview of MACS,Design by C. Brocker, C. Wrenn, and M. Murbach,NSF/NIST 10/19/00,Bragg focusing,Sourc
6、e,Sample,Rowland Circle,Focusing Monochromator,NSF/NIST 10/19/00,Doubly Focusing Monochromator,Design by Stephen Smee, G. Scharfstein et al.,NSF/NIST 10/19/00,Blade profile chosen so blades form arc when compressed,S. Smee et al. Provisional patent pending (2000),NSF/NIST 10/19/00,Focusing mechanics
7、 is out of beam,Vertical,Horizontal,Design by Stephen Smee, G. Scharfstein et al.,NSF/NIST 10/19/00,Prototype performance,2 cm,JHU IDG photo, prototype, and measurement,NSF/NIST 10/19/00,Constrained optimization : crystal mosaic,Flux versus mosaic at fixed 0.2 meV energy resolution,NSF/NIST 10/19/00
8、,Effects of cystal misalignment,NSF/NIST 10/19/00,Projected performance analytical approximation,C. Broholm, Nucl. Instr. Meth. A 369 169-179 (1996),NSF/NIST 10/19/00,Monte Carlo Simulation of MACS,Y. Qiu and C. Broholm to be published (2000),NSF/NIST 10/19/00,Resolution: Analytical and Monte Carlo
9、simulations.,Y. Qiu and C. Broholm to be published (2000),NSF/NIST 10/19/00,Multiplexing crystal analyzer system,Design by C. Brocker,One of twenty channels,BeO filter,Be filter,PG filter,Collimator 2,Collimator 1,8o vertically focusingAnalyzer crystals,“TAS” detector,Energy integratingDetector,Desi
10、gn by C. Brocker,NSF/NIST 10/19/00,Fixed vertical focusing of analyzers,Double analyzer is “compound lens” efficient vertical focusing,NSF/NIST 10/19/00,Constant energy transfer slice,NSF/NIST 10/19/00,Assembling slices to probe Q-E volume,0 meV,1 meV,2 meV,NSF/NIST 10/19/00,Projected data collectio
11、n times,Powder sample Q-E map8 x 30 pts x 0.2 min. = 1:00Single crystal constant-E slice8 x 100 pts x 0.5 min. = 6:40Single crystal complete Q-E Volume8 x 100 x 10 pts x 0.5 min.= 3 days,CuHpCl,SCGO,NSF/NIST 10/19/00,Scientific Program for NG0 spectrometer,Expanding the scope for Inelastic scatterin
12、g from crystals:0.5 mm3 samplesimpurities at the 1% levelcomplete surveys to reveal spin-wave-conduction electron interactionsextreme environments: pressure and fields to tune correlated systemsProbing short range ordersolid ionic conductors, spin glasses, quasi-crystals, ferroelectrics, charge and
13、spin polarons, quantum magnets, frustrated magnets.Weak broken symmetry phasesIncommensurate charge, lattice, and spin order in correlated electron systemsExcitations in artificially structured solidsSpin waves in magnetic super-latticesmagnetic fluctuations in nano-structured materials,NSF/NIST 10/
14、19/00,Probing hole wave function in oxide : 1 D 2D?,Y2-xCaxBaNiO5,Xu, Aeppli, Broholm, et al. Science (2000),NSF/NIST 10/19/00,NSF Share (50%) of the Construction of MACS,Design&Construction,Design,Construction&Design,Construction&Assembly,Assembly&Commissioning,$k,NSF/NIST 10/19/00,Conclusions,Larg
15、e solid angle access to NCNR cold source enables a unique cold neutron spectrometer.MACS employs Bragg optics to focus the beam and provide 108 n/cm2/s on the sample at 0.2 meV resolution. The MACS detector concept offers the versatility, resolution, and low background of a TAS with 20 times greater
16、 data rate. The highly efficient constant E mode of MACS will provide a unique capability for probing the structure of fluctuating systems.MACS will be complementary to the DCS and future SNS TOF spectrometers because of its unique data collection protocolNSF partnership is needed to realize the potential and make the unique capabilities available to widest possible cross section of the US scientific community,
