# Presentation: 669697

## American Conference on Neutron ScatteringCollege Park, Maryland6-10 June, 2004

- TECHNICAL CONCEPTS FOR A
- LONG-WAVELENGTH TARGET STATION FOR THE SPALLATION NEUTRON SOURCE
- J. M. Carpenter for the LWTS Design Group
- Argonne National Laboratory
- Oak Ridge National Laboratory

## A Long-WavelengthTarget Station for the SNS

- Contributors
- Design group
- H. A. Belcha, J. M. Carpentera, E. B. Iversonb, R. Kleba, A. E. Knoxa,    K. C. Littrella, B. J. Micklicha, J. W. Richardsona, with consultants M. Araic, K. N. Clausend, D. F. R. Mildnere
- Science Case
- L. J. Magidf and many U. S. university community members
- Instruments
- IPNS Instrument Scientistsa
- Project leader
- T. E. Masonb
- a ANL/IPNS; b ORNL/SNS; c KEK; d Risø; e NIST; f U. Tenn.,Knoxville

## Background

- DOE SNS project funded in 1998 with High Power Target
- 	Station (HPTS) only; completion 2006
- Capacity for second target station included from the start
- NSF funded second target station concept development in 1999
- Long-Wavelength Target Station (LWTS) conceptual design team		 based at Argonne/IPNS
- Workshops defined scientific applications and suggested instruments
- LWTS target system and instrument concepts developed on basis of
- 	continuous interaction with science requirements
- LWTS development work halted in May, 2001
- SNS second target station in DOE mid-term plan

## SNS 20 Year Plan

- At the present pace, all of the High Power Target Station (HPTS) beamlines will be allocated by ~FY06 and built out by ~FY13
- This implies a schedule for the second, Long-Wavelength Target Station (LWTS), which could begin with CD-0 in 06 and lead to CD-1 in 08 and CD-4 in 13

## More

**Results of the Design Study are documented on the web at:**
- _[http://www.](http://www.sns.gov/users/documents/LWTSNov021.pdf)__[sns](http://www.sns.gov/users/documents/LWTSNov021.pdf)__[.gov/users/documents/LWTSNov021.pdf](http://www.sns.gov/users/documents/LWTSNov021.pdf)_
- The LWTS concept is more advanced that SNS was at the time of its Conceptual Design Report
- Cost and Schedule Estimates are based on current SNS cost and schedule for very comparable systems
- The central design philosophy is to optimize the second target station specifically for long wavelength neutrons (a logical consequence of a lower frequency operation)
**The goal is for > 3 times the neutrons per pulse as HPTS in the wavelength range of interest, which has been substantially exceeded in some instances**
- 	An external review (with members of the SNS Target/Instrument Advisory Committee), held in January 2000, approved the preliminary concept

## Configuration

- Basic target configuration, shop areas, target remote handling cell, overall building design will be as nearly as possible the same as the HPTS
- Solid targets studied for the 1-MW IPNS Upgrade and as backup for HPTS are the basis for LWTS target technology

## Parameters of SNS HPTS and LWTS

- Accelerator:
-      SC linac delivering 1-GeV H-  ions in 1-ms bursts at 60 Hz
- Storage ring:
-      accumulating protons into ~0.5-μsec pulses
- HPTS: 60 Hz
-      flowing Hg target, Be reflector, three L-H2 moderators @ ~20 K,
-      one H2O moderator @ ~300 K; time-average power, 1.4—> 2 MW
- LWTS: 10 Hz
-      solid W target, Be reflector, three moderators, L-H2 @ ~20 K,
-      S-CH4 @ ~22 K, L-CH4 @ ~100 K; time-average power, 333 kW
- LWTS follows SNS power upgrade—no sacrifice of HPTS power

## Parameters of LWTS: Summary

## SNS April 2004

- • The SNS will begin operation in 2006—now > 75% complete
- • At 1.4 MW it will be ~8x ISIS, the world’s leading pulsed spallation source
- • The peak neutron flux will be ~20-100x ILL
- • SNS will be the world’s leading facility for neutron scattering
- • It will be a short drive from HFIR, a reactor source with a flux comparable
- to the ILL

## Bird’s-eye View of SNS witha Concept for LWTS

## LWTS Concepts

- LWTS is optimized for long-wavelength  neutrons:
- Low pulsing frequency
- Coldest spectra —> lowest temperatures, best moderator media,
- 	 e.g., L-CH4, S-CH4 (L-H2-cooled pellets)
- These require low power, consistent with low pulsing frequency
- Low power enables solid target, x ~ 1.20 (over Hg)
- Long wavelengths implies extensive use of guides
- Curved guides and beam benders enable slab moderators x ~ 2.0
- 	(over wing moderators)
- Vertically-extended target, slab geometry enable target-independent,
- 	vertical moderator access

## LWTS ConceptsContinued

- Planning for LWTS instruments, funded by DOE and NSF,
-  	has proceeded in parallel with LWTS concept development
- Breakout sessions at the major SNS Users Meetings
- (5 from 1998-2002)
- LWTS focused workshops as part of the NSF-sponsored design study
- Soft Matter (Blasie (Penn), Briber (Maryland))
- Magnetic Materials (Broholm (Johns Hopkins),
- Argyriou (ANL))
- Disordered Materials (Glyde (UDel), Loong (ANL))
- Crystallography (Wilkinson (GATech), Jorgensen (ANL)
- Chemical Spectroscopy & Dynamics (Bordallo (ANL),
- Blasie (Penn))
- Structural Biology (Dealwis (UT))
- Vibrational Spectroscopy (Larese (UT))

## Science Input Informed Technical Design Concept

**The output of the various working groups that developed the science case is documented in the summary report to NSF which is available on the web at:**
- _[http://www.sns.gov/users/documents/lwts_science_case_rpt.pdf](http://www.sns.gov/users/documents/lwts_science_case_rpt.pdf)_
- Led to a reference suite of 21 instruments (which would be refined following the peer review process already in place for HPTS when LWTS proceeds).  These aided in defining the LWTS instrument layout.
- Of these, 11 were chosen as a set of First Instruments, of which four were analyzed in greater detail

## Proposed First Instruments

## LWTS Instrument Layout

- (SANS)

## Shield and Beam Transport Arrangements

## LWTS Target

## LWTS Target/Moderator/Reflector Assembly

## Horizontal Cross Section of TMR

## Vertical Cross Sections of TMR

- Section B-B (Middle)                 Section C-C (Upstream)

## Methane Pellets

- Process of C. A. Foster, CAF Inc., Oak Ridge, TN

## Curved Guides and Compact Benders

## To Choppers

- “To choppers” are another method for reducing the intensity of fast neutrons in the neutron beams.  These are massive, synchronously-rotating blocks of stopping material located near the edge of the bulk shield, which close off the direct view of the moderator at the time of the proton pulse (To ), but open to pass the longer-wavelength neutrons of interest.  There are several forms of these; both parallel-axis and transverse-axis types work well in ISIS and IPNS.
- Time did not permit us to include To choppers in the LWTS
- layout, but they would fit into the concept described here.

## LWTS Neutronic Performance

- Monte Carlo (MCNPX) simulations of neutronics, heating rates, etc.
- 	in Target/Moderator/Reflector (TMR) systems
- Basis for engineering assessments and source systems optimizations
- Basis for instrument design and evaluation
- Figures summarize calculations of neutronic performance:
- 	Intensity for various moderator materials in different
- 	locations vs. neutron energy
- 	Pulse FWHM for various moderators vs. neutron energy

## Materials of the LWTS Neutronics Model

## Spectral Intensities

## Pulse Widths

## LWTS Moderator Performance Parameters

## Summary and Conclusions:Target Systems

- We have developed, analyzed, and documented a conceptual design for a feasible, highly efficient, Long-Wavelength Target Station intended as a second target station to complement the High Power Target Station of the Spallation Neutron Source, now under construction  at Oak Ridge.
- Not discussed here, we have evaluated in some detail the scientific case for the LWTS and devised a number of  instruments that would exploit it effectively.
- Authorization to proceed with the design and construction of a  second target station lies in the future.

## Instruments Considered in Detail 

- Instrument designers, responding to needs outlined in the Science Case, considered in detail a subset of the reference instrument suite
- The Reference Suite consists of 11 instruments (out of 21) well matched to the LWTS performance characteristics
- Four of those instruments were examined in greater detail, carrying out simulations to confirm performance projections

## BRIMS Broad Range Intense Multipurpose SANS

- Small-angle neutron scattering has extensive uses for characterizing materials in such fields as polymers, biology, ceramics, metallurgy, porous materials, and magnetism.
- SANS has high sensitivity in the size range of 1 to 100 nm and enables probing complex hierarchical structures that have several distinct length scales.
- BRIMS combines the best features of the reactor based and time-of-flight (TOF) SANS instruments and is capable of measuring data in a Q-range of 0.001–0.7 Å in a single, fast measurement.

## BRIMS Performance

- Comparison of count rates and resolution for BRIMS and D22 using the result of Monte Carlo simulations and analytical calculations

## BRIMS Science

- Confinement and extreme environments:
- SANS from the surface structure of a micellar solution under shear flow. Top: fully aligned structure; bottom: partially relaxed

## BRIMS Science

- (a) Self-assembled arrays of nanoparticles show order on two distinct length scales giving rise to
- (b) information at both high and low Q in the diffraction patterns.

## CAS Crystal Analyzer Spectrometer

- 200 neV crystal analyzer spectrometer in backscattering geometry
- Conceptually similar to HPTS backscattering except operates at longer wavelengths and employs larger d-spacing mica analyzer crystals

## CAS Science

- Studies of chemical and biomolecular dynamics often require systematic investigation of many similar molecules under slightly different conditions, demanding a large range of energy transfers and energy transfer resolutions for optimum study.
- There is a gap between the resolution accessed by neutron spin echo (NSE) techniques and NMR (in the time domain) and that accomplished in existing high-resolution direct- and inverse- geometry spectrometers.
- Filling this niche in energy resolution will allow systematic studies over the large ranges of energy transfer required by many disciplines.
- Balances the SNS inelastic suite complementing HPTS chopper and backscattering plus planned NSE

## MIDAS Magnetism Diffractometer

- Spin density measurements and diffuse/critical scattering
- Polarized beam capabilities
- High intensity at long wavelengths
- Access to large volumes of reciprocal space
- Low angular divergence, good d-spacing resolution

## MIDAS Science

- Neutron scattering from La1.2Sr1.8Mn2O7, above TC (at 130 K in the (0k0) plane showing a rod of magnetic scattering along the h0 direction).
- TOF single diffractometers measure large volumes of reciprocal space in a single crystal orientation.

## UHRPD Ultra High Resolution Powder Diffractometer

- Structural complexity—very large unit cells, phase coexistence, subtle superlattices and distortions, or expanded length scales—is increasingly important in the physical sciences; examples are proteins, designer porous solids, and self-assembled nanostructures to engineering alloys and cement.
- Neutron diffractometers with resolution comparable to or better than xray diffractometers (10-4) and good data rates (as UHRPD) will be well suited to addressing these problems because of their sensitivity to light atoms, different contrast levels, good intensity at high Q, and sensitivity to magnetic ordering.

## UHRPD Science

- Synchrotron data for BaBiO3. The splittings indicating the presence of two phases would not have been observable at medium resolution, but the use of x-rays led to problems with the superlattice peaks.

## Conclusions

- Developed concepts for a second target station for the SNS, optimized for use of long-wavelength neutrons, the LWTS.
- Design guided by extensive acquaintance with and experience at the existing spallation sources.
- Innovative and highly effective features appropriate for applications of long-wavelength neutrons.
- Evaluated the performance of a once-optimized system.

## Conclusions

- Identified a suite of instruments capitalizing on the unique features
- of LWTS in close collaboration with groups of interested scientists.
- Incorporated the instrument requirements into the facility design, a
- key feature of the LWTS effort.
- Assessed the performance of several instruments from the suite of
- possibilities.
- Unique capabilities in high resolution and high instrument throughput.
- The processes of instrument choice and design refinement continue.
- We solicit the involvement of scientists from the general community.

- Last slide—extras follow

## LWTS Reference Suite

## Instrument Selection

- The LWTS budget provides funding for construction of an initial instrument suite
- The actual instruments built would be selected following the model employed by HPTS
- All instruments proposed are reviewed in a two stage process by the Experimental Facilities Advisory Committee
- They must meet a “Best-in-Class” criterion meaning that the performance equals or exceeds the best in the world at equal source performance (i.e. minimum acceptable gain is the source gain but in general combined instrument and source gains are larger – typically an order of magnitude for LWTS vs HPTS for applications where LWTS is optimal – note HPTS already represents 10-100 times the current state of the art)

## LWTS CostBased on current SNS cost data in M$ (unescalated, 30% contingency)

|  | Year -2 | Year -1 | Year 1 | Year 2 | Year 3 | Year 4 | Year 5 | Total |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
|  | CD-0 |  | CD-1 |  |  |  | CD-4 |  |
| Conventional Facilities |  |  | 17.5 | 44.3 | 27.2 | 13.0 |  | 102.0 |
| Target |  |  | 15.6 | 29.3 | 35.0 | 27.7 | 9.4 | 117.0 |
| Instruments |  |  | 6.7 | 16.5 | 24.4 | 22.0 | 15.2 | 84.8 |
| Accelerator Facilities |  |  | 3.2 | 7.5 | 7.0 | 3.8 |  | 21.5 |
| Project Management |  |  | 3.4 | 3.4 | 3.4 | 3.4 | 3.4 | 17.0 |
| CDR, R&D | 2.3 | 5.0 | 6.5 | 5.9 | 2.9 |  |  | 22.6 |
| Total | 2.3 | 5.0 | 52.9 | 106.9 | 99.9 | 69.9 | 28.0 | 364.9 |

## LWTS Schedule

- Stages LWTS so that instruments begin to come on line once HPTS reaches saturation
- Meshes with Power Upgrade schedule so that additional beam power is realized in time to support LWTS without sacrificing HPTS performance

## LWTS Benefits

- Diversity
- More moderator types – more opportunity for fine tuning performance
- More instrument types – better optimization to specific needs and wider range of scientific capability
- Specificity
- Focus on long wavelength neutrons allows design choices (e.g., curved guides – slab moderators) that enhance performance for science with longer length scales or lower energy scales
- High Power Target Station gets narrower focus and better optimization as well
- Long-Term Growth
- With double the overall capacity SNS will be able to serve a larger and broader scientific community

## Summary

- A second, Long-Wavelength Target Station represents the optimal path to a significant number of high intensity cold neutron beams short of building an entirely new source
- By optimizing the source and instrumentation outstanding performance is obtained in areas of critical importance that support BES and DOE missions
- Soft condensed matter
- Magnetic materials
- Disordered materials
- Biomaterials
- Energy storage
- LWTS is the nanoscience neutron source and together with the SNS Power Upgrade increases the overall SNS scientific performance by a factor of 4 (for a fraction of the cost)
- The broad band characteristics of pulsed source instrumentation complement the capabilities of the proposed HFIR cold guide hall

## Ultra-High Resolution Powder Diffractometer (UHRPD)

- Moderator

- Choppers

- Guide

- Detectors

- Sample

- J. P. Hodges, J. D. Jorgensen, J. W. Richardson

## UHRPD Design Parameters

## Resolution and Intensity of UHRPD

- Very sharp pulses provided by a methane moderator in the epithermal energy (shorter-wavelength) regime facilitate high resolution performance of the UHRPD.
- The resolution degrades slowly at d-spacings larger than 1 Å.
- Monte Carlo simulations for a simple disk-shaped detector configuration at back-scattering angles indicate that ~10 min will be sufficient for a high-quality data set for a 1-cm3 sample.
- While the instrument can be operated at 10-Hz, the broader bandwidth achieved with 5-Hz operation will be desirable for many experiments.
- The choppers can also be phased to move the d-spacing range to larger values.

## BRIMS: A Broad-Range Intense Multipurpose SANS

- K. C. Littrell, P. Thiyagarajan,
- J. M. Carpenter, P. A. Seeger

## Key Features of BRIMS

- Supermirror beam bender to reduce gamma ray and high-energy neutron background
- User selectable pinhole or multiplexed pinhole collimation
- Uses neutrons with wavelengths from 1-15 Å, wavelength range determines overall length of the instrument
- Relatively short sample to detector distance to maximize range of detector at each wavelength
- Requires moveable, 1m square area detector with small pixels and a high data rate
- Space (1.4 m) allowed for spectral filters or polarizer elements between beam bender and collimation
- Frame definition choppers can be placed upstream from bender
- Can be augmented with a high-angle or backscattering PSD

## Monte Carlo Simulations

- Used the Los Alamos NISP neutron instrument simulation package
- Performed detailed simulations of settings marked * and existing instruments using identical delta function spherical-particle scattering kernels
- Effects of gravity included
- ILL-D22 SANS instrument settings as suggested by Roland Mays, D22 instrument scientist
-  ILL-D22 brilliance calculated from values plotted on the ILL-D22 website
- IPNS SAND simulations performed for actual geometry

## Comparison of Scattered Intensity at BRIMS and ILL-D22

## Comparison of Resolution At BRIMS and ILL-D22

## Performance of BRIMS

- The BRIMS instrument in its high-throughput configurations will have comparable scattered intensity and resolution relative to the ILL-D22 SANS.  Moreover, BRIMS covers nearly three decades in Q in a single measurement (about one decade per setting in D-22).
- The ILL-D22 SANS in its long configuration is better than BRIMS in terms of both counting rates and resolution below 0.002 Å-1.
- Honeycomb or bottle-case multiplexed narrow pinholes would reduce the difference in intensity substantially.
- Traditional crossed focusing sollers provide no real advantage.

## Proton Beam Transport to LWTS

## Protein Crystal Diffractometer (PXD)

- Moderator

- Area Detectors

- Sample and Orienter

- A. J. Schultz and M. E. Miller

## PXD Design Parameters

## PXD Performance

- The LWTS intense long-wavelength neutron spectrum and low repetition rate are well suited for a single-crystal macromolecular diffractometer.
- PXD will consist of a Kappa or full-circle goniometer with an array of two-dimensional position-sensitive area detectors covering a large solid angle (up to 5 steradians).
- The PXD will collect full hemispheres of 1.5-Å resolution Bragg diffraction data on ~ 1-mm3 macromolecule crystals in a few days.
- These data, in combination with X-ray diffraction data, will provide direct observation of hydrogen atoms in waters of hydration and within protein molecules and dramatically increase the number of protein and nucleic acid structures that can be determined.

## Need for PXD

- Hydrogen plays a very important role in the function of proteins through hydrogen-bonding interactions, steric interactions, and charge compensation and transport.
- The precise knowledge of the distribution of hydrogen atoms within protein molecular structures is of critical importance.
- However, hydrogen is not easily observable in X-ray structures.
- Protein crystal structures are difficult to measure on current neutron diffractometers due to limitations in flux and sample size.

## Grooved Moderator

## Flat vs. Grooved Moderator