# Presentation: 799828

## HYSPEC - Hybrid Spectrometer for the Single Crystal and Polarized Neutron Studies at the SNS

- Steve Shapiro and Igor Zaliznyak
*Center for Neutron Scattering and Neutron Scattering Group*
- Brookhaven National Laboratory

-  Unique in its class
-  Highest flux on small samples
-  Easily adapted for polarized neutron studies

## Outline

- Motivation (SMS)
- Science Case (SMS)
- IDT and Budget (SMS)
- Conceptual Design (IZ)
- Performance and Comparison(IZ)
- Summary (IZ)

## Status

- Fall, 1999
- BNL initiates an effort to design a spectrometer for the SNS
- December, 2000
- Concept of the Hybrid Spectrometer formulated and adopted
- March, 2001
- First presented to EFAC. Received positive reply
- Fall, 2001
- Instrument Development Team formed
- October: Workshop on the Hybrid Spectrometer held at BNL
- Refined HYSPEC concept presented to EFAC
- January, 2002
- HYSPEC IDT filed Letter of Intent with SNS
- April, 2002
- Formal presentation to EFAC
- July, 2002
- Letter of Intent accepted; Submit Scientific Proposal to EFAC

## Motivation

-  A and B category top priority - **“potential day-one instrument”**
- 1 Report on the SNS Inelastic Neutron Scattering Workshop, SNS Document IS-1.1.8.2-8004-MM-A-00 (2000).

- BS
- HRCS
- CNCS
- ARCS

- HYSPEC

- SNS Inelastic Neutron Scattering Workshop1
- Argonne (11/99)

## Motivation from Workshop

-  Small single crystal samples
**Focussing Bragg optics**
- Broad range of standard sample environments
**Use of collimators and beam definers**
**Sample environment separate from detector vacuum**
- Low background
**Time of flight **
**Sample area out of direct beam**
**Use of collimators**
- Vector **Q** in single crystals
**Moveable detector and rotatable sample**
- Polarization Analysis
**Proven and maintenance-free technology**

## Motivation from Workshop

- Page 5 of Report:
- “This [high time averaged flux] opens up the possibility of utilizing triple-axis like methods to examine details of excitations when the important physics can be found at specific, well defined regions of **Q** and E space”
- Recommended: “potential day-one instrument”

## Science Case

- Quantum critical points
- Low-D magnetism
- Nanomagnetism and complex systems
- Disordered and weakly ordered phases
- Anomalous phonon behavior
- Strongly correlated electron systems
- Hi Tc: YBCO experiment performed at ILL - IN22

## Polarized Neutron Study on Resonant Mode in YBCO6.85 (L.P. Regnault et al.)

- IN22
- Spin Flip
- P // Q

- Rise due to increased counting time

** ****Much faster data collection**
** ****Open new areas for polarized beam use**

- Sharp IC

- Broad C

- Unpolarized

## IDT Membership

- _I. Zaliznyak_, co-PI	BNL			HYPSEC INSTRUMENT
- _S. M. Shapiro_, co-PI	BNL			DESIGN WORKING GROUP
- G. Shirane		BNL
- J. Tranquada	BNL			I. Zaliznyak (BNL)
- L. Passell		BNL			S. Shapiro	(BNL)
- D. Abernathy	SNS			L. Passell (BNL)
- L. Daemen		Los Alamos		V. Ghosh (BNL)
- M. Greven		Stanford			(Monte Carlo Simulations)
- B. Gaulin		McMaster			S. Doran (SNS/ANL)
- K. Hirota		ISSP			(Engineering Design)
- V. Kiryukhin	Rutgers
- G. Lander		EITU
- Y. Lee		MIT
- C.Majkrzak		NIST
- S. Nagler		ORNL
- R. Osborn		ANL
- L. P. Regnault	CEN-Grenoble
- J. Rhyne		U. Missouri
- C. Stassis		Ames/Iowa St.
- A. Zheludev	ORNL

## HYSPEC IDT Organization Chart

## HYSPEC Budget Estimate

- Budget estimates from:
-  SNS engineering group (11/01)
-  HRCS Summary (7/02)
- Time Estimate:
-  5 years from funding

| Primary Flight Path |   |   |   |
| --- | --- | --- | --- |
|   | Choppers |   | 1400 |
|   | Incident beam shielding |   | 2300 |
|   | Supermirror guides |   | 500 |
|   | Beam monitors |   | 100 |
|   |   | SUB | 4300 |
| Monochromator |   |   |   |
|   | Shielding |   | 1000 |
|   | Crystals and holder |   | 400 |
|   | Collimators |   | 50 |
|   |   | SUB | 1450 |
| Sample Stage |   |   |   |
|   | Goniometer, sample table |   | 160 |
|   | Ancillary equipment |   | 250 |
|   |   | SUB | 410 |
| Analyzer, detector |   |   |   |
|   | Collimator sets |   | 200 |
|   | Polarization benders |   | 1000 |
|   | PSD, electonics mounts |   | 900 |
|   | Beam Controls-DAQ |   | 140 |
|   | Detector vessel  |   | 1500 |
|   | Beam stop/get lost pipe |   | 200 |
|   |   | SUB | 3740 |
|   | CAPITAL TOTAL |   | 9900 |
|   | LABOR (1/3 Capital) |   | 3300 |
|   | TOTAL |   | 13200 |

## HYSPEC: A Proposed Crystal-Time-of Flight Hybrid Spectrometer for the Spallation Neutron Source

- Part 2: Conceptual design

- T0 Chopper
- Disc Chopper
- Monochromator
- Goniometer
- Radial Collimator,
- or Bender Polarizers
- Flight Chamber (evacuated or Ar/He filled)
- Detectors

## Why Hybrid Spectrometer?

-  Monochromator vertical focusing gain on SPINS@NIST: factor ~3 even for m = 19 g sample (below)

-  Science challenges
-  small samples
-  subtle features
-  polarization analysis
-  small signals, background-
- limited measurements
-  Need intensity boost

## HYSPEC design choices: moderator

- 2.0*1012
- 1.6*1012
- 1.2*1012
- 0.8*1012
- 0.4*1012
- 0.0

-  20K H2 (decoupled)

- Intensity (n/sR/μs/eV/pulse)

-  Coupled supercritical H2  moderator wins in thermal neutron range Ei<45meV

-  ambient H2O

- 0     100     200     300     400     500     600
- Time (μs)

*Time-spectra of the neutron intensity from different moderators for **E**i** = 15.8 meV** *

*Moderators useful neutron flux*

- coupled 20K H2

-  ambient H2O

*Figure of merit is the total flux within ****t = **40-80 ****s** time window accepted by the spectrometer.*

-  20K H2 (coupled)

## HYSPEC design choices: energy resolution

- 	t	t/tf	E/Ef
- Ef=5.0 meV
- 	40 μs	0.0087	1.74%
- 	80 μs	0.0173	3.47%
- Ef=15.0 meV
- 	40 μs	0.015	3.0%
- 	80 μs	0.03	6.0%
- Ef=30.0 meV
- 	40 μs	0.021	4.25%
- 	80 μs	0.0425	8.5%
- Ef=60.0 meV
- 	40 μs	0.03	6.0%
- 	80 μs	0.06	12.0%
- Ef=90.0 meV
- 	40 μs	0.0368	7.36%
- 	80 μs	0.0736	14.7%

-  For given incident pulse length t instrument energy resolution is determined by the analyzer flight-path
-  Sample and detector size contribution to the instrument resolution is less than 0.5% each
-  TOF analyzer energy resolution for the length of the secondary flight-path LSD=4.5 m and pulse lengths 40 μs to 80 μs is in the range 1.7% to 15%

## HYSPEC design choices: guide curvature

*Flux on sample for different guide curvatures, parametrized by the corresponding offset at monochromator position.*

-  Straight guide with m=3 supermirror coating is an optimal solution

## HYSPEC performance: vertical focusing gain

*Crystal-monochromator hybrid spectrometer (HYSPEC, top scheme) vs traditional “straight-through” TOF setup (MCST, bottom scheme).*
-  HYSPEC wins except at 5 meV, where both concepts are rougthly equal.

## HYSPEC performance: comparison with other inelastic instruments planned for the SNS

-  MC simulations by MCSTAS, V. Ghosh (2002)
-  CNCS, ARCS and HRCS intensities are re-scaled to HYSPEC energy resolution (such rescaling may over-estimate the actual intensity)

## HYSPEC polarization analysis scheme: experimental demonstration

*S.-H. Lee, C. F. Majkrzak, Physica B ****267-268****, 341 (1999)*

- Heusler

## HYSPEC setup for polarization analysis

-  Polarized incident beam is supplied by reflection from the vertically focusing Cu2MnAl (Heusler alloy) crystal monochromator
- 10meV < Eipol < 90meV
-  Polarization analysis of the scattered neutrons is done by a set of 11-22 supermirror-bender transmission polarizers, each 2 cm wide, 5 cm thick and 15 cm high,
- 5meV < Efpol < 25meV

## HYSPEC layout in the polarized beam mode

## HYSPEC performance in the polarized beam mode

## HYSPEC performance in the polarized beam mode

## HYSPEC place in the SNS inelastic instrument suite

|  | HYSPEC | CNCS | ARCS | HRCS |
| --- | --- | --- | --- | --- |
| Incident energy range | 5 – 90 meV | 2 – 20(50?) meV  | 10 – 1000 meV | 15 – 1000 meV |
| Maximum flux on sample | 1.1 x 107 
at 15 meV | 5.6 x 106
at 5 meV | 7.8 x 105
at 100 meV | 9.6 x 105
at 100 meV |
| Energy resolution ΔE/E | 0.017 – 0.15 | 0.01 – 0.1 | 0.02 – 0.05 | 0.015 – 0.05 |
| Polarized beam | Yes | No | No | No |
| Intended sample size | 4 (w) x2 (h) cm2 | 1.5 (w) x5 (h) cm2 | 5 (w) x7.5 (h) cm2 | 5 (w) x7.5 (h) cm2 |
| Moderator-sample dist. | 21.8m | 36.2m | 13.6m | 17.5m |
| Sample-detector dist. | 4.5 m | 3.5 m | 2.5 m | 6.0 m |
| Angular acceptance | 0.27 – 0.41 sR |  | 3.1 sR | 1.2 sR |
| Beamline # | 15  | 5 | 18 | 17 |
| Guide coating | m = 3 | m = 3.5 | m = 3 – 3.5 | m = 3 – 3.5 |
| Guide Apertures 
(width x height, cm2) | entrance 4x12.8
main 4 x 15 
exit 4 x 10 | entrance 5 x 10
main 5 x10 
exit 1.5 x 5 |  |  |

## Summary

- HYSPEC will be a unique resource for probing correlations in condensed matter for
- E ∈ [5,90] meV	E/E ∈ [0.05,0.15]
- Q ∈ [0.3,10] Ǻ-1	Q/Q ∈ [0.005,0.2]
- Worlds most intense thermal neutron beam at a pulsed source
- Can optimize range of energy transfer and resolutions for experiment
- Independent variation of Q and E resolution
- Polarization analysis capability

_*The ultimate question*_: Do we need HYSPEC?
_*Lead*_: Do we need 2 to 5 times larger flux on sample compared to other SNS spectrometers and a polarized beam option?
_*Our answer*_: Yes, we do.

## Appendix. HYSPEC performance: monochromator resolution function

-  Significant part of the incident beam intensity - in the unwanted high-E tail
-  Requires a pulse-shaping chopper in a standard TOF setup
-  Is removed by reflection from the monochromator in HYSPEC

## Appendix. HYSPEC design choices: guide coating

-  Straight guide with m=3 supermirror coating is an optimal solution

*Flux on sample for m=2, 3, and 3.5 supermirror guides (for 8 cm offset at the monochromator position). *

## Appendix. Intensity and pulse length of SNS moderators

- 1013
- 1012
- 1011
- 1010
- 109

- 103
- 102
- 101
- 100
- 10-1

- 10-1       100       101        102      103       104       105
- Energy (eV)

- E*I(E) (n/sR/pulse)

- Pulse length (FWHM, μs)

-  20K H2 (decoupled)

-  20K H2 (coupled)

-  ambient H2O