SNS: an overview

SNS: an overview

Robert McGreevyDeputy DirectorNeutron Sciences Directorate

May 3rd 2012

2 Managed by UT-Battellefor the U.S. Department of Energy

Oak Ridge Neutron Sciences • Operate two world class neutron facilities• Carry out world class research• Enable an outstanding User Science Program • Develop signature science programs and partnerships• Stay at the leading edge of neutron science by developing new

capabilities, instruments and tools


Fission chain reaction continuous flow 1 neutron/fission 180 MeV/neutron

Spallationno chain

reactionpulsed

operation 40

neutrons/proton 30 MeV/neutron

How do we produce neutrons?


SNS Accelerator Complex

Front-End:Produce a 1-msec long, chopped H-

beam

1 GeV LINAC

Accumulator Ring: Compress 1 msec long pulse

to 700 nsec

2.5 MeV

LINACFront-End

RTBT

HEBT

Injection Extraction

RF

Collimators

945 ns

1 ms macropulse

Curre

nt

700 ns mini-pulse

Chopper system makes

gaps

Cur

rent

1ms

Liquid Hg Target

~1000 MeV

1 ms macropulse1 ms


H- Ion source


Designed to operate at 2.1 K (superfluid helium)

Fundamental power couplers

Return end can

Helium vesselsSpace frame

Supply end can

SNS Cryomodule

11*Medium beta

12*High beta


High Beta Cryomodule


Now standard foilU-shaped corrugations, corner cut offThis foil lasted an entire run

cycle

Stripper foils


SNS Design ParametersKinetic Energy 1.0 GeVBeam Power 1.4 MWLinac Beam Duty Factor 6%Modulator/RF Duty Factor Spec. 8%Peak Linac Current 38 mAAverage Linac Current 1.6 mALinac pulse length 1.0 msecRepetition Rate 60 HzSRF Cavities 81Ring Accumulation Turns 1060Peak Ring Current 25 ARing Bunch Intensity 1.5x1014

Ring Space Charge Tune Spread 0.15


SNS accelerator system performance continues to be outstanding – availability for FY12 so far is ~95%


Energy and power on target from October 2006


Liquid Hg target


Lifetime limited by cavitation damage


Target exceeds initial goal of 2500 MWhrs

Target # Integrated power (MW-hours)

Avg power (kW)

1 3055 125

2 3145 434

3 2791 503

4 3250 510


Moderator-reflector


Neutron moderators

Both hydrogen at 20 K

☞ coupled moderator thickness - 5 cmpre-moderator - light water

BL-2

BL-11

BL-5

☝ decoupled – 1.4 mm Cd poisoned - 0.8 mm Gd poison depth – 2.5 cm


Neutron moderators

☜decoupled – 1.4 mm Cd poisoned - 1.2 mm Gd poison depth - 1.5 cm BL8

2.5 cm BL17

☝ symmetric to the top downstream moderator

BL-8

BL-17

BL-14


Neutron Guides


Neutron Detectors

• 3He Multiwire proportional chambers

• 3He Position sensitive proportional tubes– Commercially available tubes

• Scintillation detectors with wavelength shifting fiber readout– New development

• Anger cameras with position sensitive photomultiplier tubes– New development


Instruments


Sample environment


Software


In-situ biomass degradation for cellulosic ethanol production

• Primary subunit swelled from ~8.5 Å (0 min) to ~19 Å (2 min).• In the initial state (0 min), cellulose fibrils form a random network (Q-2.5).• On treatment (2 min), large particles ~135 Å appear possibly Lignin

lumps.• Micron-sized superstructures with smooth interfaces (roughness < 50 nm)

persist even after 10 min pretreatment (Q-4).

Switchgrass. Photo Courtesy NREL.

Bio-Energy: Converting Bio-Mass to Bio-Fuel

http://www.nrel.gov/data/pix/searchpix.cgi?display_type=verbose&max_display=1&skip_hf=1&query=03246

http://genomicsgtl.energy.gov/research/DOEUSDA/NREL_switchgrass.jpg


Polymer Multilayers and Films: Charged and hydrogen-bonded polyelectrolyte films

Q (nm-1)0.0 0.5 1.0 1.5

RQ4 (n

m-4

)

10-7

10-6

10-5

10-4

z (nm)0 20 40 60 80 100

b/V

(10-4

nm

-2)

0

1

2

3

4

RQ4 (n

m-4

)

10-7

10-6

10-5

10-4

b/V

(10-4

nm

-2)

0

1

2

3

4

RQ4 (n

m-4

)

10-7

10-6

10-5

10-4

b/V

(10-4

nm

-2)

0

1

2

3

4

b/V

(10-4

nm

-2)

0

1

2

3

4

RQ4 (n

m-4

)

10-7

10-6

10-5

10-4 PVCL

PEO

PVPON

PNIPAM

d = 235 nm

N

O

n

PVCL

O

n

PEO

NH O

CH3 CH3

n

PNIPAM

N O

n

PVPON

OOH

CH3

n

PMAA

pH 2

PMAA


Nanostructuring: High-zT Thermoelectrics La3-xTe4 and nano-crystalline Si.

• The disorder in the lattice induced by the vacancies is thought to enhance phonon scattering and contribute to the low lattice thermal conductivity (between 0.4 and 0.8 W/m/K).

• The phonon DOS measured on ARCS reveals a systematic trend, associated with a change in bonding with increased vacancy concentration (below).

• Nanostructuring is an effective method to decouple electrical and thermal transport parameters to achieve high efficiency (zT).

• Dramatic reductions in the lattice thermal conductivity by nanostructuring bulk silicon with limited degradation in electron mobility can be achieved, leading to an unprecedented 3.5 times performance increase over that of the parent single crystal material.

• Phonon measurements performed on the ARCS spectrometer reveal the large effect of the nanostructuring on phonons (above).

• La3-xTe4 is capable of zT ~ 1.2 near 1300 K, making it the highest performing, bulk n-type material above 1000 K.

La3-xTe4 adopts the Th3P4 structure (left), and accommodates up to 1/9 vacancies on the La site.

S(Q,E) bulk Si, 300K (ARCS)

S(Q,E) nano Si, 300K (ARCS)

O. Delaire, M. Lucas, M. Stone, D. Abernathy (ORNL)


Superconductivity: Iron arsenides Complementarity of SNS and HFIR:

Phonon DOS - ARCS @SNSChristianson et al., PRL 101, 157004 (2008)

Spin waves – HB-1 @HFIRZhao et al. PRL 101, 217002 (2008)Spin waves – HB-3 @HFIRMcQueeney et al. PRL 101, 227205 (2008)


Neutron powder diffraction to understand the synthesis and structure of novel battery materials• Lithium transition metal fluorophosphates with a tavorite

structure have been recognized as promising electrode materials for lithium-ion batteries because of their good energy storage capacity combined with electrochemical and thermal stability.

• The structure of the pure single phase end-member Li2FePO4F was synthesized by lithiation of LiFePO4F, and solved via Rietveld refinement of the combined X-ray and neutron diffraction data, showing that Li+ occupies multiple sites in the tavorite lattice.

• Neutron powder diffraction data were collected at the HFIR HB-2A diffractometer and in this study highlight the critical need for neutron diffraction to accurately and quantitatively “see” the light atoms such as Li, which is crucial to understanding the microscopic behavior of Li battery materials.

Ellis, B.L., Ramesh, T.N., Rowan-Weetaluktuk, W.N., Ryan, D.H. Nazar, L.F., Solvothermal synthesis of electroactive lithium iron tavorites and structure of Li2FePO4F. Journal of Materials Chemistry, in press.


Small angle neutron scattering to understand polyglutamine aggregation in Huntington’s Disease

TEM image of the fibrils

fibril-fibril interactionsat lower Q

SANS on polyglutamine fibrils:

With SANS, we are learning about the structural formation of the aggregates related to Huntington’s disease. This work will aid in determining the toxic mechanism and developing treatments for the disease.

Using time-resolved small-angle neutron scattering (SANS), we capture “snapshots” of the early protein aggregates:

Stanley, C.; Perevozchikova, T.; Berthelier, V. Biophys. J. 100, 2504–2512 (2011).


Using neutron diffraction to help solve ITER’s superconducting cable degradation

Top: The 3 m long superconducting cable was mounted in a cryostat to be operated at superconducting temperatures. Each data point took about 30-60 minutes. The tubes have seen cycling under high magnetic field, and our goal is to determine the change in stress state and to assess the damage mechanism due to the magnetic cycling. Right : Cable stainless steel jacket is 50 mm on edge with superconducting bundles surrounding a center cooling channel.

• Performance of the cable had degraded much sooner than expected and ITER staff needed to determine the reason.

• Testing at the SNS on VULCAN measured the strain state of the superconducting conductor and is assisting US ITER to assess the strain’s impact on conductor degradation. The cryostat was specially developed by the ITER Team for this experiment.

• VULCAN is the only neutron scattering instrument capable of a study combining sample size with the ability to gather data in reasonable time scales.

• Initial studies show the cable has three phases: Cu, Nb3Sn, Nb. After magnetic cycling, Nb3Sn and Nb suffer a “tensile” stress. This is balanced by a “compressive” stress in Cu. Stainless steel jacket shows very little strain, consistent with mechanical measurements.

• Results were reported at a February 2012 ITER meeting in Japan.

• Studies will continue during the next SNS cycle at cryogenic temperature to assess the effect of cooling on the stress state.


SNS Second Target Station

SNS: an overview

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