Very Cold Very Cold Moderator Moderator

Development at Development at LENSLENSDavid V. Baxter and W. M. David V. Baxter and W. M.

SnowSnow

Indiana UniversityIndiana UniversityA. Bogdanov, V. P. Derenchuk, H. Kaiser, C. M. Lavelle, M. A. Lone, M. B. Leuschner, H. O. Meyer, H. Nann,R. Pynn, N. Remmes, T. Rinckel, Y. Shin P. Sokol

OUTLINEOUTLINE

What/why is LENS?What/why is LENS? Neutronic design; what is unique Neutronic design; what is unique

about LENS?about LENS? Why is LENS ideal for very cold Why is LENS ideal for very cold

netron development?netron development? ConclusionsConclusions

What is LENS?What is LENS? Low Energy Neutron SourceLow Energy Neutron Source: based on : based on

low-energy (p,nx) reactions (Elow-energy (p,nx) reactions (Epp<13MeV) in <13MeV) in Be.Be.

The source is tightly coupled to a The source is tightly coupled to a cold cold moderatormoderator (e.g. solid CH (e.g. solid CH44 at 3K<T<30K). at 3K<T<30K).

LENS will have a LENS will have a variable pulse widthvariable pulse width (from ~10 (from ~10 s to more than 1.0 ms).s to more than 1.0 ms).

In long-pulse mode, LENS will have a In long-pulse mode, LENS will have a time-time-averaged cold neutron intensity suitable averaged cold neutron intensity suitable for SANS and other materials research.for SANS and other materials research.

A small number of scattering instruments A small number of scattering instruments will be developed to utilize these neutrons.will be developed to utilize these neutrons.

Budget : Budget : $14 M+ for construction;$14 M+ for construction; $1.5M/yr operations$1.5M/yr operations

LENS MissionsLENS Missions

Education

LENS

Materials research

Instrumentation development

The Facility Timeline-The Facility Timeline-SourceSource

Phase I (Early ’05: 7MeV, 7mA, 0.2% DF; 10Phase I (Early ’05: 7MeV, 7mA, 0.2% DF; 101111 n/s)n/s) Moderator studies: Benchmarking LENS performance, Moderator studies: Benchmarking LENS performance,

lower T, different materials, …lower T, different materials, … Simple diffraction experimentsSimple diffraction experiments

Phase II (July ‘07: 7MeV, 20mA, 0.5% DF; 10Phase II (July ‘07: 7MeV, 20mA, 0.5% DF; 101212 n/s)n/s) Moderator composition studies/neutronic improvements Moderator composition studies/neutronic improvements Start pushing to lower spectral temperatures ->VCNSStart pushing to lower spectral temperatures ->VCNS Initial SANS measurements Initial SANS measurements Total cross section measurementsTotal cross section measurements

Phase III (Jan. ’08: 13 MeV, 10Phase III (Jan. ’08: 13 MeV, 101313n/s)n/s) SANS studies SANS studies Development of SESAME instrumentDevelopment of SESAME instrument

Eventual power (13MeV, 50mA, 5% DF; 10Eventual power (13MeV, 50mA, 5% DF; 101414 n/s)n/s)

The Facility Timeline-The Facility Timeline-InstrumentsInstruments

SANSSANS Commissioning of final instrument July 2007Commissioning of final instrument July 2007 Experiments on confined water, polymer networks, Experiments on confined water, polymer networks,

fractal structures in geological samples, nano-fractal structures in geological samples, nano-particles Sept. 2007.particles Sept. 2007.

SESAMESESAME Magnetic component development Summer 2007Magnetic component development Summer 2007 Initial construction Oct. 2007Initial construction Oct. 2007 Initial commissioning Jan. 2008Initial commissioning Jan. 2008

Total elastic scattering instrumentTotal elastic scattering instrument Conceptual design Summer 2007Conceptual design Summer 2007 Possible construction to begin in Fall 2007 (not yet Possible construction to begin in Fall 2007 (not yet

fully funded)fully funded) Micro-SANSMicro-SANS

Seeking fundingSeeking funding Others …Others …

IUCFIUCF

IUCFIUCF

Facility Layout: 2005 - 2006Facility Layout: 2005 - 2006

Protons in linac: 15 Dec. Protons in linac: 15 Dec. 20042004

Proton Current

RFQ power

DTL Power

Neutrons in 2-D Neutrons in 2-D Detector:Detector:

15 Dec. 2004 15 Dec. 2004

Target Moderator Reflector Target Moderator Reflector (TMR)(TMR)

Target Moderator Reflector Target Moderator Reflector (TMR)(TMR)

Empty Moderator Empty Moderator SpectrumSpectrum

Detector at 5.7 m

Cryogenics inserted in Cryogenics inserted in TMR2TMR2

Moderator AssemblyModerator Assembly

Water

CH4

Al

Poly

PT-410

50 cm

Spectra Captured every 10 Spectra Captured every 10 MinutesMinutes

5-point low-pass filter applied

Phase II Structure of Phase II Structure of MethaneMethane

Circle at the centerrepresents an essentiallyfreely rotating molecule, all others are hindered rotors that librate in place.

Calculated Cross Section of Calculated Cross Section of Methane in Phase IIMethane in Phase II

From Grieger, J. Chem. Phys. 109, 3161 (1998).

Shin kernel: Total cross Shin kernel: Total cross sectionsection

Shin kernel- freq. Shin kernel- freq. spectrumspectrum

Shin kernel: 20 K CHShin kernel: 20 K CH44 spectraspectra

MCNP kernel (Y. Shin)MCNP kernel (Y. Shin)

Free Rotational and Phonon modesTunneling, Librational and Phonon modes

Methane-Argon Moderator: Excitation Methane-Argon Moderator: Excitation SpectrumSpectrum

Prager et. al., J. Chem. Phys. Vol. 95, 569-575 (1991)

Facility Layout: 2007Facility Layout: 2007

Scattering Hall Update: 2007Scattering Hall Update: 2007

Scattering Hall Update: 2007Scattering Hall Update: 2007

22 Feb 2007 29 March 2007

Pictures of Upgrade: Pictures of Upgrade: SANSSANS

LENS has been producing cold neutrons LENS has been producing cold neutrons for some time, and has recently done so for some time, and has recently done so at its second target station.at its second target station.

Neutronic performance is within 20% of Neutronic performance is within 20% of predictions at low E (cold and thermal).predictions at low E (cold and thermal).

Spectral temperature of <30K has been Spectral temperature of <30K has been realized, and work is underway to reduce realized, and work is underway to reduce this. This will be a major goal for the this. This will be a major goal for the project over the next 3 years.project over the next 3 years.

Future improvements to neutronics Future improvements to neutronics should increase cold flux by more than should increase cold flux by more than 30% (more on this tomorrow).30% (more on this tomorrow).

We have started to explore new materials, We have started to explore new materials, and are looking for more ideas in this and are looking for more ideas in this area!area!

ConclusionsConclusions