1. Very Cold Moderator Development at LENS
David V. Baxter and W. M. Snow
Indiana University
A. 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

2. OUTLINE What/why is LENS? Neutronic design; what is unique about LENS?
Why is LENS ideal for very cold netron development?
Conclusions

3. What is LENS?
Low Energy Neutron Source: based on low-energy (p,nx) reactions (Ep<13MeV) in Be.
The source is tightly coupled to a cold moderator (e.g. solid CH4 at 3K<T<30K).
LENS will have a variable pulse width (from ~10 ms to more than 1.0 ms).
In long-pulse mode, LENS will have a time-averaged cold neutron intensity suitable for SANS and other materials research.
A small number of scattering instruments will be developed to utilize these neutrons.
Budget : $14 M+ for construction;
$1.5M/yr operations

4. LENS Missions Materials research Education LENS Instrumentation
development

5. The Facility Timeline-Source
Phase I (Early ’05: 7MeV, 7mA, 0.2% DF; 1011 n/s)
Moderator studies: Benchmarking LENS performance, lower T, different materials, …
Simple diffraction experiments
Phase II (July ‘07: 7MeV, 20mA, 0.5% DF; 1012 n/s)
Moderator composition studies/neutronic improvements
Start pushing to lower spectral temperatures ->VCNS
Initial SANS measurements
Total cross section measurements
Phase III (Jan. ’08: 13 MeV, 1013n/s)
SANS studies
Development of SESAME instrument
Eventual power (13MeV, 50mA, 5% DF; 1014 n/s)

6. The Facility Timeline-Instruments
SANS
Commissioning of final instrument July 2007
Experiments on confined water, polymer networks, fractal structures in geological samples, nano-particles Sept
SESAME
Magnetic component development Summer 2007
Initial construction Oct. 2007
Initial commissioning Jan. 2008
Total elastic scattering instrument
Conceptual design Summer 2007
Possible construction to begin in Fall 2007 (not yet fully funded)
Micro-SANS
Seeking funding
Others …

7. IUCF

8. IUCF

10. Facility Layout:

12. Protons in linac: 15 Dec. 2004
DTL Power
RFQ power
Proton Current

13. Neutrons in 2-D Detector: 15 Dec. 2004

14. Target Moderator Reflector
(TMR)

15. Target Moderator Reflector
(TMR)

16. Empty Moderator Spectrum
Detector at 5.7 m
Y550 numbers for this figure are 206 n/cm^2.uC (measured) and 180 n/cm^2.uC (MCNP) Ratio 1.14

17. Cryogenics inserted in TMR2

18. Moderator Assembly
PT-410 Al
Poly
CH4
50 cm
Water

19. Spectra Captured every 10 Minutes
5-point low-pass
filter applied
Data have been passed through a 5-point smoothing algorithm

20. Phase II Structure of Methane
Circle at the center
represents an essentially
freely rotating molecule,
all others are hindered
rotors that librate in place.

21. Calculated Cross Section of Methane in Phase II
From Grieger, J. Chem. Phys. 109, 3161 (1998).

22. Shin kernel: Total cross section
The NJOY curve is the cross section computed by NJOY from the frequency spectrum Shin’s kernel produces. It does not adequately account for the elevated cross section at lower temperatures due to the temperature dependence of the total spin projection (and presumably this accounts for the discrepancy at frequencies below 4meV).

23. Shin kernel- freq. spectrum

24. Shin kernel: 20 K CH4 spectra

25. MCNP kernel (Y. Shin) Free Rotational and Phonon modes
Tunneling, Librational and Phonon modes

26. Methane-Argon Moderator: Excitation Spectrum
Prager et. al., J. Chem. Phys. Vol. 95,
(1991)

27. Facility Layout: 2007

28. Scattering Hall Update: 2007

29. Scattering Hall Update: 2007
22 Feb 2007
29 March 2007

30. Pictures of Upgrade: SANS

31. Conclusions
LENS has been producing cold neutrons for some time, and has recently done so at its second target station.
Neutronic performance is within 20% of predictions at low E (cold and thermal).
Spectral temperature of <30K has been realized, and work is underway to reduce this. This will be a major goal for the project over the next 3 years.
Future improvements to neutronics should increase cold flux by more than 30% (more on this tomorrow).
We have started to explore new materials, and are looking for more ideas in this area!