LENS as a Resource for Cold Moderator Development David V. Baxter Indiana University

Transcription

1 LENS as a Resource for Cold Moderator Development David V. Baxter Indiana University A. Bogdanov, J. M. Cameron, P. Chen (UIUC), V. P. Derenchuk, B. Jones (UIUC), H. Kaiser, C. M. Lavelle, M. A. Lone, M. B. Leuschner, H. O. Meyer, H. Nann, R. Pynn, N. Remmes, T. Rinckel, W. M. Snow, P. Sokol

2 OUTLINE What/why is LENS? Neutronic design Neutronic Performance Fast/Thermal Cryogenic Conclusions

3 What is LENS? Low Energy Neutron Source: : based on low-energy (p,nx)) reactions (E( p <13MeV) in Be. The source is tightly coupled to a cold moderator (e.g. solid CH 4 at 4K<T<22K). LENS will have a variable pulse width (from ~10 μs s to 1.0 ms or more). 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+ (not including surplus etc.).

4 Missions

5 IUCF

6 IUCF

7 Facility Layout: Spring 2006

8 Neutron/Gamma Yields 13 MeV, 30 kw 9 Be+p ( ( )+ xn Y n = 1 x10 14 /s ; E n = 2.3 MeV 9 Be+p Li+ Li+α+γ Y γ = 7 x10 12 /s ; E γ = 3.5 MeV 9 Be+γ Y γ = < /s ; E γ = < 15 MeV Other Gammas: Hydrogen: 8x10 13 /s Boron: 3x10 13 /s Al (β):( 4x10 12 /s

9 Accelerator Upgrade Plan Now: ACCSYS PL-7 7MeV, 7 ma peak, 0.2% duty factor Peak current and duty factor limited by RF Spring 06: Upgrade RF systems 2% duty, 20mA (?) upgrade cooling on existing DTL and RFQ Spring 2007: Install new DTL and second TMR 13 MeV,, peak 20mA+, 2-3% 2 duty Eventual: Install new RFQ and Ion source 13 MeV,, mA, 5%

10 The Facility Timeline Phase I (Early 05: 7MeV, 7mA, 0.2% DF; n/s) Moderator studies: Benchmarking LENS performance, lower T, different materials, Simple diffraction experiments Phase II (Fall 06: 7MeV, 20mA, 2% DF; 3x10 12 n/s) Total cross section measurements Moderator composition studies/neutronic improvements Emission time measurements Phase III (Spring 07: 13 MeV,, 1x10 13 n/s) Initial SANS studies Development of Precession instrument, RF spin flippers etc. Eventual power (13MeV, 50mA, 5% DF; n/s)

11 Facility Layout: Spring 2007

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

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

17 Target Moderator Reflector (TMR)

18 Target Moderator Reflector (TMR)

19 Reflector Thermalization (10-100meV) 100meV)

20 Design Geometry As Built Geometry

21 LENS Floor Plan- Today Radiog. SANS TMR Accelerator

22 Moderator Intensity Measurement He3 Pancake Detector (k=4.6(2)x10-4 /A) Activation Foil Collimator Neutrons

23 Empty Moderator Spectrum Detector at 5.7 m

24 NRERP Dosimetry Nickel Foil read on Ge(Li) ) detector Sulfur Pellet read on thin scintillator and evaluated by SANDIA Transistor Gain Damage evaluated by CRANE NSWC 1.00E E Sulfur 32 (n,p) Nickel 58 (n,p) Kerma (MeV mb) 1.00E E E E-02 Silicon Damage Kerma cross-section (barns) E E E E E E E E+02 Energy (MeV) Energy (MeV)

25 Fast Neutron Measurements Ni foil Silicon Damage

26 Measured Fast Flux Summary, Empty or Poly Moderator Fast, > ~3 MeV,, Ni, S 1 MeV equiv., 2N2222A measured 10 7 n/s/cm 2 MCNP 10 7 n/s/cm / / Measured/ Simulation ma peak, 150 μs pulse width, 20 Hz rep rate (Oct 2005) Measured fast flux is ~45% lower than predicted Gamma dose negligible (TLD: 1.5 krad in 24h) One 8h shift: n/cm 2 thermal n/cm 2 fast n/cm 2 1 MeV equiv.

27 Neutronics: : Moderator thickness

28 Methane Thickness (MCNP)

29 Cryogenics Cryogenic gallery Cryogenic vacuum insert

30 Cryostat insertion

31 Moderator Assembly PT-410 Al CH 4 Poly 50 cm Water

32 Moderator Cryogenic Tests T4 T3 Dec P(W) T4 (K) T3(K) * * Estimated thermal load at 30kW

33 400 first methane cooldown - 06Apr P [torr] vapor pressure curve normalized T3 data T [K]

34 Foil Normalized Cold Spectrum 1.E+08 E*Flux (n/strad/uc) 1.E+07 1.E+06 1.E+05 3/29/2006 Measurement 6/02/2005 Measurement 7 MeV As Built Simulation YX X( mev) = Φ 0 n/cm 2 /uc ( E) de 1.E+04 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 X Energy (ev) Yx 6/02/ mev Yx 3/29/2006 Yx MCNP Ratio mev Ratio

35 Spectral Temperature vs. Moderator Temperature (CH 4 ) 50 Spectral Temperature (K Moderator Temperature (K)

36 Spectra Captured every 10 Minutes 5-point low-pass filter applied

37 Counts in Angstrom Range vs. Moderator Temperature 2600 counts-bkgd, 6-10 A rang Moderator Temperature (K)

38 Emission Time Experiment Equipment

39 Emission Time NIM A239 (1985) Ikeda-Carpenter

40 Emission Time 4 K Moderator 150 us Proton Pulse 50 us Proton Pulse

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43 1 st Order Compared to MCNP 150 us proton pulse Decay time Simulated: 320 us Measured: 360 us

44 Methane Phase I-II I II Transition

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

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

47 Phase II xs and Excitations Greiger: J. Chem. Phys. Vol. 109, 3164

48 Conclusions LENS has produced its first neutrons and is starting its work on science, education, and technology Neutronic performance is within 30% of predictions at low E (thermal), but discrepancy is greater (~50%) at high E (MeV( MeV). Spectral temperature of <30K has been realized, and work is underway to reduce this. Future improvements to neutronics should increase cold flux by more than 30% (beyond increases from accelerator improvements). We have started to explore new materials, and are looking for more ideas in this area!

49 Moderator Thickness Study Cryogenics Cavity 1.0 Cm Thick (present configuration) 2.0 cm Thick (proposed change included in study)

50 Methane Thickness

51 Cryogenics Cryogenic gallery Cryogenic vacuum insert

52 Coupling Changes Design Geometry As Built Geometry

53 Possible neutronic improvements Thermal Flux Leakag (n/cm^2/uc) Target-Moderator Water Gap Beam Right Vacuum Vessel Void Below Cavity Gap Increase in TMR Element Water Thickness (cm)

54 Conclusions LENS has produced its first neutrons and is starting its work on science, education, and technology Neutronic performance is within 30% of predictions at low E (thermal), but discrepancy is greater (~50%) at high E (MeV( MeV). Spectral temperature of <30K has been realized, and work is underway to reduce this. Future improvements to neutronics should increase cold flux by more than 30% (beyond increases from accelerator improvements). We have started to explore new materials, and are looking for more ideas in this area!