An Ultra-Cold Neutron Source at the NCState Pulstar Reactor

A. R. YoungNCState University

The Collaboration• Physics Department:

C. Gould, A. R. Young

• Nuclear Engineering Department:

B. W. Wehring, A. Hawari

• Hahn-Meitner Institute (plan: NCState in Jan, 2004)

R. Golub, E. Korobkina

• new NCState physics faculty in fundamental neutron physics (offer being made now…)

• H. Gao & D. Dutta (in the EDM collaboration)

• H. Karwowski and T. Clegg (weak interactions res.)

Local research groups with overlapping interests:

• R. Golub: co-invented superthermal source technique

• B. Wehring: constructed a CN source at the Nuclear Engineering Teaching Laboratory TRIGA Mark II reactor at University of Texas, Austin

• A. Hawari: active research program in neutron moderator modeling

All of the collaboration members have experience with neutron-related physics research and/or UCN production

PULSTAR facility is ideal for exploring new ideas for UCN production and experimentation

The PULSTAR UCN Source Project

• Establish a university-based UCN facility with a strong focus on nuclear physics applications for UCN

•Integrate the UCN facility into the undergraduate curriculum

•Involve the local nuclear physics groups (NCState, UNC and Duke, through TUNL) in fundamental physics with cold and ultracold neutrons.

NCSU PULSTAR Reactor

• Sintered UO2 pellets

• 4% enriched

• 1-MW power

• Light water moderated and cooled

• Just issued a new license for about 10 years of operation.

• PULSTAR design has several advantages for a UCN source:

- high fast flux leakage

- long core lifetime

Source located in thermal column

28 ft

Core

Takes advantage of: • large fast flux leakage – channel fast and thermal neutrons into D2O tank

• very low heating – use solid methane moderator

Conceptual Design I

(top view)

Parametric design calculations

– CN fluxes in the UCN converter and heating rates by MCNP simulations

– UCN production rates by integrating the converter CN energy spectrum with the UCN production cross sections—physics based on LANSCE measurements.

– UCN intensity at end of an open UCN guide using UCN-transport calculations.

• UCN Converter– Solid ortho D2

– 4-cm thick

– 18-cm diameter

• CN Source– Solid methane

– 1-cm thick cup around SD2

Details of UCN Source

• Averaged over UCN converter

• Integrated, 0 to 10 meV CN energies

φ = 0.9 x 1012 CN/cm2-s

CN Flux (MCNP)

• UCN converter, 200 g 1.7 W• UCN converter chamber, 696 g 3.1 W• CN source, 558 g 5.6 W• CN source chamber, 1529 g 6.0 W

Io = 2.7 x 107 UCN/sFor SD2 = 43 ms, = 1,160 UCN/cm3

Neutron and Gamma Heating Rates(MCNP)

UCN Production Rate and Limiting Density

Lifetime assumes SD2 at 5K, 1.5% para-deuterium, no H2

Low!

• CN flux averaged over UCN converter– 4-cm thick x 18-cm

diameter

φ = 1.0 x 1012 CN/cm2-s

• UCN intensity at end of open Ni-58 guide– 50-cm rise, 2-m level

Io = 1.0 x 107 UCN/s• UCN limiting density

= 1,290 cm3

Partially Optimized Design

(side view)

SD2 Source Summary

• For 1MW reactor operating power:

Io = 3.0 107 UCN/s

= 1,300 UCN/cm3

• Very small heat loads (1.7 W total to UCN converter)

-cryostat designs straightforward (D. G. Haase)

-lower operating temperatures feasible

• Accessibility of source is excellent, available year-round, reactor operable by students

• Upgrade of reactor power to 2MW being planned

Rough Comparison with Other Sources

PULSTAR (1MW, SD2) 1.3 UCN current IP=107 at shielding wall

UCNA source (4A) 1-2 (funded)

MAINZ 1 I IP/10 (funded)

PSI 3-4 (partially funded)

FRM II >10 Reactor not operational (partially funded)

KEK >100 LHe

PULSTAR (1MW,LHe) >100 I < IP , even with 20l of LHe

Facility UCN (1000/cm3) Comments

Observed baryon-antibaryon asymmetry physics beyond the standard model

How do we explore these issues at a university-based facility?

• Measure T invariance in neutron decay (D coefficient)

• Contribute to the UCN EDM project

• Perform source development work as a part of implementing a UCN neutron-antineutron oscillations experiment (NNbar)

A Nuclear Physics Science Program

T non-invarianceBaryon number violating interactions

Measurement of T-noninvariance in -decay

Experiments go here

Polarizer/spin-flipper

UCN guide

UCN source

Envisioned facility(He liquifier not shown)

Neutron decay directional angular correlations:

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The term proportional to D violates T symmetry: need to observe decay ’s and protons in coincidence use a cell geometry with UCN

A Potential D Measurement with UCNs.

D=210-4

1109 decays 25 UCN/cc -10 days

Why this experiment is suitable for a small, university facility:•Relatively compact (about 3m long)•Detectors are inexpensive and relatively straightforward to implement•Does not require a large superconducting spectrometer magnet•Does not require high precision polarimetry

From complete PENELOPE MC:

Much higher densities ultimately available…up to ~ 1000 with this source

Possible Contributions to the UCN EDM Project (M. Cooper and S. K. Lamoreaux, PIs)

Local members of the EDM collaboration:

H. Gau, D. Dutta, R. Golub, E. Korobkina

Possible measurement programs using the NCState source as a test facility:

•UCN storage

•UCN depolarization

•UCN production of scintillation light

•Dressed UCN interaction with polarized 3He

NNbar and source development

NNbar workshop at the IUCF/LENS facility, Sept. 2002:

Evaluated idealized geometry & conclusion:

Need more UCN Source R&D

(At NCState: 4 years of running produce factor of 7 improvement over ILL results (PSI or US national facility somewhat more effective)

Source Development Projects: Solid Oxygen and Liquid He

Solid oxygen (part of thesis of Chen-Yu Liu):

Freeze out magnons at 2K

UCN lifetime 9 x SD2Optimal production w/CN at 8-10K

~ 1.8 RSD2Limiting UCN density SO2 ~ 16SD2

If UCN elastic scattering length is long in SO2, more gains possible!

gap

Liquid He: R. Golub and E. Korobkina

NCState CN flux well-suited to UCN production in liquid He

Korobkina et al. calculate contribution from single and multiphonon prod for various CN distributions

Large gains possible (need to do pilot experiments)

• Easy access (by students, staff, etc…) excellent for exploring performance of various source geometries

• Low heating rate makes possible the investigation of more “fragile” moderators and converters

• Low heating rate also permits straightforward cryostat design

Source Development in a University Setting

•A Systematic investigation of source parameters is required to optimize UCN production rates and densities

-CN moderators optimize temperature and total flux of CN

-UCN converters explore physics of production, lifetimes, cooling, engineering issues

University facilities such as NCState PULSTAR and LENS:

Educational Program

Undergraduate students: already mechanism for integrating research projects at the reactor into the curriculum:

Every undergraduate in the NE program must do project at the reactor

Physics department’s advanced physics lab (PY 452) involves students doing projects in research labs; only requirement is “measure something with an error bar” (two in my lab this semester)

Nuclear Engineering Enrollment at NCSU

 

  1998 1999 2000 2001 2002

Undergrad 40 52 37 53 72

Masters 19 12 16 15 15

PhD 18 15 13 14 22

 

Graduate students: local facilities are a powerful draw for students.

Fundamental neutron physics is being established as one of the primary activities at TUNL, providing exposure to a large pool of nuclear physics graduate students

Training in neutron science and engineering is being established as a priority in the NE department (a director of reactor research is being created to expand the neutron research capabilities of the PULSTAR facility)

Faculty: NCState is committed to expanding its role at the SNS, and both the NE and physics departments are seeking to make joint hires in neutron/nuclear physics related research—this is explicitly stated in the “compact plan” for each of these departments, in which departmental funding priorities are established.

Facilities and Operations Costs

Reactor operations: funded by State of North Carolina

director: A. Hawari

budget: $490,000/y

staff: 7 technical staff, 1 secretary

adequate for daily operations: 1 shift of 8 hr/day

Rennovation costs requested in compact plan

Source Equipment Costs & Operating Grant Costs

• $1,035,905 over 3 years

-$392,315 for cryostat & related equipment (year 1)

-$408,700 for Model 1410 He liquifier (year 2)

-$234,890 for polarizer/spin-flipper magnet (year 3)

• increase to operating costs for nuclear physics group ~$80,000/year (materials and supplies, LHe and at least one more student)

Conclusion

•There is now the nucleus of a strong fundamental neutron physics group at NCState, with more faculty and staff to be joining

•Two unique local resources: the PULSTAR reactor and TUNL

•Timing is perfect to begin building a strong user group and training students for the SNS and future experiments

•We should build this source