Transcript An Ultra-Cold Neutron Source at the NCState Pulstar Reactor

An Ultra-Cold Neutron Source at
the NCState Pulstar Reactor
A. R. Young
NCState University
The Collaboration
•
Physics Department:
C. Gould, A. R. Young
•
Nuclear Engineering Department:
B. W. Wehring, A. Hawari
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Hahn-Meitner Institute (plan: NCState in Jan, 2004)
R. Golub, E. Korobkina
Local research groups with overlapping interests:
• 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.)
All of the collaboration members have experience with neutronrelated physics research and/or UCN production
• 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
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
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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
28 ft
Source located in
thermal column
Core
Conceptual Design I
(top view)
Takes advantage of: • large fast flux leakage – channel fast and thermal
neutrons into D2O tank
• very low heating – use solid methane moderator
Details of UCN Source
• UCN Converter
– Solid ortho D2
– 4-cm thick
– 18-cm diameter
• CN Source
– Solid methane
– 1-cm thick cup around
SD2
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.
CN Flux (MCNP)
• Averaged over UCN
converter
• Integrated, 0 to 10 meV
CN energies
φ = 0.9 x 1012
CN/cm2-s
Neutron and Gamma Heating Rates
(MCNP)
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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
Low!
UCN Production Rate and Limiting Density
Io = 2.7 x 107
For SD2 =UCN/s
43 ms,  = 1,160 UCN/cm3
Lifetime assumes SD2 at 5K, 1.5% para-deuterium, no H2
Partially Optimized Design
• 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
(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 yearround, reactor operable by students
• Upgrade of reactor power to 2MW being planned
Rough Comparison with Other Sources
Facility
UCN (1000/cm3)
Comments
PULSTAR (1MW, SD2)
1.3
UCN current IP=107 at shielding
wall
UCNA source (4A)
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
A Nuclear Physics Science Program
Observed baryon-antibaryon asymmetry  physics beyond the
standard model
T non-invariance
Baryon number violating interactions
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)
Measurement of T-noninvariance in -decay
Polarizer/spin-flipper
Envisioned facility
Experiments
go here
(He liquifier not shown)
UCN guide
UCN source
Neutron decay directional angular correlations:







p
m
p
p
 pˆ
WdEe de d  pe Ee ( E0  Ee ) 2 1  a e  pˆ  b e  A  e  B  pˆ  D  e
Ee
Ee
Ee
Ee

P
P



T
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.
From complete PENELOPE MC:
D=210-4
1109 decays
25 UCN/cc -10 days
Much higher densities
ultimately available…up
to ~ 1000 with this source
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
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):
gap
Freeze out magnons at 2K
UCN lifetime 9 x SD2
Optimal production w/CN at 8-10K
~ 1.8 RSD2
Limiting UCN density SO2 ~ 16SD2
If UCN elastic scattering length is long in SO2, more gains possible!
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)
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:
• 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
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
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
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)
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