DEAP-3600 and the Cryopit
SNOLAB Cube Hall Feb 2010
Location of the DEAP-3600
shield tank.
@
Mark Boulay
Queen’s University, Kingston
Mark Boulay, Queen’s
DEAP EAC Meeting August 16, 2011
Liquid argon as a dark matter target
•Less loss of coherence for lighter nuclei,
argon can provide useful information even
with relatively high energy threshold
c
40Ar
40Ar
Rate ~ A2F
c
(coherent)
•Well-separated singlet and triplet lifetimes in argon allow for good
pulse-shape discrimination (PSD) of b/g’s using only scintillation time
information, projected to 10-10 at 20 keVee
(see Astroparticle Physics 25, 179 (2006) and arxiv/0904.2930)
•Very large target masses possible, since no absorption of UV
scintillation photons in argon, and no e-drift requirements.
•1000 kg argon target allows 10-46 cm2 sensitivity (SI) with ~20 keVee
threshold, 3-year run
Mark Boulay, Queen’s
Plot courtesy of Wolfgang Rau
XENON100 arXiv:1104.2549
80 keVr threshold, without depletion of 39Ar
CDMS 2010:
XENON100 2011:
DEAP-3600:
Mark Boulay, Queen’s
612 kg-days (Ge)
1471 kg-days (Xe)
1,000,000 kg-days (LAr)
background free sensitivity
DEAP-3600 Detector
85 cm radius acrylic sphere contains
3600 kg LAr
(55 cm, 1000 kg fiducial, sealed vacuum
vessel to control backgrounds)
266 8” PMTs
(warm PMTs to increase light efficiency)
50 cm acrylic light guides and fillers for
neutron shielding (from PMTs)
Steel shell for safety to prevent
cryogen/water mixing (AV failure)
Only LAr, acrylic, and
WLS (10 g) inside of neutron
shield
8.5 m diameter water shielding
sized for reduction of (a,n) from rock
Mark Boulay, Queen’s
DEAP collaborators (Canadian groups)
• University of Alberta
D. Grant, P. Gorel, A. Hallin, J. Soukup, C. Ng, B. Beltran,
K. Olsen
• Carleton University
K. Graham, C. Ouellet
• Queen's University
M. Boulay, B. Cai, D. Bearse, K. Dering, M. Chen, S. Florian,
R. Gagnon, V.V. Golovko, M. Kuzniak, J.J. Lidgard, A.
McDonald, A.J. Noble, E. O’Dwyer, P. Pasuthip, T. Pollman,
W. Rau, T. Sonley, P. Skensved, M. Ward
• SNOLAB/Laurentian
B. Cleveland, F. Duncan, R. Ford, C.J. Jillings, M. Batygov,
E. Vazquez Jauregui
• SNOLAB
I. Lawson, K. McFarlane, P. Liimatainen, O. Li
• TRIUMF
F. Retiere, Alex Muir
Mark Boulay, Queen’s
DEAP/CLEAN collaborators
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University of Alberta: P. Gorel, A. Hallin, J. Soukup, C. Ng, B. Beltran, K. Olsen
Boston University: D. Gastler, E. Kearns
Carleton University: K. Graham, C. Ouellet
Harvard: J. Doyle
Los Alamos National Laboratory: C. Alexander, S.R. Elliott, V. Gehman, V.
Guiseppe, W. Louis, A. Hime, K. Rielage, S. Siebert, J.M. Wouters
MIT: J. Monroe, J. Formaggio
University of New Mexico: F. Giuliani, M. Gold, D. Loomba
NIST Boulder: K. Coakley
University of North Carolina: R. Henning, M. Ronquest
University of Pennsylvania: J. Klein, A. Mastbaum, G. Orebi-Gann
Queen's University: M. Boulay, B. Cai, D. Bearse, K. Dering, M. Chen, S. Florian, R.
Gagnon, V.V. Golovko, M. Kuzniak, J.J. Lidgard, A. McDonald, A.J. Noble, E.
O’Dwyer, P. Pasuthip, T. Pollman, W. Rau, T. Sonley, P. Skensved, M. Ward
SNOLAB/Laurentian: B. Cleveland, F. Duncan, R. Ford, C.J. Jillings, M. Batygov
SNOLAB: I. Lawson, K. McFarlane, P. Liimatainen, O. Li
University of South Dakota: D.-M. Mei
Syracuse University: R. Schnee, M. Kos, B. Wang
TRIUMF: F. Retiere, A. Muir
Yale University: W. Lippincott, D.N. McKinsey, J. Nikkel
CAD groups primarily focused on DEAP-3600
US groups: miniCLEAN (includes LNe target, solar neutrino R&D)
Mark Boulay, Queen’s
DEAP-3600 Background Budget (3 year run)
Background
Raw No. Events
in Energy ROI
Fiducial No. Events
in Energy ROI
39Ar
b’s
(natural argon)
1.6x109
<0.2
39Ar
b’s
(depleted argon)
8.0x107
<0.01
Neutrons
30
<0.2
Surface a’s
150
<0.2
Need to resurface inner vessel and ensure purity of
TPB and acrylic (40 mm layer, including surface)
Mark Boulay, Queen’s
PSD
Acr+H2O shield
Resurfacer,
reconstruction
Mark Boulay, Queen’s
From DEAP-STR-2011-009 (Bei Cai)
DEAP-1 prototype
(7 kg LAr)
UHV windows
poly PMT supports
Neck connects to vacuum and
Gas/liquid lines
11” x 6” (8” CF) tee
8” long acrylic guide
Acrylic vacuum chamber
ET 9390B PMT 5”
inner surface 97% diffuse reflector,
7 kg LAr
Covered with TPB wavelength shifter
Mark Boulay, Queen’s
R5912 HQE PMTs on DEAP-1 (Feb. 2010) Koby Dering
mineral oil optical coupling
Mark Boulay, Queen’s
identical to DEAP-3600 design
Light yield in DEAP-1 with Hamamatsu R5912 HQE PMTs
>4 pe/keV in DEAP-1
expect higher light yield in DEAP3600 (greater PMT coverage, 75%
vs 20%)
MC simulations (ratio of DEAP3600 to DEAP-1) show > 6 pe/keV
in DEAP-3600, meets design spec.
Mark Boulay, Queen’s
Calibration of DEAP-1 with AmBe neutron source
Mark Boulay, Queen’s
β/γ backgrounds
•
39Ar
is the most dominant β/γ background
• Expect 109 events in 3 years in (20-40) keVee
• Pulse-shape discrimination in DEAP-1
extrapolates to sufficient PSD
• Working with Princeton group for 4 tonnes
depleted argon for DEAP-3600 (>50 times
depletion)
Mark Boulay, Queen’s
a Backgrounds in Liquid Argon
a
Decay in bulk argon tagged
by a-particle energy
Decay from TPB surface releases
untagged recoiling nucleus in
argon and a in TPB
(see both with low energy)
a
Decay from TPB surface releases a in
argon and recoil nucleus in TPB
(see mostly a-particle, high energy)
on surface
Acrylic
TPB
PTFE
210Po
Decay from inside TPB or acrylic
releases a which may also enter LAr.
Could see
(a) Light from TPB only (prompt) or
(b) Light from LAr (range of energies)
both TPB and LAr scintillate
LAr
Mark Boulay, Queen’s
DEAP-1
and DEAP-3600 surface profile
a Backgrounds in LAr (DEAP-1)
chain
210Po
Acrylic
TPB
232Th
PTFE
June 2010
LAr
Events/100 keV
238U
Mark Boulay, Queen’s
DEAP-1 data
222Rn+220Rn
In DEAP-1:
100 mBq 222Rn
20 mBq 220Rn
chain
Background rates in DEAP-1 (low-energy region 120-240 p.e.)
Date
Background Rate
(in WIMP ROI)
Configuration
Improvements for
this rate
April 2006
20 mBq
First run (Queen’s)
Careful design with input from materials
assays (Ge g couting)
August 2007
7 mBq
Water shield (Queen’s)
Water shielding,
some care in surface exposure
(< a few days in lab air)
January 2008
2 mBq
Moved to SNOLAB
6000 m.w.e. shielding
August 2008
400 mBq
Clean v1 chamber at
SNOLAB
Glove box preparation of inner chamber
(reduce Rn adsorption/implantation on
surfaces)
March 2009
150 mBq
Clean v2 chamber at
SNOLAB
Sandpaper assay/selection, PTFE
instead of BC-620 reflector ,Rn diffusion
mitigation, UP water in glove box,
documented procedures; Rn Trap.
March 2010
130 mBq
Clean v3 chamber at
SNOLAB
Acrylic monomer purification for coating
chamber. TPB purification.
Feb 2011
~10 mBq
(PRELIMINARY)
Clean v4 chamber at
SNOLAB
Inner chamber redesign to remove
“Neck Light” events
Mark Boulay, Queen’s
Detector Chamber: Gen III
Neutron-like events
Mark Boulay, Queen’s
Chris Jillings – CAP Congress 2011
– Memorial University
Radon Spike
●
Used a spike of 222Rn captured from SNOLAB air
●
Introduced into argon system
●
●
Low-energy events in center of detector increased tens
of minutes before high-energy events.
The large peaks at high z-fit did not increase.
Argon inlet
Mark Boulay, Queen’s
Chris Jillings – CAP Congress 2011
– Memorial University
Detector Chamber: Gen IV, V
Better plug at
neck
Better
endcaps
Mark Boulay, Queen’s
Chris Jillings – CAP Congress 2011
– Memorial University
Gen IV Backgrounds
Mark Boulay, Queen’s
Chris Jillings – CAP Congress 2011
– Memorial University
Surface backgrounds in DEAP-1/DEAP-3600
(Toy model
of fitter
response)
Backgrounds in DEAP-1 dominated by surface events.
Projected sensitivity of 2x10-46 cm2 with DEAP-1 background levels after
position reconstruction.
(Those are upper limit: near levels of Radon emanation, neutrons in DEAP-1)
Mark Boulay, Queen’s
DEAP and miniCLEAN shield tanks at SNOLAB
Mark Boulay, Queen’s
Current Status DEAP-3600
Full capital funding (~10 M$) announced summer 2009, cash flow Nov. 2010
Construction of infrastructure at SNOLAB (support deck and shielding tanks
complete, water purification systems, chillers, etc. being installed)
Construction of acrylic vessel at Reynolds Polymer about to begin; will
be machined at U of A and installed in Cube Hall. U of A mill upgraded for
vessel machining.
20” test vessel has been constructed and bonded at Reynolds Polymer
Mark Boulay, Queen’s
Current Status DEAP-3600
Several large components ordered/fabricated:
• ultralow-background, highly transparent acrylic (> several m
attenuation length) for light guides (Spartech)
August 10 production start
• HQE PMTs (first 100 PMTs now in-house at Queen’s being
characterized)
• VME digitizing electronics (at TRIUMF)
• Large LN2 dewar and 3 KW cryocooler system being fabricated
(Stirling)
• Slow controls system in-house at Queen’s
• Argon purification system under development
• “Resurfacer” device under development
• Continued materials assay and qualification
Mark Boulay, Queen’s
20” Test Vessel Machining at Alberta
Mark Boulay, Queen’s
20” Test Vessel at the University of Alberta
Vessel now fully bonded at Reynolds; will be shipped to Queen’s in
September for cryogenic/QA testing.
Mark Boulay, Queen’s
Mark Boulay, Queen’s
Mark Boulay, Queen’s
DEAP-3600 Acrylic Vessel Construction/Assembly
Panels are thermoformed and bonded into a spherical shell and neck collar/neck
(Reynolds Polymer in Colorado)
Shell is machined (U of A) to include light guide “stubs”
Light guides are bonded on (UG due to transport constraints) onto stubs:
Vessel must be rotated to allow bonding of each light guide in approximately
horizontal position
Full vessel is annealed
Not trivial to scale to significantly larger size!
Mark Boulay, Queen’s
Acrylic light guide bonding at Alberta
Mark Boulay, Queen’s
Light guide bonding at U of A
• Developed well-controlled bonding system
• Bond parameters are monitored to ensure
consistency
• Many test bonds completed, standard LN2
“shock” tests for QA
Mark Boulay, Queen’s
Future Plans
Plan to explore possibility of “scaling-up” single-phase liquid argon,
by a factor of ~10
Currently no detailed design or timeline (focus is currently on DEAP-3600).
Some considerations:
Larger experiment would require depleted argon, and significant storage
facility; need to evaluate dominant residual backgrounds in argon after 39Ar
(including residuals from muons/spallation)
Safety considerations for large cryogenic target need to be implicit
in detector design (especially water shielding/flooding, ODH vent,
seismic concerns, and any large dewars)
Experiment much larger than DEAP-3600 should have simplified optical
readout (and lower background to reduce requirement for neutron shielding),
simplified acrylic vessel (still require “sealed” inner volume for radon reduction),
but should be simple to install (perhaps non-structural flat panels?)
Scintillation light readout should in principle be possible at larger scales.
Mark Boulay, Queen’s
Possible timeline for Cryopit
Current plan is to operate DEAP-3600 and collect some data/gain experience
before making decision to seek funding for next scale experiment
Earliest we would consider seeking funding (for detector engineering)
is around 2013; still unclear whether larger detector would require Cryopit, but
certainly a possibility
Planning some modest feasibility studies in coming year (combination of simulations
and evaluating possible designs)
Mark Boulay, Queen’s
Summary
DEAP-3600 detector under construction in SNOLAB cube hall, target sensitivity
is 10-46 cm2
Single-phase liquid argon technology should be scalable to much larger target
masses; no detailed technical design study yet completed for DEAP scale-up
Plan to collect initial data with DEAP-3600 before deciding to
pursue funding for larger experiment (2013 earliest date to seek funds)
Experiment at this scale (likely ~50 M$) would require v. significant collaboration
and several funding partners
Larger detector could require Cryopit, significant work to define infrastructure
and safety requirements
Mark Boulay, Queen’s
END
Mark Boulay, Queen’s