dan bauer - cdms project managerall experimenters meeting - december 15, 2008 cdms status, upgrades...
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Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
CDMSStatus, Upgrades and Plans
Summary of running at Soudan
Cryogenic and Detector Upgrades
The Future - SuperCDMS@SNOLAB
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
CDMS (2006)
Current CDMS sensitivity
Maximum livetime = 85%(limited by cryo servicingneed for calibration data)
>2 years of stable data taking at Soudan
Average livetime ~ 75%
Xenon 10Gamma Calibration~10% of livetime
CDMS (Feb 2008)
DAMA
MSSM
We now have >1700 kg-days of exposure, sufficient to have world’s best spin-independent WIMP sensitivity for all WIMP masses.Approaching 10 Zeptobarn cross section!
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
Cryogenic Upgrades - UPS
• Replaced UPS for cryogenics system
– Underground diesel generator backs up entire cryogenics system
– Aging UPS was used to ‘bridge’ cryogenics control systems
– Installed new 30 kVA unit to carry whole cryogenics system
– Remote control and monitoring of UPS from the surfaceUnderground diesel generator UPS remote monitoring
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
Cryogenic Upgrades - Replaced Ebox
• Have lived for 2 years with small leaks in vacuum bulkhead (Ebox)
– Air freezes out on cold surfaces, can cause vacuum bursts
– If Helium gets in, it can reach detectors and affect signals
– Occasional ~1 week warming to 4-77K has been necessary
• Problem was due to custom-design of Ebox
– Warping of rectangular box made large o-ring seals difficult
• Solution was to buy large commercial vacuum cross
– Had vendor weld high-vacuum detector electrical connections into commercial vacuum plates
• Decided to warm to room temperature in October to install
– Takes about 2 weeks to warm, another 2 weeks to cool down
– Actual work at room temperature about 2 weeks
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
Cryogenics Upgrades - Ebox
Old ebox (note the black sealant) Stripline detector connections extracted
New Ebox being installed Reinstalling the stripline connections
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
Cryogenic Upgrades - Serviced Cryocooler
• Cryocooler removes excess heat at 4K and 77K
– We cannot run 30 detectors without this
• Servicing involves replacing cold head at room temperature
• Why did we want to do this now?
– Had 150% of recommended hours on the cold head
– Valves or piston could begin sticking at some point
– No evidence of performance problems but want to run another 2-3 years at Soudan, so this was a good time to do this
– Fortunately, the vendor (Sumitomo) can replace the cryocooler head without disturbing the delicate connections to e-stem
– Challenge was supporting these connections during the operation
• New head should last for length of CDMS operation at Soudan
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
Cryogenic Upgrades - Cryocooler
Supporting the cryocooler and estem during the cold head replacement The cryocooler cold head
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
An interesting incident during cooldown
• Dilution refrigerator uses 1K pot to condense 3He
– 1K pot is filled from He bath via needle valves
– Pumping on 4He in pot lowers temperature to 1.4K
• At this temperature, liquid Helium is a superfluid
– Superfluid Helium tends to creep
– Distance it can travel depends on surface roughness
• Small amount of air was accidentally introduced in bath
– Plated out in needle valves, allowing superfluid Helium connection between 1K pot and 4K bath
• Result was a 1K pot temperature >1.9K and very poor condensation of 3He
• Had to warm again above 77K and pump away air
– Now understand earlier instability with pot temperatures
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
Additional work planned in 2009
• Soudan underground power feed
– Near maximum capacity and getting old
– Study underway to determine whether upgrades needed
– May be possible to run separate feed for water pumps
• CDMS would like to install He liquefiers at Soudan
– He costs are skyrocketing and availability is an issue• 36% increase in costs this summer
• Several recent instances where supply was very tight
• CDMS uses about 70l/day
– Purchased 3 cryocooler-based liquefiers in FY2008• Plan phased installation during 2009-2010
• Sufficient capacity to reduce He consumption by x10
– Requires additional power (8 kw/liquefier)
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
Detector Issues
• Many detectors have failed in the oldest two towers
– These towers are now 6 years old and have seen many thermal cycles
– Will do postmortem on failures when towers replaced; most suspected to be cold electronics and wire bonds
– Net loss of about 1 kg Ge for the next three months
• New issues with Si detectors in this run
– Many of our Si detectors show signs of charge leakage through the crystal
– Run at reduced charge bias to avoid heating of phonon sensors
– Si detectors are no longer crucial for WIMP search
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
Larger detectors to be deployed in 2009Remove two oldest towerslose 1.5 kg Ge, 0.6 kg Si(mostly not working anyway)
New SuperCDMS detectorseach 3” dia x 1” => 0.64 kg of Gewith new phonon sensor designto improve fiducial volume
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
SuperCDMS@Soudan
• Replace CDMS II detectors with SuperCDMS detectors
– 0.25 kg Ge/0.1 kg Si --> 0.64 kg Ge
– Each new tower has 5 Ge detectors => ~3 kg mass
– Each also has two Ge endcap veto detectors• Improves ability to reject backgrounds from nearby materials
• First ‘Supertower’ due in March 2009
– Will bring Ge mass to 6 kg
• Remaining 4 supertowers in early 2010
– Total deployed Ge mass will be 15 kg
• Two year run will yield x3 sensitivity improvement over the best that CDMS II will produce (x10 better than currently published).
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
The Future: SuperCDMS@SNOLAB
• Science goals– Increase sensitivity by x50 (compared with current published)
– Reach WIMP-nucleon cross section of 10-46 cm2
– Find WIMP signal and compare with LHC
• Technical goals– Increase detector mass in stages up to 100 kg by 2012
– Stay background free
– Challenge to deal with existing backgrounds at Soudan
– New setup needed at SNOLAB to reduce neutron background
• Current status– First Soudan stage funded by DOE/NSF; full 15 kg funding requested
– SNOLAB experiment has CD-0 and Stage 1 approval from FNAL Director
– DMSAG2 review of the field in 2009 will likely determine funding prospects
Dan Bauer - CDMS Project ManagerAll experimenters meeting - December 15, 2008
CDMS is the only DM experiment with demonstrated control of backgrounds
Expected Background: 0.6 0.5 surface events and < 0.2 neutrons
Make sure any events here are WIMPS, not background!