Gammasphere

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Gammasphere

• ATLAS Users Meeting
• August 8, 2009

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Detector Status

• Goal Provide user with 101 Ge detectors on
  continuing bases (maximum possible at FMA).
• Continued cycles of annealing, Ge detector
  becomes a candidate for annealing when FWHM gt 3
  keV - anneal 15-20 detectors every 3-4 months.
• HV-Filters for segmented GS Ge detectors are
  no-longer available in market, and home-made has
  been tested and used.
• BGO bases continue to fail. Prototype replacement
  for bases using surface mount components have
  been constructed. Replacement of bases to begin
  in 2010 (replacement parts on order).
• Bottom line Gammasphere detectors are aging and
  need more attention to assure optimal use of
  device.

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Experiments

• A total of 18 experiments with 89 days (43 of
  total ATLAS running time) of beam time have been
  performed in FY08.
• 15 Experiments have been performed in FY09.
• 32 Gammasphere publications appeared thus in
  2008.

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Recent Upgrades

• New VME based acquisition system has replaced
  original DAQ.
• Data can be written to USB drives.
• Throughput issues for high-spin measurements have
  been addressed with new VME processor (T.
  Lauritsen and C. Lionberger).
• Upgradeable path should allow us to write
  3Mbytes/sec of data equivalent to 6 Exabyte
  tapes writing simultaneously.
• System is extremely stable (rarely crashes or
  hangs up).
• Online ROOT based analysis package GSSort, has
  been developed using the Root package from CERN.
• BGO base replacement to begin in 2010 not
  sooner due to long lead time on some parts.
• Electronic logbook (ELOG) has been implemented.
• Phase I construction of Digital Gammasphere has
  begun.

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Gammasphere Limitations

• Count Rate Limitations
• processing time for Ge shaper is 10?sec which
  gives 6 pileup at 10,000 cps, 20 pileup _at_
  30,000 cps and 30 pileup _at_ 50,000 cps.
• Solution reduce Ge shaping time allows higher
  rates. Measured resolution degrades from 2.3 keV
  to 3.0 keV when going from 10 msec to 2.3 msec
  processing time.
• Trigger limitations
• Gammasphere is dead for at least 25?sec for
  triggered events.
• Single and 2-fold Ge triggers saturate
  Gammasphere rate capability.
• Readout can only be aborted at main (300-1500ns)
  and late (6?sec)?
• Solution flexible trigger incorporating
  triggerless option.

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Digital Gammasphere

• Decreasing processing time of Ge shaper from 10
  to 2?sec should allow Ge to run at 40,000 cps
  with same throughput.
• Trigglerless option will improve throughput
  limits imposed by current trigger.
• These upgrades would allow Gammasphere to take
  data in excess of 10 times current limited rates.
• Adaptive pileup algorithm could increase
  throughput further.
• Extended Gammasphere reach in these areas of
  interest.
• 100Sn region
• Z gt 100 ?
• Exotic modes (Hyperdeformation)?
• Competitors are implementing or retrofitting
  arrays with digitizers e.g. Juroball, Clarion,
  SeGA, Tigress, Gretina, Agata.

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Digital Gammasphere

• Met with GRETINA group to discuss using GRETINA
  digitizers as basis for digital Gammasphere (May
  2008).
• Two stage plan
• Digitize only high-resolution Ge channel and read
  as external data. Compton suppression done by VXI
  electronics (Phase I)?
• Full digitization of both BGO and Ge detectors
  (Phase II)?
• Submitted LDRD proposal to ANL for startup money
  (denied)?
• Project seeded with 125k from PHY base budget to
  begin Phase I (June 09).
• Project underway July 09 with GS scientific
  staff, Phil Wilt (PHY) and John Anderson (HEP).

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Phase I - Instrument Gammasphere with Gretina
Digitizers

• Instrument current Gammasphere electronics with
  Gretina digitizers.
• 16 Gretina digitizer boards
• 2 VME crates 6 backplanes (4
  digitizers/backplane).
• 3 Gretina trigger modules.
• New VXI board to sit in GS master crate to pass
  GS clock and trigger information to DGS.
• System will also be stand alone and can be used
  with other detector systems i.e. 80x80 DSSD.

Provide
GS and DGS will take data simultaneously,
triggered by GS and using syncronized time
stamps. Recover GS pileup in DGS.
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Phase II Full Digital Gammasphere

• A Gammasphere module provides up to 10 signals
  for processing
• 1 Ge central contact
• 2 Ge outer contacts
• 7 BGO signals
• One Gretina digitizer card could instrument one
  Gammasphere Module.
• Most expensive option 350k for digitizers
  alone.
• Is full digitization of individual BGO energies
  necessary?
• One Gretina digitizer card could instrument 3
  Gammasphere Modules
• Digitize 3 signals, Ge central contact, 1 side
  channel, BGO Sum Energy
• Generate externally BGO hit pattern to enable
  nearest neighbor suppression.
• Individual BGO energies not available.
• One Gretina digitizer card could instrument 2
  Gammasphere Modules
• Digitize 5 signals - Ge central contact, 1 side
  channel, 3 multiplexed BGO signals (2,2,3)
  individual BGO energies available.

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Slopebox Control (Phil Wilt)?
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CARIBU and Gammasphere

• Reaccelerated beams
• Coulomb Excitation (Safe/Unsafe)?
• Transfer
• Deep Inelastic
• Fusion Evaporation (?)?
• Decay studies (gamma/beta)?
• Decay from high-spin state
• Angular Correlations - spins
• Polarization (Gretina) multipolarity
• New Equipment
• Tape Station
• Electron detectors - decay coincidence,
  multipolarity)?
• Fast Scitillators (LaBrCe) state lifetimes
• Plunger - lifetimes
• Heavy-ion Counter (Super-Chico, Annular DSSD) -
  Coulex