SEASA hur funkar det

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SEASA - hur funkar det?
Mark Pearce KTH Fysik
SEASA _at_ Vetenskapens Hus 8 oktober 2007
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Overview

• Part 1 How SEASA works
• Demonstration The cosmic ray telescope
• BREAK
• Part 2 SEASA data analysis

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Cosmic ray air shower
Top of atmosphere
Short-lived
40 km
Long-lived
Stable
Ground
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Rymden
Jordens atmosfären
Scintillatorer
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t1 t2 t3 ?
High-schools
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Enskilda
1 km
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Detector stations

• AlbaNova Universitetscentrum
• 3 stations. 2 on main buliding, clear view of sky
  (1 station not operational). One station in the
  attic of house 1 near the bus stop.
• Enskilda gymnasium
• On balcony partial view of sky
• Nacka gymnasium
• On roof, clear view of sky
• Norra Real gymnasium
• In attic
• Thorildsplan
• In attic

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Car ski-box
1 m
Plastic scintillator
High-voltage and signal cables
Photomultiplier
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A Scintillator Detector
Cosmic ray muon
High voltage in
A charged particle excites electrons in the
scintillator. These return to the ground state
with the emission of fluorescence light,
typically at UV wavelengths.
Signal out
PMT
2 x 104 photons
Plastic scintillator
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PhotoMultiplier Tube (PMT)
(fotomultiplikator)
Fotoelektriska effekten (1905)
Muon
Current pulse out
e-
many electrons
few electrons
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Data Acquisition
Pressure sensor
HV out
GPS receiver
Ethernet
12V in
GPS antenna
Sensors
Embedded Linux processor
3 x PMT inputs
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The GPS system

• 24 satellites
• 6 orbital planes
• 4 satellites per plane
• 20200 km altitude / 55o inclination

• Anywhere on the earth ?
• 4 satellites above horizon

4 satellites ? lat. / long. / height / time 1
satellite ? time (if position known)
Clinton turns off Selective Availability May
2000
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100 MHz counter
Stop
Start
Pulse per second (PPS)
G P S
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m
1 K
PMT
22 pF
1
-
50 R

AD8055
To PLA

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AD8561
3
-
AD5300
From PLA
DAC
Vref
To PLA
ADC
Vref
AD7827
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System Design
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Cosmic Ray Telescope
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SEASA heads into space
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• PART 2 Data files

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Q What is a trigger?

• A When the three scintillator detectors at a
  station each register the passage of a particle
  during a 1 microsecond (1 x 10-6 seconds) period

• t1 lt t2 lt t3
• (t3 t1) lt 1 ms

t3
t2
t1
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Trigger (3 detectors required)
PMT 1
Trig. time 1
Coincidence gate length 1 microsecond
Coinc. window
PMT 2
Trig. time 2
ToT3
PMT 3
Trig. time 3
Time
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Data files

• Each time a station registers a trigger, the
  electronics sends data characterising the cosmic
  ray event to the stations Linux computer (more
  about the details of this data soon)
• The event data is then sent to a computer at KTH
  where it is stored in a database
• Every so often, we produce data files from the
  information stored in the database. The data file
  will typically correspond to a period of time
  (e.g. 1 month of running).
• Each line in the data file describes a different
  trigger recorded by the station
• Each column in the data file represents a
  variable describing the trigger

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Typical data file (each line represents a
trigger)
Offset (nanoseconds)
Station ID
Temperature (K)
Counting rates (Hz)
GPS time (seconds)
Pressure (hPa)
OBS! The files you analyse may look a little
different to this
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How is the trigger time defined?

• The trigger time (ie the time when a trigger
  occurs) is derived from the GPS system
  (yyhhmmss)
• This allows one to compare trigger times between
  widely separated detector stations and look for
  simultaneous activity which could indicate that a
  large air shower has been created over Stockholm
• However
• The GPS time is only accurate to 1 second
• Our electronics allows the trigger time to be
  measured with 5 nanoseconds resolution within a
  given second
• The format of this time information is under
  review because Excel can only read 15 digits.
• We will change this in the files that you receive!

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What are the counting rates?

• Each station registers a trigger approximately
  once a minute
• i.e. all three scintillators are hit within 1
  microsecond once a minute
• Each trigger corresponds to an air shower
  generated by a primary cosmic ray proton with an
  energy above approximately 1015 eV
• Since the number of shower particles hitting the
  ground depends on the primary cosmic ray energy
• Each separate scintillator is hit by secondary
  cosmic rays (mostly muons, generated by lower
  energy primaries) much more frequently about
  100 times a second (100 Hz)
• The rate of hits (number per seconds) is measured
  by the SEASA electronics
• Can be used to monitor the scintillator
  detectors, but is also sensitive to effects like
  atmospheric pressure (thinkness of atmosphere),
  and the activity of the Sun.

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What happens now?

• Before the next meeting (22 okt), we will make
  the data files available via the SEASA homepage
• PhD student Mószi Kiss will show how to study the
  data using Excel, e.g.
• How to read the files into Excel
• How to study relationships between variables
• A basic knowledge of Excel will be expected!
• We will also give some concrete suggestions for
  project work using the data
• Mån 12/11 Data analysis, continued
• Mån 14/1 Data analysis preliminary discussion
  of results
• Mån 4/2 Presentation of results to group