A CONCEPT FOR CHERENKOV TELESCOPES FOR ULTRA-II

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A CONCEPT FOR CHERENKOV TELESCOPES FOR ULTRA-II
Florian Goebel, Anton Kabelschacht, Eckart
Lorenz
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• SUMMARY PHYSICS GOALS AND PROSPECTS
• Study of the spectra of
  galactic point sources as well as extended
  galactic sources up to around 100 TeV
• Details of spectral cut-off parameters of these
  sources
• Spectral shapes of low redshift AGNs with high
  sensitivity
• All-sky monitoring with high sensitivity, alerts
  for the low threshold array and quick switchover
  to dedicated
• sources in case of flaring sources
• Study of diffuse gamma-radiation from the
  galactic plane
• Study of possible isotropic
  gamma-emission from Topological Defects
  
  
  
  
• Study of the chemical
  composition between 1012-1015
• Search for fine structures in
  the general CR spectrum
• Long-term studies of some
  flaring sources
• Possibly a search for
  quark-gluon plasma (needs theoretic input)
• Extension of GLAST studies
• No studies of GRBs
• May be use of the array as an
  air fluorescent detector in the 1016-1018 eV
  range. Needs some bright ideas
• for the trigger,
  attractive for small groups
• Coincidence studies with large
  VHE neutrino detectors for some dedicated source
  candidates.
• Crazy idea study of high
  atmosphere small discharges (Elfs etc) see EUSO
  proposal.

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• BASIC DESIGN CONSIDERATIONS
• IT IS IMPOSSIBLE TO BUILD AN OPTIMAL DETECTOR
  THAT SPANS 4 ORDERS OF
• MAGNITUDE IN ENERGY DUE TO THE STEEP POWER LAW
  OF FLUXES
• ONE NEEDS TWO DETECTOR CONFIGURATIONS FOR THE CTA
  TO SPAN FROM
• 10 GEV TO 100 TEV
• LEA ( 10GEV - gt 1 TEV)
  ULTRA II lt (1 TEV - gt100 TEV)
• ULTA II (ULTRA LARGE TELESCOPE ARRAY) 100
  TELESCOPES SPREAD OVER 1-2 km2
• EACH TELESCOPE WITH 18 m2 MIRROR AREA
• SENSITIVITY 10 x HIGHER THAN PAST ARRAYS
• LOWER THRESHOLD LIMIT 400 GEV IN ZENITH
  POSITION BUT HIGH g/h SEPARATION
• POWER AT 1 TEV
• UPPER OPERATION LIMIT 200 TEV

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• SOME SPECIAL ISSUES
• THE TECHNICAL CONSIDERATIONS ARE NOT VERY
  CHALLENGING COMPARED
• TO THE LEA PART
• THE DOMINANT COST IS DRIVEN BY THE CAMERA -gt USE
  OF CLASSICAL PMTS
• -gt USE OF 25 mm HEMISPHERICAL PMTS
  (CONSERVATIVE, LOW RISK, PLENTY
• OF EXPERIENCE, NO NEED TO MAXIMIZE QE, PANEQUE
  LACQUER OK,
• PMTS MATURE, G-APDS STILL IN EARLY DEVELOPMENT
  PHASE)
• INSTEAD OF INVESTING IN IMPROVING QE BY FANCY
  WORK-
• -gt INCREASE MIRROR AREA-gt 18m2 (gt 2x HEGRA IACT
  AREA)
• NEARLY ENTIRELY TO BE CONSTRUCTED BY INDUSTRY
• ALL WORK CAPACITY NEEDED FOR HESS II, MAGIC II
  AND LEA
• AIM FOR CONSTRUCTION TIME 4 YEARS
• INSTALL A TELESCOPE BY 4-5 PEOPLE IN lt 1 WEEK

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• SOME TECHNICAL ISSUES
• FOUNDATION a la HEGRA SIMPLE CONCRETE BLOCK 3
  x3x1 m3 thin working platform
• UNDERCARRIAGE LIKE FOR HEGRA CTS WITH CRANE BALL
  BARING
• PLUS ROTATING WORKING PLATFORM
• UPPER STRUCTURE LIKE MAGIC SPACE FRAME- ALUMINIUM
  TUBES
• BUT ONLY 2 LAYER SPACE FRAME USING A TETRAEDER
  AS BASIC ELEMENT
• DRIVE MOTORS STEPPING MOTORS LIKE FOR HEGRA
• CAMERA SUPPORT MAST GOTHIC ARC (PREFORMED
  I-BEAM) HOLD BY
• PRESTRESSED STEEL CABLES
• MIRRORS HEXAGONAL, MADE FROM HIGHGLY REFLECTIVE
  AL-ANOD PLATES
• SUPPORTED BY HEXCELL SANDWICH (a la CURRENT
  PADOVA CONSTRUCTION)
• NO NEED FOR DIAMOND MACHINING
• HIGH WEATHER RESISTANCE DUE TO MULTILAYER
  COATING
• POORER FOCUSSING THAN IN MAGIC BUT OK BECAUSE
  OF 0.25 PIXELS
• ALTERNATIVE MIRROR PRODUCTION REPLICA METHOD -
  WUERZBURG
• ALTERNATIVE MIRROR PRODUCTION THIN ALUMINIZED
  GLASS FOILS BACKED BY
• HEXCELL SANDWICH
• NO ACTIVE MIRROR CONTROL BUT AUTOMATIC MIRROR
  ADJUSTMENT EVERY

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• SOME TECHNICAL ISSUES, II
• CAMERA 5 Ø, 0.25 PIXEL SIZE -gt ALMOST MAGIC
  LAYOUT INNER SECTION
• FOR f 7 m
• -gt COPY OF MAGIC I PRINTED CIRCUIT
• PMTS 6 STAGE PMTS (GAIN 105) TRANSIMPEDANCE
  PREAMP
• BANDWITH CAN BE LOWER THAN FOR MAGIC PMTs
• DYNAMIC RANGE OF PREAMP 500 SUFFICIENT
• ET SAYS THAT PRICE FOR 33000 PMTS CAN BE
  100/PMT IF NO UV GLAS NEEDED
• ET CAN BUILD CAMERA PRINT CIRCUIT, TEST AND
  ASSEMBLE, HT PREAMPS
• SHORT COAX CABLES (RG174) FROM CAMERA TO READOUT
  ELECTRONICS
• LOCATED IN SPACE FRAME
• CAMERA WINDOW UV TRANSMITTING PLEXIGLASS
• LIGHT CATCHERS a la MAGIC, LINED WITH POSSIBLY
  DIELECTRIC MIRROR FOIL
• HT IN CAMERA, NEW COMPACT VERSION
• DIGITIZER SWITCHED CAPACITOR ARRAY (DOMINO CHIP)
  ACTING BOTH AS
• DELAY AND F-ADC (500 MHZ, HIGHER FREQ. NOT
  NEEDED). MAIN PROBLEM
• CURRENT READOUT MUCH TOO EXPENSIVE -gt CUSTOM IC
• TRIGGER RATHER SIMPLE 2 FOLD NEXT NEIGHBOR FOR
  EACH TELESCOPE

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• SUMMARY TELESCOPE PARAMETERS
• 1. mirror area 18 m2
• 2. Mirror layout see Fig 1
• 3. Focal distance 7 m (f/D 1.4)
• 4. Number of mirror elements 18
• 5. Mirror profile quasispherical, Davis-Cotton
• 6. Operation range Azimuth 350, Declination
  100-gt -75
• 7. Camera diameter 5
• 8. Pixel size 0.25
• 9. Nr of pixels 330
• 10. Photon sensors PMTs, 1 Ø, hemispherical, 6
  dynodes, max gain 105
• 11. Max slewing speed 60/min (fast slewing not
  needed)
• 12. Drive motors stepping motors with planetary
  gears of small backlash
• Angular measurements by 13 or 14 bits absolute
  shaft encoders read out by CAN bus
• or equivalent bus
• Trigger each telescope two next neighbour
  pixels. Between telescopes wide gate coincidence
  
• triggering coinciding telescopes. Under normal
  conditions at least 2 telescopes should trigger
  in
• coincidence. Alternatively, for all sky monitor
  observations, telescopes trigger autonomously.
• For air fluorescence studies a special trigger
  is needed

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SUMMARY TELESCOPE PARAMETERS COST
ESTIMATE 1. Cost per telescope Total cost lt 200
k ? Concrete foundation 5 k ? Mechanical
structure 25 k ? Motors, encoders, power 10
k ? Mirrors 10-20 k ? Camera DAQ 110
k ? Auxiliary equipment 35 k TOTAL COST OF
ULTRA II 25 M 5M DEVELOPMENT COSTS 100
TELESCOPES If you need finer pixels either more
money or fewer telescopes. For 0.12pixels
either 3x fewer telescopes or price 75 M
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• A POSSIBLE DEVELOPMENT ROAD
• A) MONTE CARLO STUDIES
• CROSS CHECK CORRECTNES OF HADRONIC SHOWER
  PHYSICS
• SIMULATION OF SENSITIVITY, TRIGGER PERFORMANCE
• B)LIST OF TECHNICAL DEVELOPMENTS
• HIGH PRIORITY DEVELOPMENTS
• PROTOTYPE MIRROR DEVELOPMENTS
• SPECIAL ASIC FOR DOMINO READOUT
• TWOFOLD NEXT NEIGHBOR COINCIDENCE LOGIC
• LOW POWER DISCRIMINATOR ASIC WITH EASY EXTERNAL
  CONTROL OF THREHOLD
• AND DELAY
• MEDIUM PRIORITY
• LOW POWER HT UNITS FOR PMTS
• MECHANICAL DESIGN OF TELESCOPE STRUCTURE
• ACTIVE MIRROR ADJUSTMENT

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Not useful, cutoff in UV
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Multilayer Quartz-TiO2
Price of MIRO 4300 per panel of 1250x1250 mm,
0.5 mm 20 panels for developments. 80 /panel
resp. mirror 2000 panels 25 /panel resp.
mirror Note 300G is not weather resistant
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Mirror work at Wuerzburg
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POSSIBLE MIRROR LAYOUT

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LAYOUT MIRRORS (BLUE) AND TOP LAYER OF SPACE
FRAME (BLACK) LOCATION OF ACTUATORS/FIX POINTS OF
MIRROR PANELS
ACTUATORS
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LAYOUT MIRROR AND TOP LAYER SUPPORT FRAME
CAMERA SUPPORT MAST
MIRROR
108 cm
CAMERA SUPPORT MAST
540 cm
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BASIC SPACE FRAME ELEMENT MAGIC
BASIC ELEMENT FOR ULTRA

CONSIDERABLY STIFFER
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PART OF TRIGGER LOGIC

2 PIXELS FIRING 2 PIXELS FIRING
ACQUIRE
ACQUIRE
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POSSIBLE MODES OF OPERATION
HIGHEST SENSITIVITY FOR SINGLE SOURCE
SEARCH/STUDY COMBINE LEAULTRA II AND
FOCUS ONTO ONE SOURCE ALL SKY MONITORING
POINT ALL TELESCOPES TO DIFFERENT POINTS ON SKY
COVER 0.5 STERAD BUT WITH LOW
SENSITIVITY CAN ALSO BE USED AS A FLYS EYE TYPE
DETECTOR VARIANT COMBINE 3(2) TELESCOPES FOR
STEREO SUBCELLS AND POINT TO DIFFERENT POINTS ON
THE SKY COVERS 0.15 STERAD, BUT WITH HIGHER
SENSITIVITY (2-3) SPLIT ARRAY INTO TWO(2,3..)
PARTS AND USE ONE PART FOR HIGH SENSITIVE SOURCE
STUDIES WHILE USING OTHER (SMALLER) PART FOR
LONG-TERM MONITORING OF DEDICATED FLARING
SOURCES (AGNS) FOR VARIOUS STUDIES .MONITORING
TOGETHER WITH LARGE NEUTRINO DETECTORS
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CONCLUSIONS
A 100 TELESCOPE ARRAY CAN BE BUILD WITHIN 4
YEARS (ASSUMES LARGE INDUSTRIAL SERIES
PRODUCTION) MOST DEVELOPMENT CAPACITY NEEDED FOR
LEA PART A COST OF 25 M IS NOT UNREALISTIC THE
BALANCE BETWEEN THE WISH FOR BETTER PERFORMANCE
AND LIMITED BUDGET WILL BE BETWEEN THE NR OF
TELESCOPES AND CAMERA PERFORMANCE RELATIVE
CONSERVATIVE APPROACH POSSIBLE, NO CHALLENGING
NEW AND UNPROVEN COMPONENTS NEEDED READOUT
ELECTRONICS TRIGGER VARIANTS MOST DEMANDING MC
SIMULATIONS NOT MADE MC SIMULATIONS WILL MOST
LIKELY GIVE GUIDANCE FOR SOME CRITICAL
PARAMETERS SUCH AS TELESCOPE SPACING, PIXEL SIZE
AND CAMERA FOV