A CONCEPT FOR CHERENKOV TELESCOPES FOR ULTRA-II

Florian Goebel, Anton Kabelschacht, Eckart Lorenz

SUMMARY PHYSICS GOALS AND PROSPECTS

• Study of the spectra of galactic point sources as well as extended galactic sources up to around 100 TeVDetails of spectral cut-off parameters of these sources

Spectral shapes of low redshift AGNs with high sensitivityAll-sky monitoring with high sensitivity, alerts for the low threshold array and quick switchover to dedicated

sources in case of flaring sourcesStudy 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. Search of extraterrestrial intelligence by using the array as an all-sky monitor for optical signals

) proposal of ManeL Martinez(

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 - > 1 TEV) + ULTRA II < (1 TEV - >100 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 /h SEPARATION POWER AT ≈ 1 TEV

•UPPER OPERATION LIMIT ≈ 200 TEV

•TELESCOPE CONFIGURATION: BLEND OF HEGRA TYPE CONSTRUCTION (LOWER PART) AND MAGIC CONSTRUCTION (UPPER PART)

SOME SPECIAL ISSUES

•THE TECHNICAL CONSIDERATIONS ARE NOT VERY CHALLENGING COMPARED TO THE LEA PART

•THE DOMINANT COST IS DRIVEN BY THE CAMERA -> USE OF CLASSICAL PMTS >- 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 - >- INCREASE MIRROR AREA-> 18m2 (> 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 > 1 WEEK

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

1-2 MONTH

SOME TECHNICAL ISSUES, II

•CAMERA : 5° Ø, 0.25° PIXEL SIZE -> ALMOST MAGIC LAYOUT INNER SECTION FOR f = 7 m

>- 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 -> CUSTOM IC

•TRIGGER: RATHER SIMPLE: 2 FOLD NEXT NEIGHBOR FOR EACH TELESCOPE + 2 FOLD COINCIDENCES BETWEEN 1,2,… OF THE 6 NEXT NEIGHBOR TELESCOPES

WILL START READOUT OF DOMINO (TRIGGER RATE 25-40 hz)•OTHER PHYSICS (FLUORESCENCE DETECTORS MIGHT NEED MORE COMPLEX

LOGIC(• USE OF DIGITAL SIGNALS VIA OPTICAL FIBERS WHENEVER POSSIBLE

SUMMARY TELESCOPE PARAMETERS1.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°-> -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

.13Angular measurements: by 13 or 14 bits absolute shaft encoders read out by CAN bus

or equivalent bus

14Trigger: 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

15.Pulse digitizing: 1024 deep switched capacitor array running at 500 MHz, ≈ 10 bit dyn. range.

16Location of readout electronics: in small containment mounted in mirror dish and single fiber

optical connection to central electronics counting house .

17High reliable and self-protecting electronics for near-remote operation

18Clock: central GPS controlled clock with fiber optics fan-out to each telescope. Relative clock

19 time precision ≈ 1 nsec.

SUMMARY TELESCOPE PARAMETERS

COST ESTIMATE

1.Cost per telescope: Total cost > 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 II25 M€ = 5M€ DEVELOPMENT COSTS+ 100 TELESCOPES

If you need finer pixels: either more money or fewer telescopes.For 0.12°pixels: either 3x fewer telescopes or price 75 M€

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

.1HIGH 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

.2MEDIUM PRIORITY • LOW POWER HT UNITS FOR PMTS

•MECHANICAL DESIGN OF TELESCOPE STRUCTURE•ACTIVE MIRROR ADJUSTMENT

•LIGHT CATCHER WITH DIELECTRIC REFLECTOR FOIL

.3PARALLEL STUDIES•HIGH RELIABILITY AND ROBUST OPERATION CONCEPT

•REMOTE OPERATION CONCEPT•COST CUTTING STUDIES

•QUICK INSTALLATION CONCEPT

Not useful, cutoff in UV

Price of MIRO 4300 per panel of 1250x1250 mm, 0.5 mm

20 panels for developments. : 80 €/panel resp. mirror2000 panels: 25 € /panel resp. mirror

Note: 300G is not weather resistant

Multilayer Quartz-TiO2

Mirror work at Wuerzburg

POSSIBLE MIRROR LAYOUT

LAYOUT MIRRORS (BLUE) AND TOP LAYER OF SPACE FRAME (BLACK)LOCATION OF ACTUATORS/FIX POINTS OF MIRROR PANELS

ACTUATORS

540 cm

108 cm

MIRROR

CAMERA SUPPORT MAST

CAMERA SUPPORT MAST

LAYOUT MIRROR AND TOP LAYER SUPPORT FRAME

BASIC SPACE FRAME ELEMENT MAGIC BASIC ELEMENT FOR ULTRA CONSIDERABLY STIFFER

PART OF TRIGGER LOGIC

≥2 PIXELS FIRING ≥2 PIXELS FIRING

ACQUIRE ACQUIRE

POSSIBLE MODES OF OPERATION

HIGHEST SENSITIVITY FOR SINGLE SOURCE SEARCH/STUDY: COMBINE LEA+ULTRA 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 FLY’S EYE TYPE DETECTOR

VARIANT: COMBINE 3(2) TELESCOPES FOR STEREO SUBCELLS AND POINT TO DIFFERENT POINTS ON THE SKYCOVERS ≈ 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 …

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 UNREALISTICTHE BALANCE BETWEEN THE WISH FOR BETTER PERFORMANCE AND LIMITEDBUDGET 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