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The engineering prototype of the wide-fieldCherenkov telescope for the Yakutsk arrayTo cite this article A A Ivanov et al 2013 J Phys Conf Ser 409 012084

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The engineering prototype of the wide-field

Cherenkov telescope for the Yakutsk array

A A Ivanov S P Knurenko A D Krasilnikov I V Ksenofontov Z EPetrov M I Pravdin L V Timofeev and I Ye Sleptsov

Shafer Institute for Cosmophysical Research amp Aeronomy Yakutsk 677980 Russia

E-mail ivanovikfiaysnru

Abstract The Yakutsk array group is developing the wide FOV Cherenkov telescopes to beoperated in coincidence with the surface detectors of the array under modernization Currentlythe engineering prototype of the reflecting telescope with front-end electronics is designed andassembled to prove the feasibility of the concept In this report the status and parameters ofthe engineering prototype are presented

1 IntroductionThe aim of the modernization program of the Yakutsk array is to construct a precise instrumentcapable of measuring the highest-energy galactic cosmic rays (CRs) ndash their sources energyspectrum and mass composition Another aim is to study a transition region between galacticand extragalactic components of CRs where some irregularities in spectrum and compositionmay be revealed [1]

A crucial role in this program should play a subset of wide field of view (FOV) telescopes -

-150

-100

-50

0

50

100

150

0 50 100 150 200 250

Figure 1 Modeling rays (yellow points) from a distant point source in the telescope Bluecurves illustrate the mirror and photocathode surface Black rectangle imitates shadowing bythe PMT case

23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics Conference Series 409 (2013) 012084 doi1010881742-65964091012084

Published under licence by IOP Publishing Ltd 1

-28125

-5625

16875

0

003

006

009

-28125

-20625

-13125

-5625

1875

9375

16875

24375

αααα=00

-28125

-5625

16875

0

003

006

009

012

-28125

-20625

-13125

-5625

1875

9375

16875

24375

αααα=70

-28125

-5625

16875

0

001

002

003

-28125

-20625

-13125

-5625

1875

9375

16875

24375

αααα=140

Figure 2 Monte Carlo image of a distant point source on the photocathode surface Lightintensity is given in arbitrary units in three cases where α is angle between the line to sourceand optical axis Pixel size is 375 mmtimes375 mm

differential detectors of Cherenkov light emitted by extensive air showers (EASs) intended tomeasure the angular and temporal structure of the signal connected to EAS longitudinal profileabove E = 1015 eV [2]

2 Astrophysical expectations for the Cherenkov telescopes working in coincidencewith the Yakutsk array detectorsOur interest in Cherenkov light differential detectors of EAS is caused by the possibility tomeasure the depth of cascade maximum xmax andor the shower age via angular and temporaldistributions of the Cherenkov signal In particular it was shown using EAS model simulationsthat the pulse width measured at the periphery of the shower r gt 300 m at sea level ispronouncedly connected with xmax [3]

Combining xmax and the shower age with other EAS characteristics measured with surfacedetectors of the array eg the energy and muon content one is able to estimate the average masscomposition of CRs Experimental arguments in elucidating the origin of the knee and ankle inCR spectrum will significantly strengthen due to the measurements of the angular and temporaldistributions of the Cherenkov signal in the energy range above 1015 eV Existing scenarios ofCR acceleration in the sources are different in composition expected around the knee and inthe transition region between galactic and extragalactic components so the accurate estimationof the average mass of the particlesnuclei in addition to the improved measurement of thesharpness of the knee and ankle should allow us to discriminate some scenarios [2]

3 Ray tracing in the telescopeThe engineering prototype of the wide FOV Cherenkov telescope consists of the spherical mirrorand multi-anode PMT as an imaging camera in the focus Data acquisition system (DAQ)includes 32 operational amplifiers and amplitude-to-digital converters (ADCs) connected to theindustrial PC

To model the focusing of the aluminized spherical mirror in the wavelength interval (300600)nm we have used a point source of light placed at infinity with angle α between the line tosource and optical axis of the mirror The image of the point source is calculated on the targetplane near the focus of the mirror The mirror size Dmirror radius of curvature Rmirror andtarget position F are optimized in order to get as wide a FOV as possible where the size ofblurred image is comparable to the pixel size of the position-sensitive PMT

We have chosen Hamamatsu R2486 series PMT with 16times16 crossed wire anode as an imaging

23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics Conference Series 409 (2013) 012084 doi1010881742-65964091012084

2

Figure 3 The prototype of the wideFOV Cherenkov telescope

-30

-165

-3

105

24

0

50

100

150

30

25521

16512

75

3

-15-6

-105

-15

-195

-24

-285

rela

tiv

e s

ign

al

Figure 4 Coordinate sensitivity of the PMT to thestandard light source

camera of the telescope With DPMT = 50 mm effective area and d = 375 mm distancebetween wires it provides approximately dtimesd pixel size In this way we have found the optimalparameters of the telescope to be Dmirror = 260 mm Rmirror = 225 mm F = 110 mmFOV=280

The scheme of ray tracing is illustrated in Fig 1 where the spherical aberration of the pointsource image is seen on the PMT photocathode surface 3D image of intensity distribution oflight in the target plane is given in Fig 2 for three typical incident angles Here we didnrsquot applythe background signal reduction to the PMT output

4 Engineering prototype of the wide FOV Cherenkov telescopeis shown in Fig 3 The spherical mirror is mounted at the bottom of the telescope housingwith vertical adjusting bolts beneath Support staffs of the PMT are used additionally to fitit exactly in the focal plane Coordinate sensitivity of the PMT1 to the light source of 1 mmdiameter (optical fiber illuminated by W-lamp) is illustrated in Fig 4

Voltage-divider circuit and 32 signal cables are attached to the bearing plate 16 two-channeloperational amplifiers are mounted on the telescope housing Block diagram of the DAQ system

1 c⃝Hamamatsu Photonics KK

Figure 5 Schematic overview of the telescope DAQ system

23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics Conference Series 409 (2013) 012084 doi1010881742-65964091012084

3

000

025

050

075

100

0 5 10 15

DeffD

0

αααα degree

Figure 6 Shadowing of the mirror by thePMT and support + cables The ratio ofunshielded effective mirror diameter to theactual diameter is given as a function ofincidence angle α

00

25

50

75

100

0 2 4 6 8 10 12 14 16

D

mm

α degree

Figure 7 Fuzzy image diameter of thedistant point source on the photocathodesurface as a function of incidence angle α

is shown in Fig 5In this design telescope provides the effective aperture Deff (0

0) = 109 cm due to shadowingof the mirror by the PMT and support Angular dependence of the telescope aperture is given inFig 6 We calculated it through a ratio of the light intensity on the photocathode surface to theinitial intensity falling into actual aperture of the telescope taking into account the reflectanceof aluminium 924 in the PMT sensitivity interval λ isin (300 600) nm

The quality of the optical system is characterized by the ldquospotrdquo size where the spot is animage of the point source at infinity on the focal plane We have measured the spot size ofthe image on the photocathode formed by the laser pointer at 3 m from the telescope Angulardependence of the spot size is shown in Fig 7 Itrsquos approximately consistent with results of ourmodeling Corresponding angular resolution of the telescope is sim 140 within FOV

5 ConclusionsWe have designed and assembled the engineering prototype of the wide FOV Cherenkov telescopeto work in cooperation with surface detectors of the Yakutsk array Our next task is field testingof the telescope and DAQ system during the next winter

AcknowledgmentsThe work is supported in part by SB RAS (integral project ldquoModernization of the Yakutskarrayrdquo) RFBR (grants 11-02-00158 11-02-12193 12-02-10005) and the Russian Ministry ofEducation and Science (contracts 02740110248 16518117075)

References[1] Ivanov A A Knurenko S P and Sleptsov I Ye 2009 New J Phys 11 065008[2] Ivanov A A Knurenko S P Petrov Z E Pravdin M I and Sleptsov I Ye 2010 ASTRA 6 53[3] Fomin Yu A and Khristiansen G B 1971 Yader Fiz 14 642

23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics Conference Series 409 (2013) 012084 doi1010881742-65964091012084

4

-28125

-5625

16875

0

003

006

009

-28125

-20625

-13125

-5625

1875

9375

16875

24375

αααα=00

-28125

-5625

16875

0

003

006

009

012

-28125

-20625

-13125

-5625

1875

9375

16875

24375

αααα=70

-28125

-5625

16875

0

001

002

003

-28125

-20625

-13125

-5625

1875

9375

16875

24375

αααα=140

Figure 2 Monte Carlo image of a distant point source on the photocathode surface Lightintensity is given in arbitrary units in three cases where α is angle between the line to sourceand optical axis Pixel size is 375 mmtimes375 mm

differential detectors of Cherenkov light emitted by extensive air showers (EASs) intended tomeasure the angular and temporal structure of the signal connected to EAS longitudinal profileabove E = 1015 eV [2]

2 Astrophysical expectations for the Cherenkov telescopes working in coincidencewith the Yakutsk array detectorsOur interest in Cherenkov light differential detectors of EAS is caused by the possibility tomeasure the depth of cascade maximum xmax andor the shower age via angular and temporaldistributions of the Cherenkov signal In particular it was shown using EAS model simulationsthat the pulse width measured at the periphery of the shower r gt 300 m at sea level ispronouncedly connected with xmax [3]

Combining xmax and the shower age with other EAS characteristics measured with surfacedetectors of the array eg the energy and muon content one is able to estimate the average masscomposition of CRs Experimental arguments in elucidating the origin of the knee and ankle inCR spectrum will significantly strengthen due to the measurements of the angular and temporaldistributions of the Cherenkov signal in the energy range above 1015 eV Existing scenarios ofCR acceleration in the sources are different in composition expected around the knee and inthe transition region between galactic and extragalactic components so the accurate estimationof the average mass of the particlesnuclei in addition to the improved measurement of thesharpness of the knee and ankle should allow us to discriminate some scenarios [2]

3 Ray tracing in the telescopeThe engineering prototype of the wide FOV Cherenkov telescope consists of the spherical mirrorand multi-anode PMT as an imaging camera in the focus Data acquisition system (DAQ)includes 32 operational amplifiers and amplitude-to-digital converters (ADCs) connected to theindustrial PC

To model the focusing of the aluminized spherical mirror in the wavelength interval (300600)nm we have used a point source of light placed at infinity with angle α between the line tosource and optical axis of the mirror The image of the point source is calculated on the targetplane near the focus of the mirror The mirror size Dmirror radius of curvature Rmirror andtarget position F are optimized in order to get as wide a FOV as possible where the size ofblurred image is comparable to the pixel size of the position-sensitive PMT

We have chosen Hamamatsu R2486 series PMT with 16times16 crossed wire anode as an imaging

23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics Conference Series 409 (2013) 012084 doi1010881742-65964091012084

2

Figure 3 The prototype of the wideFOV Cherenkov telescope

-30

-165

-3

105

24

0

50

100

150

30

25521

16512

75

3

-15-6

-105

-15

-195

-24

-285

rela

tiv

e s

ign

al

Figure 4 Coordinate sensitivity of the PMT to thestandard light source

camera of the telescope With DPMT = 50 mm effective area and d = 375 mm distancebetween wires it provides approximately dtimesd pixel size In this way we have found the optimalparameters of the telescope to be Dmirror = 260 mm Rmirror = 225 mm F = 110 mmFOV=280

The scheme of ray tracing is illustrated in Fig 1 where the spherical aberration of the pointsource image is seen on the PMT photocathode surface 3D image of intensity distribution oflight in the target plane is given in Fig 2 for three typical incident angles Here we didnrsquot applythe background signal reduction to the PMT output

4 Engineering prototype of the wide FOV Cherenkov telescopeis shown in Fig 3 The spherical mirror is mounted at the bottom of the telescope housingwith vertical adjusting bolts beneath Support staffs of the PMT are used additionally to fitit exactly in the focal plane Coordinate sensitivity of the PMT1 to the light source of 1 mmdiameter (optical fiber illuminated by W-lamp) is illustrated in Fig 4

Voltage-divider circuit and 32 signal cables are attached to the bearing plate 16 two-channeloperational amplifiers are mounted on the telescope housing Block diagram of the DAQ system

1 c⃝Hamamatsu Photonics KK

Figure 5 Schematic overview of the telescope DAQ system

23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics Conference Series 409 (2013) 012084 doi1010881742-65964091012084

3

000

025

050

075

100

0 5 10 15

DeffD

0

αααα degree

Figure 6 Shadowing of the mirror by thePMT and support + cables The ratio ofunshielded effective mirror diameter to theactual diameter is given as a function ofincidence angle α

00

25

50

75

100

0 2 4 6 8 10 12 14 16

D

mm

α degree

Figure 7 Fuzzy image diameter of thedistant point source on the photocathodesurface as a function of incidence angle α

is shown in Fig 5In this design telescope provides the effective aperture Deff (0

0) = 109 cm due to shadowingof the mirror by the PMT and support Angular dependence of the telescope aperture is given inFig 6 We calculated it through a ratio of the light intensity on the photocathode surface to theinitial intensity falling into actual aperture of the telescope taking into account the reflectanceof aluminium 924 in the PMT sensitivity interval λ isin (300 600) nm

The quality of the optical system is characterized by the ldquospotrdquo size where the spot is animage of the point source at infinity on the focal plane We have measured the spot size ofthe image on the photocathode formed by the laser pointer at 3 m from the telescope Angulardependence of the spot size is shown in Fig 7 Itrsquos approximately consistent with results of ourmodeling Corresponding angular resolution of the telescope is sim 140 within FOV

5 ConclusionsWe have designed and assembled the engineering prototype of the wide FOV Cherenkov telescopeto work in cooperation with surface detectors of the Yakutsk array Our next task is field testingof the telescope and DAQ system during the next winter

AcknowledgmentsThe work is supported in part by SB RAS (integral project ldquoModernization of the Yakutskarrayrdquo) RFBR (grants 11-02-00158 11-02-12193 12-02-10005) and the Russian Ministry ofEducation and Science (contracts 02740110248 16518117075)

References[1] Ivanov A A Knurenko S P and Sleptsov I Ye 2009 New J Phys 11 065008[2] Ivanov A A Knurenko S P Petrov Z E Pravdin M I and Sleptsov I Ye 2010 ASTRA 6 53[3] Fomin Yu A and Khristiansen G B 1971 Yader Fiz 14 642

23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics Conference Series 409 (2013) 012084 doi1010881742-65964091012084

4

Figure 3 The prototype of the wideFOV Cherenkov telescope

-30

-165

-3

105

24

0

50

100

150

30

25521

16512

75

3

-15-6

-105

-15

-195

-24

-285

rela

tiv

e s

ign

al

Figure 4 Coordinate sensitivity of the PMT to thestandard light source

camera of the telescope With DPMT = 50 mm effective area and d = 375 mm distancebetween wires it provides approximately dtimesd pixel size In this way we have found the optimalparameters of the telescope to be Dmirror = 260 mm Rmirror = 225 mm F = 110 mmFOV=280

The scheme of ray tracing is illustrated in Fig 1 where the spherical aberration of the pointsource image is seen on the PMT photocathode surface 3D image of intensity distribution oflight in the target plane is given in Fig 2 for three typical incident angles Here we didnrsquot applythe background signal reduction to the PMT output

4 Engineering prototype of the wide FOV Cherenkov telescopeis shown in Fig 3 The spherical mirror is mounted at the bottom of the telescope housingwith vertical adjusting bolts beneath Support staffs of the PMT are used additionally to fitit exactly in the focal plane Coordinate sensitivity of the PMT1 to the light source of 1 mmdiameter (optical fiber illuminated by W-lamp) is illustrated in Fig 4

Voltage-divider circuit and 32 signal cables are attached to the bearing plate 16 two-channeloperational amplifiers are mounted on the telescope housing Block diagram of the DAQ system

1 c⃝Hamamatsu Photonics KK

Figure 5 Schematic overview of the telescope DAQ system

23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics Conference Series 409 (2013) 012084 doi1010881742-65964091012084

3

000

025

050

075

100

0 5 10 15

DeffD

0

αααα degree

Figure 6 Shadowing of the mirror by thePMT and support + cables The ratio ofunshielded effective mirror diameter to theactual diameter is given as a function ofincidence angle α

00

25

50

75

100

0 2 4 6 8 10 12 14 16

D

mm

α degree

Figure 7 Fuzzy image diameter of thedistant point source on the photocathodesurface as a function of incidence angle α

is shown in Fig 5In this design telescope provides the effective aperture Deff (0

0) = 109 cm due to shadowingof the mirror by the PMT and support Angular dependence of the telescope aperture is given inFig 6 We calculated it through a ratio of the light intensity on the photocathode surface to theinitial intensity falling into actual aperture of the telescope taking into account the reflectanceof aluminium 924 in the PMT sensitivity interval λ isin (300 600) nm

The quality of the optical system is characterized by the ldquospotrdquo size where the spot is animage of the point source at infinity on the focal plane We have measured the spot size ofthe image on the photocathode formed by the laser pointer at 3 m from the telescope Angulardependence of the spot size is shown in Fig 7 Itrsquos approximately consistent with results of ourmodeling Corresponding angular resolution of the telescope is sim 140 within FOV

5 ConclusionsWe have designed and assembled the engineering prototype of the wide FOV Cherenkov telescopeto work in cooperation with surface detectors of the Yakutsk array Our next task is field testingof the telescope and DAQ system during the next winter

AcknowledgmentsThe work is supported in part by SB RAS (integral project ldquoModernization of the Yakutskarrayrdquo) RFBR (grants 11-02-00158 11-02-12193 12-02-10005) and the Russian Ministry ofEducation and Science (contracts 02740110248 16518117075)

References[1] Ivanov A A Knurenko S P and Sleptsov I Ye 2009 New J Phys 11 065008[2] Ivanov A A Knurenko S P Petrov Z E Pravdin M I and Sleptsov I Ye 2010 ASTRA 6 53[3] Fomin Yu A and Khristiansen G B 1971 Yader Fiz 14 642

23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics Conference Series 409 (2013) 012084 doi1010881742-65964091012084

4

000

025

050

075

100

0 5 10 15

DeffD

0

αααα degree

Figure 6 Shadowing of the mirror by thePMT and support + cables The ratio ofunshielded effective mirror diameter to theactual diameter is given as a function ofincidence angle α

00

25

50

75

100

0 2 4 6 8 10 12 14 16

D

mm

α degree

Figure 7 Fuzzy image diameter of thedistant point source on the photocathodesurface as a function of incidence angle α

is shown in Fig 5In this design telescope provides the effective aperture Deff (0

0) = 109 cm due to shadowingof the mirror by the PMT and support Angular dependence of the telescope aperture is given inFig 6 We calculated it through a ratio of the light intensity on the photocathode surface to theinitial intensity falling into actual aperture of the telescope taking into account the reflectanceof aluminium 924 in the PMT sensitivity interval λ isin (300 600) nm

The quality of the optical system is characterized by the ldquospotrdquo size where the spot is animage of the point source at infinity on the focal plane We have measured the spot size ofthe image on the photocathode formed by the laser pointer at 3 m from the telescope Angulardependence of the spot size is shown in Fig 7 Itrsquos approximately consistent with results of ourmodeling Corresponding angular resolution of the telescope is sim 140 within FOV

5 ConclusionsWe have designed and assembled the engineering prototype of the wide FOV Cherenkov telescopeto work in cooperation with surface detectors of the Yakutsk array Our next task is field testingof the telescope and DAQ system during the next winter

AcknowledgmentsThe work is supported in part by SB RAS (integral project ldquoModernization of the Yakutskarrayrdquo) RFBR (grants 11-02-00158 11-02-12193 12-02-10005) and the Russian Ministry ofEducation and Science (contracts 02740110248 16518117075)

References[1] Ivanov A A Knurenko S P and Sleptsov I Ye 2009 New J Phys 11 065008[2] Ivanov A A Knurenko S P Petrov Z E Pravdin M I and Sleptsov I Ye 2010 ASTRA 6 53[3] Fomin Yu A and Khristiansen G B 1971 Yader Fiz 14 642

23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics Conference Series 409 (2013) 012084 doi1010881742-65964091012084

4