Design of Optical Module
Candidates for IceCube-Gen2
Yuya Makino for the IceCube-Gen2 Collaboration@ICRC2023 satellite workshop in Chiba, August 7-8th 2023

IceCube and IceCube-Gen2
World’s largest neutrino telescope (1Gton)
Full detector operation since 2011

• Discovery of astrophysical neutrino flux (2013)• Evidence for Blazars as neutrino sources (2018)• High energy neutrinos from the Galactic Plane (2023)

A high energy extension of IceCube
for the next decades of neutrino astronomy• From discovery to astronomy• Aims 5x sensitivity from IceCube (>10x at >10TeV)• Resolving high energy sky from TeV to EeV• With Optical, Surface, and Radio arrays2

IceCube-Gen2 Optical Array
IceCube-Gen2 will expands the IceCube’s 1km3 instrumented volume to 8 km3

IceCube-Gen2
optical array(8km3)-1340m3000 m-1450m1000 m‣ 86 Strings with 125m
spacing‣ Total 5,160 opticalmodules (60/String)-2690m-2450mIceCube Upgradearray

IceCube array (1km3)‣ 120 Strings with 240m
spacing‣ Total 9,600 optical modules(80/String)

Improvement of the Optical Module is critical to achieve such a huge and sparse array of IceCube-Gen23

DOpticalModules
GG
IceCube Digital Optical Module(DOM)

ESee talk from Hiroto Ijiri 井尻

Deployment into the deep ice sheet
at the South PoleIn-moduleelectronics(HV + Digitizing +Communication)

Pressurevessel

8 inch PMT x 2high QE
Edep ~ 2.6 PeV track
UV1e5
transparentglass=>
photoelectronsobserved in total

PMTΦ = 300 mm
Narrower than
IceCube DOM.
Reduce drillingcostc

inch &PMT• Photo sensor10(PMT)
readout electronics in a pressure vessel
DOM Φ = 330 mm• 70 MPa rating (55 MPa observed at re-freezing
phaseafterdeployment)
Thickness of glass varies along longitude, for• Operation temp range from -40C to -20C mechanical tolerance and UV efficiency• High reliability (No access after deployment for >10 yr operation)• Very-expensive ice drilling cost proportional to the module diameter

9Imaging & calorimetry of neutrino eventswith a 3D array of Optical Modules
4IceCube Optical Modules and for Gen2

DGGESee talk fromHiroto Ijiri 井尻
Low-energyextension & Ice calibration(7 Strings around Deep Core in 2025/26)

High energy extension

8 inch PMT x 2high QEUV transparent glassΦ = 300 mm
Narrower than
IceCube DOM.
Reduce drilling
costc

IceCubeDOM
10inch PMT
DOM Φ = 330 mm

10’’ PMT & dia. 33 cm

Credit: N. Shimizu/ICEHAP

Credit: S. Niedworok/DESY

D-Egg

mDOM

8’’ HQE
PMTs& dia.
30 cm for 24x 3’’ PMTs & dia. 36 cm
Thickness of2xglass
variesalong
longitude,
9mechanical tolerance and UV efficiency• First Multi-PMT In-Ice Optical Module designs>98% still in operation
after 10 years

Designgoals?
IceCube-Gen2 Optical Module
development is built on• Successful design from IceCube• Updates through IceCubeUpgrade• Designs tuned for low-E events & ice measurements• Major updates in essential elements (pressure vessels,optical gel, electronics, and etc)
• New production, testing facilities, and skilled R&D teams
5Design Goals• What Optical Module do we want for a neutrino telescope with 240m string-spacing and 8 km3 volume?
‣ Highest per-module eﬀective area targeting x4 improvement compared to IceCube DOM‣ Wide dynamic range: From single photoelectron (SPE) to PeV-class (and more) events‣ Directional information with a multi-PMT design for better reconstructions• Reality hits when such a large-scale extension…
‣ Module diameter needs to be less than 12.5’’ (320mm) to suppress the enormous drilling cost <= 13’’ for IceCube DOM‣ Limited South Pole infrastructure requires low power consumption, aiming 4W/module <= 5.7 W for IceCube DOM

The biggest challenge of Gen2 DOM development is>4.0x IceCube DOM performance with a smaller module size6

Gen2 DOM Design Candidates• Two design candidates; 16 and 18 PMT models

16 PMT model

18 PMT model‣ 18 PMT opt: Max eﬀective area with a 12.5’’ vessel‣ 16 PMT opt: Relatively simple. Smaller size & weight• Technologies & concepts inherited from Upgrade R&D

540 mm• 4’’ PMTs to maximize eﬀective area

• Gel pads for optical coupling & light collector‣ Avoid complex holder structure (mDOM, Km3Net DOM)

444 mm‣ Largest possible for back-to-back layout‣ Similar ideas investigated in other experiments (e.g. NIM A 958 (2020))• Custom electronics designed for Gen2 needs‣ Single p.e. events to high energy neutrino events‣ Low power consumption & Compact design
312 mm

318 mm7

Expected Performance• Improved sensitivity at the horizontal directions• 16 and 18 PMT models show factor-of-4 improvements from IceCube‣ Either options will be the most sensitive DOM design among other IceCube Optical Modules despite smaller vessels
8Expected performance DGG

10 inch PMTDOM Φ = 330 mm

ESee talk from Hiroto Ijiri

Thickness of glass varies along lon
mechanical tolerance and UV eff9Gen2 DOM Design Candidates: Status
16 PMT model

18 PMT modelNot just looks-good-in-CAD-and-simulation, but the development is already very advanced
10

R&D Status of Each Component(*) 16 PMT model11

Pressure Vessels
Diameter < 12.5’’ / 70 MPa rated / high UV transmittance / radioactivity as low as possible• Okamoto Glass (Japan) & Nautilus(Germany)‣ Used for D-Egg and mDOM production

18 PMT option

16 PMT option‣ Glass material well studied through IceCubeUpgrade development‣ Keep-multiple-vendors strategy for
essential components in Gen2

• Improved optical performances‣ >50% transmittance at 320 nm (Both)‣ Reduced 40K: 0.74 Bq/kg (Okamoto)• Pressure rating have been proved withprototypes

New pressure vessels
have minimum eﬀects
to PMT QE response
Nautilus
IceCubeDeformation: 3.9mm (H) /2.4mm (V) at 70 MPa

12Compact-design 4 inch PMTs
As short as possible accepting minimum compromise in performance• Two vendors: Hamamatsu and North Night Vision
Technology (NNVT)

Target numbers<104 mm‣ NNVT has produced 15,000pcs 20’’ MCP-PMTs for JUNO
‣ Keep multiple vendors for for Gen2!

< 106 mm

‣ Newly-designed 4 inch box & line dynode PMTs

• Very compact, 106mm (abs max.) long
‣ Potential caveat is moderate cathode uniformity (transittime and/or collection eﬃciency, for example)< 55 mmParameter

Target valueGain

5e6 @ <1500V

Transit Time Spread< 8ns (FWHM)

Peak/Valley>2

QE>25% @400nm

Pre/late/after pulses Less than 1/5/10%13

New compact-design 4 inch PMTs
Hamamatsu Photonics K.K.

North Night Vision Technology (NNVT)

Delivered NNVT PMTs

• Designs are finalized and we have already purchased >100 PMTs fromeach vendors• Confirmed both PMTs meet our target numbers
14

New compact-design 4 inch PMTs

15

New compact-design 4 inch PMTs
Transit time spread

Transit time uniformity• Both PMT show good timing performances• Uniform time response over the cathode area & Worse delayed responses at the edge was expected dueto the short-length design, but the level is comparable with other PMTs used in other IceCube OpticalModules

16New compact-design 4 inch PMTs

• South Pole deep ice sheet is an ideal environment in terms of the PMT noise• Confirmed satisfactory low dark rates, including the details of contributions (thermal/random and “correlated”components), of both PMTs at low temperature

17

New compact-design 4 inch PMTs

Mechanical design & integration in the next Kareem’s talk18

Electronics for IceCube-Gen2
Limited space, Low power consumption,
Dynamic range from SPE to highest energy neutrino events• Combination of specialized boards instead of a “big&central” board‣ Good match with the limited available space & No need for big / resourceexpensive FPGAs

Minimainboard‣ Re-purposing existing solutions from IceCube Upgrade• Functionalities‣ Generate/regulate HV to each PMT‣ Digitization of signal waveforms from each PMT

Waveform uBases(wuBases)‣ Low level signal processing
WaveformuBases(wuBases)
Electronics only view

‣ Command and data I/O multiplexing & data buﬀering

Fanout boards‣ Communication with surface computers for high level triggering and processing
Fanoutboards

Mini mainboard
19

Waveform MicroBase• Add DAQ feature to the existing custom HV base
‣ Proven HV base design developed for the IceCube-Upgrade- MicroBase (ref: PoS(ICRC2021) 1070)

Analogfrontend

ADC

FPGARibboncable

47mm

HV generation(Cockcroft-Walton circuit)Micro controller‣ Ribbon cable for controlling and data transfer• DAQ functionalities

106mm‣ Continuous digitizing with 2-channel 12 bit ADC at 60MSPS
and captured in a low-power consumption FPGA
‣ Record Anode (high gain) and 8th Dynode (low gain) signals‣ Microcontroller manages control and regulation of HV, andbuﬀering and low-level processing of digital waveform data

90 counts forsingle PEs

Time resolution~ 2.4 ns~30ns
FWHM‣ Total power consumption 150 mW‣ 90 mW if ASICTime (ns)20Wide Dynamic Range for High Energy Events
Ch2 stays linear, Reaches
x100 higher

IceCube data

Ch1 reaches ADC count limit• Significant improvement with Anode & 8th dynode readout• Wide dynamic range, 5,000 PEs/25ns each PMT‣ Prototype version already shows 2,000 PE/25ns, plan to extend to
5,000 PE /25ns by tuning electrical gain
‣ Improvement in both energy and angular reconstruction expected21

IceCube-Gen2 Technical Design Reporthttps://icecube-gen2.wisc.edu/
science/publications/TDR22Summary and Outlook• Planned IceCube-Gen2 Optical Array requires Optical Modules to have the highest per-module sensitivity• Proposed IceCube-Gen2 DOM designs expect to improve the sensitivity of IceCube DOM by a factor of 4
‣ 16/18 4-inch PMTs in 12.5-inch pressure vessels‣ “Gel pad" approach is taken to reduce the module cost while keeping the optical performance‣ Electronics tuned for high energy neutrino events• Fully functional module within this year, plan to deploy O(10) modules in the IceCube-Upgrade array(construction in 2025/26) to verify the design towards IceCube-Gen224