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Mechanical Structure of ICAL Detector for INO


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Title: Mechanical Structure of ICAL Detector for INO

Mechanical Structure of ICAL Detector for INO
Presented by Piyush Verma, DHEP, TIFR
What is INO?
The India-based Neutrino Observatory (INO) is a
proposed pure-Science underground
laboratory. The detector housed in the INO
underground laboratory will be a magnetized Iron
Calorimeter detector (ICAL). Its primary goal
is to study the properties and interactions of
weakly interacting, naturally occurring
particles, called neutrinos.
Between Ooty and Mysore in the Nilgiri Hills.
Lab will be an underground Cavern with a rock
cover of atleast 1 KM on all sides.
Detector Cavern
Detector Cavern
Detector Cavern (Details)
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What will be the detector that will be housed at
The detector housed in the INO underground
laboratory will be a magnetised iron calorimeter
detector (ICAL). It is a static device without
moving parts. Charged particles produced in
neutrino interactions can be detected by means of
an iron calorimeter (ICAL) detector. Iron layers
will be sandwiched with the active detector
material that will detect whenever a charged
particle passes through it. The detector will be
of dimension 16 M x 48 M x 14.4 m ht. This will
be divided into 3 sub modules of size 16m x 16m x
14.4m ht. Each sub-module will contain approx.
17KT of soft Iron.
The Iron plates will be stacked with a gap of
40mm between consecutive layers. Each layer will
have 32 Iron plates of dimension 2m x 4m x 56mm
thick put in one plane to make a 16m x 16m layer.
Design Requirements of the Detector Stack Assembly
  • Total width and length of detector structure will
    be 16m x 48m, constructed in three
  • modules of 16m x 16m each.
  • Total weight of steel plates forming the
    detector structure is required to be 50kT.
  • Proposed site falls under Seismic zone II. The
    structure should withstand the
  • seismic acceleration of 0.073 m/sec2 as per
    the seismic zone requirement.
  • The flatness of each detector plates should be
    less than 2mm over its entire surface.
  • The stack should be formed without welding
    process. It should also have minimum
  • machining for minimizing the cost.
  • Each layer should be magnetically isolated from
    neighbouring layers.
  • The gap between the adjacent plates in the same
    layer should be minimum to
  • reduce the magnetic loss due to air gaps.
  • The detector stack should have provision for
    putting magnetic coils based on the
  • magnet design.

Design Philosophy of the Detector Stack Assembly
  • To achieve the design constraints, the stack is
    proposed to consist of 150 layers of soft iron of
    the dimension 2m x 4m x 56mmthk.
  • Each layer will be separated from neighbouring
    layer by 40mm spacing. There will be discrete
    spacers between the layers of cross-section 40mm
    x 80mm or 40mm x 40mm.
  • The spacers will be made of SS304.
  • There will be 20 dia. press fitted pins (material
    SS304) in the spacers, which will be used to
    locate the plates during construction of detector
  • In one Road there are eight RPCs. Four to be
    extracted on one side and the other four to be
    extracted on the other side.

Cross Section of the Main Lab
ICAL Detector Stack with RPC Handling Trolley
ICAL Detector Stack Assembly
ICAL Detector Stack (Details)
ICAL Detector Stack (Plate Layers)
ICAL Detector Stack (Plate Types)
Plate Dimensional Details
Plate Type - I
Plate Type - II
Plate Type - III
ICAL Detector Stack (Spacer Types)
Spacer Dimensional Details
Schematic of Detector Assembly in the Stack
  • With current design, the thickness of RPC with
    all components assembled together is 30mm.
  • Three options for putting RPC in the stack
  • Put RPC on Teflon rails for easy insertion and
    extraction with 4mm gap on the top and 6mm gap on
    the bottom side. Run gas lines and HV/LV lines on
    the sides.
  • Same as above but with 6mm gap on top and 4mm gap
    at the bottom.
  • Put RPC directly on the iron plates (no Teflon
    rails) and run all the lines on the top of RPC.

Teflon Rails
Gas, HV,LV
Spacer Block
Schematic of Detector Assembly in the Stack
Spacer Blocks
Iron Plate
RPC Handling Trolley
RPC Handling Trolley
Design of ICAL Foundation Structure
  • Dead load on the ICAL Detector Foundation
    Structure will be from the weight of the
    following components
  • ICAL detector plates 4m x 2mx 56mm x 150 layers
  • Spacer Plates of 40mm thick in between detector
    plates at discrete locations.
  • RPC trays of size 1.84m x 1.84m x 30mm in the
    gaps of detector plates.
  • Connecting pins of 20mm dia to connect spacer
    plate Detector plates.
  • Magnetic coils having size 625mm x 80mm.
  • Bearing Plate of 40mm thick on top of concrete
  • RPC handling trolley structure
  • Fixtures like gas lines, electric wires, RPC
    guiding Teflon rails, coil supports, magnetic
    coil mounting bracket, etc.
  • No other live loads (which are the permanent
    loads) are expected to act on to the detector
    foundation structure throughout the service life
    of the structure.
  • As ICAL detector is situated underground, no wind
    loads are considered.

Seismic Analysis of ICAL Foundation Structure
  • Design horizontal seismic coefficient for the
    calculation of lateral earthquake forces acting
    on to the foundation structure is given by
  • Ah(Z/2 ) x (Sa/g) x (I/R)
  • Where
  • Ah Design horizontal seismic coefficient
  • Z Zone factor as per seismic map of India 0.10
    (Seismic zone II)
  • Sa/g Average Acceleration Response Coefficient
    (calculated based on rocky strata underneath of
    soil bearing capacity of 92 t/m2 and having
    damping of 5 as per clause no. of
    IS1893-part 4 for RCC Structures)
  • 2.5
  • I Importance factor 1.75
  • R Response Reduction Factor (represents ratio
    of maximum seismic force on a structure during
    specified ground motion if it were to remain
    elastic to the design seismic force)
  • 3
  • This gives Ah 0.073

Seismic Analysis of ICAL Foundation Structure
  • Seismic calculation of ICAL detector foundation
    structure summaries that 7.3 of total seismic
    weight of ICAL detector structure is going to act
    on to the structure as the lateral earthquake
    forces and foundation structure has to be
    designed to with stand the above force
  • Seismic forces are considered to act at the
    centre of gravity of ICAL detector structure
    assembly and corresponding base shear force is
    acting on to the detector foundation structure.
  • Discrete Concrete pedestals are designed based on
    the axial load carrying capacity from the
    superstructure loading moment due to
    eccentricity in load application and lateral

Concrete supports for one sub-module
  • The Detector structure is supported on 81 nos. of
    concrete pedestals. Each pedestal is provided
    with 40 mm thick MS plates. The height of each
    pedestal is 900 mm.

ICAL Foundation Structure
  • The Concrete pedestals supporting the detector
    stack are categorized into following four
    categories based on the location in the detector
    modules as well as supporting arrangement of
    detector plates.
  • Corner Pedestals (900 mm 650 mm)
  • b) Edge Pedestals along the longitudinal
    direction (700 mm 650 mm)
  • c) Edge Pedestals along the lateral direction
    (900 mm 700 mm)
  • d) Inner Pedestals (700 mm 700 mm)
  • In addition to detector plate supporting
    pedestals, 8 nos. of separate pedestals are
    provided for mounting 4 nos. of magnetic coils in
    the central 8 m 8 m portion with spacing of 1

Bottom Plate Mounting details
  • Bottom most detector plate is welded to the base
    plate along the edges and consequently base plate
    is connected on to top of concrete pedestals. MS
    square flat of size (12 mm 12 mm) is welded to
    the bottom of base plate by tack welding.
  • Non-shrink grout layer of 50 mm thickness is to
    be applied in between top surface of concrete
    pedestal and base plate. MS square flat is
    embedded into the Non-shrink grout layer and at
    top connected with the base plate by means of
    tack welding

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Bottom Plate Mounting details (contd.)
  • In concrete pedestals corner angles of size (65
    mm 65 mm 8 mm) are provided at four corners
    of pedestal cross-section. This arrangement is
    not provided for magnetic coil supporting
    concrete pedestals.
  • MS flat of size (12 mm 6 mm) is welded to the
    corner angles at a spacing of 200 mm c/c along
    900 mm depth and alternately tied up along the
    depth of concrete pedestals.

Magnetic Coil Mounting
Magnetic coil supporting pedestals have a special
arrangement to support the magnetic coil by means
of Magnetic coil mounting bracket on top of
concrete pedestals having size of (875 mm 645
mm) and having depth of 640 mm. Magnetic coil
mounting bracket is resting on the Non shrink
grout layer and it is connected through MS square
flat welded at the bottom of mounting bracket in
diamond shape
Magnetic Coil Mounting (contd.)
Detector Assembly Sequence
Detector Assembly Sequence
Detector Assembly Sequence
INO Prototype Magnet (Assembly)
C section
T section
INO Prototype Magnet (Dimensional details)
INO Prototype Magnet (one layer)
INO Prototype Magnet (magnetic analysis)
Prototype Magnet Detail drawing
Prototype Magnet Section View (Front)
Prototype Magnet Section View (Side)
Prototype Magnet Initial Measurements
The measurements of magnetic flux in the iron
plates within the active zone were made and found
to be more than 1.8 Tesla at the full rating of
the magnet. This is the best that we could hope
for as the saturation flux density as measured by
us earlier had indicated a value of 1.7 Tesla.
The measurements of Field vs ampere turns in the
top plate are as follows gt Magnet
Excitation(Amp.turns) Flux density
(Tesla) gt 1. 1000 ( 50Amp in 20
turns)............ 0.5958 gt 2. 2000 (100Amp in
20 turns)........... 0.7475 gt 3. 3000 (150Amp in
20 turns)........... 1.1692 gt 4. 4000 (200Amp in
20 turns)........... 1.3300 gt 5. 5000 (250Amp in
20 turns)........... 1.4550 gt 6. 6000 (300Amp in
20 turns)........... 1.5683 gt 7. 7000 (350Amp in
20 turns)........... 1.6908 gt 8. 8000 (400Amp in
20 turns)........... 1.7383 gt 9. 9000 (450Amp in
20 turns)........... 1.7875 gt 10.10000(500Amp in
20 turns)......... 1.8133 We reapeted the
reading on this plate to check for consistency
and found the repeatability to be better than 1
percent. We also measured the flux in 3 other
plates (one in the center and the other located
below and above the center plate. The variation
from layer to layer was less than 3 percent and
that too in direct proportion to the plate
thickness. The flux density then remains better
than 3 percent which is much better considering
no control over gaps and plate parameters. The
full data is now under further analysis and will
be shared shortly.
Road Ahead
  • This is a big effort to setup a world class lab
    for basic science research.
  • Complexities arise due to the massive dimensions
  • Making the ICAL detector is a precision job which
  • Procurement of proper grade of Iron plate of
    dimension 2m x 4m x 56mm thk. (exploring
    different sources in the country and abroad)
  • Making the plate flat to the desired accuracy,
    sizing of the sides to achieve the tolerances and
    perpendicularity, making holes for locating pins,
    sand blasting to clean up the unwanted materials,
    painting for rust prevention etc.
  • Keeping the heat affected zone to the minimum
    while doing the above processes.
  • Transporting the plate to the site within the
    scheduled time period.
  • Civil work will require removal of 2.25 Lakh m3
    of tunnel muck generated due to excavation of
    under ground components.
  • 9536 RPCs required for one sub-module.
  • Many more challenges.
  • We have approached the Industry for the jobs
    involved and have got very good response from
    them and are very optimistic to overcome the
    challenges that will be encountered in our effort.

  • I would like especially to mentioned the
    excellent work done by M/s TCE and M/s TNEB
    towards preparation of the Detailed Project
    Report for INO project and also, GSI, Tamilnadu
    and GSI, West Bengal in providing us with
    Geological information of the proposed sites.