MODULAr: MODULAr: conceptconcept design design of internal detector of internal detector
mechanicsmechanics
A. Menegolli, University and INFN Pavia
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Basic Considerations
The basic requirements of a large LAr detector like MODULAr are:The basic requirements of a large LAr detector like MODULAr are:
– precision in wires positioning (~100 µm);precision in wires positioning (~100 µm);
– uniform purification of the full Argon volume.uniform purification of the full Argon volume.
The ICARUS-T600 mechanics successfully fulfills the above The ICARUS-T600 mechanics successfully fulfills the above requirements if evacuated before filling.requirements if evacuated before filling.
Scaling the T600 detector to significant larger sizes requires a Scaling the T600 detector to significant larger sizes requires a relatively small revision of the designrelatively small revision of the design: the main new task is to : the main new task is to preserve the LAr purity even in case of a filling procedure without preserve the LAr purity even in case of a filling procedure without previous dewar evacuation.previous dewar evacuation.
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The structure of the MODULAr detector has been considerably streamlined in order to reduce the number of components, their cost and increase the reliability of the system.
The modular structure allows to repeat the initial engineering design of the prototype to a series of several subsequent units, reducing progressively their cost and their construction time: the basic unit is a 10 kton sensitive LAr volume.
The main aim of MODULAr detector is the one of filling and maintaining over many years a very large amount of ultra-pure LAr in stable conditions inside a dedicated underground cave, within very rigid safety conditions.
MODULAr structure structure
Under such conditions, a 20 kton sensitive volume modular detector might be operative in 4 years, and additional clone units of 10 kton each could be built during the years depending on the physics requirements.
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Geometry of an ICARUS-T600 half-module (T300) “cloned” into a larger detector scaled by a factor 8/3 = 2.66: the cross sectional area of the planes is 8 x 8 m2 rather than 3 x 3 m2. The length of such a detector is 50 meters.
8m
8m
3 m
3 m
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ICARUS-T600: mechanics reviewLAr containers: solution with Aluminum honeycomb panels 150 mm thick: the total internal volume of a cryostat is (3.9 x 3.6 x 19.6 = 275) m3.
Perforated 142 mm aluminum honeycomb
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Each of the two T300 half-modules hosts a stainless-steel mechanical structure that sustains the different inner detector subsystems, in particular way the TPC wire planes.
Mechanical precision achieved for all the inner detector parts ~100 m
Event images are not distorted by misalignment of wire planes.
Horizontal beams
Stainless-steel structure(beams and pillars)
Peek supports
Inner detector
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MODULAr mechanical structure has been studied in order to be highly streamlined, taking as a reference the work done for the T600. It is essentially made of only three main mechanical components:
MODULAr mechanical structure
1) an external insulating vessel;
2) a linear supporting and holding structure;
3) the liquid Argon and Nitrogen supply and refrigeration.
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The external insulating vessel is made of two metallic concentric volumes with the inter-space filled with perlite as a thermal insulation.
Perlite insulationPerlite insulation
Perlite: mineral vastly used industrially; easily available at low cost.
Low conductivity foam glass light Low conductivity foam glass light bricks for the bottom support layerbricks for the bottom support layer
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A 1.5 m thickness of perlite corresponds to a specific heat loss of 3.86 W/m2, significantly smaller than the specific heat loss of ICARUS-T600 (~7 W/m2).
Taking into account the dimensions of the vessel, the total heat loss is 8.28 kW: three units of 4 kW (cold) power should be adequate to ensure cooling of the walls of the vessel during normal operation (the plant of ICARUS-T600 consists of 10 units).
Evacuation of the perlite is unnecessary
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Like ICARUS-T600, MODULAr wire frame design is based on the concept of the variable geometry design: beams of the wire frames are movable.
Frame beams are connected by a set of calibrated springs compensating for tension increase on wires possibly occurring during cooling and filling phases.
The wire mechanicalThe wire mechanicaltension is kept tension is kept constantconstant
T600 tensioning system(springs and movable frame)
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HV systemThe HV system produces a stable and uniform field over the 4 m maximum drift length. The cathode is biased with negative voltage (-200 kV for a nominal drift field of 0.5 kV/cm); the field is kept uniform by means of a series of equally spaced field shaping electrodes (race tracks) surrounding the active volume; voltage on the race tracks is distributed from the cathode by means of a resistive divider chain.
Nominal HV for a T300 half-module: 75 kV for 1.5 m drift (E = 0.5 kV/cm). HV system operated in steady conditions up to 150 kV.
To reduce the noise induced by the power supply ripple, in ICARUS-T600 a highly efficient rejection two-stage RC filter has been designed and implemented.
HV feedthrough
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The refrigeration with N2 circulation, provides cooling of the Argon volume ensuring that:
the Argon properties (drift velocity) are uniform all over the active volume;
the whole liquid is moving orderly inside the vessel volume;
also the free electrons lifetime is kept uniform.
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The MODULAr read-out wires are also scaled out by a factor 8/3 = 2.66 with respect to the existing ICARUS-T600 wires.
MODULAr wire arrangementLike ICARUS-T600, a MODULAr LAr TPC is composed of two read-out wire planes (three orders of wire planes at ±60° and 0° each) with a HV cathode in between.
Three orders wire planes
+60°
-60°
0°
Spacers
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Longer MODULAr wires have a higher capacitance and the S/N ratio is significantly decreased (wires ~ 10 pF/m; cables ~ 50 pF/m).
This factor is compensated widening the pitch from the 3 mm of ICARUS-T600 to the 6 mm of MODULAr, doubling the dE/dx signals: therefore we expect S/N ratios similar to the ones of the T600 (~ 10/1).
The average LAr mass observed by each read-out wire is about 200 Kg/channel: a 20 kton sensitive volume will then require a number of channels of the order 100,000.
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For each 10 kton modular unit, about 50,000 stainless-steel wires of several lengths will be prepared:
- 10 m for ± 60º wires;- 25 m for 0º wires (2 coplanar, adjacent sets per wire plane);- 130÷1014 cm for corner wires.
Because of the ~50 m length of the MODULAr detector, the horizontal (0º wires) read-out plane will be subdivided in two sub-planes hosting 25 m wires.
MODULAr wire features
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Stainless steel comb holder
Peek shell
Peek comb
The wires are held in place by winding The wires are held in place by winding over themselves (like guitar chords) after over themselves (like guitar chords) after having passed them around a golden having passed them around a golden stainless steel sleeve. The wires are fixed stainless steel sleeve. The wires are fixed in position by inserting the sleeves into in position by inserting the sleeves into the pins of 32 wire holding combs.the pins of 32 wire holding combs.
The 32 wire modules are fixed on the The 32 wire modules are fixed on the high precision supporting and holding high precision supporting and holding frames.frames.
MODULAr wire production, holding, tensioning and storing make use of the technologies already developed and tested for the ICARUS-T600 wires.
Golden stainless-steel ferrule
Slipknots at both ends
ICARUS-T600 9 meter wire
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Wire tension: T = 1169 ± 4 g Wire tension: T = 1169 ± 4 g
T (g)
T (g)
Breaking tension: B = 2923 ± 98 g Breaking tension: B = 2923 ± 98 g
Wire holdings Wire holdings
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Wiring devices
Wiring table Wiring table Wire module rollingWire module rollingaround a PVC spoolaround a PVC spool
PVC spools after washing and during PVC spools after washing and during dryingdrying
Tensioning group to fix and Tensioning group to fix and tension the wirestension the wires
Wire production speed for T600 wires: Wire production speed for T600 wires: 1 hour1 hour for the assembly of a 32 wires for the assembly of a 32 wires
modulemodule
Wiring could begin at any Wiring could begin at any time and the wire modules time and the wire modules can becan be cleaned and stored cleaned and stored until installation. until installation.
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PMTs for light collection
As for ICARUS-T600 a number of photomultipliers located behind the read-out wire planes are used to provide a t = 0 trigger.
This is important for the cosmic rays and proton decay events (no starting signal provided), but could as well very useful in order to tag events coming from CNGS beam.
The technique consists in glass 8” PMTs with a thin deposit of wavelength shifter in order to record the prompt (~μs) VUV scintillation light from the LAr.
New 8” PMTs are being developed with about twice the Quantum Efficiency of the PMTs originally used in ICARUS-T600, that was around 10%.The minimal requirement for MODULAr PMT trigger is the detection of 10 MeV signals (SuperNova neutrinos): in such case about 100 PMTs for read-out plane are needed (minimum signal ~ 8 photo-electrons).
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Summary (1)
The mechanical structure of the MODULAr detector will use as a starting point the ICARUS-T600 geometry, which is taken as a reference design.
The structure of the detector will be considerably streamlined in order to reduce the number of components, the cost and the construction time: a modular detector of 20 kton sensitive volume could be operational in 4 years.
The geometry will be a “clone” of an ICARUS-T600 half-module into a larger detector with linear dimension scaled by a suitable factor.
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The basic module is a 10 kton sensitive volume ICARUS-T600-like detector (2 x 5 kton) insulated by a vessel made of two metallic concentric volumes with the inter-space filled with perlite as a thermal insulation.
The detector clone modules will be located in a new experimental area, now under consideration, to be realized about 10 Km off-axis from LNGS, tailored specifically to the MODULAr experiment.
Further 10 kton modular units can be added in the course of the years, provided experimental halls are realized, depending on the physics requirements: the engineering of the modular units would strongly reduce the cost and the time for the realization of a LAr detector of several tens of kton.
Summary (2)