TPC Design Concept:From MicroBooNE to LAr20

Bo Yu

Brookhaven National Lab

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Outline

TPC Signal Characteristics MicroBooNE TPC Design Scaling Issues LAr20 TPC Concepts

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Point Charge Induction on 3 Planes of Wires

Under proper bias condition, the first two planes of wires see bipolar induction signals, but do not collect any net charge.

The 3rd wire plane collects 100% of the signal charge, enabling precise measurement of the ionization of a particle track

Simulations using “Garfield” have given us a better understanding of the TPC signals

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At large track angles, the induction wire signal amplitude diminishes, making dE/dx measurement difficult.Pulse width is largely determined

by the wire plane spacing and the electron drift velocity

6CD-1 Readiness Directors Review

Major Components in the MicroBooNE TPC

High voltage feedthrough(-128kV)

Cathode plane

Cold electronicsTop ground plane

PMT frame

Wire planes

Field cage

Rails for TPC installation

Signal feedthrough

9% ullage (Argon Gas)

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Major Parameters of the TPC

2.33m

2.56m

11.5m

Wire Arrangment:U,V,Y

Gas argon (9% ullage)

3mm wire pitch 3mm wire plane spacing

Nominal Wire Length:Y: 2.5mU, V: 5m

Number of Wires:Y: 3840U, V: 2592 each

Total: 9024

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Wire Termination and Carrier• Stainless steel wire (150µm) with copper and gold plating to increase conductivity• Break strength ~ 4kg at LN2 temperature; CTE compatible with structural material• Printed circuit board based wire carrier modules allow accurate wire placement and integration with front end electronics

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A Detailed View of the TPC

Top ground plane

Preampmotherboard

Top field cage support beam and bracket

Wire frameWire carriers

3 wire planesShielding mesh

The TPC with the cold electronics will be completely assembled and then inserted into the cryostat.

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Scale to Larger Detectors

Key issue is how to make the wire planes:• Modular: can be pre-fabricated. (<4m width, ~ 10m length to fit in

the mine lift)• Self-supporting: preferably not tied into the cryostat structure.• Minimize dead space

The use of cold electronics gives us great flexibility in designing the TPC. ASIC with multiplexed readout significantly reduces the power dissipation and the amount of cable inside the cryostat. The designs of both the TPC and the cryostat can be optimized

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Wire Length

Capacitance: ~20pF/m Electronics Noise: ENC ~ 300e + 3e per pF (JFET @ 90K)

• At 10m, ENC ~ 900e rms;• A 3mm MIP track segment gives ~ 6000e (30% recombination loss, drift 1

lifetime);• A signal to noise ratio of 7:1.

Gravitational Sagging: ~ L2/T (~0.5mm @1kg, 5m) Electrostatic deflection: probably negligible, with large tension. Intermediate

wire supports will be considered in case lower wire tension is needed.

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Wire Pitch

Wire pitch and wire plane spacing should be about the same Determines the minimal signal level:

• MIP over the wire pitch Determined by the Transverse Diffusion of electrons (DT~ 16cm2/s)

• At 5m drift, =3mm (FWHM~7mm)

Over 2.5m drift

Electron spatial distributions after 2.5m (red) and 5m(blue) of drift

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Membrane Cryostat Concept

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Modular Cryostat Concept (LANNDD)

Backup design if evacuation is necessary to achieve sufficient electron life time (LAPD outcome)Internally supported by a cubic lattice structure, capable of withstanding vacuum evacuation

15FERMILAB June 18-19, 2009 Franco Sergiampietri

Wire chamber 4

Wire chamber 3

Wire chamber 2Wire chamber 1

Cathode 2

Cathode 1

TPC Concept for the Modular Cryostat

TPC design closely coupled to the cryostat structure

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TPC Module Concepts (Membrane Cryostat)

Key consideration is to minimize the dead space in the TPC

1. Self supporting frame module2-3” dead space between frames6-8” dead space between wire planesHanging from the ceiling or standing on the floor

2. Light weight open frame module~8” dead space between frameNo dead space through the wire planesHanging from the ceiling

3. Continuous hanging constructionOne 6” wide dead zone in mid height of the chamberHanging from the ceiling

Cathode plane will be constructed with one layer of mesh, hanging from a rail and tensioned by weights at the bottom.

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Self Supporting Frame Module(Double sided MicroBooNE Style Wire Frame)

Wire Length:Y: 4m, U: 8m, V: 8m

Number of Wires@3mm pitch

Y: 3333, U: 2243, V: 2243Total: 7819 each side

At 2.5m drift: -> ~56ch/ton

Frame Load @ 1kg wire tension: 500kg/m on long edge, 667kg/m on short edge

@5mm pitchY: 2000, U:1346, V: 1346

Total: 4692 each side, 33.5ch/ton

Readout electronics on 3 sides

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Self Supporting Frame Module

Cross section of an edge of the frame

Include PMTs or light guides for light collection?

Dead space ~ 1”

~ 6” minimum

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Light Weight Open Frame Module

Full d

epth

of t

he cr

yosta

t

Full length of the cryostat

Temporary support during frame assembly

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Light Weight Open Frame ModuleFrame cross section:

Dead space*~20cm

* It is possible to construct the field shaping electrodes to deflect the electrons away from the frames and onto the wire electrodes, eliminating this dead space.

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Joining Wires

In MicroBooNE style wire arrangement, the U & V wires are always twice as long as the Y wires. To equalize the capacitive load on the preamps from all three planes, we can join two wires mechanically and read them out from both ends

Insulating wire joints can be constrained by SS bars to maintain wire pitch

Metal wire terminations can be constrained by insulating bars to maintain wire pitch

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Continuous Hanging Construction

roof joists rigid beams

electronics enclosures

wire joint strips

Needs a lot of force to keep the wires properly tensioned:Load on the bottom beam:

1ton/m (6 wire planes, 2U, 2V, 2Y, 1kg per wire, 3mm pitch 600kg/m, @ 5mm pitch

1/3 more load on the two vertical beams

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Continuous Hanging Construction

No dead space along beam direction, no dead space across wire planes, minimal dead space in one horizontal plane at mid depth.

All wires are 8m long, U & V planes have insulating joints. Eliminate most of the short corner wires in framed modules

Requires additional weights or tensioners to keep the wires stretched. A MicroBooNE style wire arrangement will require 1ton/m load at the bottom of each wire “curtain”.

Sensing wires

Cathode plane

Cold electronics

Field cage

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Next Steps

Study the impact of the dead space on the detector’s performance (fiducial cut). This may indicate which concept is the most advantageous

Develop a cost and schedule based on the experience on MicroBooNE design.

A dry mockup of the membrane cryostat will be constructed to study the construction issues. A full scale TPC prototype module will be built and installed in this mockup