19 September 2006 SuperNEMO tracker, Manchester status The SuperNEMO Tracker Manchester status Steve Snow Ray Thompson Stefan Soldner-Rembold Irina Nasteva James Mylroie-Smith Nasim Fatemi-Ghomi
Jan 21, 2016
19 September 2006 SuperNEMO tracker, Manchester status
The SuperNEMO TrackerManchester status
Steve Snow
Ray Thompson
Stefan Soldner-Rembold
Irina Nasteva
James Mylroie-Smith
Nasim Fatemi-Ghomi
19 September 2006 SuperNEMO tracker, Manchester status 2
Outline
Electrostatic simulations of Geiger cells:
• Comparison between Garfield and FlexPDE
• Results for 9-cell prototype layouts
• Results for different layouts of the SuperNEMO tracker
• To do…
Construction of 9-cell prototype:
• Status of first 9-cell prototype
• Status of second 9-cell prototype
• Single Geiger cell
19 September 2006 SuperNEMO tracker, Manchester status 3
Electrostatic simulations
of Geiger cells
19 September 2006 SuperNEMO tracker, Manchester status 4
Simulations of 3x3 cells
The 9-cell prototype is simulated with:
• X pitch = 30 mm
• Y pitch = 30 mm
• Gap = 10 mm
• Cathode diameter 50 m
• Anode diameters 50 and 30 m
Possible layouts:
• Basic octagonal cells
• Octagonal cells with 4 extra wires around mid cell
• Octagonal cells with 4 extra wires around all cells
ground plane
extra cathodes
19 September 2006 SuperNEMO tracker, Manchester status 5
Garfield and FlexPDE
Garfield:
• electrostatic simulations of wire chambers in 2D
• makes use of symmetries
• can simulate gases with Megaboltz
• used and tested in many gas detector simulations (NEMO3)
FlexPDE:
• finite element analysis
• user supplies differential equations to be solved (programme knows nothing about the physics)
• can do simulations in 3D
• easy to use
19 September 2006 SuperNEMO tracker, Manchester status 6
Applied and effective voltagesIn a wire chamber we have -
An arrangement of wires with voltages applied to them.
A resulting field distribution that can be calculated with Garfield or FlexPDE.
Very near the wires, the field always has the form E=A/r. Equivalently, the potential contours are circles centred on the wire.
It is the strong E field within 1.5 mm of the anode wire that determines the avalanche gain, which in turn drives the Geiger plasma propagation.
It is the strong E field at the surface of the cathode wire that can drive electron emission processes, leading to self-sustained discharge.
So the electrostatics of a wire chamber is characterised by the A values near each of the wires.
Instead of quoting A directly, we usually convert it to the effective voltage: the voltage necessary to produce the same value of A when the wire is in the centre of a 30mm tube:
Veff = ∫ A/r dr = A ln( rtube /rwire )
19 September 2006 SuperNEMO tracker, Manchester status 7
Gain versus Voltage and Anode radius
14.6
14.8
15
15.2
15.4
15.6
15.8
16
16.2
16.4
1620 1640 1660 1680 1700 1720 1740 1760
Voltage
ln(gain)
50 micron30 micron-
1654 V 1700 V
Nemo 3 gas
To compare layouts with different anode diameters we need to know how the Townsend coefficient varies with E.
We used predictions from Magboltz for the NEMO-3 gas mixture.
The avalanche gain is given by integration of (E) in the high field region:
Gain = exp( ∫ (A/r).dr )
The result of the integration for 30 and 50 micron wire diameters, at a range of effective voltages, is shown in this plot.
This shows that a 50 micron wire with Veff = 1700 V will give the same gain as a 30 micron wire with Veff = 1654 V.
-500.000
0.000
500.000
1000.000
1500.000
2000.000
2500.000
3000.000
0.00 50.00 100.00 150.00 200.00
Field (kV/cm)
Rate ( /cm )
Alpha
Attachment
Alpha-Att
19 September 2006 SuperNEMO tracker, Manchester status 8
Basic octagonal 3x3 cells - results
50 micron anodes: 30 micron anodes:
On the anodes we show the applied voltage, necessary to produce a gain equivalent to 1700 V on a 50 micron wire in a 30 mm tube.
On the cathodes we show (-1x) the effective voltage.
19 September 2006 SuperNEMO tracker, Manchester status 9
Octagonal+4 (mid cell) - resultsOn the anodes we show the applied voltage, necessary to produce a gain equivalent to 1700 V on a 50 micron wire in a 30 mm tube.
On the cathodes we show (-1x) the effective voltage.
50 micron anodes: 30 micron anodes:
19 September 2006 SuperNEMO tracker, Manchester status 10
Summary of 3x3 cells results
• Garfield and FlexPDE agree to within 0.4%
• We can go on to use FlexPDE for 3D simulations (wire ends)
• Adding extra cathodes around mid cell reduces Veff on cathodes …
• Decreasing anode diameter to 30 mm gives a higher gain at a given voltage
19 September 2006 SuperNEMO tracker, Manchester status 11
SuperNEMO module assumptions
We assume that:
• There will be a continuous block of Geiger cells filling nearly all the space between the source foil and the calorimeter.
• All cells have the same layout except for possible minor variations on the surface layers.
• The space between foil and scintillator must be >30 cm for TOF to work. But total module thickness should be kept down.
• The structure will be 9 cells deep in the X direction and very large in the Y direction. So the unit cell for electrostatics is the pink area.
• X pitch and Y pitch need not be identical.
19 September 2006 SuperNEMO tracker, Manchester status 12
Octagonal layouts
Simulated with
• X pitch = 30 mm
• Y pitch = 30 mm
• Gap = 10 mm
• Cathode diameter 50 m
• Anode diameters 50 and 30 m
19 September 2006 SuperNEMO tracker, Manchester status 13
Hexagonal layouts
Simulated with
• X pitch = 30 mm
• Y pitch = 30 mm
• Gap = 10 mm
• Cathode diameter 50 m
• Anode diameters 50 and 30 m
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Edge effects are small in this cell, important in the last cell
30 micron anodes
50 micron anodes
These three should be equal to 1700/4 = 425 V. Difference is due to limited simulation accuracy.
Basic octagonal layout - resultsOn the anodes we show the applied voltage, necessary to produce a gain equivalent to 1700 V on a 50 micron wire in a 30 mm tube.
On the cathodes we show (-1x) the effective voltage.
19 September 2006 SuperNEMO tracker, Manchester status 15
30 micron anodes
Edge effects are negligible except for the last cell
50 micron anodes
Field lines are no longer shared equally between these four cathodes. We could benefit by increasing the separation of the closest pair.
Octagonal+2 layout - resultsOn the anodes we show the applied voltage, necessary to produce a gain equivalent to 1700 V on a 50 micron wire in a 30 mm tube.
On the cathodes we show (-1x) the effective voltage.
19 September 2006 SuperNEMO tracker, Manchester status 16
30 micron anodes
Edge effects are negligible except for the last cell
50 micron anodes
Field lines are now shared equally between these six cathodes.
Octagonal+4 layout - resultsOn the anodes we show the applied voltage, necessary to produce a gain equivalent to 1700 V on a 50 micron wire in a 30 mm tube.
On the cathodes we show (-1x) the effective voltage.
19 September 2006 SuperNEMO tracker, Manchester status 17
Hexagonal+4 layout - resultsOn the anodes we show the applied voltage, necessary to produce a gain equivalent to 1700 V on a 50 micron wire in a 30 mm tube.
On the cathodes we show (-1x) the effective voltage.
50 micron anodes
30 micron anodes
19 September 2006 SuperNEMO tracker, Manchester status 18
Hexagonal+6 layout - resultsOn the anodes we show the applied voltage, necessary to produce a gain equivalent to 1700 V on a 50 micron wire in a 30 mm tube.
On the cathodes we show (-1x) the effective voltage.
50 micron anodes
30 micron anodes
19 September 2006 SuperNEMO tracker, Manchester status 19
Figures of merit
We want: wires/cm to be small for transparency,
cathode Veff to be small for stability.
The dominant parameter is cathodes/cell, followed by anode diameter, then Hex/Oct.
We choose the octagonal as our baseline design.
Anode Cathodes X pitch Wires Anodes Anode voltage Cathode(micron) per cell (mm) per cm per cm Max Range V_eff
Octagonal 50 4 30 15.67 3.00 2014 78 429 too highOct+2 50 5 30 18.33 3.00 1944 42 359 just OKOct+4 50 6 30 21.33 3.00 1891 32 290 safeHexagonal 50 2 30 10.58 3.27Hex+2 50 3 30 13.66 3.27Hex+4 50 4 30 16.74 3.27 2010 78 430 too highHex+6 50 5 30 20.01 3.27 1927 40 350 just OK
Octagonal 30 4 30 14.47 3.00 1937 72 386 too highOct+2 30 5 30 17.13 3.00 1874 38 323 safeOct+4 30 6 30 20.13 3.00 1877 30 269 very safeHexagonal 30 2 30 9.28 3.27Hex+2 30 3 30 12.36 3.27Hex+4 30 4 30 15.43 3.27 1931 68 385 too highHex+6 30 5 30 18.71 3.27 1859 36 315 safe
Layout
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To do …
Geiger cells:
• Simulate the NEMO3 cell to give an estimate of tolerable cathode Veff.
• Check a handful of points on the gain versus voltage and anode diameter plots by operating a test cell in proportional mode.
• Check whether Geiger propagation depends only on gain, as assumed, or whether it has some extra dependence on wire diameter.
• Find out experimentally the highest tolerable cathode surface field a) on a fresh wire, b) after some ageing.
Physics simulation:
• Are 40mm cells are acceptable for two-track resolution?
• Which of the following have most influence on acceptance of 0v events?energy loss or multiple scattering, in the gas or in wires,wire length, source foil area, foil-to-scintillator distance, …
• This was partially studied by Darren Price, could be a new student project
19 September 2006 SuperNEMO tracker, Manchester status 21
Construction of 9-cell
tracker prototype
19 September 2006 SuperNEMO tracker, Manchester status 22
First 9-cell prototype
• 3x3 cells (as in simulation)
• X,Y pitch = 30 mm
• Length = 2 m
• Cathode diameter 50 m
• Anode diameter 50 m
• Wires from NEMO3
• Gas system, He-Ar, ethanol cooler
• Trigger system for cosmics: 2 scintillators in coincidence
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Status of the first 9-cell prototype
Prototype was wired:
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Status of the first 9-cell prototype
… and closed in the vacuum vessel
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Second 9-cell prototype
Based on Forget concept of separate stackable cells:
Rail glides
Pick up points
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Some alterations to allowprototype to be fabricated by CNC machining rather than molding.
Wireclamps screwed rather than ultrasonic welding.
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Single Geiger cell
A single Geiger cell was constructed to study plasma propagation:
• Single anode inside a tube
• Diameter 26 mm
• Length = 3 m
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Total time of pulses agrees with plasma propagation at 2.5 cm/ 3- s along a m wire
0
5
10
15
20
25
90 100 110 120 130 140 150 Times
Events
Single cell tests
• He-Ar gas mixture, no alcohol yet
• Trigger on 2 scintillators
• We have seen the first signals
19 September 2006 SuperNEMO tracker, Manchester status 29
Status Summary
Single long tube - Pulses.(simulation reference)
First 9-cell prototype - Wired, in clean vacuum vessel.conventional crimp design awaiting cleaning of gas piping.
ready to switch on after Dubna meeting.
Second 9-cell prototype Most of endcap components CNCForget concepts machined.
Awaiting side closure pieces.2nd vacuum vessel ready.Need to build wired cell carrier.
Readout Currently using a scope and LabView.Need a multichannel ASIC readout card (LAL).We have bid for H1 ADC boards after decommissioning (2007).