1. 19 September 2006SuperNEMO tracker, Manchester status The SuperNEMO Tracker Manchester status Steve Snow Ray Thompson Stefan Soldner-Rembold Irina Nasteva James Mylroie-Smith Nasim Fatemi-Ghomi

2. 19 September 2006SuperNEMO tracker, Manchester status2 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

3. 19 September 2006SuperNEMO tracker, Manchester status3 Electrostatic simulations of Geiger cells

4. 19 September 2006SuperNEMO tracker, Manchester status4 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

5. 19 September 2006SuperNEMO tracker, Manchester status5 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

6. 19 September 2006SuperNEMO tracker, Manchester status6 Applied and effective voltages In 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: V eff = ∫ A/r dr = A ln( r tube /r wire )

7. 19 September 2006SuperNEMO tracker, Manchester status7 Gain versus Voltage and Anode radius 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 V eff = 1700 V will give the same gain as a 30 micron wire with V eff = 1654 V.

8. 19 September 2006SuperNEMO tracker, Manchester status8 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.

9. 19 September 2006SuperNEMO tracker, Manchester status9 Octagonal+4 (mid cell) - results 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. 50 micron anodes: 30 micron anodes:

10. 19 September 2006SuperNEMO tracker, Manchester status10 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 V eff on cathodes … Decreasing anode diameter to 30 mm gives a higher gain at a given voltage

11. 19 September 2006SuperNEMO tracker, Manchester status11 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.

12. 19 September 2006SuperNEMO tracker, Manchester status12 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

13. 19 September 2006SuperNEMO tracker, Manchester status13 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

14. 19 September 2006SuperNEMO tracker, Manchester status14 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 - results 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.

15. 19 September 2006SuperNEMO tracker, Manchester status15 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 - results 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.

16. 19 September 2006SuperNEMO tracker, Manchester status16 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 - results 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.

17. 19 September 2006SuperNEMO tracker, Manchester status17 Hexagonal+4 layout - results 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. 50 micron anodes 30 micron anodes

18. 19 September 2006SuperNEMO tracker, Manchester status18 Hexagonal+6 layout - results 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. 50 micron anodes 30 micron anodes

19. 19 September 2006SuperNEMO tracker, Manchester status19 Figures of merit We want:wires/cm to be small for transparency, cathode V eff 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.

20. 19 September 2006SuperNEMO tracker, Manchester status20 To do … Geiger cells: Simulate the NEMO3 cell to give an estimate of tolerable cathode V eff. 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

21. 19 September 2006SuperNEMO tracker, Manchester status21 Construction of 9-cell tracker prototype

22. 19 September 2006SuperNEMO tracker, Manchester status22 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

23. 19 September 2006SuperNEMO tracker, Manchester status23 Status of the first 9-cell prototype Prototype was wired:

24. 19 September 2006SuperNEMO tracker, Manchester status24 Status of the first 9-cell prototype … and closed in the vacuum vessel

25. 19 September 2006SuperNEMO tracker, Manchester status25 Second 9-cell prototype Based on Forget concept of separate stackable cells: Rail glides Pick up points

26. 19 September 2006SuperNEMO tracker, Manchester status26 Some alterations to allow prototype to be fabricated by CNC machining rather than molding. Wireclamps screwed rather than ultrasonic welding.

27. 19 September 2006SuperNEMO tracker, Manchester status27 Single Geiger cell A single Geiger cell was constructed to study plasma propagation: Single anode inside a tube Diameter 26 mm Length = 3 m

28. 19 September 2006SuperNEMO tracker, Manchester status28 Single cell tests He-Ar gas mixture, no alcohol yet Trigger on 2 scintillators We have seen the first signals

29. 19 September 2006SuperNEMO tracker, Manchester status29 Status Summary Single long tube -Pulses. (simulation reference) First 9-cell prototype -Wired, in clean vacuum vessel. conventional crimp designawaiting cleaning of gas piping. ready to switch on after Dubna meeting. Second 9-cell prototypeMost of endcap components CNC Forget conceptsmachined. Awaiting side closure pieces. 2 nd vacuum vessel ready. Need to build wired cell carrier. ReadoutCurrently using a scope and LabView. Need a multichannel ASIC readout card (LAL). We have bid for H1 ADC boards after decommissioning (2007).