The SuperNEMO Tracker Manchester status

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

3. Electrostatic simulationsof Geiger cells 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 mm • Anode diameters 50 and 30 mm • 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 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 SuperNEMO tracker, Manchester status

6. Appliedandeffectivevoltages 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 plasmapropagation. 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 ) SuperNEMO tracker, Manchester status

7. Gain versus Voltage and Anode radius To compare layouts with different anode diameters we need to know how the Townsend coefficient a varies with E. We used predictions from Magboltz for the NEMO-3 gas mixture. The avalanche gain is given by integration of a(E) in the high field region: Gain = exp( ∫ a(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. SuperNEMO tracker, Manchester status

8. Basic octagonal 3x3 cells - 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: SuperNEMO tracker, Manchester status

9. 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: 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 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. 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 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 SuperNEMO tracker, Manchester status

14. 50 micron anodes These three should be equal to 1700/4 = 425 V. Difference is due to limited simulation accuracy. 30 micron anodes Edge effects are small in this cell, important in the last cell 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. SuperNEMO tracker, Manchester status

15. 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. 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. 30 micron anodes Edge effects are negligible except for the last cell SuperNEMO tracker, Manchester status

16. 50 micron anodes Field lines are now shared equally between these six cathodes. 30 micron anodes Edge effects are negligible except for the last cell 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. SuperNEMO tracker, Manchester status

17. 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 SuperNEMO tracker, Manchester status

18. 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 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. SuperNEMO tracker, Manchester status

20. 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 0vbb 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 SuperNEMO tracker, Manchester status

21. Construction of 9-cell tracker prototype 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 mm • Anode diameter 50 mm • Wires from NEMO3 • Gas system, He-Ar, ethanol cooler • Trigger system for cosmics: 2 scintillators in coincidence SuperNEMO tracker, Manchester status

23. Status of the first 9-cell prototype Prototype was wired: SuperNEMO tracker, Manchester status

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

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

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

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

28. Single cell tests • He-Ar gas mixture, no alcohol yet • Trigger on 2 scintillators • We have seen the first signals 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 prototypeMost of endcap components CNC Forget 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). SuperNEMO tracker, Manchester status