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Modelling of VPTs

Modelling of VPTs. Work in Progress Ignacio Yaselli, Brunel University. Creating a Model for VPTs. How fast are the VPTs? What affects the performance of VPTs Allows prediction of performance under conditions which are not practical to test.

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Modelling of VPTs

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  1. Modelling of VPTs Work in Progress Ignacio Yaselli, Brunel University

  2. Creating a Model for VPTs • How fast are the VPTs? • What affects the performance of VPTs • Allows prediction of performance under conditions which are not practical to test. • Development of technical data for use of VPTs on other applications. • Compare results with previous studies and with future experiments.

  3. Electron Absorption • Photons produce primary electrons at cathode • Some e- absorbed on Anode as primary signal • Some e- absorbed on Dynode • Secondary emissions of e- from Dynode (some then absorbed by Anode, some return to the Dynode

  4. VPT Mesh RIE: 100 lines per mm, 50% transparent

  5. Sample of SIMION Simulation • Anode – Realistic Mesh at 1000 Volts • Dynode – Electrode at 800 Volts • Cathode Realistic simulation of a production (RIE) VPT

  6. Potential Arrays 0 V Kathode 1000 V Anode 800 V Dynode 0 V Aluminium Wrap

  7. SIMION User Programs • HP like programming • Separated on segments • Each independent of each other • Each called at different stages of the ION flight • Only the segment that are needed have to be defined • Access the behaviour of ION by use of reserved variables • User Programs are linked to specific instances. Therefore, SIMION relies on Instance hierarchy for running these programs.

  8. Implementation of SIMION User Programs • Determine which electrode is hit by electron. • Recall sufficient data to: • Generate secondary electron • Construct a *ion file from these secondary electrons • Generate a Signal file.

  9. Pros and Cons of SIMION CONS • Requires 3rd party program for simulation of secondary emission PRO • Powerful 3D Ion Optics Workbench • User Programs • Geometry files • 3rd party programs cooperation • Allows data recording • Used over many years for electon optic design

  10. ION-ator Functionality • Assume a Starting Ion File has been Created • Assume, that that SIMION has originated first Output • Load data files generated by SIMION • Open Output file, Read it, and Close It • Determine which Ions Have Generated Previous Secondary Ion • Generate Random New_Ions from each previously unused Ion • Generate a Poison Distributed Random Number • Parameterise characteristics of parent ion to generate subordinates • Select Ions With Sufficient Energy to Escape Electrode • Append Only the Ions Selected to the original Ion File.

  11. Relation of SIMION and ION-ATOR Sort hits on Anode from hits on Dynode Reads *.ion file and load Electrons into memory Record hits on Anode on signal file for analysis Fly Electrons Generate secondary electrons from hits on Dynode with int N= Ep/m Load User Program Store Hit List Store Secondary Electrons on *.ion file Simple dynode model will be refined

  12. Currently in Progress • Refining Simulation Model (especially the secondary emission details) • Testing Hypothesis • Analysis of simulation results: Time Delay, pulse width, gain, etc. • Generating high statistics simulations

  13. Secondary electron absorption with anode at 1kV and at a magnetic field of 0T K A D Dynode at 200V Dynode at 1005V Dynode at 800V Dynode at 1015V

  14. Measured VPT Gain at 0T Note that this is NOT data from a production VPT

  15. Simple Dynode Model • Dynode assumed noise free • Number of secondary electrons is strictly proportional to incident electron energy • Gain is 25 for an electron energy of 1000 eV • Emission energy of secondary electrons is fixed at 5 eV but the angle is random within +- 5 degrees of the normal to the dynode

  16. Simulated Gain of VPT (0T) Anode at Dynode +200V Anode fixed at 1000V

  17. Simulated Gain of VPT (low magnetic field) 0.01T with Anode fixed at 1000V 0.1T with Anode fixed at 1000V

  18. Time Response of the VPT By increasing the Dynode Voltage, the gain increases and the pulse width narrows

  19. IMMEDIATE FUTURE • Prepare poster for the Beaune Conference (we will circulate a draft around Wednesday 15th). • Setup equipment for testing model • Start experimental data collection

  20. Conclusions • The Simulation system consist of 2 different software packages: • A commercially available package called SIMION for data generation and Ion tracking in static electric and magnetic fields. • Specially written program for simulating the dynode properties of the VPT as well as data handling. • The combination of the above has been essential for understanding the behaviour of VPTs. • By comparing the results from these simulation with data acquired from real VPTs at RAL and Brunel, it will be possible to trust results from simulation which are impractical to test in the lab. i.e orientation of VPT in full 4T field etc…

  21. Appendices

  22. Secondary electron absorption with anode at 1kV and at a magnetic field of 0.01T at 15o K A D Dynode at 200V Dynode at 1005V Dynode at 800V Dynode at 1015V

  23. Secondary electron absorption with anode at 1kV and at a magnetic field of 0.1T at 15o K A D Dynode at 200V Dynode at 1005V Dynode at 800V Dynode at 1015V

  24. Time Response of VPT with VA=1000V, VD=1005V

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