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Design of a readout system for RPCs

Design of a readout system for RPCs. The LODEN Group. The group is an association of Fermilab scientists who teamed up to build a cosmic ray detector from RPCs. I was assigned as intern to this group and I helped in building a readout for RPCs. Resistive Plate Chamber(RPC).

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Design of a readout system for RPCs

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  1. Design of a readout system for RPCs

  2. The LODEN Group • The group is an association of Fermilab scientists who teamed up to build a cosmic ray detector from RPCs. • I was assigned as intern to this group and I helped in building a readout for RPCs Olu Amoda

  3. Resistive Plate Chamber(RPC) • An RPC is a glass chamber filled with a mixture of gases,an electric field supplied by an High Voltage source. It is used to detect charged particles through their interactions with the molecules of the gases. • The particles strip off electrons from the molecules of the gases, which results in a spark inside the chamber. • The spark induces a voltage on an adjoining readout system. Olu Amoda

  4. Schematics Olu Amoda

  5. Glass electrodes are used to apply an electric field of ~4kV/mm across a 2mm gap.The gap has a mixture of argon,isobutane and HFC123a gas. An ionizing particle initiates a discharge which capacitively induces a signal on external pickup strips. How it works Olu Amoda

  6. Building a Readout System • Factors taken into consideration: • Cost • Efficiency • Availability • Construction. Olu Amoda

  7. Inductive Readout System • Is a capacitor like setup • With two surfaces, one for signal transmission and the other for signal protection. • A dielectric material between the surfaces Olu Amoda

  8. Strip readout Method: A board is stripped vertically and another one horizontally. A signal is picked by a a vertical and horizontal strip Both strips locates position. Padded r/out Method: Board is partitioned into square segments. A signal is picked up a square segment Square segment locates position Two Methods of Construction Olu Amoda

  9. Strip Readout System Padded Readout System Diagram of Readout Systems Olu Amoda

  10. Strips over Pads The strips method was chosen over the padded method due to the following reasons. 1) It is easier to make strips on a board than to make square segments. 2) For a large area of RPC it will cost much more to attach signal cable to each square than to each strip. 3) For a a board of dimension a by b, we need a*b for square segments, while we need a+b for strips. Olu Amoda

  11. Material for construction • Copper strips on mylar foil is normally used for a strip readout board. • Copper and mylar are every expensive. • An home insulating board from home depot was used as a substitute for the “copper strips on mylar”. Olu Amoda

  12. The Board • As one side made of aluminum. • Another side made of aluminum coated with insulating material. • A dielectric made of foam. Olu Amoda

  13. What next ? • Make strips of different width on the board. • Setup experiment to: • Study signal transmission in each strip. • Determine the right strip for experiment • Study reflection. Olu Amoda

  14. Pre-Experiment • Strips were made on the board by a saw. • The ends of the ground plane were cleaned with ethyl , for cable attachments. Olu Amoda

  15. Purpose of Experiment:To Determine • The width of the strip that will give the least backend reflection • The terminating impedance at the back of the board for each strip • The strip that gives the least front end reflection, after termination . Olu Amoda

  16. Experimental Setup Olu Amoda

  17. Reflections in Cables • When signals travel trough two cables of different impedances, reflections are setup at the boundary of the two cables. • If two cables of impedances R and Z are connected to each other, ρ gives the value of reflection for both cables. Z R Olu Amoda

  18. Problem • A pulser was required to generate pulses. • A pulser output feeds a 50 ohm coaxial cable. • 120 ohm twisted-flat cable was to receive pulses from the pulser. • Problem: Interconnecting the two cables directly will pose a problem. • Why? Olu Amoda

  19. Avoiding Reflections • When two cables of different impedances are to be connected to each other. • The principle of termination is employed. • Termination is the addition of supplementary impedance(s) to the impedances of two cables. • Termination can be done either in series or in parallel or a combination of both. Olu Amoda

  20. Application • The circuit represented by the circuit diagram was designed to connect the 120 ohms and 50 ohms cable. • It helped to avoid reflections at the interface of the two cables. Olu Amoda

  21. Procedures • The diagram shows a typical display on the oscilloscope • Termination was done on a trial and error basis. • Resistors attached in turn, to flatten out backend • The values and displays were recorded for further analysis. Olu Amoda

  22. Results • Dimension of board: 2m x 0.9m x1.25m Olu Amoda

  23. The result was tested for experimental accuracy by comparing with a theoretical equation. The resistors vs width/thickness ratio was plotted on the same graph with the theoretical equation Impedance Equation Analysis of Results Olu Amoda

  24. Comparison • The values obtained from the experiment are accurate to a certain degree. • The experimental values were well distributed around the equation line. Olu Amoda

  25. Conclusions from experiment. • All strips widths are okay for further experimental purposes • Strip of width 1.8 cm gave the least front-end reflection • Reflections at the front end are negligible. • Strip of width 3cm was selected for further experimental purposes Olu Amoda

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