2. Design of a readout system for RPCs

3. Olu Amoda2 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

4. Olu Amoda3 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.

5. Olu Amoda4 Schematics

6. 5 How it works 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.

7. Olu Amoda6 Building a Readout System Factors taken into consideration: Cost Efficiency Availability Construction.

8. Olu Amoda7 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

9. Olu Amoda8 Two Methods of Construction 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

10. Olu Amoda9 Diagram of Readout Systems Strip Readout System Padded Readout System

11. Olu Amoda10 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. Strips over Pads

12. Olu Amoda11 Material for construction 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”.

13. Olu Amoda12 The Board As one side made of aluminum. Another side made of aluminum coated with insulating material. A dielectric made of foam.

14. Olu Amoda13 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.

15. Olu Amoda14 Pre-Experiment Strips were made on the board by a saw. The ends of the ground plane were cleaned with ethyl, for cable attachments.

16. Olu Amoda15 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.

17. Olu Amoda16 Experimental Setup

18. Olu Amoda17 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. R Z

19. Olu Amoda18 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?

20. Olu Amoda19 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.

21. Olu Amoda20 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.

22. Olu Amoda21 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.

23. Olu Amoda22 Results Dimension of board: 2m x 0.9m x1.25m

24. Olu Amoda23 Analysis of Results 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

25. Olu Amoda24 Comparison The values obtained from the experiment are accurate to a certain degree. The experimental values were well distributed around the equation line.

26. Olu Amoda25 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