1. Manolis Dris NTU of Athens CHIOS 4/2013 SIGNAL PROPAGATION IN MICROMEGAS

2. ABSTRACT The propagation of signals in Micromegas type detectors is examined. A simple scheme with only one long strip is used. It is a transmission line with losses, at its end the system of charge amplifier plus shaper is connected. A more realistic simulation needs to have several strips interacting with each other. -1-

3. INTRODUCTION Micromegas detector with long strips is considered as a kind of multiple conductor transmission line. In this work we examine the one strip case. -2-

4. The several strip situation, together with various dielectric media (as in the real Micromegas), corresponds to the inhomogeneous multiple conductor transmission line case. One might have various speeds of propagation and this can lead to more than one signal for each one original excitation. With one strip there is only one speed, even for several dielectric media. -3- -

5. DETECTOR GEOMETRY AND ELECTRICAL CALCULATIONS, -4-

6. ONE READ STRIP CALCULATIONS We make a crude estimate of the capacitance per unit length, assuming that the formula for plane capacitor with very small gap holds. -5-

7. -6-

8. -7-

9. ONE RESISTIVE STRIP CALCULATIONS This is a diffusion equation not a wave equation. -8-

10. STEP RESPONSE OF 1 m LONG RESISTIVE STRIP Pulse height vs t/s -9-

11. FOR PLANE GEOMETRY PULSE FORMATION FROM MOVING CHARGES -10-

12. 11

13. INDUCED CURRENT vs TIME -12-

14. CHARGE AMPLIFIER +SHAPER -13-

15. THE SHAPER IS AN APPROXIMATE GAUSSIAN SHAPER ACCORDING TO CALCULATIONS OF G. de GERONIMO-V. POLYCHRONAKOS (Brookhaven National Laboratory). THEY GIVE THE POLES OF A 3-POLE FILTER. ONE POLE IS A REAL ONE AND THE OTHER TWO ARE COMPLEX CONJUGATE POLES. SHAPER -14-

16. REALIZATION OF THE AMPLIFIER+FILTER -15-

17. -16 IN THE FOLLOWING THE INPUT IS VERY NARROW PULSE OF CURRENT (ELECTRON SIGNAL)

18. CHARGE AMPLIFIER OUTPUT

19. WITH TRANSMISSION LINE 1 m LONG STRIP -18-

20. 2 m LONG STRIP -19-

21. CONCLUSIONS IT SEEMS, THERE IS AN EFFECT DUE TO THE PROPAGATION OF SIGNALS ON THE MICROMEGAS STRIP, TREATED AS TRANSMISSION LINE. AN IMPROVEMENT COULD BE TO CONSIDER SEVERAL STRIPS. COUPLED TRANSMISSION LINES.