Cross-talk in strip RPCs D. Gonzalez-Diaz, A. Berezutskiy and M. Ciobanu with the collaboration of N. Majumdar, S. Mukhopadhyay, S. Bhattacharya (thanks to A. Blanco for providing us with HADES cells)

Index 1. Single strip parameters and the RPC as a current generator. 2. The induction profile. 3. The Boundary Element Method (BEM). 4. Propagation. 5. Conclusions.

1. Single strip parameters and the RPC as a current generator.

The RPC as a current generator. Signal shape. P. Fonte, private communication P. Fonte et al., IEEE, Trans. Nucl. Sci. 49, 3(2002)881. Diego Gonzalez Diaz, PhD. Thesis, Santiago de Compostela(2006), 2006 JINST TH 003

The RPC as a current generator. Amplitude distribution.

The RPC as a current generator. Correcting for propagation.

Transmission in HADES cells

Single-strip characterization measured with reflectometer

2. The induction profile.

picture from C. Lippmann's PhD T. Heubrandtner et al. NIM A 489(2002)439 fast convergent analytical formula known since What is the weighting field?

Multi-strip-MRPC (MMRPC) 1.1 mm Glass: ε=7.5, strip width = 1.64 mm, strip gap = 0.9 mm, strip length = 900 mm 1.1 mm 0.5 mm 0.22 mm copper (20 μm) A relevant example. The FOPI multi-strip design.

gap 1

gap 2

gap 3

gap 4

1 st HADES prototype FOPI prototype Input: charge distributions very different, indeed!

Charge distributions from MC (random variables: X, Q)

Charge efficiency and weighting field for different widths

cluster size dependence

rms of cluster size distribution

cluster size dependence with strip width > factor 2 ! typical CBM value

Existing data on cross-talk/charge sharing A. Blanco et al. NIM A 485(2002)328

Comparison with present code

3. Boundary Element Method (BEM).

strip width = 22 mm, gap to next strip = 3 mm, length = 220 mm glass (ε r =7.5, h=0.5 mm)‏ graphite (ε r =12, h=0.02 mm) gas (ε r =1, h=0.2 mm)‏ PCB (ε r =5, h=0.86 mm) Cu strip (h=0.018 mm) (placed in the middle of the PCB) CBM version 1 (strip region) 12 gaps

strip width = 22 mm, gap to next strip = 3 mm, length = 220 mm guard strips (1 mm) glass (ε r =7.5, h=0.5 mm)‏ graphite (ε r =12, h=0.02 mm) gas (ε r =1, h=0.2 mm)‏ PCB (ε r =5, h=0.86 mm) Cu strip (h=0.018 mm) (placed in the middle of the PCB) CBM version 2 (strip region) 12 gaps

strip width = 22 mm, gap to next strip = 3 mm, length = 220 mm guard walls (1 mm) glass (ε r =7.5, h=0.5 mm)‏ graphite (ε r =12, h=0.02 mm) gas (ε r =1, h=0.2 mm)‏ PCB (ε r =5, h=0.86 mm) Cu strip (h=0.018 mm) (placed in the middle of the PCB) CBM version 3 (strip region) 12 gaps

Preliminary calculations based on BEM. The neBEM solver.

4. Propagation.

Measurements of cross-talk with RPC mockup

Comparison with (APLAC) calculation signal t rise ~1ns

1. Generate events with the RPC signal shape and amplitude distribution starting from measured values. On the way. 2. Calculate the fraction of signal induced to each strip. On the way. 3. Calculate cross-talk in the propagation for the given strips, treating them as current generators. On the way. 4. Compare with RPC oscillograms and/or digitized beam data. On the way. 5. Introduce this knowledge in CBM-root in order to do a meaningful design. To be done. Conclusions We are progressing in the direction of having a reasonable electromagnetic simulator for RPC design !

Appendix

Cross-talk from cell with shielding vias (to 1 st and 2 nd neighbour!)

simulation of the S coefficient scattering matrix coefficient to neighbouring anode (equivalently: fraction of signal transmitted)

Comparison with data from spectrum analyzer preliminary!

simulation of a realistic structure propagation of exponential signal with 200 ps rise-time in anode and cathode simultaneously (differential mode) RPC structure: strip width = 2.2 cm, gap to next strip = 0.3 cm 16 gaps, 0.16 mm gap 0.3 mm glass 0.86 mm PCB

Transmission properties (with vias)

Transmission properties vias no vias

Transmission properties vias no vias

Transmission properties vias no vias

Transmission properties vias no vias

Transmission properties vias no vias

Transmission properties vias no vias

Transmission properties vias no vias

Transmission properties vias no vias

all in a nut-shell

Dependence with strip length