Operation of Narrow Gap RPC with Tetrafluoroethane Based Mixture.

Charge, fired strip multiplicity and arrival time distributions for the induced signal were investigated for the $2 ~mm$ gap RPC operating with several tetrafluoroethane ($C_{2}H_{2}F_{4}$) based mixtures with variation of isobutane ($iC_{4}H_{10}$) and sulphur hexafluoride ($SF_{6}$) concentrations. Suppression of the large fast charges for the mixtures containing $SF_{6}$ in comparison with the binary $C_{2}H_{2}F_{4}$/$iC_{4}H_{10}$ mixture was confirmed. This suppression allows to have a wide plateau region ($ge1~kV$) with small average charge and reduced tail of high charges. Exclusion of isobutane from the mixture with $2%$ of $SF_{6}$ does not change charge distributions.