  An electrostatic time-of-flight detector named E-MCP has been developed for
quick diagnostics of circulating beam and timing measurement in mass
spectrometry at the Rare-RI Ring in RIKEN. The E-MCP detector consists of a
conversion foil, potential grids, and a microchannel plate. Secondary electrons
are released from the surface of the foil when a heavy ion hits it. The
electrons are accelerated and deflected by 90$^\circ$ toward the microchannel
plate by electrostatic potentials. A thin carbon foil and a thin
aluminum-coated mylar foil were used as conversion foils. We obtained time
resolutions of 69(1) ps and 43(1) ps (standard deviation) for a $^{84}$Kr beam
at an energy of 170 MeV/u when using the carbon and the aluminum-coated mylar
foils, respectively. A detection efficiency of approximately 90% was obtained
for both foils. The E-MCP detector equipped with the carbon foil was installed
inside the Rare-RI Ring to confirm particle circulation within a demonstration
experiment on mass measurements of nuclei around $^{78}$Ge produced by
in-flight fission of uranium beam at the RI Beam Factory in RIKEN. Periodic
time signals from circulating ions were clearly observed. Revolution times for
$^{78}$Ge, $^{77}$Ga, and $^{76}$Zn were obtained. The results confirmed
successful circulation of the short-lived nuclei inside the Rare-RI Ring.
