Imaging Linearity Modeling and Optimization of Capacitive Division Image Readout (C-DIR) for Microchannel Plate Imaging Detectors

A 3-D lumped parameter circuit model based on the nodal analysis to simulate signal propagation and position response characteristics of capacitive division image readout (C-DIR) is proposed. The current pulses, charge collection efficiency, and position reconstruction patterns are calculated for different electrical parameters (charge division capacitor
$C_{c}$
, perimeter capacitor
$C_{p}$
, diagonal capacitor
$C_{d}$
, electrode parasitic capacitor
$C_{s}$
, and the sheet resistance of the resistive layer
$R_{\mathrm {Ge}}$
), and their influence on imaging linearity is investigated. The simulation results show that
$R_{\mathrm {Ge}}$
affects the amplitude, pulsewidth, and polarity of the current pulse in the C-DIR. The sheet resistance of the resistive layer needs to be larger than 10
$\text{M}\Omega $
for the charge to be efficiently collected by the readout electronics. Several capacitance ratios (
$C_{c}/C_{p}$
,
$C_{c}/C_{s}$
, and
$C_{c}/C_{d})$
mainly affect the imaging linearity. It has been found that to obtain good detector imaging performance,
$C_{c}/C_{p}$
should be less than 0.01,
$C_{c}/C_{s}$
should be larger than 100, and
$C_{c}/C_{d}$
should be larger than 10, and when
$R_{\mathrm {Ge}}$
is larger than 10
$\text{M}\Omega $
, the imaging nonlinearity (rms) can be less than 1%. The reliability of the simulation results was verified by experimental measurements of a prototype C-DIR detector designed by ourselves. An optimized imaging performance with imaging nonlinearity (rms) of 2.18% was achieved.