Large Dynamic Range Ion Spectrometer (LDRIS)

Single microchannel plate

Thin-window silicon photodiode

Fast, thin-window photodiode

Ammeter

Controller, Data I/O

-3 kV

Reset

Gain

105

500

Digital Output

-2 kV

Single MCP

Total Gain/Ion = 5x107

Ammeter: converts charge deposited over a short accumulation interval to a digital word, which is the output. The accumulation register in the ammeter is cleared after each accumulation.

Single microchannel plate

Thin-window silicon photodiode

20 keV H+ Beam Current [Amperes]

10-18 10-17 10-16 10-15 10-14 10-13 10-12 10-11 10-10 10-9

Det

ecto

r G

ain

105

106

107

108

109

Single Particle Detection Mode

Current Detection Mode

Time [ms]

-0.02 -0.01 0.00 0.01 0.02

Pot

entia

l [m

V]

0.0

0.5

1.0

1.5

Detection of Individual Ions:• Oscilloscope traces of detection of three individual detected ions• Custom electronics will greatly reduce noise

Gain of LDRIS as a function of input beam current:• Gain measured for both single particle mode (using oscilloscope) and sensitive ammeter.• Single MCP has unexpected nonlinear gain at high beam currents, allowing more headroom in nonlinear amplifier• MCP detector limited to about 10-

12 A; LDRIS can measure at least 10-10 A, demonstrating an extension of dynamic range by a factor of at least 100.

1) The LDRIS detector substantially extends the dynamic range of incident ion flux, allowing larger geometric factors that provide unprecedented, statistically significant measurements of low ion fluxes.

2) LDRIS uses a clocked ammeter circuit that is simpler in design and uses fewer resources than conventional CEM and MCP detectors.

2) Problems of pulse pileup and gain saturation due to high ion fluxes in CEM and MCP detectors is eliminated using the current design.

3) LDRIS has demonstrated (a) the ability to count individual ions and (b) a dynamic range approximately 100 times that of a conventional MCP detector.

Large Dynamic Range Ion Spectrometer (LDRIS)