Gas Monitor Detector Electronics

Transcription

1 Gas Monitor Detector Electronics from charged particles to digital value Fini Jastrow, TTF/VUV-FEL TTF/VUV-FEL meeting, meeting, 21. Mar Mar 06

2 The Detector Ion Current Measurement Measured Data The MCP Signal Path The Extended GMD

3 The Detector Ionisation Chamber Detection of ions and electrons Ions calibrated with CW beam (slow) Electrons fast but susceptible to secondary electrons and magnetic fields

4 The Detector 1000 V e - chamber coupling preamp integrator ions I V ADC ADC

5 Ion Current Measurement faraday cup integrator Keithley electrometer τ=30s, one pole Problems: susceptible to Petra ramping disturbed by nearby switched 230V loads tendence to self resonance at 0.2 Hz ADC Solutions: ferromagnetic plate under Keithley 230V separation transformer ferrite beads and software damping

6 Ion Current Measurement faraday cup Femto LCA τ=10s, three pole ADC 3 pole filter for faster response true active integrator independent on incoming charge pulse shape no problems with Petra or nearby loads drawback: only two conversion factors available available Mai 2006

7 Ion Current Measurement faraday cup I V preamp ADC differential amplifier high input impedance output impedance matched to ADC input preventing ground loop noise high impedance to ground at LF (shield and signal conductor) no gain at HF (impedance to ground rather low)

8 coupling integrator ADC TDR measurement 200 Ω 50 Ω 75 Ω ,5 output [mv] Ohm 125 Ohm 500 Ohm integral [a.u.] -1-1, ,5 tim e [ns] tim e [ns]

9 coupling integrator ADC SHV flange connector 75 Ω impedance match 50 Ω measured: ΓLR ΓRL 0.76 none one way both ways ΓLR ΓRL g LR

10 coupling integrator ADC measured values: bandwidth 280 MHz (g = 2) frequency response unlinear gain dependent on charge charge error 420 ppm/ C timing jitter 20 ps/ C slew rate 1400V/µs risetime 0.56 ns input Γ = 0.29 preamp frequency response 10 MHz logarithmic 400 MHz

11 coupling integrator ADC different kinds of observed gain errors 10,65 10,6 output / number of pulses [mv] ,00 2,00 number of identical pulses 10,55 0,00 gain [mv/nvs] 10,5 10,45 10,4 gain error [%] -2,00-4,00 10,35 10,3 12 ns 0.6 ns -6,00 10, input charge [nvs] -8,00 different pulses

12 coupling integrator ADC two gain setting possibilities: preamp gain integrator time constant combined a factor of 50 preamp gains is prefered because it reduces the noise input equivalent noise [pvs] integrator gain preamp gain gain

13 coupling integrator ADC The VME crate induces noise of about 3 nvs pp An aluminum foild shield reduces this to 1 nvs pp outside inside inside, shielded

14 coupling integrator ADC All channels pick up noise from the card's own digital timing part some are better, some are worse but the pickup level for each channel is the same in all cards.

15 coupling integrator ADC poor Γ of input: 0.29 pcb design weaknesses: impedance of trace not 50 Ω distance termination to amplifier too long cheap diodes in input amplifier capacitance not compensated jumper in signal path input protection diodes termination resistor input capacitance of preamp long trace on pcb

16 coupling integrator ADC Γ0 Γ1 Γ2 Γ3 Γ4 Γ5 Γ5Γ4 = (300 ns) Γ3Γ2 = (10 ns) Γ1Γ4 = 0 (2 ns) Γ5Γ2 = (310 ns) Γ3Γ4 = (12 ns) Reflection has a long round trip time and might fall into the next's pulse integration window. 1. reflex 2. reflex next pulse and 3. reflex

17 coupling preamp integrator Typical pulse charge 1 nvs, this equals 1mVµs Offset of 1mV has the same integral ADC DC coupled signal path integration window width as small as possible

18 coupling preamp integrator Short reset pulse mode: 900 ns integration Long reset pulse mode: 30 ns integration ADC Changing the timing circuitry to allow 160 ns integration: Based on LRP mode (needs other IC) with bigger capacitor 200 ns/div

19 coupling integrator ADC The signal's ringing prevents successful ADC, so we introduced a low pass filter after the integrator to get rid of the ringing on the integrator's output signal.

20 coupling integrator ADC Placement and schematics of the damping capacitor

21 coupling integrator ADC delay machine timer timing jitter extent 2.5 ps relative to input 2 ps for each daisy chain 0.46 ps for each ns of delay 160 ps pulse width 160 ps pulse distance Jitter adds: for a 1 µs delayed pulse ~ 0.66 ns No problem for integrator usage

22 coupling integrator ADC characteristics (1V range): resolution 14 bit ENOB 12.2 bit 12 bit measured 0.43 bit / C acquisition time 45 ns typ (20 ns sample and hold) next card removed ADC heated 1800 noise σ = 1 bit (0.14 mv) event count

23 Measured Data Homogeneity of the intensity signal measured by PTB at Bessy ion current independent of horizontal and mostly of vertikal position of the beam sharp signal decrease if it leaves the measuring apertue ion current measurement unsusceptible to secondary electrons Ion current / a. u. Ion current / a. u I FC + I DT Vertical position y / mm λ = 80 nm P Xe = 5.4 x 10-5 mbar U extr = 600 V Horizontal position x / mm

24 Measured Data Calibration of the beam position monitor by PTB at Bessy measures the center of the beam position signal independent on intensity Deviation / % Uncertainty / µm Signal ratio GMD #3 measurement calculation (ϕ = 0 ) calculation (ϕ = 0.2 ) Beam position x / mm

25 Measured Data First position measurements left Ion current Moved the device by 0.5 mm right I(L) / I(R)

26 The MCP Signal Path The MCP preamp measured values: rise time 6.3 ns bandwidth ~80 MHz gain 1.4 no impedance match to 75 Ω SHV cable MCP amp Femto HVA 200 Extreme ringing expected. Signal seems to be smooth due to the low pass characteristic of the amplifier.

27 The Extended GMD Extended GMD Version for Ultra-short X-ray Pulses hω Measurement at SPPS: 50 Ω