Wednesday, May 03, 2006

Jitter of laser pulse

I set the Thyratron heater and reservoir voltages back to 10.06V and 8.17V. In order to avoid the acring, I inserted a plastic plate between the thyratron and ground plate.

In the afternoon, I tried to send the TWIN laser pulse to the Prometheus. Firstly I wanted to use the method of the first pulse triggered and the second pulse amplified. However, it's very difficult to match these two pulses, I thought there was a time jitter between them. The 4 channels of DG-353 were set as: A=T+250ms 212us 236ns (Rail Gap), B=A-1.66us (M02), C=B+30ns (M02), D=A-1.42us (X-ray Anode). I used a fast photo diode to measure the laser pulse and compared it with the Prometheus trigger signals. From the measurement, I found the laser pulse jitter was more than 2.0us, which might cause the failure of two pulses matching.

Then I used only one pulse to trigger the Promethus and to be amplified. The channel A of DG-535 was changed to A=T+1.71us, and the rest channels were set as above. Please notice the time division, the above is 500ns/div, this one is 100ns/div, the tracing time is same. The jitter time is less than several nanoseconds, that's enough for matching the Prometheus pulse.

However, the time delay of 1.71us was still big, the Prometheus should be triggered early a little bit (about 0.25us). Because the Thyratron (M01&M02) would be triggered early 1.66us than the Rail Gap, it means the Rail Gap delay time must be set more than 1.66us. If we want the pulses matching, the A channel should be set A=T+1.46us. I need time to consider the whole system timing.

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