Passivating the Protmehtes

Last week, we removed the Prometheus windows for cleaning. At the same time, we cleaned the 40168 spark gap at Rail Gap Trigger Unit. Unfortunately, the pipe fittings for spark gap were broken, we had to order them. This caused us to wait for about 2 days. Now everything is already, we are going to passivate the Prometheus. The operating voltage was about 14 kV for each bank, the passivation kept about 2 hours.

Labview blcok for SDG II control box

Most functions of the SDG II can be controlled by any computer with a standard RS-232 serial port. After connecting the SDG II with computer RS-232 through data transmission cable, it's easy to control the SDG II by sending a RS-232 commands. Valid commands return the string "Ok", but invalid commands or queries return the string "Bad".

I can run a program under Labview to send or query RS-232 commands only by pushing buttons. The front control panel and LabView block diagram are shown here.

Set up timing delay for new designed nozzle

In order to synchronize the old small nozzle with laser pulses, I have added about 1 millisecond delay between the laser seed pulses and the final laser pulses. However, this delay is not enough for the new big slit nozzle, which needs at least 3 or 4 milliseconds to be operated. So I think it's better to trigger the nozzle with the first laser pulse and fire with the second laser pulse. Because the Prometheus runs at 0.2 Hz, there is 5 seconds delay between two continuous pulses. It's free to tune the delay time during this 5 seconds, the main point is how to synchronize the gas nozzle with the second laser pulse. A digital delay box was used, this box can provide the timing delay from seconds order to microsecond order. After several trials, the delay was set up at about 4 s 913 ms.

Changed resistors for 40184 spark gap

I found the resistors connected to the 40184 spark gap was broken, which caused the misfire for the Prometheus. This 40184 spark gap(SG1) was installed inside the 50kV trigger generator box. SG1 is a three electrode, 2:1 gap-space, irradiated-gas-plasma switch. The switch operates in the swinging cascade mode in which the intermediate electrode is biased at one-third of the working voltage.

Testing NI GPIB-232CV-A

We received the National Instruments GPIB-232CV-A today, I installed the converter and tested it. The interesting thing was that I could use the mouse or keyboard plug, rather than a AC/DC power supply to provide the power for this board.

In order to make sure the board worked, I connect a TDS2042 oscilloscope with GPIB cable to the converter. Before testing, it's necessary to configure the converter parameters. The DIP switches were used to set up the parameters, the setup of SW1 was shown as followed:

Indication	GPIB address					Termination		Mode
Switches	1	2	3	4	5	6	7	8
ON/OFF	OFF	OFF	OFF	ON	OFF	OFF	ON	ON
Note	This address matched the scope GPIB address					LF termination		C

The setup of DIP switch SW2 was shown as below:

Indication	bits per second			Parity	Check	Stop	Data	Flow
Switches	1	2	3	4	5	6	7	8
ON/OFF	ON	OFF	ON	OFF	OFF	OFF	ON	OFF
Note	9600 baud			Odd	Disable	1 bit	8	Disable

After several times to change the DIP switches setup, the scope data was successfully transfered to the computer through scope GPIB port, converter and serial port.