AGS snake tuning instruction

Haixin and Waldo 3/14/03

1. User XBAR to choose main magnet current (AXI.MMAG_I) and snake current (AXI.SNAKE_MAG_I) on one scope. The impedance should be chosen as 1Mohm for both signals. Set the two signals to the same scale, say 2V. Unplug both signals, then adjust the zero point to make the two signal lay on top of each other.
2. Push "Math setup" button and select channel "A" (or whatever is free)
   1. Select "Redefine A"
   2. Set "use Math" to "yes"
   3. Set "Math type" to "Rescale"
   4. at the bottom of the right column, select the channel of the snake input to be scaled by a*+b
   5. dial in the correct constants: b=0 and a=? for correct snake strength See table below.
   6. Adjust the vertical zoom button to match the snake input vertical scale. See the Channel A inset on the left of the scope screen.
   7. With the cables unplugged for the SNAKE_I and MMAG_I inputs, adjust the vertical position for Channel A to have the same baseline as the SNAKE_I and MMAG_I traces.
   8. Plug the cables back in.
3. For example: Use math function to get trace A =a*snake I +b, where a=0.777 and b=0. For a 5% snake, the trace A and main magnet current should be on top of each other. Since the ramp rate is very fast, the snake will be less than 5% when close to flat top (only about 4%). That is the best we can do.
4. If the snake current (trace A) does not follow the main magnet current, change the voltage function (use FunctionEditor) and watch the change in trace A until they match.

   The "a" coeffiecient for different percentages of snake to match the main magnet current trace are as follows:

        5%      0.777
        4%	     0.970
        3%	     1.295
        1%	     3.885
   

Scaled snake and AGS MMAG_I traces