A0 Abort Timing

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A0 Abort Timing


Bruce Hanna
This is intended to describe a prescription for adjusting the timing of the A0 abort kickers and is the result of the work of many people. These studies are done with coalesced beam ( 8 turns 5 bunches) on the central orbit.
Start by injecting P24 only and only charging up the proton set of kickers ( this is done by enabling only C:A0PAKR). The beam will be aborted at 150 Gev by pressing the red abort button (this will stop the BLM circular buffers so you can look at losses).The TEL should be on and beam left in the machine long enough to eliminate dc beam. Vary ( in December we decreased the time value) the proton kicker abort timer, C:CPATRG, until you see losses. Note that P24 is the last bunch to get kicked out of the machine so if the timing is too early P24 will get a kick and cause losses primarily at B0 and D0. Once you find this “edge” set the timing to the earliest time where there are no losses.
Now inject P25 only again with only the proton kickers charged up. Increase the proton kicker timing until you see losses (this indicates P25 is not getting a sufficient kick). Losses will be seen at A1, B0 and D0. Set the proton kicker timing so that losses are minimum for both the P24 and P25 case. Once this is done test by injecting P24 and P25 with only the proton kickers charged up and abort the beam and see that there are no losses.
Next we want to turn on the pbar kickers. The idea here is that P24 should be past the pbar kickers when the abort kickers fire and P25 should be at the upstream end of the proton kickers when the kickers are at 75% of there maximum value. The distance from the downstream end of the proton kickers to the end of A0 is 40 meters so beam takes 134 nsec (or 7 buckets) to travel this distance. Thus set the pbar kicker timing 9 to12 buckets later than the proton kicker timing (note 12 buckets was chosen last Dec when this was done). Now with both sets of kickers charged, inject P24 and vary the pbar timing and look for losses at B0 and D0 when you abort. When the minimum time is found add 3 buckets to this value (this accounts for rise time). Figure 1 shows the relative timing involved and figure 3 shows the kicker waveshape and rise time.
Now the timing is set. Test this at both 150 Gev and 980 Gev, low beta on the helix with P24 and P25 in the machine. If desired one can add 2-4 buckets to the above determined values. Figure 3 shows the proton abort kicker waveform with P1-P12 and P24 and P25. This shows the present relationship between the $AA marker , the beam position at the abort dump and the kicker voltage.
It should be noted that the vertical beam position through A0 is very important; if it is too high you can miss the abort no matter how good the timing is set. The F49 and A11 vertical positions should be about +2 mm. Figure 4 shows the beam position at the abort dump face and how much kick is required. Note that at 980 Gev and 35 kV the set of 5 kickers gives a kick of 1.4 mrad which gives a displacement of 21 mm.

Figure 1

Figure 2

Figure 3

Figure 4

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