Proceedings of EPAC 2004, Lucerne, Switzerland
TRICKLE-CHARGE: A NEW OPERATIONAL MODE FOR PEP-II *
J.L. Turner#, U. Wienands, M. Sullivan, W. Colocho, F.-J. Decker, S. Ecklund, A. Fisher, R.H.
Iverson, J.T. Seeman; C. O'Grady, M. Weaver; SLAC; Stanford, CA., 94309, USA;
W. Kozanecki, DSM/DAPNIA, CEA/Saclay, F-91191 Gif-sur-Yvette, France
detector off during injection periods. For LER tricklecharge injection, this gain was estimated to be about 15%.
Early tests comparing two similar shifts, one in normal
and one in trickle mode, confirmed this number, see Fig.
1. Luminosity life time almost doubled, reducing the
number of top-ups during a shift commensurably. The
actual gain during the first month of LER-trickle
operation was closer to 35%, credited in part to increased
reliability of the machine running at a fixed LER beam
current. Adding trickle-charge to the HER gained another
12%, close to prediction, but no significant further
reliability-gain was seen. In table 1 the different machine
operating modes are compared.
Lum (1030/cm2/s)
In regular top-up-and-coast operation, PEP-II average
luminosity is about 70...75% of the peak luminosity due
to detector ramp-down and ramp-up times plus the time it
takes to top-up both beams. We recently commissioned a
new operational mode where the Low Energy Ring is
injected continuously without ramping down the detector.
The benefits–increased luminosity lifetime and roughly
half the number of top-ups per shift–were expected to
give an increase in delivered luminosity of about 15% at
the same peak luminosity; this was confirmed in test runs.
In routine trickle operation, however, it appears that the
increase in delivered luminosity is more than twice that
due to an increase in availability credited to the more
stable operating conditions during trickle operation.
Further gains were made when continuous injection was
extended to the high energy ring as well. In this paper we
will present our operational experience as well as some of
the diagnostics we use to monitor and maintain tuning of
the machine in order to control injection background and
protect the detector.
Lum (1030/ cm 2/ s)
Abstract
INTRODUCTION
Continuous injection (trickle-charge) was first
established in the PEPII Low Energy Ring (LER) where
the stored beam lifetime is lowest, and where injection
backgrounds had been historically less of a problem than
the High Energy Ring (HER). Large vertical beta
functions outside the detector in the HER case combined
with vertical injection necessitate better control of
incoming beam parameters. In the LER, the large vertical
beta functions occur in the detector closer to the
interaction point such that sensitivity to incoming beam
parameters is greatly reduced. Several factors contributed
to the success of this trickle-charge endeavour.
• Background signals provided by the BaBar detector
gated on actual injection pulses.
• Systematic improvements of the electron beam from
the LINAC.
• Reduction of the distance of the injected beam from
the closed orbit.
• Trajectory stabilization feedback.
• Both ring kicker systems were evaluated[1] and
scheduled for upgrades.
Trickle-injection gain
The gain in delivered luminosity arises from the higher
average luminosity as well as from not having to turn the
___________________________________________
*Work supported by the Department of Energy, contract
DE-AC03-76SF00515.
#jturner@slac.stanford.edu
tau:559.56
av_to_pk:0.86
6000
.
4000
0
100
200
300
Time (m)
av_to_p k:0.72
400
500
tau:364.11
6000
5000
4000
0
100
200
300
Time (m)
400
500
Figure 1. Luminosity for a shift in LER trickle mode
(top), regular top-up mode (bottom).
Table 1. Operating Mode Summary
Lum. lifetime
Top-up
364
LER trickle
560
Both trickle
N/a
Avg./peak ratio
72%
86%
99…100%
Top-ups/shift
10
6
n/a
Gain (expected)
0
15%
29%
Gain (delivery)
0
35%
50%
TRICKLE INJECTION DIAGNOSTICS
The primary concern for trickle-charge injection is to
deliver sufficient current to keep up with stored beam
losses while not delivering excessive radiation to the
BaBar detector with all systems on and vulnerable. The
regular BaBar background detectors are insufficient for
trickle-charge tuning as they don’t discriminate between
stored and injected background. While the PEPII control
system has some built in diagnostics for measuring
injected beam parameters and beam losses, we developed
a diagnostic based on EMC triggers gated on injection
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Proceedings of EPAC 2004, Lucerne, Switzerland
pulses[2]. These diagnostics have been the primary tools
for the minimization of trickle injection related
background.
20
10
0
0
5
10
15
20
25
30
35
10
1
In Gating the BaBar diagnostics from the EMC, from
added cesium iodide detectors, and other sources we can
correlate BaBar “On” system background with other
detectors in order to tune with BaBar “Off” if necessary.
In figure 4 a cesium iodide detector and EMC
background at injection are plotted against bunch
positioin in the mini-trains in the HER ring. Lower is
more background on these plots, so the ends of the minitrains cause somewhat more injection related
backgrounds than other buckets. Injection backgrounds in
the HER were seen early on to depend strongly on the
LER current indicating the significance of beam-beam
forces. It was also seen that injection rate and background
depend on the bunch being filled. This is presumably due
to some buckets only having a single parasitic crossing
rather than crossing on both sides of the interaction point.
This condition was rapidly addressed with a small change
in the horizontal tune.
-2
10
0
2
4
6
8
10
12
CSI 7052
-1
10
14
Figure 2. Top: BaBar background signal from HER
injection to 15ms. Bottom: PSD of that signal versus
frequency.
INJRCTH
10
0
5
10
15
20
25
30
35
20
30
40
bucket mod(72)
50
60
70
0
10
20
30
40
bucket mod(72)
50
60
70
-0.2
-0.25
-0.3
Figure 4. Top is a cesium iodide detector versus “minitrain” bunch number. Below is EMC background.
JITTER SOURCE REDUCTION
1
In commissioning HER trickle-charge, the most severe
issue was high background injection pulses (“fliers”).
Linking BaBar’s signals into the PEPII control system,
we are then able to correlate incoming beam parameters
with such fliers.
10 -1
-2
10
10
-0.15
-0.35
-10
10
0
-0.1
20
0
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
-10
0
2
4
6
8
10
12
14
Figure 3. Same as in figure 2, only after the energy of the
injected beam has been corrected.
Figure 2 shows the gated trigger rate against time after
injection and its FFT. The peak at 6 kHz indicates
synchrotron related losses caused by energy or phase
offset of the injected beam. In figure 3 this has been
corrected. These BaBar generated plots are continuously
updating at one Hz in the control room.
The injected beam energy, phase (timing), transverse
position are measured and stabilized by feedbacks.
Nonetheless, jitter from faulty hardware or mis-set
parameters is still possible.
Source intensity jitter, which can cause parameter
changes of the injected beam has been reduced by
progressive tuning, then hardware repair. In figure 5 the
beneficial effect of tuning and repair is clearly visible.
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Proceedings of EPAC 2004, Lucerne, Switzerland
9
1000
vertical motion (microradians)
8
8 10
8
6 10
Gun Electronics Repair
8
4 10
8
2 10
Feedback Turned On
-1000
-1500
75
60
80
100
120
12-Feb to 5-May (days from Jan 1)
Key to the success (see figure 8) of trickle-charge has
been the diagnostics provided by BaBar, the tuning down
different sources of jitter, new stabilization feedbacks,
and moving the stored beams closer to the septum[1].
600
0.7
500
-1
40
60
80
100
120
12-Feb to 5-May (days from Jan 1)
Jun-04
0
0.1
0
100
Apr-04
0.2
200
May-04
0.3
300
Mar-04
Damping Ring RF Adjustments
400
Feb-04
0.6
Both Trickle
LER Trickle
Jan-04
PEP Daily Average (PB )
0.8
0.4
105
SUMMARY
Dec-03
In figure 6, timing jitter out of the damping ring is seen
as energy jitter in the bunch compressor. This timing jitter
will cause changes in the six dimensional beam
distribution. The reduction of this timing jitter was
accomplished by empirical adjustments of the electron
damping ring RF system.
0.5
80
85
90
95
100
16-Mar to 12-Apr (days from Jan 1)
Figure 7. Signal from trajectory stabilization feedback.
Figure 5. Intensity jitter versus day.
rms energy jitter (mev)
-500
Nov-03
40
0
Oct-03
0
500
Sep-03
RMS number of electrons per pulse
1 10
Figure 8. Daily Avg. Luminosity increase with trickle
Figure 6. Energy in MeV is indicative of beam phase jitter
(time jitter) out of the electron damping ring.
INJECTOR TRAJECTORY
STABILIZATION
The injecting beams for both rings show trajectory
drifts over the time scale of hours or longer. Stabilizing
the incoming beams very near the PEPII rings has been
successful in the case of positron injection into the LER.
Figure 7 shows the stabilizing effect of the feedback on
the vertical trajectory. A similar feedback is planned for
the electrons.
ACKNOWLEDGEMENTS
We would like to thank Mark Petree, and Mike Stanek
for their operationally useful tools for taking and
analyzing “flier” data.
REFERENCES
[1] F. J. Decker et. al, “Diagnosing the PEPII Injection
System” EPAC’04, Lucerne, July 2004.
[2] F. J. Decker et. al, “Injection Related Background due
to the Transverse Feedback” PAC’03, Portland, OR,
USA, May 2003.
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