U. Wienands, PEP-II Run Coordinator

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PEP-II Status

• U. Wienands, PEP-II Run Coordinator
• for the PEP-II team

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Outline of Talk

• Run 4 Synopsis
• Machine tuning improvements
• Issues encountered during Run 4
• Other improvements and MD items
• Outlook the remainder of Run 4

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Run 4 Synopsis

• PEP is now delivering twice the rate of Run 3
• Over 60/fb delivered in Run 4, over 200/fb tot
• Key ingredients
• trickle-charge both rings
• Raise peak Lumi to 8.34E33 (currents, ß, orbit)
• Aggressively track down reduce rf trips.
• MD program focused on near-term improvements
  strategic studies needed for upgrades.

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Run 4 Delivered Luminosity
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Running 7-day Integral (2004)
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Run Time Accounting, Run 4
BaBar up from 56 to 60 Tuning/Fill down from
22 to 20 Downtime down from 1619 to 14
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PEP-II Parameters
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Machine Tuning and Improvements

• LER HER trickle charge
• Steering of the HER
• Lowering ßy of the HER (12gt11 mm)
• Raising of the HER rf voltage
• Raising the number of bunches beam currents

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LER Trickle Charge

• PEP issues mostly resolved last fall
• BIC, diagnostics software
• Extended BaBar trickle test late Oct. 03
• followed by analysis of data quality
• Trickle in production beginning Dec. 2,03
• Daily luminosity up from 250 to 350/pb
• 15 is direct trickle gain,
• remainder is increased efficiency (less trips)
• Dec. a particularly stable month for rf.

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LER only Trickle Day
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LER Trickle Background Monitor
Injection-generated triggers(? also avail. as
EPICS PV)
FFT of Injection- triggers (?s harmonics if off
energy)
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HER Trickle Charge

• 1st test in Feb. 04
• significant reduction in injection background
• not at full beam current, high radiation spikes
• 2nd test mid-March 04
• Radiation spikes no longer an issue due to
  cleanup work in injector
• Break-even luminosity reached.
• BaBar state machine now ready for double trickle
• Double-trickling operationally since March 11.

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Double-Trickle Gain
LER-only trickleav-to-pk 87
Double trickleav-to-pk 99 gt 12 gain
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Almost Best Day of PEP-II
The best day actually had 669/pb delivered.
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HER Steering

• Steer the HER flat except for IR 2
• this has worked historically
• IR 2 steering in the past has caused difficulties
  with coupling
• Motivation
• lower vertical dispersion
• better acceptance
• better agreement of the lattice with the design

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Orbit (absolute)
Y dispersion
Coupling (C12,n)
ßx/ßx,design
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HER ßy Reduction
We used 60 of a knob designed to bring ß down
to 10 mm

• Before ßy reduction
• ßy 12.3 mm
• ßx 28 cm
• Benefit for luminosity
• HER beam stronger
• 3 increase in spec. lumi.
• Before STDZ

• After ßy reduction
• ßy 11.0 mm
• ßx 27 cm
• After STDZ
• ßy 10 mm
• ßx 25 cm
• ßx lower due to larger global ßx beat.

Significant tuning work required post-STDZ to
regain luminosity benefit
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Coupling after ßy Reduction
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Lowering HER ßy (contd)
To be able to meaningfully reduce ßy, we are
raising the HER rf voltage. At 18 MV we expect 11
mm bunch length. The rate of rise is limited by
increased rf trip rate.
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Fill Patterns Beam Currents

• At the beam-beam limit need to raise bunches
  and beam current to gain lumi.
• Need to run by-2 (4.2 ns) bunch spacing
• How will electron-cloud effects behave?
• Will luminosity scale with bunches?
• What is the effect of parasitic crossings?
• How will HOM heating behave?
• (only the last expected to be better)

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Raising Bunches Beam Currents
Bunch currents 1.5 mA (LER) 0.9 mA
(HER) fairly constant
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Spec. Luminosity vs Bunches
Fixed bunch current in both rings Fixed by-2
pattern with mini trains Vary train length, thus
of bunches
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PEP Fill Patterns
1550 bunches trains of 33, 4.2 ns
1415 bunches trains of 15, 4.2 ns
Note 1st and last bunch have lower luminosity
only one parasitic xing Pilot bunches
(no parasitics) have even less luminosity!
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Luminosity vs IHERILER
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Issues encountered

• IR 2 vacuum and background issues
• Rf issues
• LER orbit beam optics issues
• Bunch-by-bunch feedback issues

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The IR 2 Vacuum Problem

• Late March, we regnd the IR 2 NEGs
• Pressure and background had been on rise
• At Run 4 startup, NEGs regend before 1st beam
• After this, LER backgrounds and pressures much
  worse than before
• Also, long time constants (hours) observed
• Strongly bunch-length dependent
• Scrubbing very slow, almost 2 weeks
• NEGs being heated by HOMs to several 100F

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LER Vac. Gauge close to IR
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LER Vacuum Pump _at_ -28 m
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NEG Temperature at -28 m
In essence, the NEG is being constantly regend
with beam!
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Rf Issues

• Rf has been holding up better than in Run 3
• thanks to significant effort of the RFTF
• The primary issues/causes of trips
• endemic failure (again) of SCRs in the HVPS
• phase drifts (esp. LER 4-5) other board issues
• various tuner issues
• klystron issues
• misc. IOC issues

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PEP Rf Beam Aborts
Run 3
Run 4

• HER rf trips 5.0/day
• LER rf trips 2.0/day
• Total 7.0/day

• HER rf trips 2.1/day
• LER rf trips 0.9/day
• Total 2.3/dayincl. l. inst. 3.7/day

Despite the overall improvement, rf trips
actually increased significantly after Dec. 03
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LER Orbit Issues

• Steer the ring without the IR, as has worked
  before.
• LER IR steering perilous due to BPM offsets
• This caused a large drop in spec. luminosity
• Root cause was a large beat in ßx, also,
  dispersion still gt50 mm rms.
• No obvious quick fix gt backed out
• Presently using MIA to try finding a correction
  strategy.

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LER Steered Orbit
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LER ßx after Steering
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Other improvements and MD

• BPM improvements
• Modeling improvements (incl. ORM, C12)
• Transverse grow-damp measurements
• Longitudinal grow-damp measurements
• New RF 8-1 klystron
• New rf IOCs using PowerPC controllers
• Injection
• Crossing-angle experiment

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BPM Improvements

• BBA on all possible IR 2 BPM/quad pairs
• Offsets from this BBA now in DB
• Auto-calibration every 8 hours after a beam-dump
• Timing database updated
• New procedure to measure timing during delivery
• See talks by Smith Ross

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Online Model Improvements

• Updated online models for both rings
• Survey data for IR 2 elements
• More accurate parametrization of QD1
• Can run a model against machine config. orbit
• Model runs on pepoptics gt can use MAD new
  version of DIMAD.
• C12 coupling analysis now online

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HER Model vs Measurement(y)
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History of ß Functions at the IP
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Orbit-Response Measurements

• ORM (LOCO) running on pepoptics
• HER and LER data taken
• ß function analysis consistent with phase-advance
  analysis
• More work needed to understand quad-strength
  factors
• gt presentation by C. Steier

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HER ORM ß/ßdesign
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HER ORM Magnet strengths
Relative to design strengths. E(HER) 8.9732 GeV
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Multibunch Stability

• Grow-damp measurements
• HER longitudinal transverse
• HER transverse
• good margin in x, strong nonlinearity in y,
• longitudinal only 2030 margin for low-lying
  long. modes
• Low-group-delay Woofer significantly better.
• As a result of the HER measurements, we raised
  priority on the new Woofer

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HER TFB Damping (x)
HER X damping Data suggest stability up to 23 A
beam current by-2 fill pattern.
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Crossing Angle Experiment

• Xing angle or not for the IR upgrade in 2005?
• Measurements done
• Sensitivity of ?x to beam-beam
• Sensitivity of Lumi to xing angle vs currents
• Results
• L vs x separation becomes narrow at high I
• L vs x becomes somewhat narrower at high I

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Xing Angle Expt Lum. vs ?X
Simulation by I. Narsky using 3-d code by Y. Cai
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Injection Orbit Feedbacks

• With both rings trickling injection problems are
  highly visible. We are implementing feedback
  systems to stabilize the beams
• LER injecting beam now working, HER to follow
• requires BPM hardware changes
• Ring-orbit stabilization under development
• tricky because of modeling issues
• (Note we do not let the GOFs steer at injection)

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LER Injection Orbit Feedback
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Rf Improvements

• New PowerPC IOC processors
• Old 68k units above 80 CPU load, causing stalls
• New LLRF boards
• New SLAC klystron for HER 8-1

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New SLAC Klystron in 8-1
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Outlook The remainder of Run 4

• Lattice improvements
• Further ßy reduction in both rings
• Complete LER steering (MIA work)
• Fix HER ßx beat
• Beam-current increases

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ß Limits

• Bunch lengths gt 1 cm
• LER 3.8 MV (achieved)
• HER 18 MV (tough!)
• ßy 1 cm feasible meaningful
• tested knobs exist for both rings
• Lowering ßx ??
• not meaningful if beam-beam limited in both
  planes
• Maintain matched beam sizes

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Global Ring Issues

• Knob to reduce global HER ßx beat exists
• good in 1st order but beam life time reduced
• need to investigate higher-order effects
• Correction of global ßx beat in steered LER
• 1st MIA solution has some very strong quad
  changes gt may be problematic in practice
• source of ß beat not yet clearly identified

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Beam current limits

• HER
• Rf power limit 1600 mA
• Stability 1400 at present, 1600 mA with new
  woofer
• LER
• Tested up to 2400 mA, likely higher limit with
  llrf tuning
• rf power limit 3000 mA
• thermal issues with TFB, LFB kickers

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July 2004 Parameters (Goal)
Parameter HER LER
I (mA) 1450 2500
nbunches 1600 1600
ßy (cm) 1 1
?x .035 .094
?y .047 .07
Vrf (MV) 18 4
Lum (cm-2s-1) 18 4
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Acknowledgments

• The work reported on in this talk has been done
  by many, in particularF.-J. Decker, A. Fisher,
  R. Iverson, W. Kozanecki, S. Novokhatski,
  M. Ross, J. Seeman, M. Stanek, M. Sullivan,
  P. Tenenbaum, D. Teytelman, M. Woodley, G.
  Wormser, G. Yocky