Instability Observations via
Streak Camera and PMT

J. Flanagan
KEKB Review
2003.2.10

Studies of photo-electron cloud induced
vertical beam blow-up in the LER
S. Hiramatsu, T. Mitsuhashi, H. Fukuma, H. Ikeda, M. Masuzawa, J. Flanagan• Goal: Try to see details of proposed blowup mechanisms– Bunch shape distortions– Spectrum (quadrupole peak)• Methods:– Streak Camera: October 2002
– PMT + BPM data: January 2003

Hardware Improvements• New SR extraction chamber in LER– Beam-pipe section changed from stainless steel
to copper, reducing resistive wall heating andimproving stability of extraction mirror mount,and eliminating the need for optical axis
feedback compensation with changing beam
currents. Also makes study measurements
much easier.
– Similar replacement planned for HER insummer 2003.

Old LER SR Extraction
Chamber
1998 - 7/2002

New LER SR
Extraction
Chamber
8/2002 -Old Chamber

Beam-Pipe
Temperature°C

SUS: Resistive losses at
1 A → ~20 W → 100°/10cm
Cu: 1/40-1/50 of SUSLER Current (mA)
New Chamber°C

LER Current (mA)Extraction Mirror Orientation
Optical-axis feedback
compensation angles
Old Chamber

mrad

New Chamber

mrad

LER Current (mA)LER Current (mA)

•Optical-axis feedback is now unnecessary, turned off in LER

Hardware Improvements (cont.)• Reflective optics system for streak camera– Use of focusing mirrors instead of lenses
eliminates chromatic aberration, making
bandpass filtering unnecessary and greatly
increasing light intensity of beam image.
– Single bunch/single turn images now easily
obtained with streak camera.

Reflective Optics for Streak Camera
Designed by T. MitsuhashiHyperbolic
mirrorParabolicmirror

Streak camera
internal relay
optics (custom-made)Streak Camera Observations• Observation date: 2003.10.18• Beam conditions:– LER single-beam– Single bunch• Bunch length measurement– 2 trains, 140 bunches/train• Bunch length measurement• Bunch shape observation• 4 bucket spacing (8 ns) between bunches

Single Bunch, 0.134 mAtySingle Bunch, 1.54 mAty

Single-bunch dependence of length on bunch current

H. Ikeda•Natural bunch length = 5.8 mm.

Bunch length at head and tail of train

H. Ikeda•At high current bunch length longer at head than at tail of train.

226 mA (0.81 mA/bunch)
Tail of Trainty

379 mA (1.35 mA/bunch)
Tail of Trainty

Streak Camera Summary• First observations very preliminary• Bunch length measurements:– Natural bunch length = 5.8 mm.
– At high current bunch length longer at headthan at tail of train.

• Dipole oscillations (vertical offset) visible• Synchrotron motion also observed• Hints of head-tail tilt perhaps seen in somebunches, especially accompanying
longitudinally shifted ones.

SRM＋FB BOR Data
2003.1.29•

Beam: LER, single beam, solenoids OFF– Fill pattern: 4/200/4 (4 trains, 100 bunches/train, 4 RF bucketspacing) => 800 bunches– Beam current: 900 mA => 1.125 mA/bunch– ny = 0.5858, nx = 0.5319, xy = 4.94 (set), xx = 1.89 (set)– ns = 2.25 kHz– sy* = 5 mm (normally 2 mm)•Detector:– PMT + partially blocked SR beam image (Perevedentsev method)– FB Bunch Oscillation Recorder (BPM)• Both read out using FB memory system: 5120 bunches x 4096
turns worth taken at once.

PMT setup (proposed by Perevedentsev)

Beam Image
Memory(BOR)

PMTBlack Cardboard

Partially block beam image withblack cardboard, and measure lightintensity of the visible part with aPMT. The PMT signal is buffered
and then recorded using a feedback
BOR digitizer/memory board.
y: 100 mV/division
x: 10 ns/divisionAveraged Power Spectra of All Bunches
PMT Data

BPM Data

Characteristics of Spectral Peak along Train
PMTBPM•Peak shifts along train, saturates at Dny = +0.055•Maximum oscillation amplitude near 15th bunch (60th bucket)

BPM Example Bunch Time Series and Single-Bunch SpectraExample of double-burst (10th bunch)

Time Development of Instability: 512-turn slices
BPM signal, 51st Bunch

PMT Example Bunch Time Series and Single-Bunch SpectraExample showing blow-up decay time~1500 turns

Time Development of Instability: 512-turn slices
PMT signal, 51st BunchBlow-up Pattern Analysis
Find a bunch with characteristic
blow-up pattern, and take spectra of3 stages separately. Then average
the 3 spectra over all bunches thathave this pattern.

Distribution of blow-up events along train
Turn # of peak PMT signal after blow-up ramp

•32 events found in 1st train (200 bunches)•3 clusters of adjacent bunches with similar timing,but otherwise events are independent.

Bunches 1-50

Bunches 51-200

Mid-blow-up averaged spectrum of 2nd data set at same tune

Mid-blow-up averaged spectrum of 3rd data set at same tune

Mid-blow-up averaged spectrum of all 3 data sets at same tune

PMT+BPM Summary• Dipole Oscillation seen in both PMT and BPM data.
• Amplitude of oscillation in BPM data: 0.1-0.2 mm• Frequency corresponds to that of a tune shift saturating at+0.055 by ~50th bunch.
• Time Structure seen:– Maximum oscillation amplitude occurs in short bursts• ~500 turns (5 ms)– After burst dies down, beam is enlarged for a period, graduallyshrinking again over ~1500 turns (15 ms).
– Bursts occasionally occur in adjacent bunches at the same time,
but most often occur in isolation.
– No clear quadrupole signature seen yet.

• Plan to take more data with streak camera and PMT inparallel.