Commissioning progress
before JulyY. Funakoshi(KEK)Beam Operation with crabcavities• Dedicated machine study (Feb. 13 ~ June 302007)– Feb. 19 ~ Mar. 19 : reported by H. Koiso (lastMAC)– Mar. 20 ~ June 30: This Talk

• Physics run with crab cavities (Oct. 2 ~ Dec.
17): To be reported by H. Koiso

High current(Crab ON)High current(Crab detuned)

Crab warm-up

High current(Crab ON)

Recovery of luminosity
LER solenoid off
HER vertical emittance
LER SX search etc.

negative-α

HER high emittanceLuminosity performance withcrab• Specific luminosity• Beam-beam parameter• Scaled luminosity

Speciﬁc Luminosity

L18 H24

L18 H24 (3/11, 4/3)

ξy~0.089(4/10, 4/19)

L24 H24 (3/29, 4/1)

L24 H29(6/14)

22mrad crossing
L18 H24

beam-beam simulation(IbL/IbH = 7/4)

beam-beam parameter withcrab crossing (simulation)
beam-beam parameter

N% y*
re
"y =R" y***2#$ & y (& x + & y )!
: experiments

Calculation of beam-beam parameter•Method of calculation– Beam-beam tune shift of the synchronous particle– Vertical beam size is calculated from the luminosity.

•Reduction factor for beam-beam parameter" y = R" y " y 0"y0 =% y* N

re2#$ & *y (& *x + & *y )– 2 sources of reduction• hourglass effect and finite crossing angle!

2$'+z /2
R" y = ,*+ 1+ && * )) f y ( x,- x ,- y ) . ( z) dz% #y (

2$+ $' # x2 $'/5x2'#2 12k 4&i*xxkx
2" x&) # e 2" x w&)-07)+f y ( x," x ," y ) =1#ew,& " 2 1# k 2 )-7k #1 4&k ) " x 2(1# k 2 ) - & " x 2(1# k 2 ) )) (176(43%%(% x (.

Montague’sfactor!
!

k=

"y"x%

# ( z) =z2

2
1e 2" z2$" zCalculation of beam-beam parameter [cont’d]•Reduction factor for luminosity

L2 b
RL "
=ae K 0 (b)
L0
#20
*'*
$y%z
2/a=, b = a 1+ ) * tan & , 22% z/. ( % x+ 21– Luminosity

1 N +N #L=f col RL* *4 " $ x$ y!

– We use calculated values for σx* and calculate
σy* and ξy0 from observed luminosity.

!

Comparison of different emittance
εx=18/24nm (L/H)(Mar.14)

εx=24/24nm (L/H)(Apr. 1)εx=24/29nm (L/H)(June 14)Low
currents(achieved)High
currents(scaled)Low
currents(achieved)High
currents(scaled)Low
currents(achieved)High
currents(scaled)# ofbunches

51

1389

51

1389

100

1389

ILER
(mA)

61

1661

75

2043

125

1736

IHER
(mA)

34

924

30817741028

0.594

16.5

0.611

17.0

1.03

14.3

Luminosity(/nb/sec)Comparison with and w/o crab
εx=18/24nm
With Crab

εx=18/24nm
No Crab(2007/3/14)

High
currents(scaled)Highcurrents(scaled)Highcurrents(achieved)High
currents(acieved)(2007/11/15)(2005/12/25)# ofbunches

51

1389

1585

1389

1585

ILER
(mA)

61

1661

1933

1662

1800

IHER
(mA)

34

924

1078

1340

1360

0.594

16.5

18.8

17.1

15.2

Low
currents

Luminosity(/nb/sec)Summary of performance• Specific luminosity– ~30% higher than before crab• Beam-beam parameter– ξy: 0.089 (cf. 0.056 w/o crab)• Extrapolated luminosity to higher beam currents– We need to increase the number of bunches.
• 18.8 /nb/s (1585 bunches with 3.06 spacing)• poor beam lifetime

Efforts for improving specificluminosity• Knob tuning– to remove errors which we know

• Other effects?

Tuning knobs•

Legacy tuning knobs– iBump v-offset, v-angle, size-target– Waist, R1~4 (knob1, knob3), IP vertical dispersion– Tune, chromaticity (knob2)• Higher vertical tunes bring higher luminosity with crab crossing.

•New knobs– iBump Horizontal-offset– Crab Vc– R2, R4 @Crab (Vertical crabbing)– IP Horizontal dispersion•

Tuning method– Scan one by one with optimizing mainly the luminosity andsometimes the beam sizes– Almost always continued the scans• Can we reach the optimum set of parameters with starting unknown
errors in the knob parameters? (beam-beam simulation Tawada andOhmi)• Is there a more effective way of searching knobs? -> Downhill simplex
method (Oide and Koiso)

Tolerance for errors(simulations by Ohmi et al.)• Sensitive to some errors– Horizontal crossing angle– Horizontal offset• Sensitivity to errors of conventionalknobs is not so different.
– IP coupling, IP dispersion, waist

Crossing angle and luminosity• Sharp peak near zero crossing angle("%#$&'894:/0;894:/0("!#$&'<1*=;894:/0>1:7'"%#$&''"!#$&'%"!#$&!
!"!#$!!
!

%'!

'%)*+,-.*/0+1-234*56(!Are there any errors which can not
be corrected by usual tuning knobs?
• Effects of synchro-betatron resonance• What is the source of the anomalous lifetime
asymmetry with respect to the sign of the horizontal
offset?
• Vertical emittance?
• Bunch length?
• Unknown fast noise？

Importance of SX tuning••

The choice of Sextuple setting is very importance for the luminosity
performance.
The synchro-betatron resonances (2νx+ νs = integer, 2νx+ 2νs = integer) affect performance.
–––––

•

single beam beam size
single beam beam lifetime
two beam beam size
two beam beam lifetime
range of betatron tunes that can be used in the luminosity run

We made a progress both in the method of evaluation of SX
performance and the method of SX search in computers (A. Morita).
– A number of candidates of the SX sets are prepared and tested with thebeams from the view point of the beam size blowup and the lifetime
decrease at around the resonance lines.

LER σx, σy tune dependence2νx +νs =integer3νx -νx =integer

Effect of synchro-betatronresonance on the luminosity
σx (µm)σx (µm)LER

νxLERνxChromaticity tuning- We observed the horizontal sizechanged in the range of 390-330µm.
- The luminosity is improved withthe chromaticity tuning.

IPDynamic beta and emittanceνx = .510, νy = .580
εx0 =24nm, βx0 =0.8m

SRM1SRM2

Negative-α Optics• Motivation– To weaken the synchro-betatron resonance particularly inHER
2νx + νs = integer2νx + 2νs = integer
νx: .5112, .5224
with given νs ~ -.0224

2νx - νs = integer2νx - 2νs = integer– To shorten the bunch length• Results– We have succeeded to weaken the synchro-betatronresonance line in HER.
– We have successfully shorten the bunch length of bothbeam.
• ~6mm -> ~4.5mm– However, we found unexpectedly large synchrotron
oscillation in LER and gave up the trial of the negative-αoptics.

HER Optics

Positive α (now)

Negative α

H. KoisoHER Optics (cell)

Positive α (now)

H. Koiso

Negative αHER negative−α optics

LER negative−α optics

LER/HER positive−α optics
HER high emittance optics

Synchro-betatron resonance in HER• Positive-α– We could NOT operate
under the resonance(2νx+νs=integer)• Negative-α– We could operate
under the resonance(2νx+νs=integer)Bunch length

H. Ikeda

H. Ikeda

Observation of synchrotron
oscillation in LER•

Not the coupled bunch instability but the single bunch instability– Observed with single bunch beam
– Not depends on νβ, νs– Amplitude is comparable with the bunch length•

Like saw-tooth instability observed in SLAC damping ring?
– We did not see in the first trial of negative-α in 2003.
– We need to check the history of the Ring impedance.

Streak camera from H. Ikeda

2007/6/8 negative α
Bunch current=1.2mA

2007/6/13 positive α
Bunch current=1.0mA

2003/6/27 negative α
Bunch current=1.16mA

2003/6/27 positive α
Bunch current=1.09mA

Lifetime issues•

The storable beam currents are limited by poor beam lifetime
particularly for the HER beam current.
– With head-on collision, effective horizontal beam size is larger thanwith crossing angle.
– High emittance optics could mitigate somewhat the problem. But its
effect was not enough.
– We need to go for higher number of bunches with shorter bunchspacing.
– This poor beam lifetime observed is NOT reproduced by beambeam simulations.

•Lifetime asymmetry with respect to horizontal offset– The mechanism has NOT understood yet.
– It maybe indicate existence of some unknown errors.

Horizontal
offset scan
• The (HER) beam
current seems tobe limited by theshort life time ofthe LER beam.
• The (LER) beam
lifetime is very
asymmetric withrespect to Hoffset.
LER lifetimeCollision center given by thebeam-beam kickMore observations••“Egure” disappeared with the crab crossing.
Methods to make a horizontal offset at IP– We can make a horizontal offset in three methods• make an orbit bump in LER• make an orbit bump in HER• change collision point in the longitudinal direction– The asymmetric nature of the lifetime does not depend on themethods to make the horizontal offset.

••

No evidence that the horizontal ring aperture determines thebeam lifetime.
The asymmetric nature does not change even when we enlarge
the stronger beam in the vertical direction by making dispersionbumps.
– The vertical beam-beam tail is not responsible for the poor lifetime?

•The asymmetric nature does not strongly depend on thehorizontal tune.

Horizontal offset scan (2004 June 9)
Scan with high current (940mA/1200mA)← scanLumi peak(Hset ~ -20µm)

zero-offset (Hset ~ -70µm)

Scan with low current (~400/600mA)← scanReference data
61mA / 20mA
March 15

HER beamloss
HER lifeasymmetry

scan direction

With 2mm horizontal bump at Crab in HER
βx (m)

Aperture

Acceptance(mm)(µm)

crab

174

4310.6

Hmask

171819.1

Septum

403530.6

March 15

HER beamloss
HER life
asymmetry

61mA / 20mA
scan direction

iSize Bump(LER) 0 -> 2.4mm
61mA / 20mA

March 15v sizes changed

HER beamloss
HER life
asymmetryscan direction

Dynamic Aperture of KEKB with Beam-Beam
nx=x/σx

Off-momentum aperture shrinks due to Beam-Beam effects.
νx/νy=45.508/43.56

LER

Beam-Beamξy=0.07 (finite-angle)

Jy=0.02Jx(fixed)Beam-Beamξy=0.07(head-on)
No Beam-BeamOhnishiSynchrotron oscillation: ONRadiation damping: OFF#turns: 1000

Δp/p0
KEKB-LER (60 mA/50 bunches : 7.54x10 particles/bunch)
10Coupling (MINCOUP)
No Beam-Beam
Beam-Beam(ﬁnite-angle)
Beam-Beam(head-on)

Beam-Beamstrong beam: #slices= 52%
190 min70 min88 minY. Ohnishi 04/06/2007

Dynamic Aperture of KEKB with Beam-Beamνx/νy=45.508/43.56

nx=x/σx

Crossing angle = 0

LER
Jy=0.02Jx(fixed)

Head-on (Δx=0)
Δx=-σx*Δx=+σx*Δp/p0Y. Ohnishi 07/04/2007

Vertical emittance (single beam)
LER: 0.24nm, σy = 1.18µm (4/3)

HER: 0.78nm, σy = 2.14µm (3/26)
SRM Calibration

K. OhmiSimulation
σy = ~1.2µmεy(nm)•••Small vertical emittance always gives better performance.
Luminosity is saturated to 0.1% before due to flip-flop. This may bedue to a small error of code.
Better simulation should give better luminosity for incoherent effect.

Unknown fast noise?
• Fast orbit fluctuation?
• FB noise?
• Crab kick? (Akai)• Others?

Fast orbit fluctuation ?
• Fast orbit fluctuation was measured in
1999 and 2000.
– up to 50 Hzy# 0.002 [!!" ! ]"y#$%&'()*!$+,!+--.'," /0 = 10!!!
y $@)* # 20µ1#2 # 34356% $y* ! & !$+,!7'1/!89%!'--':,!!

!

LER vertical1999/Jul.01

2005/June/06

High beam current operation
with crab cavities• With crab cavities detuned– We could store the nominal beam currents before
crab test.
• 1700mA (LER) and 1350mA (HER)• With crab cavities on– Maximum beam current• 1300mA (LER) and 700mA (HER)• Trip rate of crab cavities did not seem so serious. -> K. Akai
• An orbit instability occurred above ~1100mA (LER) in thesystem of the crab cavities and the horizontal beam-beam
kick. -> K. Akai

– Peak luminosity• 10.602 /nb/s <- limited by the orbit instability

700mA
1350mA

1300mA

1700mA

10.602 /nb/s

11.156 /nb/s

Crab ON high currents

Crab detunehigh currents

Crab ON high currents

Plan for autumn run• We proposed the following plan to the Bellegroup and they accepted.
– We will start the KEKB operation with the crabcavities turned on and try to increase theluminosity.
– We assure the Belle group 20fb-1/month and theaccumulation of 80fb-1 by the end of FY 2007.
– If achievement of this integrated luminosity is
considered to be difficult in spite of our efforts, wewill switch to the conventional crossing angle
mode with the crab cavities detuned.

spare slides

Observed synchrotron oscillation(single bunch operation)
1. αp=-2.5x10-4,pilot bunch (1 mA)

2. αp=-3.4x10-4
pilot bunch (1 mA)
multibunch(99) 5 mA
~2.5kHzHigh Emittance Optics• Motivation– To increase the bunch current particularly in HER• To compare the specific luminosity with a higher bunch
current product• Preparation of the higher beam operation with crabcavities• Results– HER: high emittance optics (εx= 34nm)– LER: εx= 24→ 18nm
– We could store somewhat high HER beam
current. But it was not enough.

HER crab angle is small?
• Observed HER tilt by crab kick is half of thecalculation.
• Closed orbit distortion by crab kick isconsistent with the calculation.
• IP horizontal orbit offset created by crab kickis consistent with the calculation.
• Is there any mechanism which affects x-z
particle distribution?

Unbalance of horizontal
emittance (Ohmi)• Unbalance of horizontal emittance between
two beams can be compensated by beam
currents.

Beam-Beam Simulation withlattice non-linearity (Ohmi)• Luminosity drops abruptly at some thresholdstrengths.
• However, the threshold strengths are about 2
order higher than expected values.