Commissioning Progresssince October 2007
13th KEKB Accelerator Review
Dec. 03, 2007
Haruyo Koiso

Progress• Higher beam currents with Crab ON.
– 1300 → 1620 mA (LER), 700 → 850 mA (HER)• Shorter bunch spacing, more bunches.
– 3.5 buckets (1389 bunches) → 3.27 (1485) →3.06 (1585)• Adjust βx*– 80 → 68 → 90 → 100 cm (both rings)• Simplex knob scanOct.-Dec. 2007 Peak: 14.7 /nb/s

βx∗=803.56890

3.06 buckets

100 cmOperation History••

Oct. 2 Beam operation started with Crab OFF.
Oct. 5 Collision started with Crab ON ( 0.875(LER) /1.45(HER) MV). 3.5 rf bucket spacing, 1389 bunches.
––••

Oct. 13 Crab voltage scan with 100 bunches.
Oct. 22 Knob Optimization by Downhill Simplex Method
was put in practical use.

Oct. 24 3.27 rf bucket spacing, 1486 bunches.
Oct. 26 3.06 rf bucket spacing, 1585 bunches.
–•

Nov. 8 Green Ratio was introduced.
Nov. 12 βx* 80 → 68 cm– Nov. 19 Crab voltage scan with high currents.

•••

Nov. 21 βx* 90 cm
Nov. 26 Peak luminosity 14.689/nb/sNov. 29 βx* 100 cm (0.783 (LER) / 1.297 (HER) MV).

Best Day with Crab Cavities (Nov. 26)

Earthquake
CrabCrabEarthquake

Luminosity Optimization
by Simplex Method

Daily Luminosity

We must obtain 710/pb/day to achieve 800/fb till March 31, 2008.

Specific Luminosity
y=-16.35x+26.54 Green Ratio=100%

Crab crossing•49-sp βx*=80, 84cm
εx=18, 24 nm•3.5-sp βx*=80cm•3.06-sp βx*=80cm•3.06-sp βx*=90cm

3.06 > 3.5 buckets
90 > 80 cm

22 mrad crossing

Specific Luminosity
y=-16.35x+26.54 Green Ratio=100%Crab crossing•49-sp βx*=80,84 cm
εx=18 nm•3.5-sp βx*=80cm•3.27-sp βx*=80cm•3.06-sp βx*=80cm

22 mrad crossing

Luminosity (estimated)
Beam currents
1700/875 mA

1600/825

1500/775
3.5 buckets
3x7
4x7

3.27
3x11
4x4

1400/725
3.06
3x15
4x1

2.88
3x15
2x2

1350/700

The specific luminosity is assumed to be on the line Green Ratio=1.

Machine Parameters (Nov. 28 2007)

This is almost equal to thevalue achieved at collision withlonger bunch spacing.
Effects of high current andshort spacing are not so big?

IR Optics
LERHER

IP
IPβx,y* can be adjusted by using only 7 (LER)/6 (HER) quadrupoles oneach side of IP.

Estimation ofdynamic aperture andemittance growth(LER)

Dynamic aperture
Jy/Jx=1/9A
B
CDEF

Beam
Current

Sextupoles A

Beam Loss at Tune Jump(LER)B

C D E F
Difference between A and D

Changed from νx=0.516 to 0.506.
νx=.512 is on 2νx+νx=integer.
“D” was adopted.

Chromaticity Measurement (Mar. 05)

measuredmodelδξH =-1.7, δξV =+0.9

δξH =+0.9, δξV =+2.9

Downhill Simplex Method
Method of Minimization•{1, 2, 3} 1(best)<2(next-to-the worst)<3(worst)•
Evaluate 3R•
If 3R<1,•
If 3E<3R, {1, 2, 3E} : Expand , if not, {1, 2, 3R} : Reflect•
If 1<3R<2, {1, 2, 3R} : Reflect•
If 2<3R<3, Reflect 2 proposed by A. Hutton•
If 3C+<3R, {1, 2, 3C+} : Contract+ , if not, {1, 2, 3R} : Reflect•
If 3<3R, Reflect 2•
If 3C-<3, {1, 2, 3C-} : Contract- , if not, {1, 2S, 3S} : Shrink/Reflect2
Expand1
Reflect
Shrink3

Contract+
Contract2

Luminosity Optimization (Nov. 30)
Initial Simplex (List View)

GreenRatioStart(Centerof Mass)
79.43%

Best
83.74

Luminosity Optimization (Dec. 2)
Current Simplex (Graphic View)

5thBest83.74

σy* Minimization
Current Simplex (Graphic View)σy* Minimization by Downhill Simplex Method

LER σy*HER σy*LERHER

LER knob scan
Luminosity

Crab Voltage Scan
Oct. 13 100 bunches

Nov. 19 1585 bunches

Lifetimeσy*Luminosity

Lifetime
σy*designLuminosity

4.6 mradThe ratio of crab voltages was adjusted to give the same kick in bothrings. The scan was done, keeping the voltage ratio.

Plans• Collision at long bunch spacing (49 buckets)• Higher currents• Adjustment of βx* and horizontal emittance• Improvement of simplex scan
– Modified algorithm proposed by A. Hutton– Include other knobs (horizontal dispersion, etc.)• Larger dynamic aperture to cure lifetime degradation– Better choice of sextupoles– Better correction of both on- and off-momentum optics• Reduction of vertical emittance– Better optics correction• More knobs, better method of knob optimization