Optics Issues
Hiroshi Sugimotofor Optics GroupContents	

1. Optics Design Issues Except for IR- Tsukuba straight line, nominal tune, Beast optics, etc.
- Tunnel subsidence effect on vertical emittance2. IR Optics Design- Design changes- Dynamic aperture and Touschek lifetime
3. Error Field from Final Focusing Magnets (QCS)- Normal sextuple error field- Skew sextuple error field- Possible design change plan

03/04/2013	

The 18th KEKB Accelerator Review Committee	

2	Optics Design Issues
Except for IR

Machine Parameters	§ Change LER vertical tune from 44.57 to 44.57
LER	HER	

Energy (GeV)	

4.0	

7.00729	

Current (A)	

3.6	

2.6	

#of bunches	

2500

2500	

βx* (mm)3225	

βy* (mm)

0.27

0.30	

εx* (nm)

3.2

4.6	

εy* (pm)

8.64

11.5	

σz* (mm)65	

νx , νy44.53 , 46.57	

45.53 , 43.57	

νs-0.0247	

-0.0280	ξy0.0881	

0.0807	

Luminosity (1034 cm-2 s-1)	
03/04/2013	

8x1035	

The 18th KEKB Accelerator Review Committee	

4	LER Optics Changes - Wiggler Section -	§ Vertical beta is suppressed to mitigate the beam-gas scattering effects.
§ Integer part is increased by 2 while keeping the fractional part.

(ν x , ν y ) = ( 44.53, 44.57) ⇒ (44.53, 46.57)
Old	New	βx 	 βy 	€ηx 	 ηy 	03/04/2013	

The 18th KEKB Accelerator Review Committee	

5	

Tsukuba Straight Line is Finalized	

concreteshield	§ Interference problem between LER&HER has been resolved
while keeping optics, orbit length and IP geometry.

LER	IP	

concreteshield	HER	

03/04/2013	

The 18th KEKB Accelerator Review Committee	

6	

Off 4S Operation	
§ Capability of off-4S operation is confirmed considering limitation ofmagnet field strength.
§ Optics and hardware design is carried so that keep the capability.

03/04/2013	

The 18th KEKB Accelerator Review Committee	

7	Phase 1 - Linear Optics -	§ Optics W/O QCS and solenoid has been designed§ QCS and solenoid is replaced by drift space.
§ Machine tuning except for IR is expected to be done in this phase.
LER	
HER	

Drift	

Drift	
03/04/2013	

The 18th KEKB Accelerator Review Committee	

8	Phase 1 - Dynamic Aperture -	§ DA example assuming,- Design bunch current.
- 2% emittance ratio.
§ Beam loss estimation is ongoing from view point of radiation protection.
Funakoshi-san’s talk	HER Touscheck Life
~6.3 hours	

LER Touscheck Life
~1.4 hours	

RF Bucket	

Physical Aperture	

03/04/2013	

The 18th KEKB Accelerator Review Committee	

9	Simulation of Tunnel Subsidence 	§ The subsidence effect is investigated with numerical simulation.
§ Put the subsidence to design lattice as a vertical misalignment ofeach magnet.	
Simulation
Marker Level (Measurement)

BPM
Readings	
Numerical
Simulation

Import	Beam Orbit	

Misalignment	

IP	IP	

§ Change amplitude of misalignment, and evaluate vertical emittance.
03/04/2013	The 18th KEKB Accelerator Review Committee	

10	

Simulation of Tunnel Subsidence (cont’d) 	

εy	σηy 	εy	

W/O Optics Correction 	εy	σηy	W/ Optics Correction 	
Target (εy=5pm)	

σηy	§ Vertical emittance exceeds the target values, 5pm, after 7 years
when 2mm/year is assumed. 	
03/04/2013	

The 18th KEKB Accelerator Review Committee	

11	

Simulation of Tunnel Subsidence (cont’d) 	
§ What is the most dominant source of emittance dilution?

εy	εy	

Target (εy=5pm)	

W/ V-LCC misalignment	

σηy	σηy	εy	
W/O V-LCC misalignment	

σηy 	§ V-LCC misalignment has very critical impact on emittance.
§ Need special care for orbit control or/and alignment in this region. 	
03/04/2013	

The 18th KEKB Accelerator Review Committee	

12	

IR Optics Design

IR Design	§ All quadrupoles except for QC1P have iron yoke for preventing
field leakage to the another beam line§ Canceller coils are installed for HER beam line to suppress
leakage filed from LER QC1 magnet.
§ All magnets have super-conducting corrector coils.
- Normal&Skew Dipole, Skew Quad, Octupole
03/04/2013	

The 18th KEKB Accelerator Review Committee	14	

IR Design Upgrade	§ LER QCs now have vertical offset to reduce dipole corrector strength.

Old	New	

Beam orbit	
IP	

VerticalKick Angle	
VerticalOffset	

QC1LP	QC1RP	
QC2LP	IP	
QC2RP	

1.0mm	

1.5mm	

Vertical Kick Angle	

03/04/2013	

Magnet	

QC1LP(mrad)	

QC2LP(mrad)	

QC1RP(mrad)	

QC2RP(mrad)	

Old	

2.472	

2.746	

-2.082	

2.491	

New	-0.149	

1.651	

-0.644	

1.602	

The 18th KEKB Accelerator Review Committee	

15	

Dynamic Aperture & Touschek Lifetime	§ Touschek lifetime is optimized with Down-hill simplex method.
§ Available knobs are 54 sextupole families and 4 octupole magnets.
§ Lifetime of both beams is almost reached the target value, 600 sec. 	
HER615 sec	

03/04/2013	

The 18th KEKB Accelerator Review Committee	

LER588 sec	16	

Error Field from QCS

Field Measurements of QCS Prototype	§ Unexpected normal&skew sextupole have been observed.
Ohuchi -san’s talk	§ Their magnetic field strength is ~0.1% of quadrupole field. 	

Field strength relative toquad. field [x10-4	]Field profile along QC1P	Skew Sext.	
Normal Sext.	

Longitudinal position [mm]	

§ Impact on dynamic aperture has been investigated. 	
03/04/2013	

The 18th KEKB Accelerator Review Committee	

18	

LER DA with Normal Sextupole Error Field	§ Thin lens Sextupoles are inserted to QC1L and QC1R.
§ There magnitudes are same, but signs are independent.
§ Evaluate DA for 4 possible combinations of sign at each error field strength.	
QC1L
w/ sext. error

Same Sign	

IP

QC1R
w/ sext. error

Effect is very critical.	

Opposite Sign	

03/04/2013	

The 18th KEKB Accelerator Review Committee	

19	

Sextupole Corrector Coil	§ Only R-size design can be changed. (L-size is already fixed)§ No more space for installing the corrector to QCS itself.
§ We are considering installation between QC1R and QC2R.	
LER

OctupoleOctupole

LPHER

Q

E
C2L

Octupole

QC1

LE
1C
Q
Octupole

LPE

R
QC2

R
QC1

IP

Sextupole Coil
Sextupole Coil

QC1

RP

Octupole

Octupole
03/04/2013	

E

Octupole

QC2

The 18th KEKB Accelerator Review Committee	

QC2

RP

Octupole20	DA Improvement by Corrector Coil	§ Introduce sextupole error to ALL QCs.
§ Check whether we can mitigate DA degradation by optimizing the correctorstrength.	

§ DA degradation is improved, but B3/B2 < 0.1% is preferable.	
03/04/2013	

The 18th KEKB Accelerator Review Committee	

21	

Skew Sextupole Error Field	§ Analogous calculation for skew sextupole error field.
§ Different feature compared to the normal sextupole case.
§ DA Improvement is not enough level.	

03/04/2013	

The 18th KEKB Accelerator Review Committee	

22	Lifetime and Corrector Coil Position	§ DA survey with changing corrector position.
§ Only QC1RP has skew sextupole error.	
Design	Scan effective corrector position	

QC2R

QC1R IPw/ error

QC1L QC2L§ Corrector coil must be installed between QC1L & QC1R	
03/04/2013	

The 18th KEKB Accelerator Review Committee	

23	

Design Change Strategy	Points to be considered.	
§ Need 1 normal sextupole corrector.
§ Need 2 skew sext. correctors.
§ One of skew sext. must be installed to QC1R.
§ Each QC can have only one corrector coil§ Possible to install additional coil between QC1R and QC2R.	
OctupoleOctupoleOctupole
Octupole

Octupole
Octupole

Octupole
Octupole

03/04/2013	

The 18th KEKB Accelerator Review Committee	

24	

R-side Design Change Plan (Not Fixed Yet)	
Possible Plan	§ Install normal Sext. coil (+octupole) to between QC1 and QC2.
§ Install skew Sext. coil to both QC1 and QC2 instead of octupoles.
Skew Sext.
Octupole

LE
2
CQ
Octupole

03/04/2013	

EOctupole

QC2LP

Octupole

Skew Sext.
Octupole

QC1

LE
1C
Q
Octupole

LPE

R
QC1IP
QC1RP

Octupole

Skew Sext.

RQC2

Normal Sext.
(+ Oct.)Normal Sext.
(+ Oct.)
QC2RPOctupole

Skew Sext.
The 18th KEKB Accelerator Review Committee	

25	

DA W/ and W/O R-side Octupoles	§ Touschek lifetime estimated by DA seems OK.	

03/04/2013	

HER W/ Octupoles~ 670 sec

HER W/O Octupoles~ 660 sec

LER W/ Octupoles~ 580 sec

LER W/O Octupoles~ 590 sec

The 18th KEKB Accelerator Review Committee	

26	

Side Effect of Removing Octupole from QC1	HER§ No remarkable effect is observed so far.

LER§ FMA indicates enhancement of some ronances.
W/ Octupoles

W/O Octupoles

4th order
5th order
6th order
7th order

03/04/2013	

The 18th KEKB Accelerator Review Committee	

27	

Summary	
1. Optics Design and Issues (Except for IR)- Almost completed.
- Minor changes related to detailed hardware design is now continued.
- Need special cares for orbit control or/and alignment in V-LCC region.
2. IR Design- Vertical offset is adopted to LER-QCS
for saving dipole corrector strength.
- Lifetime of both beams is almost reached the target value, 600 sec. 	
3. Error Field from QCS- Nomal&Skew sextuple error field has critical effects on DA.
- Additional corrector coil is planned to install.
Thank you for listening!
03/04/2013	

The 18th KEKB Accelerator Review Committee	

28	

Appendix	Appendix	

03/04/2013	

The 18th KEKB Accelerator Review Committee	

29	

Touschek-Lifetime History	§ DA has been steadily improved by feedback cycle between Optics &Magnet group.	

HERLER	

2D IR Model	
03/04/2013	

3D IR Model	

The 18th KEKB Accelerator Review Committee	

30