Beam jitters
Mar. 14, 2018
Y. Seimiya

1Outline
1. Introduction
2. Investigation of beam jitter source–––––

Dependence on flux concentrator, solenoid, bridge
coil, pulsed magnet, and chicane.
Charge dependence.
Correlation between beam position before and after thetarget.
Positron beam, that does not pass though the target
hole.
Dispersion leak dependence.

3. Conclusion2

Outline
1. Introduction
2. Investigation of beam jitter source–––––

Dependence on flux concentrator, solenoid, bridge
coil, pulsed magnet, and chicane.
Charge dependence.
Correlation between beam position before and after thetarget.
Positron beam, that does not pass though the target
hole.
Dispersion leak dependence.

3. Conclusion
3

Requirement to LINAC for
SuperKEKB••••

Low emittance & high charged beam transportation is required forSuperKEKB.
Transported beam to MR must be stable to the extent that the beam
can be injected inside MR acceptance.
SuperKEKB requirement must be satisfied for emittance including jitter
emittance, called as effective emittance.
In phase 3, 40/20 nor. emittance under 4 nC is required.

SuperKEKB requirement for electron
H/V nor.
emittance
(µm)

Phase
2150/150

Phase
340/20Charge Energy spread
(nC)
(σ)

1MR acceptance
Effective emittancex’0.1%

0.07%
Effective 4emittance haveto be less than effective emittance.

4xMeasured beam position jitter (thermionic gun)• After J-ARC section, horizontal position jitter is enlarged because
position jitter is proportional to both dispersion and energy jitter.
• After target hole, hor. and ver. position jitters are enlarged.

Thermionic gun• 1 nC.
• BPM resolution ~ 10 µm.
• ηJ-ARC ~ 0.8 m→ ΔPJ-ARC/P0 ~ 0.06%.
• 1000 shot data
• Dec. 2017

J-ARC Target
5Measured beam position jitter (RF gun)• After target hole, hor. and ver. position jitters are enlarged.
• This behavior is similar to that of thermionic gun.

RF gun• 1 nC.
• ηJ-ARC ~ 0.8 m→ ΔPJ-ARC/P0 ~ 0.05%.
• 1000 shot data
• Dec. 2017

J-ARC Target
6Jitter emittance (1)• Effective emittance = Nominal emittance + Jitter emittance• If beam position and transfer matrix between two BPMs isidentified, we can derive beam angle. Using the position and angle,effective emittance is derived by✏ef f =p

< (x +x)2 >< (x0 +x0 ) 2 >< (x +x)(x0 +x0 ) > 2 .

If beam jitter is independent of particle motion,✏ef f ==qq

✏20 + ✏2jitter + ✏0 ( <x2 > +2↵ <x x0 > + <✏20 + ✏2jitter + 2✏0 ✏jitterx2 >)

<x0 >

<x>

= ✏0 + ✏jitter ,p< x2 >< x02 > < xx0 >2 ,p✏jitter = < x2 >< x02 > < x x0 >2 .
✏0 =Jitter emittance
7Nominal emittanceJitter emittance (2)• Jitter emittance remarkably increases after the target.
• This jitter emittance strongly affect the effective emittance.
Phase 3requirement toeffective emit.

RF gun, 1nC

DesignDesignbeta functionsbeta

phase space plot is not scaled by gamma factor.

εx40 µm

εy20 µm

jitter emit.
εx27.7 µm

εy7.2 µm• What is the jitter source?
• Does effective emittance satisfy
the SuperKEKB requirement?
• Unfortunately, jitter source is not clear for now. This
presentation is progress report.

9Outline1. Introduction
2. Investigation of beam jitter source–––––

Dependence on flux concentrator, solenoid, bridge
coil, pulsed magnet, and chicane.
Charge dependence.
Positron beam, that does not pass though the target
hole.
Correlation between beam position before and after thetarget.
Dispersion leak dependence.

3. Conclusion
10Positron generation target• As jitter source, components around target is suspected.
• Schematic layout of component around target.

T. Kamitani slide

Target hole for electron beam
• Electron beam straightly pass through the positron generation
11target hole, which diameter is 2 mm.

Configuration around the target• Electron come from upstream and pass through FC, target, bridge coil,and DC solenoid.
• After the DC solenoid, chicane for dump electron beam, that is generated
together with positron beam.
DC solenoid& acc. structure

T. Kamitani slide

12Dependence on flux concentrator, solenoid,
bridge coil, pulsed magnet, and chicane• We check whether these components are sources of jitter or
not by turn off these components between BPMs before
and after target.
Thermionic gun, 1nC

ON

OFF

No noticeable differences
13

Charge dependence• Maximum horizontal jitter amplitude as a function of charge.
• Linear charge dependence can be seen.
S. Ogur14

Positron beam, that does not pass though the target hole
• Difference of positron beam (hits the target) and electron beam (throughthe target hole).
• It seems that target hole enhance beam position jitter remarkably.
Wake field effect is suspected.
After target

Positron

After target

Electron

Big differences.

15

Correlation between beam position before andafter the target (1)Steering magnet current (A)Q jitter amp. [nC]y jitter amp. [mm]Before Target (SP15T)

x jitter amp. [mm]• To find the wake field effect, beam position pass through thetarget hole was changed by steering magnet.

Steering magnet current (A)16Correlation between beam position before andafter the target (2)Steering magnet current (A)Q jitter amp. [nC]y jitter amp. [mm]After Target (SP165)

x jitter amp. [mm]• It seems that there is not remarkable difference between beamposition jitter amplitude and steering magnet current.

Steering magnet current (A)17Amplification factor and correlation coefficients• From the beam position before and after target, amplification
factor and correlation coefficients are derived.
• It seems that beam jitter dependence on beam position passthrough the target is small.
• Wake effect is not found from this result.

Correlation plot

Amplification factor

Correlation coefficients

No noticeable differences.

18

Simulation analysis

Wake potential in the target hole.
•••••

In order to reveal beam jitter problem, simulation analysis is also performing.
Though target hole size is small (φ2 mm), higher order wake field affect beam.
Color variation shows difference of beam position from the center of target hole.
This simulation is performed by CST studio.
Longitudinal wake has little position dependence. While, transverse wake increase
nonlinearly.
• K. Oide, K. Yokoya, and A. Novokhatski help to analyze beam jitter problem
induced by wake field.
Longitudinal wake potential

Transverse wake potential

X = Beam position
from the center oftarget hole.
19

Dispersion leak (thermionic gun)•By dispersion leak suppression, jitter emittance is reduced.

1nC

Phase 3requirement toeffective emit.

Suppress dispersion leak.
BeforeAfterεx40 µm

εx1.8 µm

1.3 µmεy20 µm

εy1.8 µm

0.9 µm20

Dispersion leak (RF gun)• Jitter emittance is reduced to same level as thermionic gun.
1nC

Phase 3requirement toeffective emit.

Suppress dispersion leak.
BeforeAfterεx40 µm

εx27.7 µm

1.8 µmεy20 µm

εy7.1 µm

0.9 µm21

Conclusion• Jitter emittance enhanced by the target hole.
• By dispersion leak suppression, jitter emittance isreduced.
• In phase 2, beam jitter is not problem. Under 1 nC
beam operation, the jitter emittance is small even forphase 3.
• In phase 3, SuperKEKB requirement of beam charge
is 4 nC. We have to check whether jitter emittanceunder the 4 nC beam is small or not with respect tophase 3 target emittance.

22Thank you for your attention.

23• During the data acquisition, only lossless beams are considered.
Charge dependence is small.

Current of steering magnet.
24

Dispersion leak (thermionic gun)Suppress dispersion leak.
BeforeAfterεx

1.8 µm

1.3 µmεy

1.8 µm

0.9 µm25

Thermionic gun 1nC

phase space plot is not scaled by gamma factor.

• If all of the linac quadrupole magnet readout is used for simulation, beta
functions diverge. This is because initial beta function do not match real one.
26
• In jitter emittance calculation, magnetic readout is used.