Investigation Status of Emittance Blow up
in Electron Beam Transport LineT. Mori, N. Iida, M. Kikuchi, K. Kodama, T. Mimashi, F. Miyahara, T. Natsui, Y. Ohnishi, K. Oide,
Y. Seimiya, S. Takasaki, M. Tawada, T. Ueda
November 9, 2020
B2GM

1

Table of contents

Motivation to suppress emittance blow up in BT-line

BT-line overview

OTR monitor

First result of measurement with OTR monitor

2

Table of contents

Motivation to suppress emittance blow up in BT-line

BT-line overview

OTR monitor

First result of measurement with OTR monitor

3

Luminosity limitation by injected beam
K. OideLuminosity is directly depends on the quality of injection beam!
Low emittance injected beam increases injection efficiency.
4

Table of contents

Motivation to suppress emittance blow up in BT-line

BT-line overview

OTR monitor

First result of measurement with OTR monitor

5BT-line overview

6

Emittance measured with wire scanners (WS)
N. Iida7

Investigation in this summer

Until now, we have done many kinds of effort, but still not been solved yet.
• Obstacle survey in the beam duct,• Remaining part: Arc3 - Slope• Q-magnet check,• Alignment,• Simulation studies (on going).

8

Table of contents

Motivation to suppress emittance blow up in BT-line

BT-line overview

OTR monitor

First result of measurement with OTR monitor

9OTR monitor• We have just started to measure the beam with OTR monitor as our next strategy.
• Precise beam size measurement can be accomplished.
• 5 of fluorescence screens are replaced by OTR screens.

10Experimental setup•• Light of OTR is detected by gated camera
after passing through view port, mirrors,
achromatic lenses and band-path filter.
• Gate width: 2 ms due to shutter timing
jitter while OTR itself is within ∼ 20 ps.
• Position resolution by CCD: ∼ 70 µm. It
should be updated by changing zoom
factor for narrow beam.

Schematic view of setup.
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Experimental setup

MSE.06

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Images of OTR compared with fluorescent light

MSE.1013

Installed location

Locations of wire scanners and OTR monitors.
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Table of contents

Motivation to suppress emittance blow up in BT-line

BT-line overview

OTR monitor

First result of measurement with OTR monitor

15

Beam sizes measured after BT1
matching done, emittance on eachlocation calculated.
Bunch charge: ∼ 1.5 nC.
Bmag (x) = 1.1, Bmag (y) = 1.0.
1. Calc and measured in BT1 notmatched,
2. Vertical emittance on BT1 andMSE.06 are not consistent,
3. Vertical emittance blow up seems
to be seen between MSE.10 andMSE.12 (Arc2 - Arc3),
4. Calc and measured β notmatched,

Summary of measurements and calculations.

5. Horizontal emittance blow up
seems to be seen between MSE.
06 and MSE.08 (Arc1),
6. Horizontal emittance between
MSE.15 and BT2.
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Discrepancy of vertical emittances on BT1 and MSE.06

Fitting of the function of phase advance for y-component is not good.
Is this related with the emittance discrepancy between BT1 and MSE.06?
17What can we do?
1. Replace screen MSE.11 with OTR screen,
2. Set zero current for QMD4E, compare MSE.
15 and BT2 measurements,
3. Q-magnet scan with OTR beam size
measurement.

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Summary• Quality of injection beam is very important for luminosity, L = I+inj ε+ I−inj ε− τ+Nτb− Lsp ,• We have made an effort to solve the emittance blow up problem in BT-line,
and still it is on going,• As our next strategy, OTR monitors have been installed and emittances measured at eachlocation,• First result is obtained, we considered next plan.

19Thank you for your attention.

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Summary table of measurements and calculations.
Beam sizes measured after BT1 matching done, emittance calculated on each location.
Bmag (x) = 1.1, Bmag (y) = 1.0.
1. Vertical emittance on BT1 and MSE.06 are not consistent.
2. Horizontal emittance blow up seems to be seen between MSE.06 and MSE.08 where the location
corresponds to Arc1.
3. Vertical emittance blow up seems to be seen between MSE.10 and MSE.11 where the location
corresponds to Arc2 - Arc3.

BT2

MSE.06

MSE.08

MSE.10

Band path filter: 550 ± 40 [nm]

MSE.12

Short pass filter: 700 nm

MSE.15

ROI: 8-bit (this camera only, 12-bit for others)Transition radiation with normal incidence
Transition radiation is the radiation occurs when acharged particle with relativistic velocity passes throughthe boundary of two materials have different
permittivity. It is derived from Maxwell equation withboundary condition.[1]。

Figure 1: Figure in ref. [2].

d2 I1 (θ, ω)e2 β 2=dωdΩ√ε1 sin2 θ1 cos2 θ1π2 c2p(ε2 − ε1 ) 1 − β 2 ε1 + β ε2 − ε1 sin2 θ1
×q


p
(1 − β 2 ε1 cos2 θ1 ) 1 + β ε2 − ε1 sin2 θ1ε2 cos θ1 + ε2 ε1 − ε21 sin2 θ1(1)Optical transition radiation with 45◦ incidence

Though the calculation becomes complexed for 45◦
incident, will be simplified in the case of visible lightregion and metal medium.[2]。

d2 I
1−e sin θe sin θ′=+2dωdΩ4π c 1 − β cos θ 1 − β cos θ′2(2)Angular distribution

Figure 2: OTR angular distribution for E = 1.1 [GeV]. It has a peak at θ ≈ 1/γ.

Number of photons

Equation (3) is obtained by the integration of Equation (2) about whole solid angle and ω, andthe division by ℏω.
 αω2N = [2 ln γ − 1] × ln(3)πω1e2α=(CGS Gauss unit system)(4)ℏcNumber of positrons for 2 nC bunch: 1.25 × 1010
Number of generated photons per bunch: 1.2 × 109

References i[1] V. L. Ginzburg and V. N. Tsytovich, “SEVERAL PROBLEMS OF THE THEORY OF
TRANSITION RADIATION AND TRANSITION SCATTERING”, Physics Reports (Review
Section of Physics Letters) 49, No. 1 (1979) 1-89.
[2] B. Gitter, CAA-TECH-NOTE-internal-#24.