BT
M. Tawada, K. Kikuchi, K. Kodama, T. Mimashi, T. Mori,
T. Naito, T. Takasaki, S. Terui and T. Ueda
(BT group)

The 26th KEKB Acclerator Review Committee

1

Contents
1. To improve injection efficiency
2. BT hardware issues and updates
3. Upgrade plans in BT
4. Summary

The 26th KEKB Acclerator Review Committee2

1. To improve injection efficiency• Injection orbit changes and re-alignment at BT ARC4
• Field quality improvement of HER Septum 1• Injection aperture improvement for HER

The 26th KEKB Acclerator Review Committee

3

Injection orbit changes and re-alignment of BT e ARC4 (Kikuchi)
Survey results for magnets of the Electron BT and HER quadrupoles in the injection region (2018)
Green: design
Red: misalignment of quads
Blue: misalignment of bends

Slope𝐺"(mm)

Findings:
eARC40.046 mrad

QI4E

𝐺!(mm)HER• Example of septum angle adjustment
𝑋!"# = 36mm

𝑃𝑥!"# = 2.44mrad

mrad

mrad

SKB-design

SE1

38.60

44.59

39.49

SE2

37.82

28.08

35.35

SE3

36.01

37.5

37.5

SE4

35.24

37.5

37.5

Sum

147.69147.69149.84• HER line is inclined relatively to the BT designby 𝜃 = .046mrad.
• Quadrupole of HER at the injection point (QI4E)
has relative offset to the design by(Δ𝐺! , Δ𝐺" ) = (2.90, −2.73)(mm)• Final quadrupole in the BT has misalignment of(−.18, −1.42)(mm)
Countermeasure:• Septum angles were adjusted to absorb the
relative misalignment to the current HER line.
• During LS1, re-alignment will be performed forthe four quadrupoles which have large
misalignment greater than 1 mm.
4Injection orbit changes and re-alignment of BT p ARC4 (Kikuchi)
Survey results for magnets of the Positron BT and LER quadrupoles in the injection region (2018)
Green: design
Red: misalignment of quads
Blue: misalignment of bends

𝐺" (mm)SlopeFindings:• Both of BT line and LER have misalignmente+

by Δ𝐺. ∼ 2.5mm.
• Relative positions between BT and LER are
almost correct.

ARC4

QI6P

Countermeasure:• Design of BT line was adjusted to match the𝐺!(mm)LER• Septum angle adjustment
𝑋!"# = 34.1mm 𝑃𝑥!"# = 4.10mrad
mrad

SKBoperation July
2021*)

SP1

53.10554.057SP2

44.12944.090Sum

97.23498.147*) 𝑋!"# = 32.76mm, 𝑃𝑥!"# = 5.535mrad

misalignment of BT. Bend angle of ARC4
was adjusted by Δ𝜃/𝜃 = 1.816×10/0 .

• Residual misalignment to the new design
will be corrected.

• Septum angle are adjusted to match thecurrent position of the injection
quadrupole (QI6P).

5

HER Septum 1: Field quality improvement (1) (Mori)• It has been found that a fringe field near the septum plate has a sizable multipole component. A tracking simulationshows multipoles induces a vertical non-Gaussian tail, which could be a cause of a beam background as well as a bad
injection efficiency.
• Adjustment of Q-magnets at upstream of the BT line for optics matching does not work completely for non-linear
components.
• Improving the field quality of HER septum 1, which is nearest one to the injection point is important for injection
efficiencies and backgrounds.
• Field quality would be improved by (1) reducing the pulse width of 300 → 257 μs by changing power supply’s main
capacitor and (2)Fine tuning of shim shape for the reduced pulse width.
• HER injection amplitude could be reduced from 11 to 8 mm in total.
• 2mm (by field improvement of septum magnet) + 1mm (by injection aperture improvement) could be reduced.

The 26th KEKB Acclerator Review Committee

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HER Septum 1: Field quality improvement (2) (Mori)
Simulation studies are performed and we decided shim shape as shown in the lower left figure: the flat top
width h=0.24 mm, wtop=0.06mm.

Issue for fabrication•

We noticed the silicon steel plate ( JFE 0.35mm inorganic coating) used so far are not available any
more. Another candidates (0.15 mm inorganic coating or 0.35 mm organic coating) are found but it
must be evaluated for punching accuracy and outgas performance.

•

Therefore, the fabrication is delayed and installation will be scheduled in summer 2024.
The 26th KEKB Acclerator Review Committee

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Injection aperture improvement for HER (Kikcuhi)
HER injection orbit and the chamber wall

•In the current configuration the injected beam is
expected to touch the quad chamber before it
touches the septum wall.

QI4E
Stored beam

Injection Slit

•Very high residual radiation-activity, which was
found at the flange of the “Injection BPM”
chamber, supports this hypothesis.

Septum•Kicker orbit changes cannot avoid thisInjected beam

Injection BPM

Ideal wall shape to minimize theinjection amplitude

geometrical conflict because it interferes withthe constraint from the abort orbit.

•A new chamber for QI4E was designed which

has enough clearance to the injected beam (seeVac-group report).

•The “ideal shape” of the chamber wall waspartially incorporated in the new design, which
minimize the injection aperture.

•If the “ideal shape” is realized injection
aperture will decrease from 0.88𝜇m to
0.65𝜇m.

8

2. Hardware issues and updates• LER kicker issues• Leakage of LER injection bump orbit• self-firing troubles of thyratron tube

• DR extraction kicker stability issue• DR kicker temperature stability improvement• Temperature stability improvement of facility cooling water• Fast kicker for 2nd bunch in RTL• Monitor upgrades• BT-BPM• Radiation profile monitors (BT-SRM, Screen)• CSR monitor
9LER Kicker: Leakage of LER injection orbit bump (Kodama and Mimashi)
1.0

Ti coating: 1.5 um

Ti coating: 5.0 um

0.1

0.6
0.4

Expand wave

0.2

Current 900 mA
w/o additional inductance+550 nH

0.2

BOR [a.u.]r24

CT wavew/o additonal Lwith 550 nH

0.8
CT output [a.u.]

K1ダクトサイズ
28

K2ダクトサイズ
20
r20

0.0
-0.1
-0.2
-0.3

0.0
0

1

2

3

4 x 10

-6

118

119

120

Additional inductance effect for K1 CT wave

122

123

124

Additional inductance effect for BOR

l Leakage of LER injection orbit bump was observed by BOR while kicker’s current waveforms are almost same between
K1 and K2. The horizontal oscillation is coupled to the vertical. This may cause the luminosity degradation.
l Leakage kick might comes from the differences of ceramic duct shape and Ti coating thickness.
l We have tried to expand K1 current waveform with additional inductance of 550 nH in series. But the leakage
couldn’t be reduced as we expected.
l Need to manufacture new K2-type ceramic ducts and replace K1 ducts to new one in 2024. (The budget was notallowed in 2022.)
The 26th KEKB Acclerator Review Committee

10-6

125 x 10

Time [sec]Time [sec]K1(left) and K2(right) duct shape121

LER kicker: Self-firing troubles and coutermeasure (Kodama, Naito and Mimashi)l Self-firing troubles in 2021-2022• By using the thyratron which had been stocked for a long time but new one, self-firing had been occurred several
times.
• Self-firing of new thyratrons recently purchased had also occurred.
l Countermeasure for self-firing• Prepare test stand for incoming inspection and aging of thyratrons.
• R&D of the double kicker driven by one thyratron unit.
• Double kicker has different output between K1 and K2 due to different cable length to make the time delay.
K1:K2 ratio will be fixed for the double kicker. If optics accepted this condition, we will continue to design
double kicker system.
1.2
0.10
Thyratron unit

Schematic image of double kicker system

K1
K1-K2

0.8

K2

0.08
0.06

0.6

0.04

0.4

0.02

0.2

0.00

0.0

-0.02

-0.2
0

2

4

6

K1 - K2

Transmission line
7m
23 m
Tdelay = 80 nsec
(5 nsec/m)
Kicker2
Kicker1

Kicker output [a.u.]

1.0

-0.04
-6
8 x 10Time [sec]Simulated Kicker waves for double kicker system(1)The 26th KEKB Acclerator Review Committee11

DR ext. kicker stability (Tawada)
Ceramic capacitance〜0.8%/℃

Mica capacitance〜100ppm/℃

1 hour• Slow orbit drift was observed at the Linac BPM. These orbit drift changes when therepetition changed, which is more prominent in the 2nd bunch.
• It takes long time to reach the equilibrium for the high repetition rate (> 2 hour for
12.5Hz).
• This may be due to the temperature dependence both of capacitance and FINEMET
core, which is used as a saturable inductance in the magnetics switch and thus
determines the fire timing. We will replace the capacitor from a ceramic to a mica type,which is less temperature dependent. And cooling system of FINEMET will be improvedby using a water-cooled forced circulating oil.
The 26th KEKB Acclerator Review Committee

12Temperature stability improvements of facility cooling water (T. Naito)
The temperature control parameters of the facility cooling water were optimized. In order tominimize the temperature change, the on/off temperatures of the cooling towers are set todifferent value and the PID parameters of the three-directional valve are set to the long interval.
DR magnet (M22-B cooling water)Less than 0.5℃
2℃

Before improvements

After improvements

The temperature change was reduced from 2deg to less than 0.5deg. The most of time,
the temperature kept to 0.1 or 0.2 deg.
The other region of the the facility cooling water in BT, KEKB-BT magnet (AS-PWP-5
cooling water) and Septum magnet (FM-PWP-3 cooling water) can be stabilized by usingsame method.

DR-RTL: Fast Kicker (Naito and Kodama)
96ns
20ns

DR-RTL fast kicker

Ø It takes time to adjust kick angles (〜5mrad) of two bunches extracted fromDR, because two successive kicker pulses are overlapped each other and they
are interrelated in the fire-timing as well as in the pulse height.
Ø Installed a fast kicker system to kick 2nd bunch only to RTL.
• Stripline kicker for ATF (L=0.33m) are reused and PS are newly built.
• Kick angle: 0.14 mrad with ±8kV, pulse width:20ns, Horz./Vert.
• Kick angle could be larger if longer kicker is used.
The 26th KEKB Acclerator Review Committee

Before EVR change

After EVR change

0.4

w/o SL kicker with SL kicker

0.2

0.0

X orbit [mm]DR extraction kicker

-0.2

①

②

-0.4
LIiBM:SP_DC_4_1:XSNGL:KBP:1S
LIiBM:SP_DC_4_2:XSNGL:KBP:1S
LIiBM:SP_32_4_1:XSNGL:KBP:1S
LIiBM:SP_32_4_2:XSNGL:KBP:1S

-0.6

-0.8
14:00
2022/05/23

14:15

14:30

14:45

15:00

15:15

15:30

Date and Time

Stripline kicker test with beam
14

BT-BPM status: (Mori)• Old BT-BPM Oscilloscopes• Eight old oscilloscopes (Tektronix DPO7104, 4-ch, 1 GHz, 8-bit) have been used for BT-BPMs
since 2007 and hardware troubles have occurred several times.
• Those should be updated and Rhode & Schwarz RTO2014 (4-ch, 2 GHz, 10-bit), which was
only one candidate and can work at 50Hz repetition rate but it was sold out last year. We arelooking for a oscilloscope or digitizer which meets the required specifications.
• Some BPM must be re-cabled not to make the 2nd bunch signals overlapped each other.

• Libera SPE• Libera SPE will be ready for BPMs at BT end of e-/e+ lines, which have direct cables , during
next run.
• It can receive EVR data buffers and change parameters by event code (31=e-/41=e+) andmark it by ShotID.
• Switching of e-/e+ is performed by RF switch, which is prior to Libera SPE.

The 26th KEKB Acclerator Review Committee

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BT-SRM (Synchrotron Radiation Monitor): (Mori)••

SRM for e- was installed at the beginning of ARC3 (BH3E.1) and second
one will be installed at ARC1 (BH1AE).

SRM@BH3E.1

We have just started to measure the beam profile. The measured beam
sizes are good agreement with the rough calculation. But it is still
preliminary and the further check is needed.

The 26th KEKB Acclerator Review Committee

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BT-OTR monitors : (Mori)• Changing fluorescent screen monitors to OTR monitors in BT e±-lines.
• Will measure the bunch-by-bunch beam profiles by using an imaging intensifier (Hamamatsu C14245),
which can control gate width with accuracy of a few ns.
• The beam profile data can be related to BPM’s position data by using ShotID or event timing.
Locations of OTR monitor at BT line

BT EndLinac ENDe-

The 26th KEKB Acclerator Review Committee

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Emittance growth: CSR monitor (Terui)BTp:
BH1P.9• Plan to replace one vac. chamber of BTp 1st arc bending magnet
with a branch pipe to monitor CSR. (No space for BTe.)• Gap height of vac. chamber can be changed.
• Simulations for infinite parallel plates with various gap height
are also on-going by Fujita-san. Smaller gap height is preferable
to reduce CSR effect.

The 26th KEKB Acclerator Review Committee

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Upgrade plans in BT• BT e- ECS by Linac group• New BT e- Line for HER

The 26th KEKB Acclerator Review Committee19

BT e- ECS• Because the budget of 1.7 oku-yen (1.25M$) for e- ECS fabrication had been already approved, the e- ECS
components and the facility cooling water system must be fabricated in three years.
• Linac group has just started the study of the effectiveness and feasibility of e- ECS, including beam loss rates.
• Because BT tunnel has poor radiation shields (0.4 m of concrete + 1.1 m of soil) for public area, additional radiation
shields might be needed to incorporate e- ECS but it will be problems with maintainability.
The Twenty-Fifth KEKB Accelerator Review Committee

The 26th KEKB Acclerator Review Committee

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New BT line for HER (Kikuchi)①•New BT line for the HER has been proposed, that envisages ease of the CSR/ISR emittance
growth.

•New line share the tunnel in part with PF-AR transport line.
•If we preserve the current BT e- line and can switch the beam pulse-by-pulse, the current
line could be used for beam diagnosis.

Current HER transport line

Linac

③

②

②

①

④
New HER transport line

④

③

21

New BT line for HER (Kikuchi)
Tunnel structure①
Junction with the utility tunnel

Downstream tunnel

③

②

①

Upstream tunnel
Above the MR tunnel,
floor level is elevated by 50
cm.

SOIL
Downstream tunnel

Junction partSOIL②•The tunnel of PF-AR BT has two independent tunnels. They
Upstream tunnel

are loosely connected to the utility tunnel via bellows pipes
which are embedded in soil. Beam pipes pass through thebellows pipes.

•The junction part has to be excavated to construct the new③

HER BT line.

•The utility tunnel houses many cable-ladders inside, and the
BT line has to avoid collision with them; the beam pipeshould pass in between the cable ladders, adjusting beamheight with vertical translation.

22

New BT line for HER (Kikuchi)
Beam line①
New ARC1
ARC2②①

PF-AR BT line

• ARC1 part is located side by side with the PF-AR line in thepresent plan .
• Beam level of the new line is 0.6 m lower than the PF-AR line.
• Transverse free space between the magnets of two lines are
0.5 m at minimum, which will make the maintenance work
difficult.
• Bend angle is smaller than current ARC1. Since longer bend ispreferable for the CSR we plan to reuse the bend in the ARC2,or to fabricate new bend that has smaller width.

②

New ARC1

PF-AR BT line

23

New BT line for HER (Kikuchi)

Emittance at Injection

Optics• Emittance growth due to ISR
Results of tracking simulation are fitted to, where,(New BT line)(Current BT line)
New ARC1

ARC3•ISR induced emittance growth 𝜀# of the new
Current BT line

𝜀(𝜇m)

𝜀(𝜇m)

New BT line

BT line decreases to 1/3 of that in current BTline

𝜀0 (𝜇m)𝜀0 (𝜇m)24

Summary• For better injection efficiency, a few countermeasures will be performed.
• Some hardware have issues to be solved. The countermeasures are also in progress.
• The budget for e- ECS has already approved and the fabrication of ECS components are on-going.
The effectiveness and feasibility study of e- ECS should be performed as soon as possible.
• New BT e- line for HER has just started to study. No apparent showstopper is found so far.
• Need to consider a consistent upgrade plan including e- ECS and New BT e- line for HER.

The 26th KEKB Acclerator Review Committee

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backup

The 26th KEKB Acclerator Review Committee

26

Injection orbit changes and re-alignment of BT e ARC4 (Kikuchi)•We have also found some mysterious discrepancy in the design•In design of SKB, alignment of BT line in the KEKB era was preserved except for septum magnets.
•But we have found discrepancy in the design between SKB and KEKB:•At the entrance ofSE4 SKB design has (Δ𝐺" , Δ𝜒$ ) = (−2.5mm, 2.08mrad) relative to KEKB design.
•Considering misalignment of Δ𝐺" = −2.73mm for QI4E, net effect is a translation in 𝐺" for both of BT
and HER by Δ𝐺" ∼ 2.5mm

Official Design of HER line in the KEKB era

27

BT-BPM updates: (Mori)

The 26th KEKB Acclerator Review Committee28

BT-BPM updates: (Mori)

The 26th KEKB Acclerator Review Committee

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DR-RTL: Fast Kicker (Naito and Kodama)

BITF_20220603_Iida

⼊射効率に関しては、⼩⽟さんより物⾔い有り“Raw” injection efficiency of #1“Raw” injection efficiency of #2
The efficiencies have been almost
same since the kicker worked.

Extraction kickers
The fast strip line kicker

DX at BPM2

DX at BPM1

The fast strip line kicker ON

DX: Horizontal orbit difference (X_2-X_1)
BPM1

BPM2

6

HER/LER Abort Kicker : Trigger systeml Rising time of abort kicker is less than 200 ns but It needs about 1 μs before the fire the thyratron by using
Teledyne E2V triggering system.
l Will replace the trigger system to new one. (1 μs → 250 ns)
The 26th KEKB Acclerator Review Committee31