SuperKEKB Accelerator Review Committee
2024 March 25

Linac upgrade with Pulsed Magnets

Takuya Kamitanion behalf of

KEK e+/e- injector linac groupPulse magnet related upgrade items
1. Pulsed quads at J-arc matching sectionv Installed in 2023 summer

2. Pulsed quads at e+/e- compatible optics regionv Installed in 2023 summer

3. Linac fast kicker for bunch orbit difference tuningv Installed at J-arc, linac-end & HER-BT until 2024 January
v To be installed at linac low energy region in 2024 summer

4. Pulsed beam switch-yard for beam diagnosis
v To be installed in 2024 summer2

3

Upgrade item [1]Pulsed quads
at J-arc matching section

4

J-arc in injector linac
B
1.5 GeV@J-arcC

A

Thermionic gun+RF bunching
Photo-cathodeRF gun3.0 GeV @target
10 nC x 2 (prim. e-)
4 nC x 2 (inj. e-)

1e+ target &1.1 GeV
Damping Ring
PF

Bunch
Compression
SystemLAS capture section

2.5 GeV e0.1 nC x 1

Energy-spread
Compression System

S-bandlinac

2

50 Hz (e+ or e-)pulse-by-pulse
mode switching

LER

4.0 GeV e+
ECS 4 nC x 2

3

4

5

HER

7.0 GeV e4 nC x 2

AR

6.5 GeVe-l Four different modes of beams pass through 180-degree beam turn (J-arc).
KBE(injection e-), KBP(primary e- for e+ generation) and PF, ARl J-arc was designed to be achromatic (for emittance(ε) preservation) andisochronous [R56 = 0] (for bunch-length preservation).
l Later, it was modified to be non-isochronous [R56 ≠ 0] for bunch compression.

Motivation for pulsed quads in matching section
l beam optics situation @J-arc
v since it has large beta-function andenergy dispersion, beams have large
beam size, so beam optical matchingis essential to avoid beam loss anddegradation.
v optical mismatch tend to cause aparticle loss in primary e- beam forlarge emittance (KBP).
v tuning of quads for matching often
makes emittance degradation in
injection e- beam (KBE).

l motivation for pulsed quadv pulsed quads in matching section
enables independent beam optics
matching for each mode5

e- beammatching
sectionmatching
sectione- beamY. Seimiya, Y. Okayasu

achromatic &isochronous
opticse- beamPulsed quads layout at J-arc

6l 6 DC quads at entrance and exit of J-arc à 8 pulsed quads
v ensure sufficient free matching parameters (αx, βx, αy, βy) @ (entrance, exit) in J-arc regionl These quads required to have large apertures to accept large beta-function
for matchingl quads layout slightly modified to lower the peak value of beta-functionl In 2023 summer, the layout renewed, 7 pulsed quads installed and
1 DC quad remained for investigation of coil heating issue
e- beamDC quads x 6

e- beam

Pulsed quads x 8

7

specification of pulse quad for J-arcl requirement on field strengthis minimized by simulation
while keeping the beam
matching performance andmargin.
l bore size remains the samefor sufficient aperture.
l current and turns/coil are
optimized, however, requires
larger capacity pulse driver.
l magnet (size) and ceramic
duct are designed to bealmost comparable to existing
DC quad and duct.
K. Yokoyama

parameters

DC quadR0_01 type

new pulsed
quad R0_01

bore diameter [mm]4444field gradient [T/m]

26.1

21

max. current [A]

56

600

pole length [mm]

300

300

effective length [mm]

323

333

B’L [T]

8.43

7nI [A.turn]

5040

4200

turn of coil /pole90

7

inductance [mH]

200

1.5

600mm

length300mm

bore diameter: φ44
field grad.：21[T/m]@600[A]8

new pulse driver for J-arc quads
l new pulse driver is developed
for large-aperture J-arc pulsed
quads.
l scheme was changed fromcurrent feedback to pulse
width feed-forward control.
D0IN+

3-5 sector typeNew pulse driver

Max Voltage

230 V

400 V

Max Current

330 A

600 A

Magnet aperture

23 mm

44 mm

Magnet inductance

1 mH

1.5 mH

Control method

ID-VGE analog

Pulse Width Feedforward control

control

M0

CHV

D4

M3

Flywheel stage (~ 50 usec)
IN+

OUT+

D0

energy-recovery stage
M0

OUT-

CHV

D4

M3
D3

M4
OUT+

D3

Pulse current waveform
IN+

D0

M0

CHV

D4

M3

OUT+

D3

OUT-

M4

time scale (horizontal) 0.4 ms/div

T. Natsui

OUT-

M4

Current amplitude and Magnetic flux

9l Pulse width control scheme in pulse driver
make a difference in current amplitude
for 1Hz and 50 Hz pulse repetitions.
(due to change in effective inductance)l However, change in magnetic flux (beam feels)
is small. (1Hz, 50 Hz in figures)l Pulse current variation upon coil-temperature
should be monitored.
Pulse current & Magnetic flux waveforms

Magnetic flux is measured
with one-turn pickup coil.

diff. in current amplitude ~ 2%
diff. in magnetic flux ~0.1 %excessive heating in quad coilsl In the full-spec. (600A, 50 Hz) operation test
before installation, excessive heating in innermost layers of quad coils was observed.
l It is due to eddy current in coil conductor byleakage field from the pole.
l The coils were designed to be air-cooled,
the temperature rose up to 80 degree(~interlock limit) in 80 minutes at 600A, 50Hz.
power OFF10

forced air cooling with blowers

11

l temperature rise test operation showed
v 600A, 50 Hz (full spec.) à NG
v 600A, 25 Hz operation à OKv < 400A, 50 Hz operation à OKl blowers for forced air cooling installed for 4 quads whose operation current
higher than 400 A.
l with the blower, coil temperature was kept below 58 degree at full spec.
l new water-cooled coils are designed and to be tested soon for future
replacement. An uninstalled pulse quad is used for this test.

KBP 10nC e- beam matching with pulsed quadsl BMAG~1 means good beam optical matching achieved for KBP e- beamge [µm]BMAG

X

216.0±32.9

1.02

Y

525.4±193.2

1.12(N. Iida 2023.10.25 LCG report）

12

13

Improved beam transmission after J-arc upgradel Almost 100% transmission for KBP beam at J-arc after Natsui-san’s
automatic Bayesian parameter tuning of quad strength, orbit and RF phases.
l Improvement in optical matching contributes to the result.

（T. Natsui 2023.10.23 LCG report）

Independent KBE beam tuning at J-arc

14l Under the situation with optimized matching for KBP beam,
independent matching parameter tuning for KBE beam
can be performed with the pulse quads.
l Variation in magnet current for KBE beam tuning is seen in the plot,
while that for KBP is constant at the already optimized value.

pulse quad PF_R0_01 : operation current for KBE
pulse quad PF_R0_01 : operation current for KBP

15

Upgrade item [2]Pulsed quads
at e+/e- compatible
optics region

e+/e- compatible optics region in injector linac
B
1.5 GeV@J-arcC

A

Thermionic gun+RF bunching
Photo-cathodeRF gun3.0 GeV @target
10 nC x 2 (prim. e-)
4 nC x 2 (inj. e-)

1e+ target &LAS

50 Hz (e+ or e-)pulse-by-pulse
mode switching

1.1 GeV
Damping Ring
PF

Bunch
Compression
System

2.5 GeV e0.1 nC x 1

Energy-spread
Compression System

S-band
linac

2

16

LER

4.0 GeV e+
ECS 4 nC x 2

3

4

5

HER

7.0 GeV e4 nC x 2

AR

6.5 GeVe-l beam optical design in the region (after e+ capture section to LTR entrance)is optimized for low-energy e+ beam transmission (E(e+) ~ 0.12 to 1.1 GeV)l plenty of DC quads are used for this optics
l e- beam (with higher energy E(e-) ~ 2.9 to 4.2 GeV)
experiences very weak focusing with large beta-function.
l slight change in orbit causes emittance growth of e- beam in this regionmagnet layout in Sector-1, 2
l quads wrapping around the accelerating structure
cannot be pulsed because of eddy current in copper
l only quads in between the structures can be pulsed
l only four DC quads shown below
replaced with pulsed magnets
beam line layout in Sector-1, 2

Accelerating structures

quad between structures

Y. Seimiya

17

emittance growth reduction by low beta optics

18

l lower beta-function can be achieved by setting four pulsed
quads to e- oriented focusing strength
l it can reduce emittance growth rate less than half (simulation)
Y. SeimiyaΔγε𝑥 ~ 100 um, 𝛽𝑥 = 45.2 m••Δγε𝑥 ~ 40 um, 𝛽𝑥 = 16.3 m

End of LAS
cavityStart of S-band
cavityBunch tail is kicked backby quad, and temporally
emittance is reduced.

e+ targetachieved smaller
betatron function

e+ targetspecification of pulse quad for Sector-1, 2
l requirements on bore sizeand field strength areminimized by simulation
while keeping theperformance.
l magnet (size) and ceramic
duct are designed to be
replaceable with existing DC
quad and duct.
l current and turns/coil are
optimized to be compatible
with ordinary pulse driver.

parameters

DC quad17_14 type

new pulsed
quad 17_14

bore diameter [mm]4432field gradient [T/m]

20.9

23.6

max. current [A]

80

300

pole length [mm]

160

160

effective length [mm]

173.8

168.0

B’L [T]

3.63

3.96

nI [A.turn]

3760

2400

turn of coil /pole47

8

inductance [mH]

32.3

0.94

19

K. Yokoyama
DC quads

pulsed quade+ beam transmission improved

20

l e+ beam transmission greatly improved after Natsui-san’s automatic
Bayesian parameter tuning of quad strength, orbit and RF phases.
In the previous situation, e+ beam
intensity gradually decrease typicallyto 3 nC at end of sector-2

e+ intensity exceeded
5 nC for both bunches（T. Natsui 2023.11.13 LCG report）

l since thorough tuning of all the DC and pulsed quads resulted in this success,the contribution of pulsed quads are just a small part.
l However, we can proceed to low-beta optics tuning for e- beam with pulsed quads
while keeping the good condition for e+ beam.

21

Upgrade item [3]Linac fast kicker
for bunch orbit
difference tuning

22

2-bunch operation in injector linac
B
1.5 GeV@J-arcC

A

Thermionic gun+RF bunching
Photo-cathodeRF gun3.0 GeV @target
10 nC x 2 (prim. e-)
4 nC x 2 (inj. e-)

1e+ target &1.1 GeV
Damping Ring
PF

Bunch
Compression
SystemLAS capture
section

2.5 GeV e0.1 nC x 1

Energy-spread
Compression System

S-bandlinac

2

50 Hz (e+ or e-)pulse-by-pulse
mode switching

LER

4.0 GeV e+
ECS 4 nC x 2

3

4

5

HER

7.0 GeV e4 nC x 2

AR

6.5 GeVe-l Linac can inject two bunches per pulse to increase injection charge forSuperKEKB main rings (HER and LER).
l The 2nd bunch follows the 1st with 96 ns interval.
l The 2nd bunch can have slightly different beam orbit and Twiss parametersfrom the 1st, even their beam energies are equalized.
l The 2nd bunch tend to lose a fraction of charge at J-arc or at target-holedue to a deviation of the orbit.
l The 2nd bunch tend to have lower ring-injection efficiency as well.

Need for Fast Kicker

23

l The bunch interval 96 ns is too short for ordinary pulsed
steering magnet (pulse rise time ~ several ms) to kick only
either bunch.
l Fast kicker (< 96 ns) is necessary to control the bunch orbit
independently.
l The kicker should have very low inductance.
l The pulse power supply should have pulse rise time < 96 ns.
l Locations to install fast kicker
v [1] entrance of J-arc
for orbit tuning in J-arc, prototype test of kicker and power supply
v [2] linac-end & BT-line
for tuning of injection orbits for HER and LERv [3] low energy region of linac (sector-A)
for orbit tuning at low energy

24

Ceramic chamber type Fast Kicker
C. Mitsuda

dipolefieldl CCiPM : Ceramics Chamber with integrated Pulsed Magnet
developed by C. Mitsuda was introduced for linac bunch orbit
kicker.
l Magnetic field type kickerl This kicker has four parallel coil wires.
l The current configuration described above(parallel and anti-parallel currents) generates
horizontal dipole magnetic field, (vertical beam kick).

Prototype fast kicker and power supply @J-arcl fast kicker (installed in 2022 summer)

25

capacitor bankv CCiPM D40 typev inner diameter 40 mm
v coil length 300 mm
v field strength 5.6 mT@200A

switch module

l pulse power supply
v SiC FET high-voltage switch
developed in collaboration of C. Mitsuda
and Nexfi technology co.
v pulse rise time < 96 ns (spec.)
to kick only 2nd bunchachieved rise time ~ 200 ns
v max current 400 A
v mac voltage 10 kVv precise timing control
for kick angle fine tuning
v unipolarv switch module installed in the tunnel
close to kicker magnet(needs thick radiation shield)
v interference occurred in ordinary pulsed
steering magnet power supply（kicker support exchanged with insulator）

fast kicker

Y. Enomoto, T. Natsui, Y. Okayasu, C. Mitsuda

pulse rise time ~ 200 ns

the slow rise time is expected to be due toadditional inductance by connection cables.

Fast kicker at linac-end & HER BT line

26

l Vertical fast kickers are installed in the linac end (58_4) and HER BT-line
in 2023 summer.
l Kicker FY_58_4 started operation in 2023 autumn, FY_61_E in 2024 January.

Linac
Fast Kicker
FY_58_4e+ beam

BT line for LER
e- beam

BT line for HER
Fast Kicker
FY_61_E

Kicker magnet

Pulse PS module

Y. Okayasu

27

Pulse power supply [ver-2 compactified]l pulse power supply for fast kicker
v SiC FET high-voltage switch
v pulse rise time < 96 ns
v max current ~ 400 Av max voltage 10 kV
地下

5V
24 V
Trig

in linac tunnel
inductance~1 1uH程度
uH

地上

Switch module

1 kW

in klystrongallery

40 nF
DC

Pulse current

kickermagnet

1 kW

10 kV

current
monitorswitchmodule筐体
shieldbox
Current monitor

capacitors

l pulse rise time ~ 100 ns achieved withv newer version SiC FET switch (Nexfi)
v compact layout of circuit components in a box
v parallel plate bus bar line
v compact connection of transition wiring
between the terminals

pulse power supply for FY_58_4
installed in a radiation shield box
beside beam line at linac end
Y. Enomoto, T. Natsui,
S. Shinohara, Y. Okayasu

Observed vertical beam position at downstream of FY_58_4

Beam kick test with kicker FY_58_4

1st bunch and 2nd bunch
are independently kicked.
Pulse rise time ~ 100 ns

AT this trigger timing,
only 2nd bunchis kicked.

T. Natsui, Y. Okayasu, T. Kamitani

28

29

orbit jitter issuel With fast kicker FY_58_4 ON,
beam orbit of 1st and 2nd bunches
at LER BT line was tuned to be at
the same position by adjusting thetrigger timing.
l However, the magnitude of
position jitter increased with kicker.

kicker ON
kicker OFF

1st and 2nd bunch
beam position at LER BT line

l By adjustment of pulse timing
closer to the peak, the jitter
magnitude can be smaller, but
present.
l Timing jitter in switch module itself
is < 0.1 ns.
l Investigation on the timing jitter oftrigger signal after transmission isnecessary.

kicker ON

kicker OFF

N. Iida, T. Natsui, H. Ito

30

Upgrade item [4]Pulsed beam switch-yard
for beam diagnosis

Need for pulsed beam diagnostic branch line
B
1.5 GeV@J-arcC

A

Thermionic gun+RF bunching
Photo-cathodeRF gun3.0 GeV @target
10 nC x 2 (prim. e-)
4 nC x 2 (inj. e-)

1e+ target &PF

2.5 GeV e0.1 nC x 1

Energy-spread
Compression System

S-bandlinac

LAS capture section

50 Hz (e+ or e-)pulse-by-pulse
mode switching

1.1 GeV
Damping Ring

Bunch
Compression
System2

31

LER

4.0 GeV e+
ECS 4 nC x 2

3

4

5

HER

7.0 GeV e4 nC x 2

AR

6.5 GeVe-l Linac beam quality (energy-spread, emittance) is gradually degraded.
l e+ beam for LER is rather stable since e+ DR stabilize the beam condition.
l Degradation of e- beam quality directly lowers the injection efficiency to HER.
l e- emittance tuning needs a trial-and-error search for optimum orbit offset
that takes at least several minutes or longer.
l the tuning is performed by extracting beams to linac switch-yard (SY3) or
beam dump at the end of HER-BT line by interrupting the injection.
l it is to avoid storage beam abort initiated by a beam with large orbit deviation.
l pulsed diagnostic line enables emittance tuning in parallel with the injection.

Linac switch-yard No.3 (SY3) beam dump line
Linac beam switch-yard No.3 (SY3)
Linace+ beam
BT line for LER

e- beam BM

BT line for HER
Linac SY3 beam dump line
beam dumpl For HER injection, the bending magnet (BM) deflect e- beam to HER BT line.
l For beam diagnosis, the BM deflect the beam to east beam dump line.
l This switching takes several minutes for changing polarity and current alonghysteresis loop.

By replacing the existing large BM withtwo pulsed BMs,a DC BM for HER-BT anda DC BM for dump line,
pulse-by-pulse beam switching can be done.

32

33

beam lines proximityl New beam line for beam-dump runs in the vicinity of pole of thebending magnet for HER-BT line
l a magnetic shield is required to avoid the beam to be deflectedby leakage field from the poles
l the magnetic shield can deform the field distribution in between the poles
l careful designing of the shield required to meet the both requirements

bending magnet (BM_61_H1)
for deflecting the beam for HER-BT
magnet polebeam orb
beam
it for HER
orbit fr
-BT
om pu
l
s
e
beam
d bendorbit bing may energnet
gy switch

magn
etic shield

bending magnet (BM_61_A1)
for deflecting the beam
for the beam-dump

Pulsed beam switch-yardl Components to be installed in 2024 summer

pulsed bending magnets(BP_61_11, BP_61_12)
with ceramic ducts
BPM, screen monitor(SP_61_H1, SC_61_H1)

collimator(CO_61_H1)
DC bending magnet(BM_61_H1)
DC bending magnet(BM_61_A1)

34

Component preparation statusl DC bend BM_61_H1 (completed)l DC bend BM_61_A1 (completed)l beam duct for DC BM and magnetic shield (to be manufactured)l pulse bend BP_61_11, _12 (completed)l ceramic duct for pulse bends (completed)l beam collimator (to be manufactured)l beam position monitor, screen monitor (completed)pulsed bending magnet

DC bending magnet (BM_61_H1)

screen monitor

beam position monitor

35Summary (Linac upgrade with Pulsed Magnets)
l Achieved items
1. large aperture pulsed quads, ceramic ducts and new pulse drivers
installed in J-arc matching section in 2023 summerà flexible matching tuning for each beam mode
2. pulsed quads, ceramic ducts and ordinary pulse drivers
installed in e+,e- compatible optics region in 2023 summerà flexible focusing tuning for each beam mode
3. fast orbit kickers and pulse power supply
installed in J-arc, linac-end, HER-BT until 2024 January
à tuning of orbit difference between 1st and 2nd bunchesl remaining upgrade items and issues
v Pulsed beam switch-yard for beam diagnosis (in 2024 summer)v J-arc last DC quad will be replaced with pulsed (in 2024 summer)and coil replacement in the futurev fast orbit kickers in low energy region (sector-A) (in 2024 summer)and settling the jitter issue36