Belle2 General Meeting
10 October, 2022

Linac status and upgrade during LS1

KEK e+/e- injector linac group
Takuya Kamitani

Contents of my talkl Linac statusvoperation history (injection beam charge)
vrecent improvement[1] RF-gun laser window replacement & addnl. pumping[2] RTL (from DR to Linac) Fast kicker
for DR extraction angle difference compensationl Linac upgrade items during LS1v[1] Pulsed quads at J-arc matching sectionv[2] Pulsed quads at e+/e- compatible optics regionv[3] Linac Fast kicker for bunch orbit difference tuning23

Linac Statusl Linac stably injects e-/e+ beams to HER, LER, PF & AR.

B
1.5 GeV@J-arcCA

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

1.1 GeV
Damping Ring
PFBunchCompression
System

2.5 GeV e0.1 nC x 1

Energy-spread
Compression System

S-bandlinac

1e+ target & 2
LAS capture section

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

LER

4.0 GeV e+
ECS 4 nC x 23e- Injection charge history
Q(e-) ~ 2.0 nC @RF-gun

45HER

7.0 GeV e4 nC x 2AR

6.5 GeV
e-e+ Injection charge history
Q(e-) ~ 11.5 nC @AT-gun
Q(e-) ~ 10 nC @target

Q(e-) ~ 1.7 nC @linac-end

T. NatsuiStart charge feedback(Laser feedback)Q(e+) ~ 5 nC @e+ capture sec.

Q(e+) ~ 3 nC @linac-end

[1] RF-gun laser window replacementl laser photon intensity attenuatedby dirt on inner surface of the quartz windowl Replaced the window to new onel Added an ion pump to mitigate degradation
X. Zhou
e- beamquartz
window
laser photon into RF-gun
vacuum chambernewquartz
or CaF2window

extensionductaddedpump4

5

e- beam intensity recoveredl RF-gun uses 2 lines of laser
l photon transmission degraded to 40% due to dirt on window
and dependent upon incident positionl e- beam intensity recovered by window replacement
e- intensity by 1st-line laser

new window
degraded window

1st-line laser incident position [mm]e- intensity by 2nd-line laser

M. Yoshida

new window
degraded window

2nd-line laser incident position [mm]

[2] RTL bunch orbit difference reductionl DR extraction kicker pulse shape madedifference in 1st/2nd e+ bunch orbits and injection efficiencies
l Fast strip line kicker installed for compensation
N. Iidal [1] Reduced bunch orbit difference
at BPM1 and 2Extraction kickers
l [2] Coincided injection efficiencies
at LER
Strip line kicker[2] inj. eff.

[1] orbit diff.
Strip line
kicker ON

BPM1

BPM2

6

7

fast strip line kicker
l Fast strip line kicker in RTL (DR to Linac) kicks only 2nd bunch(originally developed for KEK ATF)l Electric field type kicker

kick angle 0.14 mrad with +/- 8 kV
pulse length ~ 20 ns

K. Kodama, T. Naito
DR Extraction Kicker pulse

Strip Line Kicker pulse≒ 20 nsec

8Upgrade item [1] pulsed quad @J-arc
l beam optics situation @J-arc
v 180-degree J-arc has a special opticaldesign, so beam matching to periodic
focusing systems in straight lines
is essential to avoid beam loss anddegradation.
v optical mismatch tend to cause aparticle loss in primary e- beam oflarge emittance (KBP).
v tuning of quads for matching often
makes emittance degradation in
injection e- beam (KBE).

l motivation of pulsed quadv pulsed quads in matching section
enables independent beam optics
matching for each mode
Y. Seimiya, Y. Okayasu

e- beammatchingsection

matchingsection

e- beamachromatic &isochronousoptics

e- beam9optics matching simulation
l number of quads: 4 in entrance and 4 in exit (3 + 3 at present)l matching performance is evaluated by simulations
with random initial Twiss parameters.
l almost all cases, good matching result (Bmagx,y ~ 1) obtained
within designed field strength.

Y. Seimiya

field strengths after matching(plot boundary shows design limit)

initial unmatched
conditions

4BmagYat J-arc
entrance

after matching

32

1

PDR001 vs. PDR003
PFR002 vs. PFR004

65BmagY (Match Point)

564
PDR003/PFR004 [T]

64

3

20-2

2-4

1-600

123BmagX

456088776601234BmagX (Match Point)

56-6-4-202
PDR001/PFR002 [T]46PFR061 vs. PFR063
PDR062 vs. PDR064

6432

PFR063/PDR064 [T]

5BmagYat J-arcexit

BmagY (Match Point)

454320-22-4

11-6001234BmagX

567

800

123456BmagX (Match Point)

78-6-4-202
PFR061/PDR062 [T]4610specification 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 power
supply.
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]56600

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

11

new pulse power supply
l new pulse driver
Max Voltage [V]for J-arc pulsed quads
Max Current [A]is developing.
Magnet inductance [mH]Control method

3-5 sector typeNew pulse driver

230

400

330

600

11.5

ID-VGE analog

Pulse WidthModulation

controlT. Natsui

Upgrade item [2] pulsed quad in Sect-1, 2l e+/e- beam optics situation in Sect-1, 2v beam optical design in the region (after e+ capture section to LTRentrance) is optimized for e+ beam transmissionv unfortunately, plenty of DC quads are used for this optics
v e- beam (with higher energy) experiences very weak focusing withlarge betatron function
v slight orbit deviation causes emittance growth of e- beam

l motivation of pulsed quad installationv beam optics simulation shows that
installation of only four pulse quads achieves
significant reduction of the betatron function
and suppression of emittance growth

12

13

magnet layout in Sector-1, 2
l quads wrapping around the accelerating structure cannot bepulsed because of eddy current in the copper
l only quads in between the structures can be pulsed
l four quads shown below are replaced with pulsed magnets
beam line layout in Sector-1, 2Y. Seimiya

emittance growth reduction by low beta optics

14l lower betatron function can be achieved by setting four pulsed
quads to e- oriented focusing strength
l it can reduce emittance growth rate less than half
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 functione+ 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 bereplaceable with existing DC
quad and duct.
l current and turns/coil are
optimized to be compatible
with the existing pulse
power supply.
K. Yokoyama

parameters

DC quad17_14 type

new pulsed
quad 17_14

bore diameter [mm]4432

field gradient [T/m]

20.9

23.6

max. current [A]80300

pole length [mm]160160effective length [mm]173.8168.0

B’L [T]

3.63

3.96

nI [A.turn]

3760

2400

turn of coil /pole47

8inductance [mH]

32.3

0.94

15

Upgrade item [3] Linac Fast Kicker
l 1st/2nd bunch orbit difference tuning is important because ofv Injection efficiency improvement for both of bunches
v Suppression of emittance growth with orbit offset in linac
v Reduction of beam loss due to orbit differencel Requirements for the linac fast kicker
v pulse rise time < bunch interval (96 ns)
v sufficient kick angle ~ 0.4 mrad @1.5 GeV
BL = 2.0 x 10-3 T.m16

17

Ceramic chamber type Fast Kicker
C. Mitsuda

dipolefieldl CCiPM : Ceramics Chamber with integrated Pulsed Magnet
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).

Pulse power supply for fast kickerl Characteristics of pulse power supply
v SiC FET high-voltage switch(supplied by Nexfi company)v pulse rise time < 96 nsto kick only 2nd bunchv max current 1000 Av mac voltage 20 kV
v precise timing control
for kick angle fine tuning
v switch module installed in the tunnel
close to kicker magnet(needs thick radiation shield)
Y. Enomoto, T. Natsui, Y. Okayasu

first prototype
pulse power supply
at test stand18

Fast Kicker Installationl The first prototype of ceramic chamber type fast kicker
has been installed in summer of 2022 in J-arc.
l Stand-alone operation test and beam-kick test in this winter.
Y. Okayasu

e- beame- beame- beaml Next two kickers will be installed at linac Sector-4 and 5
in summer of 2023 for the operation after LS119

Summary & schedule

20

l Linac status & recent improvementsv Linac stably injects e-/e+ beams to HER, LER, PF & AR.
v [1] e- beam intensity recovered by RF-gun laser window replacementv [2] e+ bunch orbit difference compensated with fast strip line kickerl Linac upgrade items during LS1
v [1] Installation of 8 pulsed quads at J-arc matching section
for independent optics matching for each mode (summer of 2023)v [2] Installation of 4 pulsed quads at Sector-1, 2
for e- beam betatron function reduction (summer of 2023)v [3] Installation of ceramic chamber type fast kicker
for 1st, 2nd bunch orbit difference tuning
first prototype (installed in summer of 2022),
operation test (this winter)
2nd, 3rd model (summer of 2023)