1KEKB Review 2012

Positron Source Upgrade
KEKB injector linac
Takuya Kamitani
KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

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SKB Injector
SuperKEKB injector

high current
gun
low emittanceRF gun3.5 GeV
10nC x 2 (prim. e-)
5nC x 2 (inj. e-)

1.1 GeV
Damping Ringcirc. 136 m

Bunch
Compressor

Energy-spread
Compression System
3T
RF gunS-bandlinac

PF

50 Hz (e+ or e-)pulse-by-pulse
mode switching
AR (later)
6.5 GeV e-

2.5 GeV e0.1nC x 1

LER, AR

4.0 GeV e+
4nC x 2ECS

e+ target &L-band+LAS
capture section

C-bandmodules

7.0 GeV e5nC x 2

HER

positron target relocation from 2-1 to 1-5
for energy margin in DR injection

1-3 1-4 1-5 1-6

1-7 1-8DR

2-1 2-2 2-3 2-4

target solenoid

FODO singlet system

L-band LAS

normal S-band

2-6 2-7 2-8Q triplet 3m

Large Aperture S-band

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

Q triplet 5m

3-2

Positron Source Upgrade items
 positron production target positron matching device
 capture accelerating structure capture DC solenoid positron beam line & quad focusing system damping ring, LTR, RTL

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

3

SuperKEKB Capture section

4

KEKB e+ capture section
 QWT system (2.0 T x45mm+ 0.4 T x8m)
air-core pulse coil
DC solenoids
 KLY1 (S-band) -> 2 x 1m 12 MV/m, aper 2a = 27 -> 25 mm
 KLY2 (S-band) -> 2 x 2m 10 MV/m, aper 2a = 25 -> 21 mm beam energy at capture section exit : 80 MeV
N(e+)/N(e-) = 10 % at 3.5 GeV linac-end
N(e+)/N(e-)/E(e-) = 2.5 %/GeV

SuperKEKB e+ capture section
 AMD system (6.0 T x200mm+ 0.4 T x15m)
Deceleration mode
flux concentrator
DC solenoids
 L-band-> 2 x 2m 10 MV/m, aper 2a = 39 -> 35 mm full L-band configuration
LA S-band -> 4 x 2m 10 MV/m, aper 2a = 32 -> 30 mm
 beam energy at capture section exit : 110 MeV
L-band + LAS configuration
N(e+)/N(e-) = 65 % at 1.1 GeV DR for comparable performancewith reduced costN(e+)/N(e-)/E(e-) = 19 %/GeV
KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

5flux concentrator
R&D+ SC solenoid

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)Flux concentrator BINP-type
 in collaboration with BINP,

prototype field measurement& high-power operation test
performed at KEK from Nov.
2010 to March 2011.

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

6

BINP FC breakdown issue
 Breakdown problem (vacuum

burst by sparking) above 7
Tesla field level investigation with BINP experts
continued at KEK until March
11 2011, collaboration work
interrupted by the Earthquake.
 investigation of the FC will be
performed at BINP by
disassembling the magnet
body.
 we continue collaboration
study for future upgrade of FC.
KEKB Review Comittee (2012.02.21)

abnormal pulse shape

Positron Source Upgrade (Takuya Kamitani)vacuum burst

7Flux concentrator SLAC-type8

 with helps of SLAC and IHEP

we are going to fabricate
SLAC-type FC for linac
commissioning from 2013
autumn and stable operation
at T=0.

SLAC-type FC at IHEPKEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)FC fabrication R&D
 careful discharge wire cut

processing is needed tohave smooth surface of FCslit.
 sapphire pulley and wire
support structure areprepared, test processing
soon starts.
 hardening of copper FC
body is necessary to shiftmechanical resonancefrequency from 50 Hz.
 manual pressing
 hard copper material (HRSC)KEKB Review Comittee (2012.02.21)

Heat Resistance, high Strength & Conductivity copper (Mitsubishi Material co.)hard even after brazing !
conductivity ~ 80% of OFC

Positron Source Upgrade (Takuya Kamitani)9FC simulation study design trial study in modified shape is ongoing for possible

performance improvement (by Zang Lei)forhigher peak ﬁeld
lower transverse ﬁeld
be5er adiaba6c ﬁeld

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

10

Superconducting solenoid11

 Beam irradiation tests are

performed to evaluate
quenching limit.
 No quench in 10 minutes at
3.2 Tesla with irradiation of
1.7 GeV e- beam of 6nC x2x 49 Hz. The Earthquake
has discontinued the further
study.
 Cost of refrigerator to makeup for radiation heating will
be a problem.
 need more time of R&D for
future e+ source upgrade
KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

1.7 GeV e- beam
6nC x2 x 49 Hz

12

Positron Production
TargetKEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

SKB positron target
 KEKB target was optimized to

KEKB e+ target

KEKB Review Comittee (2012.02.21)

pulsed air-core coil configuration.
 SKB target need to be optimized
to FC configuration.
 amorphous Tungsten is used at
T=0 and will be upgraded to
crystal. (precise axis alignment needed)

Positron Source Upgrade (Takuya Kamitani)13

target destruction issue

14

peak energy density

destruction limit

peak energy density of SKB target is 27 J/g below the limit 35 J/g,
but margin is small ! Needs some protection mechanism.
KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)electron bypass hole in target
 pulse-to-pulse e+/e- beam switch

by orbit bump with pulse steering
magnets.
 injection e- beam pass throughsmall hole in target assembly.
 to preserve e- low emittancee- orbit on the beam axis ande+ orbit 4 mm offset at SKB.
 FC axis at 3 mm offset considering
FC field center offset andDC solenoid on the axis.
 to avoid transverse kickby solenoid fringe field and spiralexcursion
KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

15

16

L-band &LAS (Large Aperture S-band)
components
development

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)why L-band + LAS ?
L-band large aperture (d=39~35mm) of accel. structure is desirable
for transverse acceptance of Positron Capture Section
 coprime (5:11) frequency relation is effective to sweep out
satellite bunches critical to DR radiation shield issue.
Full S-band (LAS) capture section gives comparable e+yield, but with plenty of satellite particles
LAS (Large Aperture S-band) medium large aperture (d=32~30mm) is desirable fortransverse acceptance of PCS and quad focusing system existing S-band rf source, SLED, DC solenoids areavailable & compact Q at FODO (reduction in initial cost)

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)17

L-band klystron 40 MW L-band(1298 MHz) klystron PV-1040

designed by KEK and Mitsubishi Electric
 compatible with existing S-band
modulator and KLY tank in KEKB linac
 first PV-1040 delivered in March 2010
 performance test since June 2011
 KLY operation spec. at SKB linac
30 MW x 1.5 us x 50 pps achieved !
 another two PV-1040 will be delivered,
we will have three L-band klystrons for(1) positron capture section(2) bunch compressor at DR(KLY data by(3) spare
S. Matsumoto)

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)18

klystron PV-1040 performance
Klystron Output

316kV; 1.5us, 50pps

Opera+on

Frequency

1300MHz

1298MHz

Output power

>40MW

30MW

Voltage<350kV<350kV

Perveance2±0.25μRF pulse width

4μs

1.5μs

Rep rate

50pps

50pps

Gain

>50dB

Eﬃciency>40%

Cathode Current

Establishedoperational spec. !

2011.9.30

RF Output(performance data
by S. Matsumoto)
KEKB Review Comittee (2012.02.21)

DesignCathode Voltage
Reﬂec6on

Positron Source Upgrade (Takuya Kamitani)

33.4MW19

L-band accelerating structure
 first L-band structure completed in March 2010
 operation test at test stand from April 2012
 RF frequency 1298 (=2856 x5/11) MHz
 traveling-wave structure (short rf pulse) constant gradient (2/3)pi phase advance per cell structure length 2.2 meter disk aperture 2a = 39.4 ~ 35.0 mm
 field strength 12 MV/m@15 MW input
 single feed coupler (with field symmetrized)
 attenuation constant tau = 0.26

(structure data
by T. Higo)
KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)20

L-band structure test stand high power

L‐band Klystronoperation test
stand in linac
tunnel (offline)

Upstairs Klystron Gallery
High power
RF LoadLinac Accelerator
tunnelKEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

21

built-in collinear rf power load
 L-band rf coupler limits DC

solenoid inner radius >= 180 mm
 for regular cell region, the radius
can be 130 mm
 with built-in collinear power load,
the output coupler can beomitted and end-tail become thin

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

22

Kanthal as rf absorber Kanthal (A1) : Fe (72.2%) + Cr (22%) + Al (5.8%) alloys
 trademark owned by Sandvik in Sweden used for making protective layer electrical insulator, high thermal conductivity
 melting point (1,500 °C)
 used for high power load in S-band structure at DESY

Kanthal cavity cellat DESYKEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)23

L-band Kanthal cell24

 various spraying techniquestudied for 50 times higher
surface resistance and layer
stability
 HVOF gives best
performance but bad layer
quality for slanted injection
 APS is the best candidate
no Coa6ng
Arc
APS
VPS
HVOF
DESY/LHTKEKB Review Comittee (2012.02.21)

α
1
60
80
50
120
50

ARC: Electric arc spraying
APS: Atmospheric plasma spraying
VPS: Vacuum plasma spaying
HVOF: High velocity oxy‐fuel coa6ng spraying
DESY/LHT: Coa6ng over a bonding layer (Ni‐Al)

Positron Source Upgrade (Takuya Kamitani)

waveguide and power load WR650 (165.1mm x82.55mm)
 evacuated waveguide25

Aluminium(A6063)E‐bendsystem (no gas inside) Al guides in most part +some Cu guides
 MO flange
Copperwaveguidewithdirec+onal
coupler

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)high power
SiC loadLarge Aperture S-band structure26

 LAS structures are used, in second unit of capture section
 in two accelerator modules just behind capture section

 large aperture and compact outer diameter existing rf source available
 existing DC solenoid available
 compact quad outside LAS structure compared with L-band

 cost-performance balance

KEKB Review Comittee (2012.02.21)

 traveling-wave structure
 constant gradient (2/3)pi phase advance per cell structure length 2.2 meter disk aperture 2a = 31.9 ~ 30.0 mm
 field strength 16.4 MV/m with SLED
6.9 MV/m w/o SLED two port input coupler (J-shape side-couple)
two port output coupler (ordinary shape) attenuation constant tau = 0.112

Positron Source Upgrade (Takuya Kamitani)

27

Beam optical design& tracking simulation

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)capture section solenoid field FC + DC solenoid field distribution determines transverse

acceptance of capture section and e+ initial emittance.

FC + DC Solenoid fieldpeak ~ 6 Tesla

KEKB Review Comittee (2012.02.21)

DC solenoid field(long range)

Positron Source Upgrade (Takuya Kamitani)

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29

compensation with huge solenoid adding three huge solenoid

compensates field dips inwaveguide regions.
 e+ yield estimation isunderway to judge whether
to install these hugesolenoids or not.

KEKB Review Comittee (2012.02.21)

parameters for a solenoid
module (L=447mm)

L-bandsolenoidHugesolenoid

outer radius (mm)

295

680

1-turn wire length (m)

1.28

3.79

# of turns

245

189

current (A)

650

650

wire cross section (mm2)

171

132

power consumption (kW)

14.1

48.3

weight (kg)

606

1341

Positron Source Upgrade (Takuya Kamitani)particle simulation
 e+ capture section (Zang Lei (GPT code), T. Kamitani) linac 1~2 sector + LTR (N. Iida (SAD code)) DR beam dynamics (H. Ikeda)
 RTL + linac 3~5 sector + BT-line (N. Iida (SAD code)) e+ capture section tracking
 e+ generation by GEANT4 or EGS4
 FC field evaluated by CST EM Studio DC solenoid field evaluated by CST EM Studio and data smoothedby approximating with analytic function
 L-band structures Eacc = 10 MV/m, aperture 2a = 35 mm
 LAS structures Eacc = 10 MV/m, aperture 2a = 30 mm
 acceleration and deceleration phase modes

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)30

tracking in capture section
 tracking results with GPTlongitudinal
phase space(by Zang Lei)transverse
phase space
animationtransverse
phase spacee+ survival curve

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)31

e+ capture animationfrom target to capture section exit (120 MeV)
Deceleration phase modein capture section

Energy (MeV)

Energy (MeV)

Acceleration phase modein capture section

longitudinal position (mm)longitudinal position (mm)Capture efficiency is comparable
in either mode.

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

32

optical matching & e- elimination
 optical matching fromsolenoid focusing region to
FODO quad system e+/e- separator chicane
and e- stopper for low
energy e- from target,(injection e- go beside thestopper) collimators to remove offmomentum particles(op6cs calcula6on
by T. Miura)
KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)33

e+ beam optics (before DR) quad focusing system FODO in 60 m + triplets in 45 m

before LTR to DR

improvedbeta-function

FODO

triplets

LAS(optics calculation
by T. Miura)
KEKB Review Comittee (2012.02.21)

ordinary S-band

Positron Source Upgrade (Takuya Kamitani)34

e- beam optics
 e- beam transport in e+ oriented optics of focusing magnet strength.

[e+/e- compatible optics] (because most of quads are existing DC
magnets in Sector1 and 2 before DR)
 in Sector3 ~ 5 after DR, most quads will be replaced with pulse magnets
for flexible optical setting for better matching in difference beam modes(e+, e-, PF e-)(optics calculation
by T. Miura)
KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

35

ECS in LTR & BCS in RTL

36

Bunch
Compression
SystemEnergy‐spread
Compression
System

BCS reduce bunch-lengthof e+ extracted from DR

ECS reduce energy-spreadof e+ entering DR

energy gradient by RF field+ non-isochronous arc

non-isochronous arc +energy correction by RF field
R56 = -0.61 m
Vc = 41 MV (S-band)
compression 1/3

Vc = 37 MV (L-band)
R56 = -1.05 m
compression 1/9

RTL
KEKB Review Comittee (2012.02.21)

LTR

schema6c view
scale is not precise !

Positron Source Upgrade (Takuya Kamitani)

compression performance+/-5.0%

ECS

8.0mm

BCS

37

+/-1.5%0.6mm(trackingby N. Iida)
KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

38

Schedule & Summary

Positron Source Upgrade (Takuya Kamitani)

Schedule

KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)

39

Summary concentrate on fabricating SLAC-type FC for T=0
 need consideration on target protection
 1st L-band structure to be high-power tested
 L-band collinear load in R&D
 waveguides & loads in fabrication
 L-band klystron 1st tube ready LAS structures in fabrication
 DC solenoid field dips are moderated by huge solenoids
 beam optical design almost OK
 particle tracking simulation is ongoing for e+ yield andhardware parameter optimization
 DR, ECS, BCS are in construction
KEKB Review Comittee (2012.02.21)

Positron Source Upgrade (Takuya Kamitani)40