Status of the Normal Conducting
Accelerating Cavities
for the MRs and DR
of SuperKEKB in JFY2013
Tetsuo ABE

JFY2013 starts on April 1st in CY2013
and ends on March 31st in CY2014.

For SuperKEKB‐RF / ARES‐Cavity Group(T. Abe, T. Kageyama, H. Sakai, Y. Takeuchi, and K. Yoshino)

The 19th KEKB Accelerator Review Committee Meeting
March 4, 2014

Main Ring (MR) Cavities

1

Accelerator Resonantly‐coupled with Energy Storage
3-cavity system stabilized with the /2-mode operationconsists of HOM-damped accelerating cavity (A-cav), Energy-storage cavity with TE013 (S-cav), Coupling cavity(C-cav)
with a parasitic-mode damper.

Along the beam axis
Perpendicular to the beam axis

Successful Operation of the 32 ARES Cavities at KEKB

2

Fundamentals of the ARES Cavity System

Δf a
Detuning against beam loading: Δf / 2 = fa / 10
1  Us / Ua
3

ARES Cavity System / Input Coupler / Performance Upgrade
Fine grooving inside the outer conductorof the coaxial line to suppress
multipactoring discharge.

The coupling loop is extended toincrease the input coupling factor.
The optimum input coupling factor βopt is givenby βopt = 1 + Pbeam/Pc .

Input Coupler
Power Handling Capability (Spec.)
PinputPc
Pbeam
SuperKEKB : 750 kW = 150 kW + 600 kW
KEKB: 350 kW = 150 kW + 200 kW
Pc = 150 kW generating Vc = 0.5 MV per ARES cavity.
T. Kageyama

3D Transparent View of ARES Cavity System

Increasing the Input Coupling Factor
Input couplers with increased input coupling (max = 56) needed for the stations with theKlys:Cav=1:1 configuration to accelerate beams with the design currents (Appendix A).

Used at the KEKB-MRs

With increased input coupling for the SuperKEKB-MRs

5

Typical cycle time of RF conditioning for one coupler
Includes:1) Setup & low‐level measurements : 2 days (net time: 8x2 = 16 hours),
2) Vacuum evacuation: 4‐5 days (about 100 hours), and
3) RF conditioning up to Pin= 750 : 15 days (weekdays only, net time: 8x15 = 120 hours),‐ 800 kWso that the cycle time is 1) + 2) + 3) + weekends = 4 weeks.

6

We have applied ozonized water rinsing (OWR) of ceramic
RF windows, followed by Baking
Based on the recipe for the SCC couplers
In parallel to HTP
1. Ozonized water rinsing (5 – 10 min)2. Baking (150degC x one week)

Ozonized water

Ceramic RF window

HTP

For more details, see
H. Sakai et al., “Ozonized Water Rinsing of RF Windows” (Japanese),in the Proceedings of the 4th Annual Meeting of Particle Accelerator Society of Japanand the 32nd Linear Accelerator Meeting in Japan (August 1-3, 2007, Wako, Japan).

7

Without OWR+Baking

With OWR+Baking

8Typical cycle time of RF conditioning for one coupler
Includes:1) Setup & low‐level measurements : 2 days (net time: 8x2 = 16 hours),
2) Vacuum evacuation: 4‐5 days (about 100 hours), and
3) RF conditioning up to Pin= 750 : 15 days (weekdays only, net time: 8x15 = 120 hours),‐ 800 kWso that the cycle time is 1) + 2) + 3) + weekends = 4 weeks.
 OWR+Baking
Includes:1) Setup & low‐level measurements : 2 days (net time: 8x2 = 16 hours),
2) Vacuum evacuation: 4‐5 days (about 100 hours), and
3) RF conditioning up to Pin= 750 : 8 days (weekdays only, net time: 8x8 = 64 hours),‐ 800 kWso that the cycle time is 1) + 2) + 3) + weekends = 3 weeks.
9ARES Cavity System / Input Coupler / Production & Processing
T. Kageyama (updated by T. Abe)

ARES
Storage Cavity

Input Coupler
used asOutput Coupler

Input Coupler
Under Test

High Power Test Stand

To 1MW Water Load

•
•
•
•

RF Power from
1MW CW Klystron(TOSHIBA E3786)

Snapshot of Status Monitor for RF Processing
Created by Mikio Tanaka (Mitsubishi SC)
under the supervision of T. Kageyama

Status & Plans
So far, 11 couplers have been processed up to 750‐800 kW.
Now, one coupler being processed.
By this March, one more coupler to be processed.
Couplers existing in the MR tunnel will be replaced with new ones for thestations with Klys:Cav=1:1 configuration.

For “T=0” in the 4th Quarter of JFY2014
JFY2014 starts on April 1st
in CY2014, and ends on
March 31st in CY2015.

10 input couplers
to be replaced in T<0

4 input couplers to be replacedin the summer shutdown
in 2015 (T>0)
No vacuum breaksince the KEKB operation ended.

11

Damping Ring (DR) Cavities

12

RF Accelerating Structure for the DR
Based on the ARES cavity with the long successful operation at KEKBBlue : Vacuum region
Gray : HOM absorber (SiC)

We can supply total Vc : 2.4MV
at maximum.
Very low comparedto the (Super)KEKB-MRs
More compact
than the SiC bullets
Pumping port on each cavity(Dimensions in mm)

400
Taper
Flange

1100

40

150

72

50
1200

Taper End

150
128
72
5308

50

50

300

150

256 150
72

72

300
50

200
Bellows

Taper End

1. Accelerating-Mode Frequency: 508.887[MHz] (same as for the MRs)
2. Cavity Voltage (spec.): 0.7[MV/cav] (Wall-loss power: ~120kW/cav)
3. Cavity Voltage (spec): 0.8[MV/cav] (Wall-loss power: ~150kW/cav)
4. Max. stored beam current: 70.8[mA]
5. HOM absorbers: Silicon Carbide (SiC) tiles (Appendix B)
6. Grooved Beam Pipe (GBP) common between cavities
7. Cavity-GBP Joint with a weld-ring gasket (not using a usual flange)
8. ”Multi Single Cell” structure
9. Reuse of high-power input couplers and tuners proven at KEKB-MRs/ARES
10. Good vacuum in cav. (~10^-6[Pa]) needed for high-power input couplers
11. Loss factor (incl. the taper sections): 2.4 [V/pC] (for zmm)
12. No coupled bunch instabilities (CBIs) due to this structure occur (Appendix C).

110
GV
13

Cavity No.1
Low‐ and High‐Power Test Results
Made in JFY2012
Tested in JFY2013

f a  508.887 MHz
Rsh Q 0  150 
Q0  30000

Appendix D Just after the delivery,
Cooling pipes not yet attached
14

The Endplates of Cavity No.1 Electro‐Polished (EP)

Endplate
w/o the tuning bump

Before EP
Ra=~1.5mMaterial: OFHC(class1)
Etching: 40m

(Skin depth@500MHz: 3m)

After EP

Ra=~0.2m

Endplatew/ the tuning bump

500mm15

Low‐Power Measurements (1/2)
Accel.‐Mode Frequency

1. Before the freq. tuning (inside: Air)
2. After the freq. tuning, before the brazing (inside: Air)
3. After the brazing, before the delivery (inside: Nitrogen)
4. During the setup work of the HPT (inside: Nitrogen)
5. Just before the start of the HPT (inside: Vacuum)+-100kHz

Accel.-Mode Frequency [MHz](converted to one with 30degC & vacuum inside) Target (508.887MHz)

Accuracy: 0.02% Achieved!
Measurement Number

16

Low‐Power Measurements (2/2)
Unloaded Q‐factor (Q0)
(Tuner Pos.:15mm)

97%IACS(Cf. 93%IACS for Prototype)

Coupling-Loop Angle [deg]17Setup of the HPTis the same as that of the prototype (Cavity No.0)
except for the control system improvements

18

Control System Improvements
to solve the RF Power Fluctuation Problem(Appendix E)(I) We measured Pin and Prefl with power sensors directly connected to thedirectional coupler in the radiation shield,
then transmit the values via the LAN to the D1 control room in digital.
(II) We laid new coaxial cables from the radiation shield to the D1 control room
for Pin and Ppickup (used in the feedback) and Prefl (used in the I/L).

19

(I) RF Power Measurements of Pin and Prefl close to the Cavity
in the Radiation Shield of D1‐A Test Stand The power sensors are directly connected to the directional coupler.
 The power meter is also put in the shield with its ethernet interface
connected to the control network.
Power Sensors
Ethernet Cable (CAT.6)
on the Control Network
Waveguide (WR-1500)

During this HPT, the sensors
and meter were surrounded
and protected with lead
sheets (5-10mm thickness)against radiation.

Power Meter

Directional
Couplers20

(II) Coaxial Cables:
Radiation Shield <‐> D1 Control Room
OLD

NEW

Laid ~30 years ago
~70m-long cables of 10D-WF-H50-S4
Total cable loss (meas.) : ~5.2dB (> spec.: ~3.6dB)

Laid in Jan., 2013
91m-long cables of 10D-WFLEX-FR
Total cable loss (meas.) : 4.4dB (< spec.: 5.5dB)

Above the ground High Accessibility

Under the ground Low Accessibility

21

Control System Improvements
to solve the RF Power Fluctuation Problem(Appendix E)(I) We measured Pin and Prefl with power sensors directly connected to thedirectional coupler in the radiation shield,
then transmit the values via the LAN to the D1 control room in digital.
(II) We laid new coaxial cables from the radiation shield to the D1 control room
for Pin and Ppickup (used in the feedback) and Prefl (used in the I/L).

No RF Power Fluctuation During this Test!
 Ready for Vc-holding endurance tests
with this improved environment

22

Just before the start of the HPT
Almost Full Radiation Shield

23

Pin – Prefl [kW]Pin – Prefl [kW]Vc [MV/cav]

Vc [MV/cav]

Aging Histories up to Vc=0.9MV/cav

The light blue lines indicate the reference vacuum pressure
specified by the computer controlled automatic aging.
If the vacuum pressure is higher than the reference, Pin isslightly stepped down until the vacuum pressure becomes
lower than the reference, and then Pin is slightly stepped up as
long as the vacuum pressure is lower than the reference.

 Pin (Prefl) : input power to (reflected power from) the cavity
 Wall-loss power: Pwall = Pin – Prefl = ~0.99 x Pin
 Vc calculation described in Appendix F
 The prototype cavity was not electro-polished.
 Better performance with electro-polishing for Cavity No.1
→ Lower vacuum pressure and lower trip rate Smooth conditioning for Cavity No.1
24

Setup of the HPT25

TV Camera Footages
when the I/L with Prefl worked
Time series: T1  T2  T3  T4
Surface Magnetic Field(Vc=0.82MV/cav)

(I/L)

(I/L)
Surface Electric Field

Explosion!

Lightning!

(Vc=0.82MV/cav)

T1

T3

TV Camera1

TV Camera 2 TV Camera1

TV Camera 2

T2

T4
26

As the conditioning progressed, these phenomena disappeared.
Conditioning progress confirmed also visuallyVc‐Holding Endurance Test
Vc
Wall‐Loss Power[MV/cav][kW]

Total Holding
Time [hours]

Number of
Cavity Trips(Appendix G)Time series 

0.80

144

30.5

1

0.85

164

18

0

0.90

186

14.5

3

0.95

210

8

1

(No vacuum-pressure spikes during this test)

Stable operation with Vc=0.8MV/cav verified Further conditioning effect expected No performance limit observed during this test27

Effects of EP Observed
Comparing the results between the Prototype and Cav.No.1
1. Higher Q0
2. Lower vacuum pressure during the HPT
3. Lower cavity trip rates
4. Lower radiation
 Less field emission
 Smaller local-field enhancement factors(Cavity No.1)(Measured, in the radiation shield, at the same position about 2m away from the cavity)

28

Mounting Test with the HOM Waveguide Loads
and Grooved Beam Pipes
has been Performed Successfully with Vacuum Sealing.
Four HOM Waveguide Loads
with SiC Tiles Inside (Appendix I)

Turbo-Molecular Pump

Movable Tuner

Sputter Ion Pump
Baseplate

Two Grooved Beam Pipes
with SiC Tiles Inside(Appendix J,K)

Status of Cavity No.2
• Passed a final vacuum leak test after the brazing• RF performance (low‐power) after the brazing: OK
Cavity No. 2(preliminary)fa
Q0

Cavity No.1
(published)

509.007MHz(=f0+120kHz)

508.977 MHz(=f0+90kHz)

30792（98%IACS)

30506 (97%IACS)(f0=508.887MHz)• Being fabricated almost in the final stage• To be High‐Power Tested in May‐June, 2014.
30

Summary on the DR Cavities
1. The accelerating structure for the DR
 Based on the KEKB‐MR/ARES cavity with the long successful operation at KEKB Cavity No.0 (prototype) made in JFY2011, and tested in JFY2012
 Cavity No.1 made in JFY2012 based on the prototype, and tested in JFY2013
 Cavity No.2 being made in JFY2013

2. Results of the High Power Test of Cavity No.1
 Smooth conditioning up to Vc=0.95MV/cav (Pwall=210kW)
 Vc limited by the radiation regulation for this test stand Clear effects of EP observed Stable operation with Vc=0.8MV/cav verified
 No performance limit observed up to Vc=0.95MV/cav→“Pass“
3. High‐Power Test of Cavity No.2
 To be performed this coming spring

4. X
X

31

Schedule of the MR and DR Cavities
 CY2014

in JFY2014

MR cavities related
DR cavities related

1. Apr.
• Setup change of the test sand (D1‐A): coupler  DR cavity• Installation of two “new” cavities (kept as spares) to the beam line in the OHO D4
RF section, including lip welding and alignment

2. May• Installation of six used cavities (moved HERLER) to the beam line in the OHO D5
RF section, including lip welding and alignment

3. May – June : HPT of DR Cavity No.2 @D1‐A
4. June – Oct. : Preparation works in the MR tunnel to (re)boot the 30 MR
cavities
5. Nov. – Dec. : RF conditioning of the 30 MR cavities

 CY2015
6. Jan. – Feb. : Installation of the DR cavities, including lip welding andalignment
7. Mar. : Check of the RF system for the DR, including the digital LLRF
8. Apr. : RF conditioning of the DR cavities
32

Fin

Appendices34

Appendix A

35(T. Kageyama, MAC’11)

Appendix B:

A Set of SiC Tiles for the DR Cavity/HOM‐WG or GBP
6 SiC Ceramic Tiles
Brazed on a Copper Plate

Copper Plate with a Cooling Channel(Y. Takeuchi)

SUS Frame for Welding
Cooling-Water Pipe Joint36

Appendix C (1/2):
Longitudinal Impedance of the RF section:
and CBI
Estimated from Finite-Difference Time-Domain parallel computations of GdfidL
with the PC cluster
̶ CBI threshold for Total V : 1.4MVcGrowth Time ＞ 20ms
＞ 5ms (rad. damping time)37

Appendix C (2/2) :Transverse Impedances of the RF section:
and CBI

Estimated from Finite-Difference Time-Domain parallel computations of GdfidL
with the PC cluster
CBI threshold for Total Vc: 1.4MV(Tuner Position: 30mm inside)
and a growth time of 30ms or 200ms

Growth Time ＞ 30ms
＞ 10ms (rad. damping time)38

Appendix D (1/2): Cavity (main body)Material: OFHC (Class1)
except for the flanges, ports, GBPs, and HOM-WGs
Mirror symmetry except for the E-bends, tuner, and monitor ports.
Two input-coupler ports, one of which is to be used as a pumping port

(Along the beam axis)

110deg

70deg

R=150

R=150

Cross-section: 240mm x 28mm

150

340

Tuner Port (ICF203)

525

Input-Coupler or Pumping Port (ICF203)

556 +- 3
View Port(ICF70)(Cross-section perpendicular to the beam axis)
150

256

150 (Dimensions in mm)

39Appendix D (2/2): Cavity (Main Body)
240
220

ICF34

200

ICF203

30
R10
4-R10
R10

256

63.9

55°

110

10(Nose Cone)

161.8

200(Nose Cone Top)

260

340

304

280(Nose Cone Region)

R10

16

28

(Along the Beam Axis)

ICF203

120.2
ICF70

(Perpendicular to the Beam Axis)

ICF203

Appendix E (1/2)

RF Power Fluctuation (1)~~ Fast ~~Klystron Output Power
Pickup Field

Arbitrary Linear Scale

Arbitrary Linear Scale

Pin measured in the D1 control room41

Appendix E (2/2)

RF Power Fluctuation (2)Recalibration Constants~~ Slow ~~Pin(corr) = cin x Pin(meas)
Prefl(corr) = crefl x Prefl(meas)

Recalibrated for calorimetric powers andpowers measured in the radiation shield42

Appendix F

How to Calculate Cavity Voltage (Vc )Pin , Prefl: Input and Reflected RF powers measured, respectively
Assuming the cavity to be tuned
Input Coupling Factor :

l

(HP)

(over-coupling)(HP: High Power)lUnloaded Q :

(HP)

(HP)

(We use Qext= 21814 from the LP meas.)(LP: Low Power)

Shunt Impedance :

(HP)

(HP)

(HP)

(HP)

(We use Rsh(HP)/Q0(HP) = Rsh(cold)/Q0(cold) =150from the simulation.)

Cavity Voltage :

(HP)

l

||
Pwall
For more details, see
T. Abe et al., “Development of RF Accelerating Cavity for the Positron Damping Ring at SuperKEKB” (Japanese),in the Proceedings of the 9th Annual Meeting of Particle Accelerator Society of Japan, 2012 (Paper ID: THLR06).

43

Appendix G : How to Identify “Cavity Trip” (1/2)
If the cavity pickup signal decays with a decay
time constant of 10m ( QL=15000),- - - Envelope of the Cavity Pickup(Appendix H)
Signal (508.9MHz)
it is NOT “Cavity Trip”.

When the RF Switch
turned off manually

When the output of the
Klystron fluctuated

2s

2s

44

Appendix G : How to Identify “Cavity Trip” (2/2)
If the cavity pickup signal decays much faster than 10m ( QL=15000),
it is “Cavity Trip”.
- - - Envelope of the Cavity Pickup(Appendix H)
Signal (508.9MHz)

2s

When a discharge occured in the cavity,(confirmed visually with the TV cameras, and the I/L with Prefl)
We can count real number of cavity trips.
For more details, see
T. Abe et al., "High Power Testing of the RF Accelerating Cavity for the Positron Damping Ring at SuperKEKB“ (Japanese),in the Proceedings of The 10th Annual Meeting of Particle Accelerator Society of Japan, 2013 (Paper ID: SAP057).

45

Appendix H: High‐Power Pickup Antenna

Port2: Pickup Antenna:

Port1: Input Coupler(Assuming 0.1% accuracy)

46

Appendix I: HOM‐WG Load
6 SiC tiles (=1set)20

12

Cross-section: 240 x 28
Material of the WG: SUS
HOM Absorber: SiC (Silicon Carbide) ceramics•Brazed on a copper plate•Water-cooled via the copper plate•Same as used for the KEKB-MRs/ARESPower Capability: 1.2kW/set(@1.3GHz)
Max. HOM Power absorbed: ~30W/WG
Max. Accl.-Mode Power absorbed: ~130W/WG (for Pwall=180kW)

HOM

Flange on the load

Flangeon the E-bend

300

50

50

(Dimensions in mm)

550

47

Appendix J: GBP (btwn)
Material: SUS
4 sets of SiC tiles (same as used for the HOM-WGs)
Max. HOM Power absorbed: ~200W/GBP (incl. the loss factor)
Max. Accl.-Mode Power absorbed: ~100W/GBP (for Pwall=180kW)
Loss factor: ~0.2 [V/pC] (for zmm)(Dimensions in mm)

4-R10
4-R3

544
340

45deg
4-R2

30

(Cross-section perpendicular to the beam axis)(Along the beam axis)

48Appendix K: GBP (end)Material: SUS
4 sets of SiC tiles
Max. HOM Power absorbed: ~200W/GBP (incl. the loss factor)
Max. Accl.-Mode Power: ~100W/GBP (for Pwall=180kW)
4-R10(Dimensions in mm)

544

4-R3

340

253

45deg
4-R2

30

HELICOFLEX flange(Cross-section perpendicular to the beam axis)(Along the beam axis)

49

EOF