ARES Cavity SystemforSuperKeKB＊KEKB Machine Review
2010.02.16
KAGEYAMA, T.
KEK Accel. Lab
ARES Cavity Group
T. Abe, T. Kageyama, H. Sakai, Y. Takeuchi, K. Yoshino＊SuperKeKB stands for Nano Beam Scheme / SuperKEKB for High Current Beam Scheme in my presentation.

CONTENTSn

Overviewn

ARES Operation for SuperKeKBProjection, especially for LER✦•

CBI† issues•

Tuning range for the accelerating cavity•HOM power absorber issues
R&D✦•

Input coupler upgrade•

RF accelerating structure for DR (Talk by T. Abe)

†Coupled Bunch Instability

ARES Cavity System for KEKB
Flywheel energy ratio
US /UA = 9
Δfπ/2 = ΔfAC / (1+US/UA )Parasitic (0 & π )Mode Damper

Storage Cavity(SC)

Four HOM Waveguides (HWG)
at the upper and lower sides of AC.
Two SiC bullet-shaped absorbers
per HWG.

Two Grooved Beam Pipes(GBP) at both ends of AC.
Eight SiC tiles per groove.

Coupling
Cavity (CC)
Accelerating
Cavity (AC)Input Coupler
400 kW,β = 3.0 ~ 3.6

3D Schematic View of ARES Cavity System

KEKB RF System

At present, 32 ARES cavities in operation, 20 for LER and 12 for HER.

Regular Configuration of NC RF System for KEKBNC RF System Configuration for SuperKeKB

Two OHO RF stations (D5C and D5E) already have this configuration
to support the HER beam, where the total current has reached 1.35 A.

Conceptual Sketch of SuperKeKB RF System

Reuse 26 out of the 32 ARES cavities, 18 for LER and 8 for HER.

absorbers per HOM WG

Fundamentals of ARES Cavity System

The flywheel energy ratio US /UA = 9 unchanged for SuperKeKB.

absorbers per HOM WG

Operation of ARES Cavity System
for SuperKeKB LER (3.6 A)

Flywheel Energy Ratio US /UA9Cavity Voltage Vc

0.47 MV

Detuning Frequency Δfπ/2 / ΔfAC-28 kHz / -280 kHz

Input Coupling Factor β

5.1

CBI due to the Acc. mode

τ = ~ 5 ms

CBI due to the 0 and π modesτ = ~ 30 ms

CBI due to the HOMs
(the fastest longitudinal driven
by ~300 Ω at 1.85 GHz)

τ = ~ 15 ms

RF feedback

bunch-by-bunch FBCBI due to the Accelerating Mode (π/2)Δfπ/2 = -28 kHz
KEKB LER
20 x ARES (0.4 MV, β＝3)Δfπ/2 = -17 kHz for 1.8 A

Re(Z//) [Ω]SuperKeKB LER
18 x ARES (0.467 MV, β = 5)Δfπ/2 = -28 kHz for 3.6 A( f - frf ) / frev

Δfπ/2 = ΔfAC / (1+US/UA )CBI due to the Accelerating Mode (π/2)

SuperKeKB LER
18 x ARES (0.467 MV, β = 5)

τ (-1 mode) = 5.2 ms for 3.6 A

(R+ − R−) / Cavity [Ω]Re(Z//) / Cavity [Ω]CBI due to the Impedance Imbalance
between the Parasitic 0 and π Modes

SuperKeKB LER 3.6 A
τ = 30 ms for ΔfAC = -280 kHz

KEKB LER 1.8 A
τ = 70 ms for ΔfAC = -170 kHz( f - frf ) / frev
ΔfAC = (1+US/UA ) Δfπ/2

Tuning Range for the Resonance Frequencyof the Accelerating Cavity-140 kHz+100 kHz

fRF-410 kHz

Accelerating Cavity Freq. [MHz]from Freq. Meas. Data for AC#03~#25
out of ARES Cavity Production AC#01~#28 at MHI

fH
fave
fL-5 mm+50mm

Tuning Plunger Insertion [mm]Min | Δf tuner + Δf thermal | = 390 kHz > |ΔfAC | = 280 kHz
Δf tuner = -310 kHz ~ -550 kHz
Δf thermal = -80 kHz for ΔT = +10 K
not include Δf (tuner travel from 0 mm to -5 mm) = ~ -100 kHz

HOM Power Absorbers

Storage Cavity(SC)

Four HOM Waveguides (HWG)
at the upper and lower sides of AC.
Two SiC bullet-shaped absorbers
per HWG.

Two Grooved Beam Pipes(GBP) at both ends of AC.
Eight SiC tiles per groove.

CouplingCavity (CC)

AcceleratingCavity (AC)3D Schematic View of ARES Cavity System

HWG Load

400 mm

ああY. Takeuchi

Each HOM WG (HWG) is terminated with two bullet-shaped SiC absorbers.
The power handling capability = 2.5 kW / bullet (5 kW/HWG, or 20 kW/cavity).

Vacuum Pressure [Torr]

GBP LoadRF Power [W]
300 mmAbnormal vacuum pressure riseobserved above ~1.2 kW.
Y. Takeuchi

Each groove has eight SiC tiles brazed to a water-cooled copper plate.
The power handling capability = 1.0 kW per groove,
80% of the power level where the abnormal vacuum pressure rise starts.

HOM Power Estimation for SuperKeKBKEKB LER
Sep. 21, 2004

SuperKeKB
LERIbeam [A]

1.6

3.6--

Nbunch1293

2503--σz [mm]76--k [V/pC]

0.40 (0.39†)

0.44--

PHOM /ARES
[kW]

5.4†

17--

PHOM /HWG
[kW]

1.05†

3.3

5.0

5.0/3.3 = 1.5

PHOM /Groove
[kW]

0.3†

0.93

1.0

1.0/0.93 = 1.1

calorimetric measurement†

RF Power Handling Capability
Factor of Safety
verified at 1.3 GHz

Backup Design for HOM-damped AC(originally studied for SuperKEKB)
R&D being continued
as a side businessof the development of
the accelerating
structure for DR.

T. Abe and Y. Takeuchi

Replace the grooved beam pipes with winged chambers.
Each wing equipped with a bullet-shaped SiC absorber.

absorbers per HOM WG

Input Coupler Upgrade

Storage Cavity(SC)

Input Coupler

CouplingCavity (CC)

Accelerating
Cavity (AC)upgraded to800 kW
βmax = 6
for SuperKeKB

3D Schematic View of ARES Cavity System

Input Coupler Upgrade
Monitor port
for arc detection
Door-knob transformer
from rectangular WG
to coaxial line

Over- and under-cut structure
for impedance matching
Ceramic RF window

Fine grooving on the outerconductor surface (yellow part)to suppress multipactoring
discharge. (by T. Abe)

Coaxial Line WX77D

CouplingLoop

RF Power ( = Pc + Pbeam )400 kW for KEKB
800 kW for SuperKeKB

Monitor port
for arc detection

Capacitive iris

ICF-203
FlangeCoupling Loop Height
extended from 20 mm
to 40 mm for βmax = 6.

High Power Test Stand for the Input Coupler
Storage cavity

Input coupler usedas output coupler

To 1MW water load

Input coupler under test
(up to 900 kW)

RF Power from1MW CW Klystron(Toshiba E3786)

Power handling capability over 800 kW has been demonstrated
for the current type of input coupler for KEKB.

Fine grooving on the outer conductor surface of the coaxial line
in order to suppress the multipactoring discharge.

T. AbeSuccessfully demonstrated at the test stand first,
and in the actual operation for KEKB.

Input Coupling Factor vs. Loop Height-3 %Optimum Design

KEKB

Unloaded Q Value

β (Input Coupling Factor)

copper spacers

Prototype

Loop Height [mm]Loop Height
K. Yoshino, H. Sakai, T. Kageyama

A prototype coupler with a loop height of 60 mm is under fabrication.
High power testing is scheduled in April. If the test results are OK,
it will be installed on the ARES cavity at D5C in May.

ARES CAVITIES ARE GO!

影山達也

THANK YOU SO MUCHFORYOUR ATTENTION.