ARES Upgrade for Super KEKB

ARES Upgrade for Super KEKBARES Upgrade for Super KEKB

KAGEYAMA Tatsuya

for the KEKB RF ARES cavity group

• Introduction • Fundamental mode issues• HOM load issues• Input Coupler R&D• Summary

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KAGEYAMA, T. Super-KEKB WSNov. 28, 2003

2CA-2: T. Kageyama et al., “The Growth Potential of the ARES Cavity System toward Super-KEKB”, SAST’03

1P-071: 阿部哲郎、他『高周波入力結合器におけるマルチパクタリングの研究』、 SAST’03

1P-074: 竹内保直、他『炭化珪素セラミックスの誘電特性と HOM 減衰器設計への応用』、 SAST’03

Accelerator Resonantly coupled with Energy Storage

ARES3-cavity system stabilized with the π/2-mode operation

Accelerator Resonantly coupled with Energy Storage

ARES3-cavity system stabilized with the π/2-mode operationQuickTime˛ Ç∆

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Pumping Port

SC CC AC

GBP

HWG

Eight SiC tiles per Groove

Two SiC bullets per Waveguide

Tuner Port

Tuner Port

HCCCF

Input Coupler Port

Mode Shifting Groove

HWG

Two SiC bullets per Waveguide

GBP

CF

SS

C damper

AC: Accelerating Cavity (HOM-damped)

SC: Storage Cavity (TE013)

CC: Coupling Cavity damped with an antenna-type coupler (C damper)


Fundamentals of the ARES cavity systemFundamentals of the ARES cavity systemQuickTime˛ Ç∆


The longitudinal CBI (Coupled-Bunch Instability, µ = -1, -2, • • • ) driven by the accelerating mode, which is to be detuned downward from the fRF by ∆fa where |dfa| would amount to ~2Xfrev . cf. frev = 99kHz for KEKB

€

Δfa ∝ beamPacc. modeU

€

Δfa = −Isinφs2Vc

×R

Q× fRF = −

Pb tanφs4πU

Operation of a conventional copper cavity under the heavy beam loading (2.6A for KEKB LER) would bring on


Fundamentals of the ARES cavity systemcont’d

Fundamentals of the ARES cavity systemcont’dQuickTime˛ Ç∆


A flywheel is a device for storing energy or momentum in a rotating mass, used to minimize variations in angular velocity and revolutions per minute, as in a machine subject to fluctuation in drive and load.

S-cav functions as a kind of EM flywheel.

How to couple A-cav with S-cav is the most important issue.

C-cav engaged to stabilize the coupled cavity system with the π/2-mode operation and also suppress CBI due to the parasitic modes.



Fundamentals of the ARES cavity systemcont’dQuickTime˛ Ç∆


ks kaUs

damper

Ua

S-cav A-cavC-cav

π/2

π

0

mode

0.0001

0.001

0.01

0.1

495 500 505 510 515 520

π/2 mode

0 modeQL≈100

π modeQL≈100

frequency [MHz]

S21 response

QC-cav ≈ 50


€

UsUa

=ka

2

ks2 for /2 mode





• The stored-energy ratio of the π/2 mode:

• The EM field distribution of the π/2 mode is stable against detuning of A-cav (= ∆fa) loaded with the beam.

• The amount of detuning of A-cav can be reduced as:

• The parasitic 0 and π modes can be selectively damped (QL ≈ 100) with an antenna-type coupler attached to C-cav.

• Furthermore, the damped 0 and π modes are located almost symmetrically with respect to the π/2 mode. Therefore, their impedance contributions to CBI can be counterbalanced.

• C-cav functions as a filter to isolate S-cav from A-cav’s HOMs.

€

UsUa

=ka

2

ks2

€

Δfπ 2 =Δfa

1+Us /Ua


ARES Operation Status in KEKBARES Operation Status in KEKBQuickTime˛ Ç∆


LER (e+): 20 ARES cavities Total Vc = 8 MV (0.4MV/cav) Beam current (max.): ~1.8A Input RF power/cav: ~300kW HOM power/cav: ~5kW Trip rate: ~1/cav/3months According to stats for Apr.~Jun., 2003

HER (e-): 12 ARESs and 8 SCCsTotal Vc = 15 MV = 3.84MV(ARES) + 11.16 (SCC)Beam current (max.): ~1.1A

ARES cavities in the LER RF section Fuji D7

RF Parameters of the π/2 mode: Us / Ua = 9 R / Q = 15 Ω Q0 = 1.1 x 105 Pc = 150 kW / cav Vc = 0.5 MV /cav


ARES Upgrade for Super-KEKBARES Upgrade for Super-KEKB

LER: 2.6 A by 20 ARESsHER: 1.1 A by 12 ARESs + 8 SCCs







LER: 9.4 A by 28 ARESs

HER: 4.1 A by 16 ARESs + 12 SCCs

We are planning to remodel the accelerating cavity part and the HOM loads for Super-KEKB LER.

Coupling SlotWidth: 120 mmHeight: 160 mm

WG HOM Load

GBP HOM Load

1000 mm

Half-Cell CC

Grooved Beam Pipe

CC

AC

HOM WG


€

UsUa

=ka

2

ks2

ARES Upgrade for Super-KEKBFundamental mode issues

ARES Upgrade for Super-KEKBFundamental mode issues

2.6 A by 20 ARESs for LER∆fa = -200 kHz

9.4 A by 28 ARESs for LER∆fa = -710 kHz

CBI driven by the π/2 accelerating mode: We need to increase the stored-energy ratio Us / Ua. ∆fπ/2 = 71 kHz if Us / Ua = 9 unchanged. (cf. frev= 99 kHz)

CBI due to the parasitic 0 and π modes: We have investigated the impedance imbalance caused by larger detuning of A-cav.








CBI due to the π/2 modeCBI due to the π/2 mode

Table 1: RF parameters of ARES cavity for Super KEKB LER.

Us /Ua 9 15 18Coupling Slot 120 160120 175 120 182 W mm2

I 9.4 (2.6) A # of Cavities 28 (20) fRF 508.887 MHz h 5120 Vc 0.5 MV Q0 1.11 1.27 1.32

R/Q input Pc kW Δ f kHz

Numbers in ( ) for KEKB LER




CBI due to the π/2 mode (cont’d)CBI due to the π/2 mode (cont’d)QuickTime˛ Ç∆


100

101

102

103

104

9 12 15 18

Us/Ua

μ = −

μ = −

μ = −

Growth rates of the CBIs (µ = -1, -2, -3) due to the π/2 mode, plotted as a function of Us / Ua .

By increasing Us / Ua from 9 to 15, the growth rate of the severest CBI (µ = -1) can be reduced by one order of magnitude and down to = 1.5 ms, where some RF feedback system could manage to damp it.

Coupling Impedance of the π/2 mode loaded with 9.4 A for Us / Ua = 9, 15, 18.

S. Yoshimoto et al., “The -1 mode damping system for KEKB”, in this conferenceKAGEYAMA, T. Super-KEKB WSNov. 28, 2003

CBI due to the 0 and π modesCBI due to the 0 and π modesQuickTime˛ Ç∆


The damped 0 and π modes (Ua:Uc = 1:1 when Δfa = 0 kHz) are located almost symmetrically with respect to the π/2 mode ( ≈ fRF ).

For KEKB (Δfa = -200 kHz), Re[Z //] has a small asymmetry with respect to fRF.

|R+ - R-|max ~500 Ω/ARES → ~46 ms

cf. rad ~23 ms (KEKB)

0.0001

0.001

0.01

0.1

495 500 505 510 515 520

π/2 mode

0 modeQL≈100

π modeQL≈100

frequency [MHz]

S21 response

The EM field distributions (Ua:Uc) of the 0 and π modes aresubject to the perturbation of order of Δfa / (fπ - f0).

Δfa = -200 kHz (KEKB) 　→　 -710 kHz (Super-KEKB)

The delicate counterbalancing may be deteriorated in Super-KEKB.KAGEYAMA, T. Super-KEKB WSNov. 28, 2003

CBI due to the 0 and π modes (cont’d)CBI due to the 0 and π modes (cont’d)QuickTime˛ Ç∆


The CBI due to the 0 and π modes:

= 3.3 ms for Us / Ua = 9 (9.4 A) cf. = 46 ms for Us / Ua = 9 (2.6 A KEKB)

= 4.0 ms for Us / Ua = 15 (9.4 A) to be damped by longitudinal FB kickers

the first order term Δfa / (fπ - f0) where fπ - f0 ∝ ka (∝ Us / Ua)1/2 　

Top: Re[Z//] of the 0 and π modes

Bottom:Re[Z//] imbalance R+ - R- with respect to fRF.


ARES upgrade for Super-KEKBHOM load issues

ARES upgrade for Super-KEKBHOM load issues



HOM WG: Monopole & Dipole(V) HOMs

GBP: Dipole(H) HOMs

HOM-damped structure for ARESBased on the conceptual demonstrator ARES96Carefully designed to be smoothly embedded into the whole ARES schemeConsists of 4 HOM WGs and 2 GBPs (Grooved Beam Pipe)

1000 mm

Half-Cell CCCC

AC


WG HOM load (KEKB)WG HOM load (KEKB)QuickTime˛ Ç∆


WG HOM load: Two bullet-shape SiC absorbers at the end of the HOM WG. Each absorber directly water-cooled. Power capability tested up to 3.3 kW / bullet (26 kW / cavity).


GBP HOM load (KEKB)GBP HOM load (KEKB)QuickTime˛ Ç∆


GBP HOM load: 8 SiC tiles per groove, brazed to a water-cooled OFC plate. Power capability tested up to 0.5 kW / groove (2 kW / cavity).

SiC TileOFC SUS

Cooling Circuit

OFC

OFC Compliant Layer


HOM load status in KEKBHOM load status in KEKBQuickTime˛ Ç∆


0

1

2

3

4

5

0 200 400 600 800 1000 1200 1400

Total HOM PowerWG HOM PowerGBP HOM PowerPrediction from Cavity Loss FactorPrediction from GBP Loss Factor

LER Beam Current (mA)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

2 4 6 8 10

AC + 2 x GBP2 x GBPAC + 2 x CBP

Bunch Length (mm)

k (fundamental) = 0.12 V/pC

WG and GBP HOM powers per cavity measured in the KEKB LER, compared with theoretical predictions (z = 7 mm).

Loss factors computed for the whole damped structure (3D) and the GBPs (3D), together with those for a simplified axially symmetric structure (2D) with circular beam pipes (CBPs).KAGEYAMA, T.

Super-KEKB WSNov. 28, 2003

Prospect of HOM power for Super-KEKBProspect of HOM power for Super-KEKBQuickTime˛ Ç∆


Super-KEKB LER:9.4 A, ~5000 bunches, z = 3mm.

　　　　 Extrapolation

HOM data taken in KEKB LER: 1224 bunches, z = 7mm.

cf. KEKB LER design:2.6 A, ~5000 bunches, z = 4mm

0.1

1

10

100

0.1 1 10

2 x GBP (Nb=1224, BL=7mm)2 x GBP (Nb=4896, BL=4mm)2 x GBP (Nb=4896, BL=3mm)4 x HOM WG (Nb=1224, BL=7mm)4 x HOM WG (Nb=4896, BL=4mm)4 x HOM WG (Nb=4896 BL=3mm)

Beam Current (A)

WG HOM: ~80 kW / cavity

GBP HOM: ~20 kW / cavity


Upgrading WG HOM load for Super-KEKBUpgrading WG HOM load for Super-KEKBQuickTime˛ Ç∆


WG HOM load for Super-KEKB LER: ~80 kW / cavity

HPT’d up to 26 kW/cavity (3.3 kW/bullet) for KEKB: The limit due to the maximum RF power stably supplied by the current L-band klystron.

Perform HPT over 3.3 kW/bullet: Resume HOM load test bench, hopefully with a new klystron supplying more than 10 kW.

Increase # of absorbers per WG.


Upgrading GBP HOM load for Super-KEKBUpgrading GBP HOM load for Super-KEKBQuickTime˛ Ç∆


GBP HOM load for Super-KEKB LER: ~20 kW / cavity

HPT’d up to 2 kW/cavity (0.5 kW/groove) for KEKB.

Need to upgrade the power capability by one order of magnitude.

?A new design with directly water-cooled SiC absorbers.


GBP evolves into Winged ChamberGBP evolves into Winged ChamberQuickTime˛ Ç∆


Winged chamber loaded with directly water-cooled SiC bullets:

Developed under collaboration between the KEKB vacuum and ARES cavity groups.

Used in the movable mask sections in KEKB since 2002.

Perform HPT over 5 kW / bullet.

SiC

Slot

Beam Chamber

Y.Suetsugu et al., “Development of Winged HOM Damper for Movable Mask in KEKB”, Proc. PAC2003.


Input Coupler UpgradeInput Coupler UpgradeQuickTime˛ Ç∆


Over- and under-cut structure for impedance matching

Door-knob transformer from rectangular WG to coaxial line

Coaxial line WX77Dmultipactoring discharge problem

Coupling loop

Ceramic RF window

Monitor port for arc detectionCapacitive iris

ICF-203 flange

Monitor port for arc detection

RF power ( = Pc + Pbeam ) ~400kW for KEKB~800kW for Super-KEKB


Input Coupler Upgrade (cont’d)Input Coupler Upgrade (cont’d)QuickTime˛ Ç∆


RF power

Dummy load

S-cav (TE013 mode)Multipactoring-free

/2-mode terminator

RF power

HPT setup (old)RF power < 1 MW

HPT setup (new)RF power < 500 kWKAGEYAMA, T.

Super-KEKB WSNov. 28, 2003



HPT setupKAGEYAMA, T. Super-KEKB WSNov. 28, 2003

Input Coupler Upgrade (cont’d)Input Coupler Upgrade (cont’d)



SAST’03 1P-071: 阿部哲郎『高周波入力結合器におけるマルチパクタリングの研究』KAGEYAMA, T. Super-KEKB WSNov. 28, 2003




Single-surface MP @ the WX77D outer conductorRF input power: 160~180kW


TV camera


SAST’03 1P-071: 阿部哲郎『高周波入力結合器におけるマルチパクタリングの研究』

ΔT of the cooling waterfor the outer conductor



Dummy loadRF power

HPT setup (future)RF power up to ~1 MW



SummarySummaryQuickTime˛ Ç∆


By increasing Us/Ua from 9 to 15, the severest CBI (µ = -1) due to the π/2 accelerating mode can be eased by one order of magnitude and down to = 1.5 ms (Super-KEKB LER) where some RF feedback system could manage to damp it.

The growth time of the CBI due to the impedance imbalance between the 0 and π modes has been estimated as = 4 ms (Super-KEKB LER). Some longitudinal FB kicker system will be needed.

For Super-KEKB LER, we need to upgrade the power capabilities of the WG and GBP HOM loads to ~80kW and ~20kW per cavity, respectively. The GBP with indirectly water-cooled SiC tiles may evolve into a winged chamber loaded with directly water-cooled SiC bullets.

R&D of the input coupler for Super KEKB is being carried out with a new HPT setup using an S-cav. First, single-surface MP discharge on the outer conductor of the coaxial line section (WX77D) should be suppressed.

We should first resume HPT for the HOM loads, hopefully with an L-band klystron supplying more than 10kW.




And that’s all?And that’s all?


Documents

ARES Upgrade for Super KEKB