ARES Status 2004(JFY)
Tetsuo Abe
for KEKB-RF/ARES-cavity group

High Energy Accelerator Research Organization (KEK)＜Outline＞
1. Fundamentals of the ARES-cavity system
2. Operation status
3. D04C/ARES multipactoring problem
4. Summary

KEKB Review@KEK2005.02.21

Accelerator Resonantly-coupled with Energy Storage
3-cavity system stabilized with the π/2-mode operationconsists ofz HOM-damped accelerating cavity (A-cav)
z Energy-storage cavity with TE013 (S-cav)z Coupling cavity(C-cav)with a parasitic-mode damper

Along the beam axis
Perpendicular to the beam axis
2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)1Operation with the Accelerating π/2 Mode The field of the π/2 mode is thestablest againstz Beam loading,z Detuning of A-cav (=Δf a ) The stored-energy ratio: Us/UaÆ can be changed
Us ka2=
Ua k s2Δfπ / 2 =Δf a
1 + Us / Ua

 The parasitic 0 and π modesÆ can be damped selectivelyout of C-cav (C-damper)

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)2

Energy-storage Cavity (S-cav)¾Q0(S-cav) =~ 1.7x10^5¾Stores large electromagnetic energies in TE013¾To suppress the longitudinal CBIs
Optimum detuning ∆f = ωR − hω0
I sin φs Rafa=−2Vc Q0= −Pb tan φs
4π U∆fπ /2 =∆f aUa∆f a =
1 + Us Ua
Ua + Us

Ua : energy in A-cav
Us : energy in S-cav=9 (in KEKB)
Δf a : optimum detuning of A-cav

Δ f a = −200 kHz in KEKB/LER

S-cav’s（ 2.6A, 20 sets）

Δf a = 710 kHz in SuperKEKB/LER（9.4 A, 28 sets）

Cf. f rev = 99kHZ

Movable tuner on A-cav

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)3

ARES in the KEKB Tunnel
Design Parameters
Vc

0.5MV

Ra/Q015 Ω

Q011x10^5Pin400kW

Pc

150kW

Us/Ua

9(Waveguide from klystron)

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)4Operation Status @(Jan.~Feb., 2005)¾ LER: 20 cavities
z Total Vc:
8.0MV (0.4MV/cav)
z Beam current: ~1.6A
z Input RF power /cav: ~300kWz HOM power:>~ 5kW
z Trip rate:<1 /cav /3months¾ HER: 12 cavities (+ 8 SCCs)z Total Vc = 15MV (Å13MV)= 4.09MV(ARES) + 10.91MV(SCC)(0.34MV/cav)

z Beam current:~1.20~1.27A

z Trip rate (ARES): < 1 /cav /3months

Stable Operation!!!
2005.02.21 KEKB Review

ARES cavities in the LER RF section

ARES Status 2004(JFY)by T. Abe (KEK)5

D04C/ARES Multipactoring Problem--- worse vacuum and discharge ---HER beam current [mA]

CCG [V]z The vacuum in the ARES cavities(No.1 and No.2) of the D04C station
became worse significantly (~3 times).
z Even with lower Pkly-out and/or Vc
z No conditioning effectz Input-power dependencez Discharge in the input couples
observed with the TV cameras
6.8x10^-6 Pa

2.3x10^-6 Pa

Vac(D04C-cav1)
Vac(D04C-cav2)
Vac(D05C-cav1)

Input coupler

Nov. 2003
Example of the discharge snapshotsÆ

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)

6The input couplers were wipedwith dilute sulfuric acidin Nov. 2003 (winter shutdown)

BeforeAfterSoot?

Clean!

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ARES Status 2004(JFY)by T. Abe (KEK)7

Still bad! (on cav1)

HER beam current

Vac(D04C-cav1)
Vac(D04C-cav2)
Vac(D05C-cav1)

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)8

In the summer shutdown 2004
zTwo input-couplers replacedzInput-coupler ports scraped
zIon pumps replacedzHigh power test (with no beam) ÆOK
9The vacuum condition was good.
9No discharge observed
9We reached a target power soon!

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)9Again bad on Cav1in the KEKB operation

HER beam current

Vac(D04C-cav1)
Vac(D04C-cav2)
Vac(D05C-cav1)

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)10

OptionsI.

To leave the cavities as they areÆÆII.

No effort, no cost and no time to be spent
Might cause terrible accidents.

To replace the whole ARES cavities
Æ
Æ

III.

Effort, high cost and long time to be spent
No guarantee (?)

To do studies, not to replace the cavitiesÆÆ

Effort and time to be spent, free of costMore scientific2005.02.21 KEKB ReviewARES Status 2004(JFY)by T. Abe (KEK)11

ChoiceI.

To leave the cavities as they areÆÆII.

No effort, no cost and no time to be spent
Might cause terrible accidents.

To replace the whole ARES
ÆÆ

III.

Effort, heigh cost and much time to be spent
No guarantee (?)

To do studies, not to replace the cavitiesÆÆ

Effort and time to be spent, free of costMore scientific2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)12

Simulation Study on the Multipactoringin the coaxial line of the Input Couplers

 Solving eq. of motion with theRunge-Kutta method
 Assuming the SEY of conditionedcopper Count number of collisions.
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ARES Status 2004(JFY)by T. Abe (KEK)13

Multipactoring Zone from the Simulation

Over-coupling

Under-coupling

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)14OLD route before summer 2004
Vc(D04C)=0.54MV

Recovery (no beam)
D04C-cav1 data
in 2004.05.09_13:41:45-14:50:00

Be
amcIn
ree
as

Over-coupling

Under-coupling

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)15Machine StudiesSearch for an operating region withz good vacuum,
z no discharge,z low trip rate

based on the simulation results.
(at the D04C klystron)(in the D04 local control room)

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)16

NEW route in 2005
With a higher Vc(D04C)=0.68MV

Recovery (no beam)
Be
amc
Inree
as

Over-coupling

Under-coupling

D04C-cav1 data
in 2005.01.30_16:37:45-17:50:00

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)17

Comparison with the Data

After aging

Measurements

Good Agreement !
D04C-cav1

Simulation

Measurements

Simulation

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ARES Status 2004(JFY)by T. Abe (KEK)18

Prediction comes true!

Measurements
D04C-cav1
Base pressurein the other cavities

Simulation
D04C-cav1 data
in 2005.02.13_18:23:40-18:25:30

2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)19

But the region is not so wide.

D04C-cav1 data
in 2005.01.28_22:40:00-23:22:00

HER beam current

Vac(D04C-cav1)
Vac(D04C-cav2)

HER beam current

LER inj.

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ARES Status 2004(JFY)by T. Abe (KEK)20

Considering the fact that
“Cavities out of condition are in a minority”,

We can keep an input RF power in a region witha good vacuum condition by changing the cavity
phase (or beam loading) automatically.

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ARES Status 2004(JFY)by T. Abe (KEK)21

Scan of the vacuum pressure
and a target power region

Targetregion

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ARES Status 2004(JFY)by T. Abe (KEK)22

HER beam current

BeforeVac(D04C-cav1)
Vac(D04C-cav2)

After

AutoPhaseChanger ON
Monotype Corsiva

Quick passage through the multipactoring zone!
2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)23

BeforeHER beam current
Vac(D04C-cav1)
Vac(D04C-cav2)

After

AutoPhaseChanger ON

No beam-current dependence!
2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)24

BeforeD04C-cav1 data in CIM(Vc(D04C)=0.68MV)

After

AutoPhaseChanger ON

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ARES Status 2004(JFY)by T. Abe (KEK)25

AutoPhaseChanger ON

HER beam curre

Feb. 3Feb. 4Vac(D04C-cav1)
Vac(D04C-cav2)

Feb. 52005.02.21 KEKB Review

Feb.6
ARES Status 2004(JFY)by T. Abe (KEK)26

Summary and Future 20+12 ARES cavities are working well.
Æ Low trip rateÆ Stable operation

 D04C/ARES multipactoring problem
Æ Good operating region found by the simulation and machine studies
Æ Solution: keeping an input RF power in a region with a goodcondition by changing the cavity phase automatically.
Æ The feedback program has been working well since Feb.4.

 R&D activities for SuperKEKB
Æ To be continued on the tomorrow’s talk…
2005.02.21 KEKB Review

ARES Status 2004(JFY)by T. Abe (KEK)27