DTL, S(F)DTL & CCL

KEK Fujio Naito

　 Cavity fundamental & technology of J-PARC linac

Contents

•I. Introduction to the RF cavity.

•II. Short story of beam motion

•III. DTL & SDTL for J-PARC.

•IV. ACS

Block diagram of the linac for J-PARC

Current Average 675 μA Peak 50 mAPulse Pulse width 500 μsec Repetition 50 Hz Chopping ratio 56 % RF duty (600μsec) 3 % Beam Energy 400 MeV Momentum width Δp/p = ±0.1 % (100 %) Emittance 3~5 πmm-mrad (99 %)

Requirements for the linac of J-PARC

Microwave in the cylindrical waveguide

Microwave in the pill box cavity

Multi cell cavity

I. RF field in the cavity

Cylindrical coordinates (r,θ,z)

Wave equations for Ez & Hz.

i) Ez ＝ 0, Hz ＝ 0 (TEM)ii) Ez ＝ 0, Hz≠0 (TE)iii) Ez≠0, Hz ＝ 0 (TM)

TM mode: Standard mode for RF accelerating cavity since Ez≠0.

Mode of the traveling wavefor z-direction

Solution for Ez ( TM mode )

Boundary conditions:•R is finite at r=0.•Ez, Eθ is zero at r=a. ( a: cylinder radius )

A2=0,Jm(kca)=0, n-th root:Pmn=kca then kc=Pmn/a

Solution for R

Bessel functions

( P01=2.405, λc=2πa/P01=2.61a )

Electric field pattern of the TM 01 mode

(Tangent of the dispersion curve)= vg/c

(Tilt of the line) = vp/c

Dispersion curve

(Forward wave) + (Backward wave) = (Standing wave)

TM010

TM011

TM012

Boundaries for z-direction (cavity)

TM modes in the cylindrical cavity

Principle of the DTL

TE modes in the cylindrical cavity

( EPAC2000, Kesler, et al. )

*Advantages High Q High Z

*Disadvantages Et≠0 Ez: non-uniform

TE111

Inter-digital H (IH) structure linac

Dispersion curve for the cylindrical cavity

DTL-1 for J-PARC

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Ez distribution for DTL-1

(Forward wave) + (Backward wave) = (Standing wave)

TM010

TM011

TM012

Boundaries for z-direction (cavity)

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Ez distribution for DTL-1

Pill box cavity (TM010)

Transit time factor

If E(z,0)=constant,

Energy gain & Transit time factor

Z: shunt impedanceZTT: effective shunt impedance

Q-value

Other mportant parameters

ZTT

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Measured Ez of the first 3 cells of DTL-1

Ez distribution of SDTL-3

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Example) 2 cells case

Freq( 0-mode) < Freq.( π-mode )

Multi-cells cavity

EM field in the magnetically coupled 2 cell cvity

f(0) > f(π)

Dispersion curve (Brillouin zone)

Vg=0

Vg=0

Vg=(max)

Infinitely long cavity-chain structure

APS

ACS

SCS

π/2 mode cavities

EM field in SCC 0 π/2 π

f(0) < f(π/2) < f(π)

Et≠0

Bridge coupler

TM010 mode ( +TM014 )

TM012 mode ( +TM010 )

TM010 π/2 mode

Bridge coupler for ACS

•Longitudinal　oscillation•rf　defocusing　• (　Transverse　oscillation　)

II.　Beam　motion　in　the　DTL

Velocity of particles

Phase stability principle

øs ≠ 0　　　　 　〜30

Phase acceptance ~ 3 |øs|

RF defocusing

III. DTL & SDTL for J-PARC.

•RF power source: Klystron

•Tunable & compact quadrupole magnet in the DT

•Precise alignment of DTs in the tank.

•Higher Q-value of the tank

•Uniform & stable accelerating field

Requirements for DTL & SDTL:

R&D subjects

•Periodic Reverse (PR) Cu electro-forming method

•Thick Cu plating on the tank inside

•Compact quadrupole electro-magnet in the DT

•Shield of ceramic vacuum chamber (by Vac. Gr. )

•DT alignment ( Results )

•Post-coupler tuning

•( Input coupler )

Layout of the DTL for J-PARC

Inside view of the DTL-1

A smooth deposit is obtained by periodically reversed current using a low copper-content acid copper sulfate bath containing no organic additives.

Advantages of the PR process;(1) It produces thick deposit with smooth surface.(2) Deposit by this process has high electrical conductivity, 　　　　　 low outgassing and sufficient thermal stability.(3) Mechanical properties of deposit is controllable.

+

-t

Electroforming

Electropolishing

( Test cavity : (-) 20 sec (+) 4 sec )

Periodic Revers

e (PR) Electroforming without brightning agent ~ OFC

(1) pre-processing on the inner surface of the iron cylinder for the followed electroforming;(2) first PR copper electroforming (+0.5 mm); (3) lathing the copper surface (-0.2 mm);(4) 2nd electroforming(+0.5mm);(5) lathing(-0.2mm);(6) finishing by the electropolishing (-50μm), of which the depth has been chosen in order to get the better surface condition.

Standard fabrication process of PR elctroforming of Cu for the cavity:

Types of electroforming applied to specimens and IACS [%]reference material

Acid sulfate bath without brightener ( PR process) 101.9Acid sulfate bath with brightener 76.8Pyrophosphate bath with brightener 80.1 Annealed copper standard 100.7Oxygen free copper (OFC) 102.0

IACS: International Annealed Copper Standard

Electrical conductivity of electroformed copper specimens

Materials The 1st breakdown field (MV/m)EF (PR, Pure copper sulfate) 41EF (Copper sulfate with brightener) 13EF (Pyrophosphate) 10OFC (Lathe finishing) 20OFC (Electro polishing) 16OFC (Diamond bite) 70

(EF : Electro-Forming, PR : Periodic-Reverse OFC: Oxygen Free Cooper)

S. Kobayashi, K. Sekikawa, M. Shibukawa (Saitama University)

Y. Saito (KEK)

Breakdown experiment

f [MHz]E [MV/m]

Kilpatrick’s sparking criterion

17.8 MV/m for 324 MHz

Anode for PR Cu formingSetting of the long test tank (~3m) in the bath

Long test tank after PR Cu electro-forming

Inside of the tank Check of the inside surface

Test cavity (length:3321 mm, diameter:560 mm)

(a) (b)

Tank

Stem

Vac.

Copper

SUS spring

Vacuum and rf test of the test cavity

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

100 150 200 250 300 350 400 450 500

3m_Test_cavity

TM010(409MHz)_Q

0

Q0(exp)/Q

0(calc)

Torque　　[kgfÅEcm]

Q0　(measured)　:77000　=　97　%　of　Q0(calc.)

RF property of the test tank

Vacuum property of the test tank

PR electro-forming hollow coil

(1)

Oxygen-free copper block Grooves and through holes for water channel

(2)

Filling wax into grooves and through holes to protect from a solution.

Remove unnecessary wax and alkali cleaning with sandpaper.

The surface coating with silver powder to give electrical conductivity.

The surface is electroformed by PR process. Hollow structure is obtained when the wax filled inside the grooves and through holes is removed by heating.

Forming the coil by cutting between the grooves and through holes.

Cutting out unnecessary parts of the block.

(3) (4)

(5) (6) (7) (8)

Oxygen-free copper block Grooves and through holes for water channel

(1) (2)

Q-process 1

Filling wax into grooves and through holes to protect from a solution.

Remove unnecessary wax and alkali cleaning with sandpaper.

(3) (4)

Q-process 2

The surface coating with silver powder to give electrical conductivity.

The surface is electroformed by PR process. Hollow structure is obtained when the wax filled inside the grooves and through holes is removed by heating.

(5) (6)

Q-process 3

Forming the coil by cutting between the grooves and through holes.

Cutting out unnecessary parts of the block.

(7) (8)

Q-process 4

Q-mag in DT

-100

-50

0

50

100

-100 -50 0 50 100

estimated

∆Y

∆X

(µm)

(µm)

Discrepancy between the magnetic field center

and the beam axis.

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

DTs　for　DTL-1

YÉ∆Å@Å@Å@(mrad)

ÇwÉ∆Å@Å@(mrad)

Tilt of the assembled DTs

DT alignment in the DTL-1

Vacuum / 3 GeV RCS■Ceramic duct with a thin TiN film inside, copper rf shield outside (rf

leakage & coupling impedance)

■Pressure < 10-6 Pa

■Inner surface: TiN film 1-2 nm

■suppress secondary electron smissions

■wall current to flow copper rf shield outside

■coupling impedance to be measured

for the bending mag.

for the Q-mag.

Post-coupler tuning

Vg=0.006c

Measured dispersion curve for DTL-1

Uniform adjustment Fine adjustment

TM011 TM011

PC-1 PC-1

Ez distribution of the nearest neighbor mode

Fine tuning of the post-coupler

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Ez distribution of DTL-1

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Ez distribution of DTL-1

*32 SDTL tanks*Two SDTLs/one Klystron*Doublet focusing*Optimised DT shape

SDTL for J-PARC.

Inside view of the SDTL

1st　DT　of　SDTL-1

High-power test of the SDTL-2

* Inside surface of the SDTL tank: The periodic reverse (PR) copper electro-forming method.*The basic properties the PR electro-forming have been confirmed by the high-power model tank successfully. *The number of the copper layers of the electroforming for the Alvarez DTL is two. The high performance of the double layered surface has been already proved by the high-power test of the DTL model tank.

Single layered electroforming has been applied to the SDTL-2 for decreasing the fabrication cost of the tank, while the SDTL-1 has double layers of the PR copper electroforming for comparison.

Double or single ?

0

100

200

300

400

500

600

0

3

6

9

12

15

18

0 10 20 30 40 50

Apr.　2000　　　DTL　high-power　model

Peak　Power

average　power

Average　power

kW kW

peak　power

Conditioning　time (hour)

0

100

200

300

400

500

600

0

3

6

9

12

15

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0 10 20 30 40 50

SDTL-2peak power

average power

kW kW

Conditioning time

Average powerpeak power

(hour)

0

100

200

300

400

500

600

0

3

6

9

12

15

18

0 10 20 30 40 50

SDTL-1peak power

average power

peak power

Average power

Conditioning time

kW kW

(hour)

Doublelayers

Mono layer

High-power conditioning history

Doublelayers

IV. ACS

•Side coupled structure (SCS)

•Disk and washer strcture (DAW)

•Annular coupled structure (ACS)

Candidates of the CCL

ACS (972MHz) for J-PARC

Cell of ACS

RF-Thermal-Structural Coupled Analysis of ACS Model

Accelerating Cell Side

Coupling Cell Side

( done by S. C. Joshi / CAT )

HF Modal Analysis of ACS cavity model for the TM010 π/2 mode.

The magnetic field vector H Plot.

HF Modal Analysis of ACS cavity model for TM010 mode.

The vector plot of Electric Field E

Steady state Thermal Analysis of ACS Cavity Structure Temperature

distribution for the 3.5% duty factor

Deformation Plot in longitudinal direction for 3.5% DF

Total deformation plot of the ACS cavity Structure for 3.5% DF

ACS status

Basic design has been done.High-power model of short tank is under construction.

References

• “Microwave electronics”, J. C. Slater (1950)

• “Accelerators”, P. M. Lapostolle & A. L. Septier (1970)

Summary

•Microwave in a cavity

TM mode, Pill-box cavity, Multi-cell cavity, Bridge cavity

•Energy gain & transit time factor

•R&D results of DTL, SDTL & ACS for J-PARC.

Thank　you　for　your　attention　!!

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