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
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3
6
9
12
15
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Apr. 2000 DTL high-power model
Peak Power
average power
Average power
kW kW
peak power
Conditioning time (hour)
0
100
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500
600
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3
6
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SDTL-2peak power
average power
kW kW
Conditioning time
Average powerpeak power
(hour)
0
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600
0
3
6
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15
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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 !!
ありがとう