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STABILIY EVALUATION WITH LONG FB LOOP DELAY IN THE ACS CAVITY RF CONTROL FOR THE J-PARC 400-MeV LINAC
Tetsuya Kobayashi1
Japan Atomic Energy Agency (JAEA) 2-4 Shirakata-Shirane, Tokai, Naka, Ibaraki, 319-1195
Abstract
For 400-MeV upgrade of the J-PARC Linac. ACS (Annular Coupled Structure) cavities, which are driven by 972-MHz RF, will be installed.
The ACS cavity has complicated structure. Its Q-value is very low and the operation frequency is tree times high in comparison with that of the SDTL cavity. So the stabilizing control of the ACS accelerating field will be more difficult than present RF system. Further more the chopped beam loading compensation is required. Especially, a debuncher will be located very far from the klystron, then the feedback loop delay will be about 1.5 μs.
This presentation will show the simulation results of the feedback control of the ACS cavity field including long loop delay and the effect of the chopped beam loading.
J-PARC400MeV FB ACS RF
1 E-mail: tetsuya.kobayashi@j-parc.jp
J-PARC
[1] 400MeV 3GevRCS: Rapid Cycling Synchrotron
50GeV MR: Main Ring 3
181MeV 324MHzRCS 400MeV
400MeV
972MHz ACS Annular Coupled Structure[2] 21 RF
3 ACS Q8000 DTL 20000 FB324MHz RF
RCSACS
100m FB3 ACS
FB
LLRF 50mA 500μs
25Hz 50HzMEBT
RF RCS RF1MHz
RCS 50mAΔp/p 0.1%
1 1%LLRF
FPGAFB [3]
FFACS
[4][5] 181MeV 324MHz
SDTL 240.2
0.2RCS
DB2
Proceedings of the 7th Annual Meeting of Particle Accelerator Society of Japan (August 4-6, 2010, Himeji, Japan)
-1082-
RCS ACS
DB2RF
IOT
100m220m
FB 1.5μs RFACS
SDTL 3 Q
DB2 100kW500kW3MW FB
IQ PI
Hclose
Hclose = E + HdelayR ⋅G⎡⎣ ⎤⎦−1⋅G (1)
G = Hcav ⋅HdelayF ⋅Hkly ⋅HPI
Hcav Hkly HPI=Pgain+Igain/s HdelayF=exp(-sTdF)HdelayR=exp(-sTdR)PI TdF, TdR
Hcav[6]
Hcav =ω1/2
Δω 2 + s +ω1/2( )2s +ω1/2 −ΔωΔω s +ω1/2
⎛
⎝⎜⎜
⎞
⎠⎟⎟ (2)
Δω =ω0 −ω , ω1/2 =ω0
2QL
ω0 QL Q
Hkly=ωkly/(ωkly+s)ωkly 5MHz
DB2 1.5μs QL=8000Δω=0Hclose (1,1)
10dB Pgain~3 PI
Pgain
Pgain=1.5DTL 324MHz QL=20000
Q
Igain
FB
DTL 324MHz
Proceedings of the 7th Annual Meeting of Particle Accelerator Society of Japan (August 4-6, 2010, Himeji, Japan)
-1083-
100kHz FB
PIFB FPGA
Vr t( ) +ω1/2Vr t( ) + ΔωVj t( ) = RLω1/2Ir t( )Vj t( ) +ω1/2Vj t( ) − ΔωVr t( ) = RLω1/2I j t( ) (3)
V I
r jRL
10% 30FPGA 48MHz
48MHz -60
optimum β = 1+ b = 1.3, QL =
Qo
1+ β( ) ≈ 8000
Δfopt =frf2QL
tan Ψopt( ) = −13.7kHz, Ψopt = arctanb
1+ βtan φs( )⎛
⎝⎜⎞⎠⎟= −12.7deg.
(4)
b Pb/Pc β
φs ΔΨopt Δfopt
RF
FB FB Pgain, Igain
(3)I (5)
Ibeam =b
1+ β⋅
Icavcos φs( ) (5)
650μ RF 300μs 200μ-
500μ
0.1% 0.1FB
FFFF
3
300μs
optimum
[5] ACS
FB [7]
J-PARC 400MeV ACS
FB220m
FB
PI
100kHzACS FB
[1] URL: http://www.j-parc.jp/ [2] H. Ao, et al., “Fablication Status of ACS Accelerating
Modules of J-PARC LINAC”, Proc of PAC07, pp. 1514-1516, 2007
[3] S. Michizono, et al., “Performance of a Digital LLRF Field Control system for the J-PARC Linac", Proc. of LINAC2006, pp. 574-576, 2006
[4] S. Michizono, et al., “Digital Feedbac Control for 972-MHz RF System of J-PARC Linac”, Proc of PAC09, WE5PFP082, 2009
[5] T. Kobayashi, et al., “Beam Test of Chopped Beam Loading compensation for the J-PARC Linac 400-MeV Upgrade”, in this annual meeting, 2010
[6] T. Schilcher, "Vector Sum Control of Pulsed Accelerating Fields in Lorentz Force Detuned Superconducting Cavities", Doctor Thesis, Hamburg University, 1998
[7] T. Miura, et al., “Measurements of Feedback-Instability due to 8/9π and 7/9π Mode at KEK-STF”, Proc. of LINAC08, pp. 1051-1053, 2008
DB2 FB RF
FB
Proceedings of the 7th Annual Meeting of Particle Accelerator Society of Japan (August 4-6, 2010, Himeji, Japan)
-1084-
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