stabiliy evaluation with long fb loop delay in the …...stabiliy evaluation with long fb loop delay...

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: [email protected]

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)

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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


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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


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stabiliy evaluation with long fb loop delay in the …...stabiliy evaluation with long fb loop delay...

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