Design and Offline tests of Button BPM for an IR-FEL project at NSRL

Transcription

1 Design and Offline tests of Button BPM for an IR-FEL project at NSRL

2 Contents: 1. Introduction of the IR-FEL project. Design of Button BPM 3. Offline tests 4. Conclusion and Outlook

3 1. Introduction of the IR-FEL project Machine Layout Table 1: Electron beam parameters Beam energy Bunch charge Bunch length, rms Bunch repetition rate Macro pulse length Macro pulse repetition rate 15~60MeV Q=1nC σ=~5ps 59.5,119,38,476MHz Max:10μs 0Hz Compact : Room area: 1*4m

4 . Design of Button BPM Table: Design parameters Requirements: 1. Low cost and Compact. Resolution<50μm for different repetition rates Bean pipe radius Longitudinal length Electrode deviation angle from horizontal axis Feedthrough impedance b=17.5mm 5mm ϕ=30 degrees Z=50Ω Fig.1 3-D model Fig. Cross section view

5 . Design of Button BPM Fig.3 RMS value < >input signal level Back-end electronics: Libera Single Pass E (Central frequency: 476MHz) Assuming the biggest movable range for x and y directions: -5 > +5 mm Fig.4 Calculation region(green)

6 . Design of Button BPM Follow signal from beam pipe to the Libera Single Pass E: Bunch current: Image charge on button: Image current on button: Equivalent resistance: Image voltage on button: Attenuation of coax-cable LMR-400: Voltage out of cable: I t imag Q ( ) Q πσ S e t σ button vacuum I ω a I ω C βc b βc a iω Iimag ω I ω b βc Z ω (Z iωc) 1 1 V ω I ω Z ω imag πε L 0 C r w ln r Att L 0.19 F F cable MHz MHz V ω V ω 10 cable Att. 0 Ref: Smith S R. Beam position monitor engineering. AIP Conference Proceedings. AIP, 1997, 390(1):

7 . Design of Button BPM Q ( ) imag S button vacuum I ω a I ω C βc b βc Visual beam pipe a > button radius b >beam pipe radius beam at (0,0): Sbutton π a beam at P(r,θ): for Button i (i=1,,3,4) S i πa b cos θi button ri Real beam pipe

8 . Design of Button BPM Delta over Sum Linear fitting Q Q Q Q U / Q Q Q Q Q Q Q Q V 1 3 / Q Q Q Q x K U X x / m y K V Y y / m Region: (-5,-5)~(5,5)mm Kx / mm Ky / mm Boundary element method Derived formula Error / % 0.156%.954% Ref: Shintake, Tsumoru, et al. Sensitivity calculation of beam position monitor using boundary element method. NIMPRSA: (1987):

9 . Design of Button BPM Condition : Q=1nC, bunch length=5ps, macro pulse length=5μs, cable length=80m Bunch repeat frequency 59.5 MHz 119 MHz 38 MHz 476 MHz Signal level maximum dBm dBm dBm.01dBm minimum dBm dBm dBm dBm Signal range \ db (1) Resolution induced by electronics σx1/μm σy1/μm Libera single pass E Required RMS noise

10 . Design of Button BPM () Intrinsic resolution only considering thermal noise: P b 1 signal σ,snr, P ktb int SNR P noise W noise k J / K, T 300K, B w 10MHz Bunch repetition rate 59.5 MHz 119 MHz 38 MHz 476 MHz Intrinsic resolution σx=σy/μm x x1 x y y1 y Resolution σx/μm σy/μm

11 3. Offline tests Wire Method 1. X Y moving range : -5mm~+5mm, step : 0.5mm. X-Y motor:position resolution =.5μm 1 0.6mm Tungsten Wire Labview CW 3 4 Motor Controller X axis Signal Generator Y axis D C B A Libera Single Pass E T Trigger Signal Generator 1

12 3. Offline tests Results for multiple tests with all 11 BPMs deviation within 5% search for mechanical center venier caliper

13 3. Offline tests Lambertson Method B A g g1 The mechanical center offset relative to the electrical center : C D g4 g3 X K g g g g 1 K g g g m x g g g g 1 g g g Y m x g g g g 1 g g g K y K g g g g 1 g g g y Vj g j j Gij i g i Vi V S V 50G g g i ij ij ij i j Vj V g V B j j j I G V Vi 50Gij gi g j Vj B i ij j Ref: Chung, Y., & Decker, G. Offset calibration of the beam position monitor using external means. AIP Conference Proceedings (Vol. 5, No.

14 3. Offline tests Assuming: G =G G G G ij ji G 1 34 G 13 4 G 3 14 S S G S S G S S 50g S4 G1G 3 S3 G1G13 S43 G 3G13 S S G S S G S S 50g S31 G1G 3 S14 G1G13 S43 G 3G13 S S G S S G S S G 50g S4 G1G 3 S14 G1G13 S1 G 3G13 S S G S S G S S G 50g S31 G1G 3 S3 G1G13 S1 G 3G13 G G Lambertson Method X Y m m 1 g g g K x 1 g 1 g 31 g 41 1 g g g K y 1 g 1 g 31 g 41 g g g g S S S S S S S g S S S S S S S g S S S S S S g S S S S S S g S S S S S S S g S S S S S S S Ref: Chung, Y., & Decker, G. Offset calibration of the beam position monitor using external means. AIP Conference Proceedings (Vol. 5, No.

15 3. Offline tests Lambertson method s Precondition: Each BPM has four electrodes with good Consistency TDR-test: Cable version: Tflex-40 Length: ~1m Velocity: ~0.695*c

16 3. Offline tests Fitting equation: a3= 1/(R*C) Capacitance / pf A B C D Theoretical value BPM# BPM#

17 3. Offline tests BPM Number Lambertson method f=476mhz Xm /μm Ym /μm No.1 1# # No.9 1# # Not enough tests to get a general Conclusion!

18 4. Conclusion and Outlook 1. Kx & Ky both have ~9% deviation from the theoretical value.. How to improve the precision of wire method? THANKS!