Beam Position Monitor for KAERI

KNU Accelerator Physics Laboratory

Contents • The principle of a cavity BPM • Why 5.602 GHz? • Design results of the KAERI cavity BPM(5.6GHz) • Request list • Cylindrical cavity BPM design(2.8GHz) • Resonant mode of cylindrical BPM • Cavity dimensions for HFSS simulation • Antenna position scan • Design parameters of cavity BPM • Output signal of X-port for 2.8GHz and 5.6GHz • Test scheme for each BPMs • Cavity dimensions for HFSS simulation (40mm&50mm) • Dipole mode of cylindrical BPM(50mm) • Antenna position scan and antenna depth scan(50mm) • Isolation • Design parameters of a final decision cavity BPM (50mm) • Output signal for X-port and effect of the timing jitter in BPM • Homodyne Receiver and heterodyne Receiver • Comparison and discussion

The principle of a cavity BPM

• Beam position measurement by using dipole-mode

An advantage of a cavity-type BPM - Achievement of higher beam position resolution (~nm) - Short decay time - Beam position measurement possibility of the bunch train

Calibration factor = 0.674 mV/ nm

Beam position [μm]

Calibration factor with beam position

Beam signal calibration

Base plate

post

mover

BPM

beam )R/Q(Q

Z2qV

ext0 out

ω= 2

2

0

2 28)( ybab

LTyQR

=π

ωε

1.348mV

Oscilloscope/ ADC

Voltage variation due to beam postion = 0.674mV/nm

The principle of measurement of BPM

Calibration

Beam position [μm]

The constraints of BPM design of KAERI

•RF frequency= 2.801[GHz]

•Resonant frequency =5.602[GHz]

•Micro beam space= 357[ps]

•Micro pulse charge= 14.28[pC]

•Micro pulse length= 10~20[ps]

•Total bunch length= 5[μs]

•Average current= 40[mA]

•Vertical beam size= 2~3[mm]

•Radius of BPM < 86[mm]

•Drift beam pipe= 45[mm]

•Cut-off frequency=5[GHz]

22 )()(2 b

na

mcfcππ

π+=

Why 5.6GHz ?

• We should use resonant frequency of n x 2.801 GHz for the KAERI BPM to make constructive interference.

2.801 GHz 5.602 GHz

Cylindrical cavity BPM design

•2.801 X 2=5.6 [GHz]

•Cavity width= 6[mm]

•Beam pipe(radius)= 10[mm]

•Sensor cavity(radius)=30.7[mm]

23

8 )102

83.3(103 −××××=

Rf

mnlTM π

)exp()

2

2sin

( 2

2222

3

4

ccL

cL

Lxc

U zσωω

ωω −

=

Resonant mode of cylindrical BPM

TM010 mode f=4.07596[GHZ]

TM110 (X di-pole) f=5.64620[GHZ]

TM110 (Y di-pole) f=5.64649[GHZ]

전기장 (Electric field) 자기장 (Magnetic field)

Cavity dimensions for HFSS simulation

20

30.7

5 15

8

37

6

1.5

50

Unit: [mm]

Antenna position scan

Wave Guide

Antenna

1.8

3.2

6.3

4.1

Ap1

Unit: [mm]

Antenna position scan was performed to find the position with high transmission and high isolation.

S parameter by HFSS simulation

X-port

Y-port

0.7669

0.7654

0.5423

0.5412

Mode f0[GHz] Δf[GHz] S21

X-port 5.5976 0.0057 0.7669

Y-port 5.5976 0.0057 0.7654

Mesh number=118,690

Design parameters of cavity BPM

Mode f0[GHz] β QL Q0 Qext τ[ns] Vout[mV]

X-port 5.5976 3.290 982.035 4212.935 1280.526 27.922 0.26466

Y-port 5.5976 3.263 982.035 4185.998 1283.035 27.922 0.2644

•f0= Resonant frequency

•β= Coupling constant

•QL= Loaded quality factor

•Q0= Quality factor of the cavity

•Qext = Quality factor of the external coupling

•τ= Decay time constant

•Vout= Output voltage

Lext QQββ+

=1

21

21

1 ss−

=β

fQQ LL

πωτ

2==

ffQL ∆

=LQQ )1(0 β+=

Output signal for X-port

10μm offset

)sin()2

exp(

)2

exp()/(2

0,

2

22

0,

φωτ

σωω

+−=

−=

ttVV

cQR

QZqV

outout

z

extout

t

A

………...

357ps

10~20ps

0.7

Request list

• There is beam corrector to sweep the beam? • We need the beam current profile • What do you want see? Version 1 Version 2

Oscilloscope, Diode, Cables Oscilloscope, Diode, Cables, ADC, Electronics, Code, Ref. Cavity or

Signal Generator (~GHz)

Cylindrical cavity BPM design

•f=2.801 [GHz]

•Cavity width(L)= 12[mm]

•Beam pipe(radius)= 20[mm]

•Sensor cavity(radius)=61.4[mm]

)exp()

2

2sin

( 2

2222

3

4

ccL

cL

Lxc

U zσωω

ωω −

=

2.8 GHz

5.6 GHz •2.801 X 2=5.6 [GHz]

•Cavity width= 6[mm]

•Beam pipe(radius)= 10[mm]

•Sensor cavity(radius)=30.7[mm]

Resonant mode of cylindrical BPM

TM010 mode f=2.03503[GHZ]

TM110 (X di-pole) f=2.82356[GHZ]

TM110 (Y di-pole) f=2.82345[GHZ]

TM120 mode f=4.59769[GHZ]

S-band BPM dimension

214

252

40 Beam pipe

Unit: [mm]

][77597.2

)()(2

11,

22,

GHzfb

na

mcf

c

mnc

=

+=ππ

π

BPM condition •RF frequency= 2.801[GHz]

•Resonant frequency =2.8035[GHz]

•Micro beam space= 357[ps]

•Micro pulse charge= 14.28[pC]

•Micro pulse length= 10~20[ps]

•Total bunch length= 5[μs]

•Average current= 40[mA]

•Vertical beam size= 2~3[mm]

•Drift beam pipe= 45[mm]

Waveguide

Coupling slot

Cavity

122.8

Cavity dimensions for HFSS simulation

40

61.4

8 31

14

70

12

3

85

Unit: [mm]

Antenna

Waveguide

Cavity

Beam pipe

Antenna position

Waveguide Antenna

1.8 3.2

4.1

Unit: [mm]

14

35

12.7

50

14

80

70

Antenna position scan

Waveguide

Ap1

Ap1 scan The antenna position (AP1) was selected at 14mm.

80

70

Antenna depth scan

Depth

Depth scan

Antenna

The antenna depth was selected at 12.7mm.

S parameter for X-port transmission and Y-port transmission calculated by HFSS

X-port

Y-port

0.9023

0.9025

0.6380

0.6381 Mode f0[GHz] Δf[GHz] S21

X-port 2.8034 0.004 0.9023

Y-port 2.8033 0.004 0.9025

Mesh number=118,916

Design parameters of cavity BPM

Mode f0[GHz] β QL Q0 Qext τ[ns] Vout[mV] Offset=10

[um]

X-port 2.8034 9.235 700.850 7173.490 776.737 39.789 0.07374

Y-port 2.8033 9.256 700.825 7187.949 776.537 39.789 0.07374

•f0= Resonant frequency

•β= Coupling constant

•QL= Loaded quality factor

•Q0= Quality factor of the cavity

•Qext = Quality factor of the external coupling

•τ= Decay time constant

•Vout= Output voltage

Lext QQββ+

=1

21

21

1 ss−

=β

fQQ LL

πωτ

2==

ffQL ∆

=LQQ )1(0 β+=

Compare with 2.8GHz and 5.6GHz

Frequency [GHz] Mode f0[GHz] β QL Q0 Qext τ[ns]

Vout[mV] Offset=10[um]

2.8

X-port 2.8034 9.235 700.85 7173.49 776.73 39.78 0.0737

Y-port 2.8033 9.256 700.82 7187.94 776.53 39.78 0.0737

5.6

X-port 5.5976 3.290 982.03 4212.93 1280.52 27.92 0.2646

Y-port 5.5976 3.263 982.03 4185.99 1283.03 27.92 0.2644

)sin()2

exp( )2

exp()/(2 0,2

22

0, φωτ

σωω+−=−= ttVV

cQR

QZqV outout

z

extout

Output signal of X-port for 2.8GHz

10μm offset

t

A

………...

357ps

10~20ps

0.7

Output signal of X-port for 5.6GHz

10μm offset

)sin()2

exp(

)2

exp()/(2

0,

2

22

0,

φωτ

σωω

+−=

−=

ttVV

cQR

QZqV

outout

z

extout

t

A

………...

357ps

10~20ps

0.7

Test scheme for each BPMs • 2.8 GHz BPM • 5.6GHz BPM

Sensor Cavity BPM Electro

nics Sensor Cavity BPM

Micro tron

Oscilloscope

ADC Beam Dump

Sensor Cavity BPM Electro

nics Sensor Cavity BPM

Micro tron

Oscilloscope

ADC Beam Dump

Ref cavity

Cavity dimensions for HFSS simulation

40

61.4

8 31

14

Unit: [mm]

Antenna

Waveguide

Cavity

Beam pipe

50

8 29

14

Unit: [mm]

Antenna

Waveguide

Cavity

Beam pipe

61

50 mm 40 mm

The height of the designed BPM is increased by 10 mm due to the growth of the radius of the beam pipe. The radius of the sensor cavity and size of slit is adjusted to control the frequency.

Dipole mode of cylindrical BPM

TM110 (X di-pole) f=2.8043[GHZ]

TM110 (X di-pole) f=2.8034[GHZ]

50 mm 40 mm

The stored power of sensor cavity was sinked into the beam pipe, which consequently reduced the strength sensor cavity’s electric filed to the half the previous strength.

Antenna position scan

Waveguide

1.8

3.2

Unit: [mm]

Ap1

35

50 mm 40 mm

•We scanned the position of antenna for high transmission and isolation. •The isolation of 50mm beam pipe is fluctuates greatly. •When BPM is processing, It can be problems that the section changed heavily.

Antenna depth scan

Depth

Antenna

40 mm 50 mm

•By looking at this graph, we can find out that the transmission has a small changes, but isolation shows extreme changes. •We found 7.5mm depth as the most appropriate point for having adequate transmission and isolation for BPM.

• When the signal produced from the signal generator is put into the Y-port, the signal from Y-port is only observed in reduced rate in X-port.

Example) When the off-set of horizontal direction beam of BPM with over -40[dB] isolation is 1mm, it gives 10 μm process error in the vertical direction beam.

• We designed the BPM by using isolation with over -40[dB]

Isolation

=

in

out

VVdB 10log20][

X Port

X Port

Y Port

Y Port

Transverse

Transverse

Input

Opposite

2.8Ghz 10dBm

Signal Generator

-10 dBm

Spectrum Analyzer

2.8 GHz

Isolation -20 dB

A final decision

7.5

42.5

35

Waveguide

Antenna

•The position of the antenna is finally decided for the middle of waveguide and the depth is 7.5mm. •The process error of antenna place is ±300μm and it is ±100μm for depth.

Design parameters of cavity BPM

Mode f0[GHz] β QL Q0 Qext τ[ns] Vout[mV]

X-port 2.8043 1.25 3115 6994 5619 176 0.0381

Y-port 2.8045 1.24 3505 7847 6335 198 0.0359

Mode f0[GHz] Δf[GHz] S21

X-port 2.8043 0.0009 0.5545

Y-port 2.8045 0.0008 0.5533

Mesh number=110,000

Mode f0[GHz] β QL Q0 Qext τ[ns] Vout[mV]

X-port 2.803 9.24 700 7173 776 39 0.1027

Y-port 2.803 9.26 700 7187 776 39 0.1027

50 mm

40 mm

Output signal for X-port

10μm offset

)sin()2

exp( )2

exp()/(2 0,2

22

0, φωτ

σωω+−=−= ttVV

cQR

QZqV outout

z

extout

50 mm 40 mm

10μm offset

Effect of the timing jitter in BPM

2.801 GHz

Q0

t0+Δt

Q0+ΔQ

t0 =357 ps Δt = 3.57 ps (1 %) Q0=14.28 pC ΔQ = 0.14 pC (1 %)

Beam offset : 100 μm

Effect of the timing jitter in BPM

Q0

t0+Δt

Q0+ΔQ

t0 =357 ps Δt = 35.7 ps (10 %) Q0=14.28 pC ΔQ = 0.14 pC (1 %)

2.801 GHz

Beam offset : 100 μm

Due to the timing jitter, the decrease of the output voltage is observed.

39

Analog Signal Processing

The readings are waveforms in 2.8 GHz, so we need a downconversion electronics. Basically, two methods are available: ►homodyne receiver ►heterodyne receiver.

Homodyne Receiver

40

The signal is downconverted to the “direct current” in one stage. Just a few components are needed, the losses are low.

HR is very sensitive to the isolations between LO and RF ports of the mixer. I/Q mixer is usually used.

For example 1, electronics for IP-BPM@ATF2 (by KNU)

5.712GHz(X) 6.426GHz(Y)

From Ref. cavity

5.712GHz(X) 6.426GHz(Y)

From sensor cavity

Conversion Gain 54dB

Noise Figure < 1.8dB

linear Range -57dB ~ -96dB

41

In-phase signal Quadrature phase signal Reference signal x100

Heterodyne Receiver

42

Downconversion is realized in several stages. That gives a better possibility for the filtering and amplification of the signal. The mirror frequency issue does not seem to be really dangerous in this case.

In order to extract the amplitude and phase information necessary to recover the position, this waveform(left fig.) is downconverted again in software by multiplying by a LO signal at the same frequency as the waveform.

For example 2, electronics for S-band BPM@ATF2 (by UK)

43

Comparison

Homodyne Receiver

• A single stage • Output : direct current • Just a few components • low loss • Very sensitive to the

isolations between LO and RF ports of the mixer.

• I/Q mixer is used.

Heterodyne Receiver

• Several stages • Easy to filter and

amplify the signal • No effect of the mirror

frequency • Useful in case of long

distance between BPM and electronics

Discussion • The output voltage of 40mm beam pipe case shows three times of

50mm case. • What beam pipe size need? • To fabricate BPM, we need three months.

– Feed through order &shipment (two month) – BPM design (one month ) fabrication (two month)

• To design electronics, – BPM data – Location to install electronics – Required resolution and dynamic range

• The fabrication will be taken about 3 months after the measurement of signal from BPM.