1. Re-entrant BPM R&D for ILC Main Linac
AWG
Re-entrant BPM R&D for ILC Main Linac
A. Heo, J.-Y. RYU, Y.-I. KIM, E.-S. KIM
Department of Physics Kyungpook National University, Daegu, Korea
H. Hayano
KEK, Tsukuba, Ibaraki, Japan
S.-Y. RYU, J.-K. Ahn
Department of Physics Pusan National University, Pusan, Korea

2. Main Linac Cold-BPM in Cryomodule
BPM chamber
Quadrupole Magnet

3. Requirements for Main Linac Cold-BPM in Cryomodule
(1) The BPM measures beam position in cryomodule, bunch by bunch,
with a resolution of less than 1 µm at 2x1010 electrons/bunch.
-> low Q value for fast signal damping at 2K circumference
-> good signal-to-noise ratio for high resolution
-> high precision on mechanical center definition and electrical center definition
-> high common-mode rejection, high isolation for x-to-y coupling
(2) The beam pipe diameter 78mm (big diameter).
-> low frequency resonant-mode BPM
-> no coupling to cavity HOM and no conflict with cavity dark-current exitation
(3) BPM is installed inside of cryomodule, next to SC-cavity.
-> simple structure with no contamination inside (clean-room compatible)
-> HPR rinse applicable
-> light weight for easy to handle and to install in clean-room
Design Base : Saclay re-entrant BPM
adding waveguide loading for CM-rejection and X-Y coupling rejection

4. Proto-type model (Cold-model)
magnetic coupling pickups
Material: SUS
small holes for rinsing water outlet
dipole mode: 2.04GHz

5. RF characteristics of prototype model
Input port
Output port
f[GHz]
Df [MHz] QL Q0 b
t[sec] 1 3
2.049
9.90
205
335
0.635
6.69E-8 2 4
7.81
262
475
0.808
8.57E-8
Port
Slot
Isolation [dB]
Transmission [dB] 1 2
-27.18 3
-8.54 4
-27.34
-27.19
-7.03
-29.49

6. Antenna scan of prototype model

7. Beam response test of prototype model at ATF-LINAC (1)
using simple circuit (diode, amp, integration ADC)

8. BPM setups Proto-type BPM housing TM010 refernece cavity
Inside of Proto-type BPM housing
Proto-type BPM
TM010 refernece cavity

9. Beam response Raw signal After 2.04GHz BPF FFT of Raw signal FFT of
BPF output
ATF LINAC beam
1.3GeV
single bunch
1 x 1010 electron/bunch
1.5Hz repetition
Diode detection output

10. Resolution estimation by (pedestral noise)/(response slope)
setup (A)
setup (C)
beam scan
pedestal distribution
with gaussian fit
beam scan
red line shows
response slope
red line shows
response slope
setup (B)
beam scan
pedestal distribution
with gaussian fit
pedestal distribution
with gaussian fit
red line shows
response slope
electronics setup
axis
pedestal noise [count]
response slope [counts/µm]
estimated resolution [µm]
(A) Hybrid+BPF+diode+LF-amp X
3.47
4.57
0.75
(B) Hybrid+BPF+RF-amp+diode+LF-amp Y
3.65
8.02
0.45
(C) Hybrid+BPF+RF-amp+diode
1.96
5.33
0.36

11. Beam response test of prototype model at ATF-LINAC (2)
using phase detection circuit
(phase between BPM cavity, Reference cavity)
Electronics setup
BEAM TEST on Jan 2011
Phase detector
+side (CH 0)
-side (CH 1)
beam intensity (CH2)
detection (CH 3)
ADC
10dB att.
Ref.
BPF
future plan : ----
30dB
amp.
BPM
hybrid
X-ports or Y-ports
att. S Δ
20dB att.
LO: 1329MHz
LO generator
Down
convertor
Down convertor
Both signal were down converted to 714MHz, then fed into the phase detector.
Analog output of the phase detector were fed into integration ADC (charge ADC).

12. Waveforms in the phase detector circuit
X RF IN(2043M)
Y RF IN(2043M)
Down convertor
X RF IN(714M)
Y RF IN(714M)
REF IN(714M)
Phase detector
Ref.
BPF
Down
convertor
+side (CH 0)
-side (CH 1)
beam intensity (CH2)
detection (CH 3)
ADC
future plan : ----
30dB
amp.
BPM
hybrid
X-ports or
Y-ports
att. Ξ Δ
changed
LO: 1329MHz
SCOPE (1)
SCOPE (3)
SCOPE (2)
SCOPE (4)
SCOPE (5)
SCOPE (6)
SCOPE (7)
SCOPE (1) rawsignal_Ch1
SCOPE (5) phasedetection_2_Ch1
SCOPE (6) phasedetection_2_Ch2
SCOPE (3) downconverteroutput_Ch1
data_24Jan2011

13. Y-ports data with 28dB att. _27 Jan 2011
Resolution estimation : phase detector circuit
Y-ports data with 28dB att. _27 Jan 2011
R2:
ATF LINAC beam
1.3GeV
single bunch
0.5 x 1010 electron/bunch
1.5Hz repetition
Resolution = noise level [counts]/ slope [counts/um]
BPM signal with 28dB att.
+ side
side
Noise level [counts]
Gradient [counts/um]
Resolution [um]

14. Vacuum-tight Model (hot-model)

15. Vacuum-tight model (Hot model)
Hot model fabrication was completed on May 2011
Feed-through + loop-antenna are demountable for final adjustment

16. Cold model Measurement
RF characteristics of Vacuum-tight model (Hot model)
BPM
Network analyzer QL β
Isolation
Data
Hot model measurement
0.874
-20.7
Cold model Measurement
0.350
-29.8 46 40 5
4.4 22
28.2
78.27
78.17 8 R5 2 4
4.27 14
Measured as 13.7
Waveguide
cold-model
hot-model
Difference of isolation may come from loop position difference.

17. Preparation of mechanical center measurement
for Vacuum-tight model (Hot model)
<<<Measurement is not yet done.>>> A
Z mover stage B
XY mover stage C
Rotational stage D
Cavity E
Goniometer Stage F
Antenna
G1,G2
edge measuring device H
Flange Adapter
750 20
137 50
330
160
125 90
380
170
350
162
225
150 35
222 55 3 40 70
130
210
152
200 75 21 10 G1 F A G2 E B C D H
Range110
5+100
H20.5
H14
H34.27
Antenna: X-Y-Z movement
-> Antenna scan
Cavity-BPM: on rotational stage
with X-Y stage
-> BPM 180deg. Rotation with
keeping mechanical center z y x

18. Beam Experiment plan for Vacuum-tight model (Hot model)
Reference cavity
3-BPM for resolution estimation
Digital signal acquisition
Down-converter(2043MHz ->93MHz) + ADC(14bits 400Ms/s) + FPGA

19. Summary of Re-entrant BPM R&D for ILC Main Linac
The Re-entrant BPM was designed based on “Saclay re-entrant BPM”
by waveguide loaded pickup. Demountable-cold-model was fabricated and tested.
(2) Demountable-cold-model was fabricated and tested.
-> RF characteristic: -27dB port isolation,
0.12mm mechanical-to-electrical center difference
-> beam test for resolution estimation was done for two electronics setup.
~0.4mm resolution at 1x1010 electron/bunch in simple circuit,
~0.4mm resolution at 0.5x1010 electron/bunch in phase-detection circuit.
(3) Hot model was fabricated and under test.
-> port isolation became worse, it will be revised.
-> mechanical-to-electrical center difference will be measured by the rotation stage setup.
-> digital detection circuit is under design.
-> 3 BPM setup for resolution estimation will be done in ATF extraction line.
-> cool-down test and High-pressure-rinse test are under planning.