DEVELOPMENT OF HIGH PRECISION BEAM POSITION MONITORREADOUT SYSTEM WITH NARROW BANDPASS FILTERS FOR THE
KEKB INJECTOR LINAC TOWARDS THE SUPERKEKB
R. Ichimiya#, K. Furukawa, F. Miyahara, M. Satoh, T. Suwada KEK, Tsukuba, Japan
dynamic range. In addition, there may be readout position
The SuperKEKB accelerator complex is now being drifts due to several reasons, we implemented calibration
upgraded to bring the world highest luminosity tone generator on the readout circuitry. This gives BPM’s(L=8x1035 /cm2/s). Hence, the KEKB injector linac is electrode calibration tone pulse and induced pulses at theare readout to measure the interrequired to produce: electron: 20 mm mrad (7 GeV, 5 nC), adjacent two electrodes䌒䌥䌶䋮䋱䋮䋰㩷䇭䋲䋰䋱䋳䋯䋱䋯䋱䋷䋱䋸䌋䋱䋲ဳ䇭䋲䊌䊦䉴ኻᔕ䌂䌐䌍ାภಣℂ࿁〝䇭䋨㪭㪤㪜䋲᏷䋩We employed FPGA to calculate
positron: 10 mm mrad (4 GeV, 4 nC). To achievethis, the channel gain balance. 䊂䉳䊁䉾䉪䉴⎇ⓥᚲ
㪭㪼㫉㪅㪉䈪䈜䇯䋨㪘㪆㪛䊂䊷䉺෼㍳േ૞䈱䉂᦭ല䇮ᓟಣℂ䋨䊂䊷䉺ಣℂ෸䈶㪚㪘㪣Ṷ▚ಣℂ䋩ήലbeam position/charge on board within 1 ms. This paper
accelerator components have 䂓᭎䇭䇭ⷐ
to be䇭䇭䈗ᵈᗧ䋺ᧄข⺑䈲ᯏ⢻㒢ቯaligned withinᧄ䊝䉳䊠䊷䊦䈲䇮䋵䋰䌈䌺Ფ䈮䋹䋰䌮䌳㑆㓒䈱䋲䈧䈱䊎䊷䊛ାภ䉕ᬌᵄ䊶䌁䋯䌄ᄌ឵䈚Ṷ▚ಣℂ䉕ⴕ䈉䊝䉳䊠䊷䊦䈪䈜䇯䋨䌖䌍䌅䋲᏷䊝䉳䊠䊷䊦䋩
reports
current development status of the BPM readout± 0.1 mm (1 !). A beam position
monitor(BPM)is䋴䌣䌨䋨䌘䋫䋬䌘䋭䋬䌙䋫䋬䌙䋭䋩䈱䊌䊦䉴ାภ䉕䌂䌐䌆䋨䋳䋰䋰䌍䌈䌺䋩䊶䌁䌔䌔䊶䌒䌆䌁䌍䌐䈪ᬌᵄ䈚䈢ାภ䉕䇮䋵䋰䌈䌺Ფ䈮䌁䋯䌄ᄌ឵䋨䋲䋵䋰䌍䌈䌺䊶䋱䋶䌢䌩䌴䋩ᓟ䋱䋰䋲䋴㪮㪆䌣䌨䉕䊜䊝䊥䈮଻ሽ䊶Ṷ▚ಣℂ䉕ⴕ䈇䌖䌍䌅䌢䌵䌳䈮಴ജ䈚䉁䈜䇯䉁䈢ᩞᱜାภ಴ജᯏ⢻䈮䈩䊎䊷䊛ᬌ಴ㇱ䉕฽䉄䈢ᩞᱜ䈏น⢻䈪䈜䇯
system.
essential instrumentation for ౝㇱ䌆䌐䌇䌁䋨䌓䌰䌡䌲䌴䌡䌮㪄䋶䋩䈱䊒䊨䉫䊤䊛䈲䊗䊷䊄਄䈱䌊䋭䌔䌁䌇䉮䊈䉪䉺෸䈶䌖䌍䌅䌢䌵䌳䉋䉍ኾ↪䌆䌌䌁䌓䌈䌒䌏䌍䈻䈱䌕䌰䌤䌡䌴䌥䈏น⢻䈪䈜䇯
beam-basedalignment䊶Ṷ▚ಣℂ಴ജ䇭䇭䇭㽲䊎䊷䊛૏⟎䇼㱘䌭䇽䇭䇭㽳㔚⩄㊂䇼䌮䌣䇽(BBA), and is required to be䂓઀䇭䇭᭽
one magnitude better䊶৻⥸઀᭽
position resolution to get better alignmentresults. 䉻䊑䊦䊊䉟䊃䌖䌍䌅䋲᏷䊝䉳䊠䊷䊦
Since a䌁䋳䋲䊶䌄䋳䋲䇭᜛ᒛ䉴䊷䊌䊋䉟䉱䊥䋯᜛ᒛ㕖․ᮭ䇭䊂䊷䉺䉝䉪䉶䉴᷹ቯ⚳ੌഀㄟ䉂ᯏ⢻᦭䉍
current BPM readout system 䊶౉ജାภusing oscilloscopes has䋱䋮᷹ቯାภ䊎䊷䊛ᬌ಴ାภ㩷㩷㩷䋴䌣䌨䋨䌘䋫䋬䌘䋭䋬䌙䋫䋬䌙䋭䋩౉ജ䊧䊔䊦 to develop㫧䋵䋰䌖એౝ䇭ᢙ䌮䌳䈱䊌䊦䉴ାภ~50 µm position resolution, we decidedhigh౉ജ䉟䊮䊏䊷䉻䊮䉴䋵䋰㱅౉ജ䉮䊈䉪䉺
䌓䌍䌁䉮䊈䉪䉺
precision BPM readout system 䋲䋮䊃䊥䉧with narrow bandpass䌁䋯䌄ᄌ឵䉴䉺䊷䊃ାภ㩷㩷㩷౉ജ䋱䋬಴ജ䋱䋨䊋䉾䊐䉜಴ജ䋩➅䉍㄰䈚䋵䋰㪟㫑䋨䋲䋰䌭䌳䋩䋲䋰䌮䌳એ਄
filters. It handles two bunches with䊌䊦䉴᏷
96 ns interval andhas䊌䊦䉴㔚࿶䊶䉺䉟䊚䊮䉫䌎䌉䌍䊧䊔䊦䇭┙䈤ਅ䈏䉍䉣䉾䉳౉ജ䋬಴ജ䉟䊮䊏䊷䉻䊮䉴䋵䋰㱅
a dynamic range between 0.1 nC (forphotonfactory)to౉ജ䋬಴ജ䉮䊈䉪䉺䌌䌅䌍䌏䉮䊈䉪䉺䋳䋮ᄖㇱ䌁䋯䌄䉪䊨䉾䉪䊌䊈䊦䉴䉟䉾䉼䈮䉋䉍ౝㇱ䉪䊨䉾䉪䈫ಾᦧ౉ജ䊧䊔䊦these criteria,䌒䌆ାภ䇭䋭䋱䋰䌤䌂䌭䌾䋫䋵䌤䌂䌭
10 nC (positron primary). To achievewe౉ജ๟ᵄᢙ
䋲䋰䋰㪤㪟䌺䌾䋲䋵䋰䌍䌈䌺౉ജ䉟䊮䊏䊷䉻䊮䉴䋵䋰㱅
adopt semiconductor attenuators andoptimized two-stage౉ജ䉮䊈䉪䉺䌓䌍䌁䉮䊈䉪䉺䋴䌣䌨㩷䌂䌐䌆㩷䌒䌆䊡䊆䉾䊃䋨ਃశ␠⵾䋩䇭䋻⹦⚦䈲೎ㅜ઀᭽ᦠෳᾖ
Bessel filters at 300 MHz center䊶ାภᬌ಴ㇱfrequency
to meetboth䌂䌐䌆䋱䋬䋲䊓䊥䉦䊦䊐䉞䊦䉺䇭䌦 䋺䋳䋰䋰䌍䌈䌺䇭䌂䌗䋺䋳䋴䌍䌈䌺䊶䋲ᰴ䋬䋲䋸䌍䌈䌺䊶䋳ᰴ䌒䌆䌁䌍䌐䋱䋬䋲䋬䋳䋲䋰䌤䌂㩷㬍䋳time and frequency domain constraints.
To 䋰䋮䋵䌤䌂䌾䋳䋱䋮䋵䌤䌂䋨㪆䋰䋮䋵䌤䌂䋩㩷㬍䋲correct䌁䌔䌔䋱䋬䋲䊶䌁䋯䌄ᄌ឵ㇱ䋴䌣䌨position drift due to gain imbalance
during operation,䉰䊮䊒䊦䉺䉟䊚䊮䉫䋲䋵䋰䌍䌈䌺䋨ౝㇱ䋩㩷䋻䌍䌃䋱䋰䌅䌐䋱䋹䋵䋨䉥䊮䉶䊚⵾䋩䊂䉞䊧䉟ᯏ⢻᦭䉍䌁䌄䌃䌁䌄䋹䋴䋶䋷䋭䋲䋵䋰䋨䉝䊅䊂䊋⵾䋩䇭䋱䋶䌢䌩䌴䇭䋲䋵䋰䌍䌓䌐䌓䌁䌄䌌䋵䋵䋶䋲䋨䉝䊅䊂䊋⵾䋩䇭䋳䋮䋳䌇䌈䌺䋨䌁䌶䋺䋶䌤䌂䋩calibration pulses are output to the䌁䌄䌃Ꮕേ಴ജ䉝䊮䊒BPM
betweenbeam䊂䊷䉺▸࿐䋭䋱䋲䋵䋰䌭䌖䌾䋫䋱䋲䋵䋰䌭䌖䉰䊮䊒䊦ᢙ䋱䋰䋲䋴䌗㬍䋴䌣䌨䇭䋻䋵䋰㪟㫑Ფ
cycles (20 ms). The beam positionandcharge✚ว♖ᐲ㫧䋰䋮䋲䋦㩷䌯䌦䇭䌆䋮䌓䇭䊶Ṷ▚ಣℂ䇭䌆䌐䌇䌁䋨䌓䌰䌡䌲䌴䌡䌮㪄䋶䋻䌘䌩䌬䌩䌮䌸⵾䋩
calculations are performed by onboard
FPGA to achieve㽲䋲ਸ਼ᐔဋ䇭㽳ᄙ㗄ᑼṶ▚䇭䇭䋻䋳䋲䌢䌩䌴ᶋേዊᢙὐ䊶䌖䌍䌅಴ജ䊂䊷䉺㽲䋲ਸ਼ᐔဋ䇭㽳ᄙ㗄ᑼṶ▚䇭㽴䌁䋯䌄ᄌ឵䊂䊷䉺䇭䋻䋵䋰㪟㫑Ფfast readout cycle.
䊶䌖䌍䌅᷹ቯ⚳ੌ䌉䌒䌑䉅䈚䈒䈲⚳ੌ䊐䊤䉫

Abstract䌃䊶⴫␜䋨䌌䌅䌄䋩 䌖䌍䌅䌁䋯䌄䌔䌒䌉䌇㪚㪘㪣䌆䌐䌇䌁䌁䌌䌁䌒䌍䌁䋯䌄㩷䌏䌖䌅䌒

INTRODUCTION✛䋺䌖䌍䌅㪹㫌㫊䉝䉪䉶䉴✛䋺㪫㪩㪠㪞᦭ല㩷ᯍ䋺㪘㪆㪛䊶Ṷ▚ಣℂਛ✛䋺䌔䌒䌉䌇ᬌ಴✛䋺㪚㪘㪣᦭ല䇭ᯍ䋺㪚㪘㪣േ૞ਛ✛䋺㪝㪧㪞㪘ᱜᏱ䇭⿒䋺㪝㪧㪞㪘䊑䊷䊃䉣䊤䊷⿒䋺ౝㇱ㔚Ḯ⇣Ᏹ䈭䈬⿒䋺䌁䋯䌄䊧䊮䉳䉥䊷䊋䇮䌁䌄䌃䉣䊤䊷䇭㬍䋴䌣䌨KEKB Injector Linac is now being upgraded as a part䊶ᩞᱜ಴ജ䋴䌣䌨㩷䌂䌐䌆㩷䌒䌆䊡䊆䉾䊃䋨ਃశ␠⵾䋩䇭䋻⹦⚦䈲೎ㅜ઀᭽ᦠෳᾖ
of SuperKEKB accelerator complex[1] to achievethe౉ജ䋱䌾䋴䌣䌨䈱䈇䈝䉏䈎䈮䌒䌆䋳䋰䋰㪤㪟䌺ᄌ⺞಴ജ䊶䌅䌅䌐䌒䌏䌍䉻䉟䊅䊚䉾䉪䉭䉟䊮䊐䉜䉪䉺䊷଻ሽ䇭䋻䊥䉶䉾䊃ᓟ䊨䊷䊄
world brightest luminosity. In䊶䌆䌌䌁䌓䌈䌒䌏䌍order to obtainthe䌆䌐䌇䌁䊒䊨䉫䊤䊛↪㩷䇭䌊䋭䌔䌁䌇䇮䌖䌍䌅䌢䌵䌳⚻↱䈪䉝䉾䊒䊂䊷䊃น⢻䊶૶↪㔚Ḯ䋨䌖䌍䌅䋩 㩷䋫䋵䌖and 㩷䋫䋱䋲䌖
positron䋶䌁એౝ
beam
8x1035 /cm2/s luminosity, electronᧂ૶↪
㩷䋭䋱䋲䌖䋰䋮䋵䌁એౝ
1:㪪㪬㪙㩷㪝㪧㪞㪘㩿㪪㫇㪸㫉㫋㪸㫅㪄㪍㪀㩷㫏㪋㪺㪿
Photograph of BPM Readout System Board.
emittances have to be 20 mm mrad(5nC)
and10mm 㪛㫀㪽㪽㪘㪤㪧Figure㪉㪌㪇㪤㪟㫑䍙䍻䍪䍽䍷㪭㪤㪜㪹㫌㫊
䂓ో૕䊑䊨䉾䉪࿑㪚㪟㪈 䇭ାภᬌ಴ㇱ㩿ਃశ␠⵾䋩䇭㪈㪍㪹㫀㫋㪘㪛㪚
mrad (4 nC), respectively. To realize this, due䇭䇭㪙㪧㪝㪂㪪㪮㪂㪘㪫㪫㪂㪘㪤㪧to the beam㩷㩷㪝㪠㪆㪝㪦㪛㪊㪉㪹㫌㫊READOUTSYSTEMOVERVIEW㩷㩷㪛㪜㪣㪘㪰㪚㪟㪉 䇭䇭䇭䇭䇭䇭䇭㩿ห਄䋩
optics reason, accelerator structures㪰㪂 haveto be align㪘㪊㪉㪹㫌㫊䇭㪈㪍㪹㫀㫋㪘㪛㪚㩷㩷㪝㪠㪆㪝㪦㪯㪄㪯㪂䇭㩷㪤㪘㪠㪥㩷㪝㪧㪞㪘㪠㪩㪨㪁At the 㩷㩷㪛㪜㪣㪘㪰
KEKBinjector 㪛㪫㪘㪚㪢linac, there are 100 BPMs
within ±0.1 mm accuracy. To perform theBBA stably,㪚㪟㪊 䇭䇭䇭䇭䇭䇭䇭㩿ห਄䋩㩷㩷㩷㩷㪪㫇㪸㫉㫋㪸㫅㪄㪍䇭㪈㪍㪹㫀㫋㪘㪛㪚㩷㩷㪝㪠㪆㪝㪦㪰㪄
inner diameter !=27 mm, electrode length
BPMs are required to have one magnitude㪚㪟㪋better position (electrode㩷㩷㪛㪜㪣㪘㪰䇭䇭䇭䇭䇭䇭䇭㩿ห਄䋩䇭㪈㪍㪹㫀㫋㪘㪛㪚㩷㩷㪝㪠㪆㪝㪦
installed and㪡㪄㪫㪘㪞 almost BPMs will be
resolution than the required alignment accuracy. l=132.5 mm)
㩷㩷㪛㪜㪣㪘㪰㩷㪝㫃㪸㫊㪿㩷㪩㪦㪤㩷㩷ᩞᱜାภ಴ജㇱ㩷㪦㪪㪚remained.
BPMs for positronline will be replaced withHowever, current BPM readout system with oscilloscopes㩷㩿ਃశ␠⵾䋩䇭㪊㪇㪇㪤㪟㫑㩷㪉㪌㪇㪤㪟㫑㩷㪂㪌㪭㩷㩷㩷㩷㩷㩷㩷㩷㪘㪛㪚㪣㪢largediameterones(!=63mm,l=132.5mm) [4].
㩷㔚Ḯㇱ[2-4] has ~50 µm position accuracy,isnotmetthe㪂㪈㪉㪭㪉㪇㪇䌾㪉㪌㪇㪤㪟㫑㩷㩷㪛㪚㪆㪛㪚
㩷㩷㪩㪜㪞㪅
In this design, we employed㪄㪈㪉㪭requirement. To accomplish <10 µm㪫㪩㪠㪞㩿㪥㪠㪤㪀
positionresolution,㩷㩷㪠㪥 䃁㩷㩷㪇㪭narrow bandpass filter㩷㩷㩷㪌㪇㪟㫑
㩷㪦㪬㪫 䃁 filter (BPF)(BPF) type readout system [5], which uses only specificwe have designed dedicated narrow bandpass
type readout circuitry with 250 MSa/s 16 bit pipeline frequency component of short beam impulse and formsᩣ ࠺ࠫ࠹࠶ࠢࠬ⎇ⓥᚲ
䋱䋸䌋䋱䋲ဳ㩷䋲䊌䊦䉴ኻᔕ䌂䌐䌍ାภಣℂ࿁〝ADC. Since at the SuperKEKB two bunches with 96 ns into long burst signal to measure the beam powerinterval are accelerated, we have optimized BPF precisely. Figure 3 shows our BPM frequency response toconfigurations to keep both position accuracy and bunch the beam with 35-m-long cable losses. We have chosen
separation. As the SuperKEKB injector injects electron / 300 MHz for the BPF center frequency to meet both BPM
positron beams into four different energy rings frequency response and the Nyquist zone of the ADC(SuperKEKB HER/LER, PF and PF-AR) simultaneously, (fs=250 MHz).
BPF bandwidth and its filter characteristics were
we employed electrical attenuators to keep enoughdetermined
to meet following criteria: (1) passband is#ryo@post.kek.jp㩷㪜㪜㪧㪩㪦㪤____________________________________________

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Figure 2: Block diagram of the BPM readout system.
㫄㫆㪻㪼㫃㩷㪈㪏㪢㪈㪉㪃㩷㪉㪄㫇㫌㫃㫊㪼㩷㪙㪧㪤㩷㫊㫀㪾㫅㪸㫃㩷㫇㫉㫆㪺㪼㫊㫊㫆㫉

enoughwithin the ADC’s third Nyquist zone (250 MHz ~&+)+6':.#$%Q.VF
375 MHz), (2) burst signal must be settled within 96 ns
not to disturb second bunch’s signal. Narrower passband
helps achieving first criterion, but it gives longer burst
signal.

Figure 3: BPF frequency response with 35-m-long cable
losses is shown. 300 MHz is at near peak response
frequency and at the center of third Nyquist zone.
We employed Bessel filter, which shows good burst
settle characteristics and gradual frequency cut-off
characteristics. We implemented second-order Bessel
filter (fw=34 MHz) third-order Bessel filter (fw=28 MHz)in series using helical-coils. It gives ~60 ns burst lengthand -45 dB isolation at the Nyquist zone edge. (Fig. 4shows time domain response.)

Block diagram of the BPM readout system is shown in㩷㪹㫆㪸㫉㪻

Fig. 2. We employed four 16 bit 250 MSa/s pipeline
ADCs (AD9467-250) and each ADC clock can be
adjusted in 10 ps step (MC10EP195).
The KEKB injector provides wide range of beam
charge to four different accelerator ring simultaneously;
for PF ring, it provides 0.1 nC (2.5 GeV) and for theSuperKEKB positron primary, it provides 10 nC(3.5 GeV). Therefore, two 31.5 dB electrical attenuators
were implemented to operate in best operating point ateach condition.

60ns
Figure 4: BPF time domain response for beam impulse isshown. Burst signal settles within 60ns.
During operation, measured position drifts may beoccurred due to unequally gain drift among opposite
channels. To compensate it, calibration tone generator
was implemented. This gives calibration tone pulse to aBPM electrode and induced charges at two adjacentelectrodes are readout. Their charge ratio gives offset
compensation factor.
All operations including beam position and charge
calculation are performed by onboard FPGA (XilinxSpartan-6 [6]) within 1 ms.

We took 300 events with this setup and resulted inposition resolution: !x=11.9 µm, !y=9.8 µm (preliminary).

Beam Test

OUVW

6Y7#.94.& P>X
P>X

()9$ ()."($#()9$0)(#-3$90)#"(#*"0&A#*#3-4,)<# 0(+11)(# JN'# QJ8#,G,0);

Figure 7: Beam test setup of BPM readout system.

5PR8A#H-,/*1# Figure 5: Timing diagram of BPM readout system.
Readout timing diagram is shown in Fig. 5. Before
the beam injection, beam type information is provided
via an event system (MRF, EVR) and the BPM readout
system set proper value for its attenuators. When a trigger
signal is given, ADCs start conversion and 1024 cycle(4096 ns) ! 4 channels data are fed to the FPGA via each
FIFO memories. FPGA performs beam position andcharge calculation and then issues an interrupt (IRQ) tonotice Single Board Computer (SBC) data ready. Whenan EPICS IOC process detects the IRQ, it read the data
and updates its records.

PERFORMANCE TESTPulsar Test Figure 6: Pulsar Test setup of BPM readout system.
For the first step, we performed pulsar tests with a 1 kV
monocycle pulsar (Kentech Instrument, Model SPS/V/L
pulse width: 1ns, positive unipolar). Figure 6 shows
pulsar test setup. Pulsar output is equally divided to each
input in order to emulate ideal beam (no beam jitter)
passing through center of the beam pipe.

Figure 8: Position histogram example of beam test
(0.3 nC). X-axis is position in !m.
We performed beam test to confirm the BPM readout
system performance at real condition. Actual beam is also
equally divided to two opposite electrode to emulate ideal
beam. In addition, 96 ns interval double pulse is emulatedwith 20 m delay line. (Fig. 7)
We took 300 events with 0.3 nC per bunch and resulted
in "x=11.9 #m (1st bunch), "x=14.4 #m (2nd bunch),"y=14.4 #m (preliminary).
We increased beam charge up to 0.45 nC per bunch
and took 100 events. It resulted in "x=5.7 #m (1st bunch),"x=8.2 #m (2nd bunch), "y=5.1 #m (preliminary).

SUMMARY AND FUTURE PLAN
This new BPM readout system will be needed in theSuperKEKB injector linac commissioning, therefore weplan to install this new BPM readout system at 2014
summer shutdown time. So far, we have confirmed it
achieve less than 10 µm at the beam test.
We will perform 3-BPM tests [4] to check it in realconditions (identical with normal operation). Based on
the knowledge obtained in its debugging and tests, wewill make updated (final) prototype board. And then wewill perform final check and software preparation.

ACKNOWLEDGMENT
Through this BPM readout system development, wethank Dr. Steve Smith, Dr. Andrew Young at SLAC andDr. Makoto Tobiyama at KEK for their suggestions andadvice in design and development.

REFERENCES[1] M. Masuzawa, in Proceedings of the FirstInternational Particle Accelerator Conference(IPAC’10), Kyoto, 2010, pp. 4764–4768.
[2] M. Satoh et al., “Development of a Fast BPM DAQ
System Using Windows Oscilloscope-based EPICSIOC”, Proceedings of the 4th Annual Meeting ofParticle Accelerator Society of Japan and the 32ndLinear Accelerator Meeting in Japan, Wako, Aug,2007.

[3] K. Furukawa et al., “Beam Feedback Systems andBPM Read-Out System for the Two-Bunch
Acceleration at the KEKB Linac”, in Proceedings ofthe ICALEPCS2001, San Jose, November 2001,
pp.266-268 (2001).
[4] T. Suwada et al., “Stripline-type beam-position
monitor system for single-bunch electron/positron
beams”, Nuclear Instruments and Methods in Physics
Research A 440, pp.307-319 (2000).
[5] S. R. Smith et al., “LCLS Stripline BPM SystemCommissioning”, in Proceedings of the 23rd Particle
Accelerator Conference (PAC’09), Vancouver,
Canada, 2009, pp4027-4029.
[6] Spartan-6
FPGA
Family,XilinxInc.
http://www.xilinx.com/products/silicondevices/fpga/spartan-6/.