Zhichu CHEN
On behalf of Beam Diagnostics group of SSRF
Shanghai Institute of Applied Physics

Outline• Introduction to SSRF
• Overview of the DCCT system on the SR• Noise Study characterization
 noise exploration
 modeling workaround result• Future tests• SummaryZhichu CHEN / SSRF BI group

Oct. 1, 2012

Introduction to SSRF

Zhichu CHEN / SSRF BI group

Oct. 1, 2012

Introduction to SSRF
3.5GeV storage ringfull energy booster

7 beam lines for now

DBALow Emittance mode

Normal mode

EnergyGeV

3.5

3.5Circumferencem432432

Natural Emittance

nm*rad3.9

11.2

CurrentmA

200-300/5

200-300/5

Tune

22.22/11.32

22.22/11.32

Chromaticity-56/-19-56/-19

RF Voltage

MV

4.0~6.0

4.0~6.0

Energy Loss/Turn

MeV

1.448

1.448

Max beam power

kW~600~600

150MeV LINAC
The only third generation light source in China
2465 proposals, 235 research teams, 3780 users since formal operation in 2009
Availability 97.6%, MTBF 55.3 hours, MDT 1.55 hours in 2011
Zhichu CHEN / SSRF BI group

Oct. 1, 2012

Overview of the DCCTZhichu CHEN / SSRF BI group

Oct. 1, 2012

The Primary Requirements
At least 2 DCCTs required:Display current details during ramping cycle @ Booster(whole ramping cycle 250ms, average current < 2mA)

C15

Precise average current & lifetime measurement @ Ring(typical current [140mA 210mA], lifetime 20~30hours)

Design goals

C17Ring DCCT

10μA @ 1Hz

Booster DCCT

50μA @ 10kHz

A general solution adopted to cover two applications:
Raw sampling rate 10kHz, to capture booster current waveform
The 2Hz high resolution data were produced by averaging the 10kHz data at the PC end
Both 10kHz and 2Hz data available to users
Total 2 DCCTs installed in the Ring
DCCT15, primary average current monitor
DCCT17, online backup
Zhichu CHEN / SSRF BI group

Oct. 1, 2012

System Configuration
ComponentSolution

SensorNPCT175 HR, 1 μA/√HzShielding

Fabrication locally, design borrowed from SPEAR3DAQPXI NI4070, 6.5bits DVM, 10kHz sampling rate

Data processing digital filtering + averaging
Data server

10kHz and 2Hz data, EPICS IOCcore @ LinuxIn tunel

In diagnostics station

Beam pipewith a ceramic gap

DCCT Sensor

Electron beam

Zhichu CHEN / SSRF BI group

DCCTFEDVM

PXI busPXIIOC

Control network
EPICS CAaveraging 10kHz data
to 2Hz; signal filtering
Oct. 1, 2012

Shielding Design• Design borrowed from SLAC
• Well tested during SPEAR3 operation• Easy for fabrication and installation• Modular structure, can be used forboth Booster and Ring with similar
designZhichu CHEN / SSRF BI group

Oct. 1, 2012

DAQ
Noise test has performed for:NI PXI 4070 (6.5bit)
NI PXI 4071 (7.5bit)
NI PXI 4070 combined with NPCT175
NI4070NI4071
NI4070 + NPCT175

1E-3

1E-3

1E-4

1E-41E-5

1E-5
1E-6

1E-6
1E-7
100

1k

10k

100k

1M

Current RMS noise level @ 2A range (A)DVM RMS noise level (Volts)

0.01• 4071 do not have asignificantly betterperformance• The measurement
noise mainly
comes from NPCT
sensor under thesampling rate of40kHz and less
• The main source
becomes the DVM
electronics when
the sampling rate
is above 40kHz

Sampling rate (Hz)Zhichu CHEN / SSRF BI group

Oct. 1, 2012

System Performance
SSRF DCCT resolution test @ 2009.03.31

R M S noise /  A

10102

1

Current readings deviation (A)1.6

NPCT175 specification
DCCT15, data rate 2Hz
DCCT17, data rate 2Hz
DCCT15, data rate 10kHz
DCCT17, data rate 10kHz

real beam
current calibrator

1.5
1.4
1.3
1.2
1.1
10.9
0.8
050

100

150

200

250

300

Input current (mA)

10measurements STD @ 10kHz / mA

Resolution < 2uA @ 1Hz BW
00.1

110100frequency / Hz

1k

10k

0.3
DCCT15,raw data,80~116A
DCCT17,raw data,184~269A0.25
0.2
0.15
0.1
0.05

140150160

170
180
beam current / mA

190

200

Resolution @ 5kHz BW
DCCT15 is better than DCCT17 (installation, ground loop, etc.)

SSRF Ring DCCT linearity test @ 2009.03.31

Resolution of 2Hz data is close to the hardware limitation, hard toimprove further
Various noise have been found at 10kHz data, lots of room for
optimization

DCCT readings / IDCCT (mA)

350
Measured data
Linear fitting

300
250
200

I

DCCT=IINPUT*A+B

A = 1.000327  0.000005
B = 0.0189  0.0009

150
100
500050

100

150

200

250

300

Calibration current setting / IINPUT (mA)

Nonlinearity < 0.03% @ 0 ~ 300mA
Zhichu CHEN / SSRF BI group

Oct. 1, 2012

Noise Study

Zhichu CHEN / SSRF BI group

Oct. 1, 2012

Noise Study: Characterization
Type of noise

frequency

amplitude

occurrence

power line noise

50Hz and its harmonics<10μA for
DCCT15alwaysfrequency specific noise

1.147kHz for DCCT15~300μA

alwaysfrequency drifting noise

few kHz~100μA

alwayssquare wave noise/-600μA~once a week

zero drift

white<1μA@1Hz

alwayspowerline (50Hz)
10& harmonics

fixed frequency noise

4101032

frequency drifting noise
1

measured current / mA

amplitude / a.u.

10

104
103.8
103.6
103.4
103.2
103
102.8
102.6

10

0

0

0.5

1

1.5

2

2.5
3
frequency / kHzZhichu CHEN / SSRF BI group

3.5

4

4.5

1

2

34
time / s

5

6

7

8

5

Oct. 1, 2012

Square Wave Noise: Characteristic
210
209

It hurts the resolution
badly, especial for
lifetime measurement

208.1

beam current / mA

208.05beam current / mA

208
207

208
207.95207.9
207.85
207.8

206

0.145

0.15

0.155
0.16
time / hours

0.165

205
204
203
202
00.1

0.2

0.3

0.4
0.5
time / hours0.6

0.7

measured current / mA

0.9

appear randomly without anywarning

104
103.8
103.6
103.4
103.2
103102.8
102.6

0.8

Hard to be removed
with traditional timedomain or frequencydomain filtering means

12

3

4
time / sZhichu CHEN / SSRF BI group

5

6

78

shaped as a square waveformwith indefinite periods andfixed amplitudes

Oct. 1, 2012

Narrowband Noise : Characteristic
6

•

0.5
4

•

1.5

22
0

2.5
3

•

-2

3.5
-4

4
4.5

-6

amplitude / A

5
010

310

210

1

10

010•0.2

0.4
0.6
0.8
time / hours

1DCCT15
DCCT17-1

0.5

1

1.5

2
2.5
3
frequency / kHz

Zhichu CHEN / SSRF BI group

3.5

44.5

measurements STD @ 10kHz / mA

frequency / kHz

1power line noise (50Hz) and its
harmonics
frequency specific noise(1.147kHz)
frequency drifting
noise(4.4kHz—2.2kHz during
this period)
The total intensity of thenarrowband noise isapproximately proportional to thebeam current
0.3
0.25

DCCT15,raw data,80~116A
DCCT17,raw data,184~269A

0.2
0.15
0.1
0.05

140150160170180
beam current / mA

190

200

Oct. 1, 2012

Noise Study: InfluenceType of noise

influence

power line noise

the resolution of the 10kHz data

frequency specific noise
frequency drifting noise
square wave noise

resolution of both the 10kHz data and the 2Hz data; systemmeasurement error; lifetime measurement error

zero drift

resolution of both the 10kHz data and the 2Hz data

Zhichu CHEN / SSRF BI group

Oct. 1, 2012

Noise Study: Exploration
Type of noise

exploration

power line noise

feed reverse current to cancel out the DC component of thebeam current, to see whether it comes from: sensor, nonlinear
ADC, etc.

frequency specific noise
frequency drifting noise
square wave noise

try to find the correlation between the noise and other machineparameters: RF voltages, beam current, etc.

zero drift/Zhichu CHEN / SSRF BI group

Oct. 1, 2012

Narrowband Noise Exploration
exploration

power line noise

feed reverse current to cancel out the DC component of thebeam current, to see whether it comes from: sensor, nonlinear
ADC, etc.

frequency specific noise
frequency drifting noise

feed inverse current
at the calibration portnoise amplitude / A

Type of noise

10310210

1

10010

-1

no beaminternal 100mA test singal
180mA beam

0.5

1

1.5

2
2.5
3
frequency / kHz

3.5

4

4.5

5

Noise spectrum without beam, with test signal and with beam
104amplitude / a.u.

beam current at 180mA••

Most of the NB noise is excited by the beam
The spectrum scarcely changed after the reverse
current was fed. Hence, the noise is DC unrelated.

Zhichu CHEN / SSRF BI group1010

2normal measurement
reverse current of 179mA was feeded

000.5

1

1.5

2

2.5
3frequency / kHz

3.5

44.5

5

Noise spectrum with & without inverse current

Oct. 1, 2012

Square Wave Noise: Exploration
Type of noise

explorationsquare wave noise

try to find the correlation between the noise and other machineparameters: RF voltages, beam current, etc.

No other relations have been found between the noise and machine parameters
except that this type of noise does not appear when the beam current is below
197mA, and has an interesting distribution around the high current area
Zhichu CHEN / SSRF BI groupOct. 1, 2012

DCCT Modeling-0.02-0.04

Kalman Filter

-0.06

210.5

beam current / mAbeam current / mA

0-0.08square wave noise-0.1

123

4
5
6time / minutes

78

910

Square wave

209.5
209
208.5
208

Ideal DC
componentof beam
current

1

2

3

4
5
6time / minutes

78

910

DVM readings
Frequency
shifter
and amplifier

210

ideal beam + All noise

210

Power line
0.15

ideal beam

zerodrift

other NBnoise

NB noise

208

1

23

4
5
6time / minutes

78

910

NB noise0-0.05-0.10.1

-0.15

0.05

-0.2
00.03

0.2

0.4
0.6
time / minutes

0.8

1x 10

-3

0-0.050.15-0.1

NB noise

0.1

-0.15
-0.2
00.2

0.4
0.6
time / minutes

0.8

1

x 10

random zero drift

0.025

-3

beam current / mA

208.5

0.05

beam current / mA

0.15

beam current / mA

209

beam current / mAbeam current / mA

0.1

209.5

0.02
0.015
0.01

0.05

0.005

000-0.05

0.002

0.004
0.006
time / minutes

0.008

0.01

-0.1
-0.15

Notch FilterZhichu CHEN / SSRF BI group

-0.2
00.2

0.4
0.6
time / minutes

0.8

1x 10-3

Oct. 1, 2012

Noise Study: Workaround
Type of noise

workaroundpower line noise

narrowband, multiple frequencies, unstable frequencies:
adaptive notch filter

frequency specific noise
frequency drifting noise
square wave noise

unpredictable occurrences, wideband, hard to remove in timedomain as well as in frequency-domain:
Kalman filter

zero drift

installation optimization
frequencydriftingnoisepower line &harmonicsf  t   f 0  t   F 1 g  F  t    h  t    pi  t    ni  t   z  t 
original
beamsignal

Zhichu CHEN / SSRF BI groupsquarewave

other NB
noise

zerodrift

Oct. 1, 2012

Workaround: Adaptive Notch Filter
0.2

FFTspectrum

measured current / mAoriginal signal

DCCT15,raw data
DCCT15,filter applied

0.15
0.1
0.05
0-0.05
-0.1
-0.15
-0.2

50

100

150
time / ms200

250

300

current waveform before and after filtering
5000

frequency
detectorcounts4000

time-domain filter

DCCT15,raw data,STD=82A
DCCT15,filter applied,STD=12A

3000
2000
1000
0-0.2

-0.15

-0.1

-0.05
00.05
measured current / mA

0.1

0.15

0.2

noise
foundthresholddetectorsignalqualified
output signal

Zhichu CHEN / SSRF BI groupamplitude / A

histogram before and after filtering
10

310

210

1

10010

-1

DCCT15
DCCT15,filter applied

0.5

1

1.5

2
2.5
3
frequency / kHz

3.5

4spectrum before and after filtering

4.5

Workaround: Kalman Filter

Time Update (“Predict”)(1)Project the state aheadX̂-k=Ax̂k-1+Buk-1(2)Project the error covariance ahead
P-k=APk-1AT+Q

Measurement Update (“Correct”)
Compute the Kalman gain
Kk=P-kHT(HP-kHT+R)-1
Update estimate with measurement zkx̂k=x̂-k+Kk(zk-Hx̂-k)Update the error covariance
Pk=(I-KkH)P-k

Initial estimates for x̂k-1 and Pk-1

Zhichu CHEN / SSRF BI group

Oct. 1, 2012

Noise Study: Result
Type of noise

resultpower line noise
frequency drifting noise

resolution reduces from (DCCT15/DCCT17 @10kHz)
80μA~116μA/184μA~269μA
to12.4μA/30μAsquare wave noise

resolution reduces from 53μA to 6μA for 2Hz data

zero drift/measurements STD @ 10kHz / mA

frequency specific noise

0.35
0.3
0.25

DCCT15,raw data,80~116A
DCCT15,filter applied,12.4A
DCCT17,raw data,184~269A
DCCT17,filter applied,30A

0.2
0.15
0.1
0.05
0140

150

160

170
180
beam current / mA

190

200

Resolution before and after
adaptive notch filtering @ 5kHz BW
Zhichu CHEN / SSRF BI group

Resolution before and after
Kalman filtering @ 1Hz BW
Oct. 1, 2012

Comprehensive Evaluation
2RMS noise / A10110

NPCT175 specification
DCCT15
DCCT17
DCCT15, raw data
DCCT17, raw data
DCCT15, filter applied
DCCT17, filter applied

0100.1110100frequency / Hz1k10k•No significant improvement for 2Hz data
•Much better than the specification for 10kHz sampling rate after the filtering•Improved 10kHz data could be useful for machine study (such as energy calibration)

Zhichu CHEN / SSRF BI group

Oct. 1, 2012

Future Tests

Zhichu CHEN / SSRF BI group

Oct. 1, 2012

What We Will Do Next• Make more correlation analysis to locate the source of thesquare wave noise• Optimize the installation to minimize the zero drift
 The 10kHz data (on the storage ring) is filtered in order to increase the2Hz data performance, which turns out it’s limited by the zero drift• Use BPM sum signals as a replacement for some special
situations
 Some algorithms have already been tested to pick up the “good” BPMs
as talked in another article of these proceedings.

• And more . . .

Zhichu CHEN / SSRF BI group

Oct. 1, 2012

SummaryZhichu CHEN / SSRF BI groupOct. 1, 2012

Conclusions• The combination of NPCT175+NI 4070 DVM with sampling
rate of 10kHz was picked up to meets the basic needs in SSRF
• Various kinds of noise exist and affect the system despite theshielding, including NB noise, random square wave fromnowhere and zero drift problem• After using the adaptive notch filter and the Kalman filter, theperformance of the DCCT has a significant improvement
 Adaptive notch filter (DCCT15/DCCT17 @10kHz):• 80μA~116μA/184μA~269μA to 12.4μA/30μA
 Kalman filter (@2Hz):• 53μA to 6μA• Anyway, the methods are intended only as a stopgap. We willkeep looking for where the noise comes from and try to get ridof it from the first place
Zhichu CHEN / SSRF BI group

Oct. 1, 2012