Progress of Turn-By-Turn System for HLS *
J.H.Wang, J.H.Liu, B.G.Sun,W.M.Li,
Z.P.Liu, Z.F.Zhang, P.Lu
NSRL, University of Science and Technology of China, Hefei, Anhui 230029
P.R.China
Abstract. During the Phasell project of NSRL, a turn by turn system is proposed for storage
ring diagnostics which engages log-ratio electronics circuit to measure machine properties of the
HLS storage ring. The log-ratio processor works at 408MHz which is 2* RF of HLS. A injection
kicker and the stripline resonant exciting methods are used to excite beam for nonlinear beam
dynamics studies and phase space of stored beam. Up to 2 seconds data acquisition is ensured. In
this paper we present the performance of each components and preliminary test results of the
turn-by-turn BPM system.
INTRODUCTION
A 200MeV injected beam and operation at SOOMeV and 200-300 mA for HLS
storage ring. The multicycle multiturn injection system is used for current
accumulation.
In order to monitor the injecting efficiency, damping rate and P oscillation after
update of injection and RF system, a turn-by-turn system of HLS has been started[1]
and just tested now. The turn-by-turn system based on the Log-ratio technique, which
is a fairly new idea for BPM and tends to become mature gradually. Compared with
the familiar A/Z and AM/PM method, highlighted features of the log-ratio technique:
low noise, high bandwidth and wide dynamic range, as well as responsible linearity [2].
Electronics working at bunch pass frequency can reduce the complexity of deal with
signal chain and make it easy to implement.
Because the injection rate of HLS is 0.5Hz, the data acquisition module is
designed to capture data and write into disk simultaneously so the max sampling-time
is up to 2 seconds. That is one time records 9 million turns, which is flexible for data
processing.
Both using stripline exciting controled with a gate in timing system and a injection
kicker for exciting and perturbing storaged beam are tested.
* Supported by National Important Project on Science- Phase II of National Synchrotron Radiation Laboratory
CP648, Beam Instrumentation Workshop 2002: Tenth Workshop, edited by G. A. Smith and T. Russo
© 2002 American Institute of Physics 0-7354-0103-9/02/$19.00
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THE TURN BY TURN SYSTEM ARCHITECTURE AND
FUNCTION
HLS turn by turn system consists of front end pick-up electrodes, Log-ratio
electronics, timing system, and data acquisition system which will be placed in IPC.
We adopt the Log-ratio electronics from Bergoz company. The timing system home
made put in NIM Crate. The principle architrave is as Fig 1 shows.
RF Divider
Delay Generator
Exciting Ctrl
FIGURE 1. Block diagram of the turn-by-turn BPM system
The turn by turn system has two functions. One BPM for turn by turn
measurement and two BPM are selected for phase space measurement. HLS ring can
be operated in single bunch and multi-bunch mode, with 50mA and 350mA as the
achievable maximum storage current respectively now. RF is 204.035MHz, and
harmonics is 45. So request the sample rate of timing system is 4.533MHz and the
dynamic range no less then 60db. The parameter is as Tab.l shows.
TAB. 1 The parameter of HLS turn-by-turn system
Dynamic range
Output S/N
Linearity
Trigger
Repeat period
Adjust precision
Jitter in 2s
-50dbm-10dbm
40db
<1%
220ns;
0. Ins
0.2ns
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LOG-RATIO PROCESSOR
We utilized a Log-Ratio Module(LR-BPM) from Bergoz company. The LR-BPM
processor works at 408MHz and oprates at three modes: Sample & Hold and Track &
Hold and Track-Continuous. Ensured dynamic range of LR-BPM is 65dbm.
The beam position calculated with the log-ratio technique is formulated by the
following expression[3]:
20
1
_x log | — | =
(1)
SG STM
SG
V^ /
^^ STM
where A and C are the electrode potentials; S[dB/mm] is the detector sensitivity, for
X
=
circular aperture BPM
s
80 1
= ———.—
(a-radius); Vout[V] is the output from the
ln(10) a
differential amplifier; GSTM (mV/dB) is system gain which includes both log-ratio and
differential amplifier gain.
TIMING AND CONTROL SYSTEM
The timing and control system is illustrated in Fig.2. The circuits module includes
pulse-shaping, frequency dividing, timing delay and exciting signal switching gate etc.
It has two inputs and three outputs. One of the inputs is synchronization RF, another is
frequency sweeping signal for exciting the stripline kicker.
204MHz
-*
Pulse
Shaping
BPM1
Data
Acquisiting
BPM 2
FIGURE 2. Timing and control system of the turn by turn
The rise time of trigger of the timing system and jitter of trigger with RF signal
during 2 seconds are shown in Fig.3 . From Fig.3, we can see that the rise time
(down curve) is about 2ns and its jitter is better then 200ps during 2 second.
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ciii
FIGURE 3. The jitter with RF synchronous signal during 2s
DATA ACQUISITION
Revolution frequency of HLS storage ring is 4.533MHz. We choose two 20SPS
lObit ADC for data acquisition of two BPMs. Since the 200MeV injected beam,
coherent oscillation damping time is about 1.38s. While for the SOOMeV stored beam,
it is 22ms. In order to be competent for these two modes, the data acquisition module
is designed to capture data and write into disk simultaneously to provide enough
details. PCI bus MASTER DMA makes fast data acquisition possible. The max
sampling-time is up to 2 seconds.
For different operation mode of ring(GPLS and HBLS), different BPMs are chosen.
All modules of the timing system can be controlled via corn-ports of IPC.
The acquisited data is transmitted to control room via local area Ethernet network.
And another favorable character of this system is that it is designed to be operated
under single bunch and multi-bunch modes.
EXCITATION SIGNAL
In order to nonlinear beam dynamics studies and phase space measurment of stored
beam, the max sampling length of this system is 2 seconds. First we use a injection
kicker, which's repeating rate is 0.5Hz with pulse width 3.5 ju s, perturb storage beam.
We also make experiments to load exciting signal to horizontal or vertical stripline,
controled with a gate module packaged in the timing system, can aim for exciting
beam. The excitation power and gate width been maked certain according to test and
calculate to provide enough for beam motion. After the excitation ends, a delayed
trigger is sent to start the turn by turn detect. In our case the delay time(gate width) is
about 10ms and need power about 30dBm for excitation beam in operating at 200MeV.
Adopted a gate pulse excitation sketch diagram is shown in Fig.4
262
i ime
FIGURE 4. Sketch diagram of the excitation system
TURN BY TURN MEASUREMENT
Measasurement result of Turn by Turn
With the LR-BPM module we have made measurements of turn by turn first when
there is no any excitation and analyzed beam spectrum from the data when ring is
operating at SOOMeV.
L
- FFT of Y Turn by Turn data 1
Qy
Cleaning
Electrode
C
\
,
i
h i l l ll
0.1
ill
ll III Illll
0.2
0.3
I il
,.il i
0.4
Q(f0*2Pi)
FIGURE 5. The beam spectrum from the turn by turn data
In the beam spectrum include the Qy, Qx and the power spectrum of clearing
electrode. Some spectrum are still being investigated. When we using a injection
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kicker perturb storage beam at 200MeV, the LR-BPM output as below Fig.6. It also
clearly shows that the distorting orbit and there's coupling between x and y plane.
22 Acqs
FIGURE 6 Beam position caused by injection kicker
In most cases the beam position variation is transformed to freq field for better
understanding. The max available frequency is half the revolution freq. So fraction Q
such as 0.54 is leaked to lower frequency 0.46. If we think it as one value close to 0.5,
we can also divide it into two columns, so the spectrum line we are interest is the one
responding to the fraction part less than 0.1, for instance, 0.51 gives 0.02 in 2 column
FFT. Time domain plot of each column is sine like. In a similar way, we can divide
data into 5 columns to study the tune close to 0.6, for which the fraction part less than
0.1 is the interested one. One example is the tune y, FFT spectrum of turn by turn and
freq spectrograph results are 2.598/3.552 seperately.
Phase Space Measurement
Two BPMs are chosen for phase space tracking and analysis. Different BPM pairs
are chosen for different operation mode of ring. They are chosen according as such
principles as: large (5X and (5y, phase advance between the BPM pair be close to n/2 or
371/2.
x
O
X
X
n
FIGURE 7 Phase space sketch
For Fig. 7, from the transport matrix we can calculate phase coordinates of any
point between Xi and X2(including these two points), f x0,/?0X0'
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From the phase space ellipse equation:
(4)
To minimum the error of W due to position measurement error:
= 2X0AX0+2(j30X0'+a0X0)A(j30X0'+a0X0)
————————r-^———————- X
J32 sin 2 (O j + O 2 )
2
AX
2
+ ———————7——-——————r- X * AX i
/?! sin (O x + O 2 )
VA^7sin(<D 1 + cD 2 )
Then it requires that |sin(Oi+O2)|=l and (5 to be as large as possible. Besides this, to
assure the resolution and precision of system, all BPMs should be in sections with no
nonlinear devices.
SUMMARY
The newly developed turn by turn system which is based on log-ratio processor
working at 408MHz has been implemented for HLS machine study. With the
application of high speed data transmission and acquisition technics, the system can
accomplish turn by turn measurement of sampling-time up to 2 seconds. And to make
use of a injection kicker and horizontal or vertical stripline for excitating beam. Phase
space measurement be maked and operation serving the study of parameters of storage
ring soon.
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ACKNOWLEDGEMENT
Authors would like to thank Dr. K.T. Hsu for the beneficial discussion and
communication. Authors thanks Dr. H.L.Xu and L.Wang etc colleague friendly
cooperate in machine operating.
REFERENCES
[1] J.H.Wang, W.M.Li etc, Turn-By-Turn system design ofHLS, APAC01, Sept. 2001, Beijing.
[2] R.E.Shafer, Log-Ratio Signal-Processing Technique for Beam Position Monitors, AIP conf. Proc.(1993),
pp!20-128
[3] G. Roberto Aiello, Log-ratio technique for beam position monitor systems, AIP conf. Proc.(1993), pp.301-310
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