Development of Beam Diagnostic System for HIRFL
Zheng Jianhua and Beam Diagnostic Group
Institute of Modern Physics, Chinese Academy of Sciences
P.O.Box 31, Lanzhou 730000,ChinaAbstract
Beam diagnostic is an essential part of any accelerator.
The beam diagnostic system for HIRFL had beendeveloped and used for years, and the system is being
improved continuously to satisfy the requirements of theoperation and beam tuning of HIRFL. This paper describes
the present status and development of the beam diagnostic
system at HIRFL.
1 Introduction
The beam diagnostic system for HIRFL is a distributedmicrocomputer system, which can be divided into threelayers. In the top layer, the microcomputer control station
manages the diagnostic system of HIRFL and offers manmachine interfaces and operation functions used byoperators. In the middle layer, the CAMAC system with
serial highway and function modules receive commands
from the computer and return status and measurements
information. In the bottom layer, a variety of beamdiagnostic devices along the beam lines and inside SFC and
SSC are installed, such as profile monitors, Faraday cups,
slit devices, radial probes, the capacitive phase probes andso on for the measurement of beam intensity, beam profile,energy and energy dispersion, beam phase, beam emittanceand other parameters of beams.

analyze the charge states and also use as the beam stop. 19
sets of movable and static probes inside SFC and 29 sets of
one are set to measure the internal beam intensity.
Any beam current from each probe can be measured by acurrent-to-voltage converter which should have good
insulation and shielding property, low offset voltage, andwide frequency responsibility. The careful calibration forevery converters is also important to assure themeasurement accuracy. But fabrication technology and thecalibration error of converters made in factory may cause
errors in measurement of system. New improvement of thebeam intensity measurements has been considered, as
shown in Fig.1, which will decrease the error ofmeasurements system.

2 Improvement of the beam diagnostic system
2.1 Beam profile measurements

Fig.1 The system of beam intensity measurements

About 40 sets of secondary emission multi-wire profile
monitors are installed on beam transportation lines ofHIRFL to measure the horizontal and vertical profile ofbeam. The measurement can be done with several monitors
simultaneously at different position along the beam line,
the beam loss is only 3%. They can display the beamprofile on the oscilloscopes of the main console andprocess the profiles with computer. The measurement
sensitivity is about 10nA.
In the beginning of operation, the main problems werethat the wires sometimes were broken off, and the accuracyof the profile measurement was low. Then the mechanicaldriver parts of probes and the electronic unit used tomeasure the beam profile were improved, themeasurements of profile are reliable and the position
accuracy of the profile measurement is about ±1mm.

2.3 Beam slit and energy measurement

2.2 Beam intensity measurements

The phase detection system of HIRFL is based on theheterodyne principle using RF_signal mixing and filtering
techniques to monitor continuously phase inside SFC, SSC
and on the beam line. The new HIRFL phase measurement
system is shown in Fig.2.

Beam intensity is a main parameter for accelerators.
About 30 sets of Faraday Cups have been installed in thebeam lines to measure the beam intensity, beam energy andThere are two kinds of slits, about 19 sets installed onbeam lines of HIRFL. One is a changeable width slit,
which is used to limit the beam emittance. The another is afastened width slit, which is used to measure the ion energy
and the energy dispersion. The main functions of them are:the adjustment for slit width and position, accurate
measurement for slit width and position, beam intensity
measurement on the slit plates, remote control of the driver
power and the safe protection of slit limit position. The
precision of position adjustment is about ±0.5mm. Theenergy measurement device with the slit control device has
been developed. It is convenient to measure and analyze
the beam energy during the beam tuning.
2.4 Beam phase measurement

Some problems were found in operation in the oldsystem. In order to improve its performance, a selftest
system

Fig.4 Constructure of control software for phasemeasurement
The data of beam phase measurement in the accelerator
operation shown in Fig.5. has been analyzed. All results
show that the repeatability, and reliability are satisfactory
and the accuracy of measurement is about ±0.5°.

Fig.2 Diagram of phase measurement system for HIRFL
Shown in Fig.3 has been designed and developed. Bymeans of the selftest system, the accuracy of the old system

Fig.5 SSC 12C6+ Phase measurement curve
2.5 Emittance Measurements

Fig.3 Principle of the selftest system for HIRFL phasemeasurement system
was detected and the system is improved from ±6° to±1.5°. A new method to match the cable electrical length
has been developed according to our present condition. It
can not only match the cable made of the same medium but
also match the cable in difference medium. Using themethod, the phase difference between the cables connectedwith the probes had been decreased to 0.3°. Double shieldsignal preselectors have been developed to improve thecrosstalk of signal channels to -70dB. The new control
software shown in Fig.4 has been developed to improve thesystem reliability, The error probability of measurement is10 -3.

In order to monitor the transverse beam emittance in beamtuning, the three-profile-method have been used to measure
the beam emittance. Three profiles of a beam in a field-freedrift space of beam line can be obtained to calculate thethree parameters of the emittance ellipse. The measurement
results are processed by a least square fitting and Gaussian
distribution fitting. The measurement result is shown inFig.6.
The observation of beam profiles on fluoresent screenshas been changed from a qualitative approach to aquantitative method due to the availability of high quantity
video imaging systems and the progress in suitablesoftware. The pepper-pot method based on the measurement techniques will be used in the ECR beam line andpre-beam line of HIRFL to measure beam emittance. Thismethod shown in Fig.7 uses an array of identical holes in aplate oriented in beam transverse X-Y plane, after drift
distance L the fluorescent screen is placed.
The transmitted beam strikes the fluorescent screen andproduces an image that is proportional to 4-dimensional
emittance ε(x,x′,y,y′) of the beam.

3 Beam diagnostic control system

Fig. 6 The result of transverse beam emittancemeasurements in Pre-beam line

The beam diagnostic system for HIRFL is a branch ofHIRFL control system and is also an independent control
subsystem. According to the location of the probes
distributed at HIRFL, the system is divided into three
microcomputer control stations: SFC diagnostic control
station, beam line diagnostic control station and SSC
diagnostic control station. The system has been improved
and the microcomputers have been updated. The computers
for diagnostic system are being linked with the network of
HIRFL control. The software based on the windows
programming technique, is being developed, instead offormer FORTRAN program. The accelerator parameters
will be calculated and their graphics will be displayed on
the computer screen that will make the beam tuning easierand more directly visible.
4 Conclusion
All the beam diagnostics use in HIRFL use interceptive
probes except the phase detection system. In order tooptimize the efficiency of beam tuning, some noninterceptive beam diagnostic devices will be developed
which is also necessary for the development of HIRFL infuture.
It is a pleasure to acknowledge Dr. Liu Wei, whoparticipated in the design of the emittance measurements,
and I would like to thank Dr. F. loyer for valuable
information and help.

Fig. 7 Schematic of measurement facility for emittamce
When the pepper_pot plate is moved from the beam line,
the images produced on the scintillating plate viewed by aCCD- Camera can display the beam shape and position andoperators can see the effects of parameter adjustments
directly.

References[1] Z.Q.Shen et al, The Beam intensity and Emittancemeasurements,IMP Annual Report 1989.
[2] J.G.Wang et al,Beam Emittance Measurement by the
Pepper-pot Method, Nuel.Instr. and Meth.,A307,1991.