Control and Timing of the 250kA Pulsed Magnetic Horn
Y. Suzuki, Y. Yamanoi, M. Kohama(a), M. Ieiri, H. Ishii, Y. Kato
M. Minakawa, H. Noumi, K. H. Tanaka, M. Takasaki, and K. Nishikawa
Institute of Particle and Nuclear Studies, KEK, Tsukuba, Ibaraki, Japan(a) Kobe University, Kobe, Hyogo, Japan
Abstract
This paper reports on an interface used in a pulsed
magnetic-horn system which generates a 250 kA 3 msec
magnetic field to enhance the neutrino beam, synchronized
to the 12-GeV KEK proton synchrotron. The interface isimbedded in the system, and offers the capability tocommunicate with an upper-level computer through theGPIB and LAN. The functions of the interface are not only
to operate the system, but also to control and check thetiming, and to return messages to help the supporting staff.
Before completion of the whole physics experimental
arrangement of the neutrino beam line and its control
system, this magnetic-horn system is capable of operating
effectively to check its function, and to test the reliabilityof the horn magnet with a PC in local-area in a short time.
This interface design has been shown to save time in theconstruction of a large physics experiment arrangement.
1 Introduction
In a large physics-experiment facility, there are manycomponents in a wide area. Some problems are raised dueto the scale, which is larger than a small one. One of the
problems is how to control the many components at
minimum cost. The next is how to maintain thosecomponents for long-term physics experiments. The first is
a problem of choice. However, when we obtain anadequate answer from two, the choice is more limited,
especially in the recent engineering environment using a
PC or WS and LAN. Those tools are a great help with bothcontrol and maintenance work by reporting on theconditions instantly of many components over a wide area.
Presently, at KEK a neutrino beam line has been
constructed. One of the components, a 250-kA magnetic
horn and a pulsed power supply is under testing. Also aninterface for controlling the pulsed power supply has been
designed and is now under testing. The interface must havethe remote-control function of a normal magnet power
supply, and additionally to have the function of timing
control of the charging unit and the trigger gate of thehigh-voltage thyristor switch, and monitoring its
synchronizing condition with the fast-extracted beam fromthe 12-GeV proton synchrotron(PS). As an answer to theabove mentioned demands, a microprocessor and somecircuit boards have been selected and embedded in thepulsed power supply: the STD-bus cards and an 8-bit
microprocessor.
2 Hardware for control
The main parts of the hardware for controlling the pulsed
power supply, and its functions are as follows:

Z80: ROM-based 8-bit microprocessor performs thefunction of a pulsed power supply;
TMS-9914: Provides a GPIB connection;
CTC: Counter/timer circuits to control and measure thetime of the operation of the pulse power supply;
PIO: A programmable input/output circuit to control thetrigger gate of the high-voltage thyristor switch;
DAC1: DAC701KH controls the charging voltage of thecapacitor;
DAC2: AD7546KN (dac with external reference)
modulates the output voltage of DAC1 to generate a ramp
voltage;
Some other IO boards: Operate the pulse power supply andmonitor the status;
LAN adapter: LAN/HP-IB gateway connects with GPIBand LAN.
3 Operation of the pulse power supplyFig. 1 shows the pulse power supply. It consists of acharging unit, a capacitor bank, a thyristor switch, and apulse transformer. The charging-unit rating is 8.5kV dc at
the maximum voltage. The capacitor bank has 12capacitors of 500 micro-farad, and totally 6 milli-farad.
The thyristor switch is a stack of three thyristors ofTOSHIBA-SF3000GXs. The I2t is 18E6(A2s). The turnratio of the pulse transformer is 10 (20:2). The dimensions
are 1530mm wide, 1070mm high, 1430mm deep. The
weight is about 11 tons. The operation of the charging unit
is performed by a microprocessor-based circuit with a 2second repeated cycle, which starts to charge the capacitors
synchronously with the PS. Fig.2 shows the capacitor
voltage and time. A charging process is started after a
triggering signal (TS) is received. The charging unit has avariable-value control. The reference voltage of thecapacitors is generated from a ramp voltage by a circuitof serial connections with DAC1 and DAC2. The output
voltage of DAC2 is (DAC1)x(DAC2 set value/ 2048). The
value is counted up by a Z80 every 994 micro-second
periodic interrupt of a timer of the CTC. Since the fullcount-up value is 2048, the DAC2 outputs the same
voltage as that received from the DAC1. DAC1 constantly
outputs a voltage, the value of which is received from theGPIB controller. In Fig. 3, the period of DAC1 to be set avalue is when the charging unit is cutoff. When thecapacitors have charged up, the charging unit is cut off
from the capacitors, and the gate of the thyristor switch isopened by a signal from the PS to trigger the thyristorswitch. When the thyristor is triggered and turned on, thecircuit of the capacitors and the reactance of the load makea simple oscillation circuit. A 25kA pulse current as asingle half sine wave is obtained. The negative part isThyristor switch
Charging unit

Pulse transformer.10:1
250kA

Capacitor

Magnetic horn
BeamFig. 1 Pulse power supply and magnetic horn

dumped in the resistors through diodes. Then, the gate of
the switch is closed, and the charging unit starts again tocharge the capacitors.
DAC2

DAC1

Reference voltage

DAC1
DAC1 x (count/2048)

DAC2Count up to 2048
2 secTSTA

TS: Trigger of charging capacitors
TA: Trigger of 250kA pulse current
Fig. 2 Capacitor voltage and time
4 Timing
The timing signal used to trigger the thyristor switch
comes from the PS, and is supplied to a delay circuit, asshown in Fig.4. The triggering time is controlled by thedelay circuit to meet the time of fast-extracted beam passthrough the Horn. The circuit consists of threetimer/counter circuits (CTC0, CTC1, CTC2). Those areoperated with a 4-MHz clock, and are set to below thecharacteristics.
CTC0: programmable timer of 4 to 996 microseconds;
operation is started by an external signal;
CTC1: 1 millisecond timer. Start of operation is triggeredby the CTC0;
CTC2: programmable counter. Preset value is 1 to 255.
The circuit has totally a delay range of 4 microseconds to255.996 milliseconds with a 4 microsecond programming
resolution. The delay value is controlled through the GPIB
and LAN communication path.

5 Monitoring of timing
Monitoring of the timing is performed by the processor toread out a time counter CTC3, shown in Fig. 4. The time
counter is started when a signal triggers the thyristorswitch. The timer counts up time with a 4-microsecond
step resolution. When a beam signal is received from abeam monitor (CT), an interrupt occurs for themicroprocessor to read the time counter, and check thetime value. If the value is out of a range, a SRQ signal issent out through the GPIB and LAN to the controller.
6 Control of the pulsed power supply
The total operation, including the timing control of thepulsed power supply, is performed by the same processor
as the timing control. The commands for operation arereceived through the GPIB and LAN. For example, whenthe “V 5000” command is received, the processor does asfollows:
1. check status;
2. turns on the main contactor of the charging unit;
3. sets DAC1 to output 5000 volts;
4. enables an interrupt of the charging unit to start.
Synchronization of the charging and the generation of apulsed current are controlled and checked by the processor.
When an error or a problem is detected, a message is sentout for help from a maintenance staff to fix it within a shorttime. The functions of the other commands are to read-out
the status, including the load horn, and the conditions of
the internal low-voltage power supplies. Those also greatly
help to care for the system remotely through the GP-IB andLAN.
7 Conclusion
The design of the control is message-based, anddistributed. The complicated operation process, which isdepend on the device, is performed internally by its
microprocessor through a single interface. The remotecontrol message becomes simple, and easily passes overBeam250kA HORN
Current
Trigger Gate
Charging unitof capacitor

CloseOpen

ActiveClose

Cut off
10

Active105

Charge up start[msec]

Fig. 3 Timing of the charging unit and trigger gate

Beam signal from CT
250kA Pulse current
Trigger

Read out

Beam extraction signal
Delay

CTC0

Interrupt (PIO)

CTC1

CTC2Gate

Time check
No

Delay
CTC3Direct

SRQ

TimerFig. 4 Control and monitor of timing
the LAN, and helps the maintenance staff to correct thecondition.
The pulsed power supply has been under test in a local
experimental house, and is expected to be installed in theneutrino beam line one year later. The installation is
expected to be easier than that for a device with aninterface requiring much wiring.

Acknowledgments
The authors would like to thank Dr. J. M. Maugain, Mr. S.
Rangod, Mr. G. Acquitapce, and Dr. J. Falaleef of CERNfor help with the design and the test operation of themagnetic horn system.