UPGRADE OF ABORT TRIGGER SYSTEM FOR SUPERKEKBS. Sasaki#, A. Akiyama, M. Iwasaki, T. Naito, T. T. Nakamura, KEK, Ibaraki, JapanAbstract
The beam abort system was installed in KEKB toprotect the accelerator equipment and the Belle detector,
and for radiation safety, from high current beams. For
SuperKEKB, the new abort trigger system has beendeveloped. It collects more than 130 beam abort request
signals and issues the beam abort trigger signal to theabort kickers. The request signals are partially aggregatedin local control rooms located along the SuperKEKB ringand finally aggregated in central control room. In order toincrease the system reliability, the VME-based moduleand the E/O module was developed, and all the abort
signals between the modules are transmitted as opticalsignals. The system also has the timestamp function tokeep track abort signal received time. The timestamps areexpected to contribute to identify the cause of the beamabort. Based on the feasibility tests with a prototype
module, the new module design has been improved andfixed. This paper describes the details of the new abort
trigger system.

INTRODUCTION
SuperKEKB is the upgrade of the KEKB asymmetricenergy electron-positron collider in Japan [1]. The
designed luminosity is 40 times as high as the peakluminosity of KEKB.
SuperKEKB consist of two storage rings, low-energy
ring (LER) and high-energy ring (HER). Each ring has abeam abort system to protect the accelerator equipment
and the Belle detector, and for radiation safety, from highcurrent beams. The abort trigger system collects morethan 130 beam request signals and issues a beam abort
trigger signal to abort kickers.
In KEKB, the modules of the abort trigger system wereconnected with twisted pair cable to transmit the electricalrequest signals and low pass filters were inserted toreduce electrical noise. The low pass filters caused timedelay and the total system response time was about 100
μs. For SuperKEKB, the optical request signals aretransmitted and the low pass filters have been removed.
The response time is improved to be less than 20 μs.
The new system has the timestamp function to keep
track of the abort signal received time. The resolution of
the timestamp is 0.1 μs. It is expected to contribute toidentify the cause of beam abort.
This paper describes the design and the status of the
new abort trigger system.

____________________________________________#shinya.sasaki@kek.jp

SYSTEM DESIGN
Modules
The system is composed of two kinds of modules. First
is 2ch E/O module which converts electrical signals fromabort request source to optical signals. It can receive 3
kinds of electrical inputs: TTL, RS422, or relay, and cantreat the input as active-high or active-low. They are setby slide switches in front panel. Figure 1 shows picture of
the 2ch E/O module.

Figure 1: Picture of the 2ch E/O module. Input type andpolarity can be set by slide switches (1424).
Second is VME-based 8ch beam abort optical input
module (18K15). It gathers 8 optical signals and output an
OR optical signal. Since it latches the input signals until
reset, pulse input can also be detected and it keeps
outputting once request signal is detected. Abovefunctions are processed on FPGA, software is not runningon the module. The module can be controlled andmonitored via VMEbus. Figure 2 shows picture of theVME-based 8ch beam abort optical input module.

Figure 2: Picture of the VME-based 8ch beam abort
optical input module (18K15).

Timestamps
Abort request signals are usually occurred sequentially.
Therefore an order of the request signals are important toidentify a cause of the beam abort. The new abort trigger
system records timestamps when it received the request
signal. The timestamps reveal the order of sequential
request signal.

counter counts an external clock. Each counter is 32-bitand cleared when the module is reset. The internal clock
counter is also cleared when the external clock input isdetected. After the module reset, each counter starts tocount up after the external clock is detected. The external
clock synchronize the counters of the all modules in thesystem. When the module detects an abort request signal
the counters are latched until reset. Figure 3 shows thetiming diagram of the counter.
The resolution of the timestamp is 0.1 μs since theinternal clock counter counts up at 10 MHz. We cannotice relative time differences from the counters.
However absolute time cannot be calculated without
software processing. We can calculate absolute time withthe time when an external clock source send a signal.

System Configuration

Figure 3: Timing diagram of two counters fortimestamps. Internal clock counter counts up at 10 MHz.
When the module detects an abort request signal thecounters are latched until reset.
The timestamps are generated from two counters, aninternal clock counter and a trigger pulse counter, in
18K15. The internal clock counter count up at 10 MHz
synchronized to FPGA operation clock. The trigger pulse

Figure 4 shows entire system configuration. The
electrical abort request signals from equipment areconverted to optical signals on 1424 E/O modules. The
optical signals are partially aggregated in Local ControlRooms (LCR) located along the SuperKEKB ring andfinally aggregated in Central Control Room (CCR). The
longest distance from LCR to CCR is 2 km and its
transmission time is about 10 μs.
The system needs external clock source to synchronize
the timestamp among 18K15s. We use a software trigger
system [2] as external clock. It provides thesynchronization pulse and/or the interrupt signal toInput/Output Controllers (IOCs) or devices. The time
when the software trigger system send a synchronization
trigger is recorded on the IOC at CCR.

Figure 4: Schematic diagram of the abort trigger system for SuperKEKB. Abort request signals are converted to opticalsignals on E/O modules and aggregated on VME-based modules. The signals are partially aggregated in LCR andfinally aggregated in CCR. The time when EVT (EVent Transmitter module) send a synchronization trigger is recordedon the IOC at CCR.

PERFORMANCE TESTS
Response time
We have tested the response time of 1424 and 18K15.
The setup of the test is shown in figure 5. We havemeasured TTL outputs of the modules equivalent tooptical output. Function generator generates pseudo abort
request signal which is 500 ns pulse width.
Figure 6 is result of the test. The system detected 500
ns pulsed request signal. It takes about 150 ns for 18K15
to output after E/O module output. This latency is cabledelay and processing time of 18K15. Considering that thelongest cable delay from LCR to CCR is 10 μs, thelatency is sufficiently low and the latency of the abort
trigger system mainly depends on the cable delay.

Figure 7: Latched counters of 18K15. TRIG_TIME is thetrigger pulse counter and ABORT_TIME is the internal
clock counter. The counters show CH1 is the firstdetected signal.
Figure 8 shows timestamps of time and date format.
The timestamps are calculated by software processing
based on recorded time which the software trigger systemsend a synchronization trigger. A relative error among
timestamps is several microsecond caused of an error ofinternal 10 MHz clock on 18K15s and a synchronization
error among 18K15s. On the other hand, an absolute errorof timestamps is several millisecond caused of an error of
the recorded time on IOC at CCR.

Figure 5: Schematic diagram of the response timemeasurement.

Figure 8: Timestamps of time and date format calculated
by software processing.

CONCLUSION
Figure 6: Response of 1424 and 18K15 to 500 ns pulse
request signal input. CH1 is pseudo abort request signal
generated from Function Generator. CH2 is TTL output
equivalent to output of E/O module. CH4 is gathered
output on 18K15.

Module control and timestamp
Since the SuperKEKB control system was based on
EPICS [3], we have developed EPICS software to control
and monitor 18K15.
We have tested the timestamp function with EPICS
control system. Abort request signals were input to 18K15
on arbitrary timing and we confirmed latched countersshown in figure 7. The counters revealed an order of abort
request signals.

We have developed the new abort trigger system forSuperKEKB. The total response time of the systemsignificantly depends on cable delay and it is improved tobe less than 20 μs. The system can record timestamps
when it receives abort request signals. Timestamps reveal
the order of sequential request signals.

REFERENCES[1] Y. Ohnishi et al., “Accelerator design at
SuperKEKB”, Prog. Theor. Exp. Phys., 2013,
03A011.JACoW.org[2] T. Naito et al., "Performance of the timing system for
KEKB", ICALEPCS’99, Italy, Oct. 4-8, 1999
[3] http://www.aps.anl.gov/epics