BEAM DYNAMIC INTERLOCK AND BEAM ABORT TRIGGERINGSYSTEMS OF THE IHEP ACCELERATOR COMPLEX
V.V. Gotsev, V.V. Komarov, I.V. Lobov, A.A. Matyushin,
A.V. Popov, Yu.S. Tchernoousko, V.I. Terekhov*
OEA Department, IHEP, Protvino, Russia.
*Corresponding author, E-mail: terekhov@tx.oea.ihep.su
Abstract
The presented systems are aimed at increasing the accelerator radiation safety. They are built as standalone hardware
distributed systems. The Beam Dynamic Interlock System prevents the beam transfer to the next stage of the acceleratorcomplex if that stage is not ready for the operation (e.g., magnetic field is out of range, bad vacuum, etc.). The Beam
Abort Triggering System reacts immediately to an emergency situation at the accelerator by triggering the kicker magnets
to dump the beam. Conventional computer control means are only used for post-mortem diagnosis and self testing during
beam pauses. This paper describes the conception and components of UNK Beam Abort Triggering System underdevelopment and Beam Dynamic Interlock System of U-70/UNK Transfer Line, which was successfully launched in1994.

I. INTRODUCTION
The IHEP Fast Ejection System (FES) extracts beams to external targets of channels 8,21,22,23 [1] and UNK–I, via theBeam Transfer Line (BTL) [2]. Fig.1 gives a schematic layout of the beam ejection area. A finite probability of pulsed
transfer line malfunctions can cause appreciable radiation losses, exceeding tolerable levels. To avoid such a situation
permanent monitoring of the magnet excitation currents is used. If operating variables are out of preset range the fastejection must be interlocked for the corresponding line. The problem at hand is solved by the Beam Dynamic Interlock
System (BDIS).
A second aspect of accelerator radiation safety is concerned with the necessity of a single-turn ejection (emergencyejection) of the beam from the UNK–I to the beam absorber when the danger of radiation losses arises. The so-called
beam abort is executed by kicker-magnet 10KM1 within the energy range of 70 GeV to 600 GeV [3,4]. The triggering
pulse for 10KM1 is generated by the Beam Abort Triggering System (BATS) which acquires and processes the emergency
signals from threshold devices distributed along the ring. The radiation monitors are mainly used due to their fast reaction
to emergency and preemergency situations. In the framework of the given paper main components of both BDIS andBATS are outlined.

II. BDIS
The main components and structure of the BDIS are shown in Fig.2. This system is distributed, as dynamic permission
signals are created at the Ejection Building (EB) and at 3 Surface Buildings along the BTL. These signals are input
parameters of the BDIS. They are yielded by permanently monitoring in hardware the excitation currents of the pulsed
magnets (window monitoring). The output of the BDIS is the dynamic permission signal for the KM14 and KM16triggering.
In addition, a fraction of the BDIS inputs is used for monitoring the status of vacuum valves and the pressure at the beam
pipes. At the EB some inputs are connected to the radiation monitoring system of the experimental area.
At the heart of the BDIS is a module called Concentrator and Analyzer of Dynamic Permissions (CADP). It has 8 inputs
with Diode Optoelectronic Couplers (DOC) for galvanic decoupling that is important for such a distributed system. Abuilt-in time-delay analyzer permits time monitoring of input signals with reference to ejection time with an accuracy ofup to 2 ms. A mask register gives an opportunity to disable any input on operator command. That is very useful whilemodes are changing or during comissioning. A Multibus–I interface allows one to identify inhibition sources and to test
the BDIS itself. An emergency switch for the operator is provided.

III. BATS
The system monitors and acquires all local alarm signals (LAS). Their sources are distributed over 16 Auxiliary Buildings
located mainly along the UNK ring at typical distances of about 1.8 km from each other. The following original signals
are used to generate the LAS:•the RM signals;
beam position monitor signals;• signals from pick-ups of dampers of coherent beam transverse and longitudinal oscillations;• signals from pressure monitors of the Vacuum System;• signals “Failure” of the Timing System, etc.
•The LASs are generated by the threshold devices associated with the corresponding systems and are sent to a Concentrator- Repeater (CR). The inputs of the CRs are optically isolated from all external devices. All CRs are interconnected bymeans of an independent loop (coaxial cable). Activity of the BATS takes place during the period between beam injection
and beam transfer to the 2nd UNK stage. A Driver Generator (DG), located in the Main Control Room, feeds a 1 MHz
pulse train into the loop and receives it. The presence of any LAS at the input of any CR interrupts the train propagation.
Having detected train disappearance, the CR of the Abort System building promptly outputs a kicker trigger pulse.
Such an algorithm ensures a time lag between firing of an LAS and the trigger pulse of less than 100 ms including the time
propagation delays. Thus the kicker trigger pulse is generated only by hardware. All the CRs are linked to a Multibus–I
backplane for post-mortem diagnosis, selftesting in no-beam states and masking any CR input on operator command. It
is important to notice that the BATS provides for injection inhibition after an ejection trigger pulse has been generated.
As it was mentioned above, the fastest response is ensured by the RM signals. That is why the associated threshold
device was given special attention. The simplified block diagram of the Alarm Level Discriminator (ALD) of radiation
losses is given in Fig.3. The signals from the RMs, located near septum magnets, scrapers and other so- called “narrowplaces”, are individually input to Current - to - Voltage Converters (CVC). Their rise time is about 05 ms over an input
current range of 15 nA - 15 mA. The output voltage of the CVC is compared with a predetermined reference. When thatreference is exceeded, that comparator creates the LAS. A counter registers the event time for post-mortem processing.
The reference levels are changed during the period of beam circulation, taking into account the rising risk of radiation
as the beam energy increases. That energy is provided by using timing pulses at the major points of the UNK–I magnetcycle.

IV. CONCLUSION
The created BDIS was successfully used during the launching of the BTL in March 1994. The main principles ofthe BDIS have been confirmed by long-term operation of dynamic interlocking at the FES of U–70. Prototypes of themodules for the BATS have been tested. The electronics modules of the both systems are packed in Euromechanics. The
systems are expected to be extended to UNK–II as well.

References[1] Yu.M. Ado et al. Particle Beam Channels Development at IHEP Accelerator. Preprint IHEP 85–182, Serpukhov,
1985 (in Russian).
[2] V.T. Baranov et al. UNK Injection System. Preprint IHEP 92–118, Protvino, 1992 (in Russian).
[3] Design Study on the UNK–I Control System. IHEP Internal Report, 1988.
[4] V.N. Alferov et al. The UNK Control System, Proceedings of the 1991 IEEEE Particle Accelerator Conference. SanFrancisco, May 1991, pp.1356–1358.

Figure. 1. Schematic Layout Of The Beam Area Of The IHEP Accelerator Complex

Figure. 2. Block Diagram Of The Beam Dynamic Interlock System

Figure. 3. Block diagram of the Alarm Level Discriminator (ALD)