Automatic High Voltage Conditioning of the Electrostatic LEP Separators
without Conventional Programming
B. Balhan, A. Burton, E. Carlier, J. H. Dieperink and V. Mertens.
European Organization for Nuclear Research (CERN) - SL Division,
CH - 1211 Geneva 23, Switzerland
Abstract
The TS Tool Kit is a generic, fully data-driven and user-configurable software system developed at CERN forsupervisory, control and data acquisition applications. It provides a comprehensive framework to solve fairly complex
process control problems requiring response times of the order of a second, without any need for conventionalprogramming. The characteristics and benefits of this approach are discussed in the context of the new high voltage
conditioning process for the electrostatic LEP separators.

1. EQUIPMENT
Separation of the e+e- beams in LEP is achieved by a vertical electrostatic separation system comprising 40 bipolar
separator units, arranged to provide local vertical separation bumps at all eight LEP interaction points. Each separator
consists of a vacuum tank of 50 cm diameter and 4,5 m length and contains two high-voltage electrodes mounted on two
insulating supports as shown in figure 1. Each electrode is connected via an alumina feedthrough to a high-voltage (HV)
generator (± 175 kV DC). The gap width can be varied between 6 and 16 cm [1].

Fig 1. Separator tank with electrodes.
In order to improve the HV behaviour at the nominal field (15 - 30 kV/cm) after assembly, loss of vacuum, or polarity
change, a separator is (re-)conditioned by increasing the voltage slowly to the maximum field (56 kV/cm). The maximum
speed of voltage increase is determined by two parameters: the spark rate and the vacuum pressure in the tank. After themaximum field has been reached and maintained during several hours for consolidation, the field is reduced to 50 kV/cm fora total of 72 hours, during which the tank is checked for a low spark rate.

2. PROJECT OVERVIEW
To speed up the procedure and to save manpower a software regulation process has been used for many years to performthe HV conditioning automatically. Its original implementation was a stand-alone C program [2] designed to run on thelocal process controllers (PCs under SCO XENIX) widely used for LEP control. For screen handling, user input, anddisplay of historical and trending curves the program made abundant use of the CGI (Computer Graphics Interface) graphics
package, conveniently available under XENIX. Many of the parameters needed during the conditioning, like maximum
voltages, flat-top timeout interval, etc., were hard-coded, as the program was only foreseen to be used with the initialseparator setup [1]. As it was conceived, this program could also run only locally and not be interrogated or influenced overthe network. Therefore, its use necessitated a lot of travel between the equipment specialists’ offices and the various LEP
interaction points.
The recent migration from XENIX to LynxOS [3] (which no longer offers CGI) as operating system in the processcontrollers, the evolution of the separator layout over the years (e.g. for the ‘LEP bunch train scheme’ [4] or LEP2) has
rendered this old implementation of the automatic conditioning obsolete. Therefore a new solution has been recentlyconceived and realised.

3. CHARACTERISTICS
The new automatic conditioning process has been developed in the framework of the fully configurable, event and datadriven ‘TS Tool Kit’ described already elsewhere [5, 6]. This provided:
••
•
•
•

No need for conventional (e.g. C) programming;
Portability (runs so far on HP-UX, ULTRIX, and LynxOS) (applications are platform-independent);
Full on-line remote control;
Separation between algorithm and user interface;Equipment independence (can be used for all types of LEP separators but also other equipment, e.g. the SPS extraction
electrostatic septa).

In particular the suppression of conventional programming has allowed one to set up the new system in a remarkably shorttime, permitting concentration on the proper implementation of the conditioning algorithm. It largely favoured a clear
communication between users and developers, resulting in a successful transfer of the desired functionality into the final
product. The user interface was largely conceived by non-software specialists, using functions of the TS Tool Kit together
with other easily configurable tools [7]. Non-software specialists will also be able to perform most of the future upgrade
work in case the applications evolve.

4. TS TOOL KIT
The core of the TS Tool Kit [5, 6] is a shared database to which the access is handled by a client/server mechanism.
This database is the run-time repository for all the data needed to run the application. It is surrounded with a set of clientmodules, each dealing with a specific control task, like data acquisition, running control algorithms, or user interaction. The
general application behaviour is given through flat data files which are read in and interpreted at startup. The TS Tool Kit
configuration needed to implement the automatic conditioning process is shown in figure 2.
User interface

Process controMenuTSplot

TScontrol

TSserver

TSlog

Shared database

TSequip

Equipment accesFig 2. Software layout.
The various modules perform the following functions:
TSserver: shared database.
TScontrol: runs control and supervision algorithms specified in ‘rules’.
TSlog:
stores, at definable time intervals or on change, any set of data in the shared database onto files or onto aremote Oracle database.
TSequip: sends commands to, and reads data from, the equipment.
TSplot:writes selected data onto files in a format understandable by ‘gnuplot’ to provide trending curves.
Menu:
generic alphanumeric user interface which permits, based on simple text files, the organization of operating
system commands or calls to user-written programs into a tree of menus, to display the menus, to move inthe menu tree and to invoke commands by single-key actions [7].
Several auxiliary modules (not shown here) are used from within Menu, for user access to the shared database for
information and run-time control of the application.

5. SCENARIO and ALGORITHM
The automatic conditioning procedure is determined through ‘scenarios’, made up from a set of parameters and ‘rules’,executed by the TScontrol module. Various scenarios are available for positive, negative, or bipolar conditioning, selectablefrom Menu. Likewise, parameters are pre-set as appropriate for the chosen scenario, but can be modified dynamically at runtime to influence the procedure.
The rules are formulated as conditions and subsequent actions in term of data in the shared database, and specified in asimple “controls language” [8]. These rules are read from a text file at start-up and continuously evaluated at run-time. Allrules are executed completely asynchronously when their respective conditions (WHEN ...) are evaluated as ‘TRUE’.
A largely simplified version of the rules constituting the automatic conditioning algorithm is shown in figure 3.
The overall process regulation loop is made up of three parts: hardware acquisition, algorithm checking, and hardware
setting modification. A frequency of 1 Hz has been chosen for the acquisition providing a sufficiently fast reaction time incase of vacuum degradation or sparks (spark bursts are interlocked by software in the HV generators itself). It is noteworthy
that the TS Tool Kit is able to provide considerable shorter reaction times if run on sufficiently performant hosts. Separator
conditioning for the whole of LEP is presently run from a central HP workstation, even when several tanks need to beconditioned in parallel. Due to the full platform independence of TS Tool Kit applications, individual processes could bealso be run locally or separately for each interaction point, without any modification.
WHEN Maximum electrical field reachedDOIF First timeTHEN
Double charging current
ELSE
Check spark rate
ENDIF
ENDDOWHEN Poor vacuum
DODecrement charging current
ENDDO
WHEN Sparks
DO
Decrement charging current
ENDDO
WHEN Conditioning rate too low
DOIncrement charging current
ENDDO
WHEN Conditioning rate too highDO
Decrement charging current
ENDDO
Fig 3. Set of TScontrol rules constituting the main conditioning algorithm (largely simplified).
In terms of numbers the new algorithm comprises 25 rules with a total of 500 lines. In comparison, the previous
implementation comprised about 6500 lines of C code and some minor parts in assembler.

6. CONCLUSION
Despite its considerable advantages in flexibility and user-friendliness over the previous solution, the new automaticconditioning of the LEP separators has been realised, using the TS Tool Kit software package, in a much shorter time scale(ca. 2 man-months counted from after the user specification phase compared to ca. 1.5 man-years for the old process). Alltests have so far been successfully achieved. The process will be intensively used during the coming LEP shutdown.
The new solution will be much easier to maintain and adapt to new needs if necessary, even outside its original LEPapplications.
As the TS Tool Kit is nicely integrated into the CERN SL accelerator control system (offering interfaces to the X userinterface, the general CERN alarm system, and Oracle on-line databases) further extensions of the automatic conditioning,
like alarm generation and forwarding or graphical user interfaces are quite straightforward.

ACKNOWLEDGEMENTS
The authors would like to thank Noel Garrel for providing the initial user specifications of the automatic conditioning
process, Brennan Goddard for his help and suggestions, and Alberto Aimar for upgrading the TScontrol module.

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