A CAMAC based system for an electromagnetic isotope separator

Nuclear Instruments and Methods in Physics Research A244 (1986) 213-220 North-Holland, Amsterdam

213

A CAMAC B A S E D S Y S T E M F O R A N E L E C T R O M A G N E T I C

ISOTOPE

SEPARATOR

D. C A M I N , J. M O N I C O a n d M. S A T I N O S K Y Departamento de F'tsica, CNEA, Av. del Libertador 8250, 1429 Buenos Aires, Argentina

Considering the new emplacement of the isotope separator close to the 20 UD tandem, an entirely new control and monitoring system was conceived. The system is built around a CAMAC serial highway driven by a microprocessor based crate controller developed in our laboratory. Because the ion source and its power supplies are at a 100 kV off ground potential, a fiber optic link is used for the serial highway. At the control console a TV monitor and a light pen allow the assignment of four parameters to a set of two meters and two knobs. The hardware and software organization of the system is described together with the technique used in spark protection for CAMAC modules and associated circuitry.

1. Introduction

accelerator. The basic idea of this project is to use a deuteron beam out of the 20 MV electrostatic accelerator to bombard a beryllium target. The nuclear reaction generated in this way produces fast neutrons which

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D. Camin et aL / A CAMAC based system for isotope separation

induce the fission of heavy nuclei (uranium, plutonium, etc.). From this fission process radioactive isotopes are obtained and detected. The fission of heavy nuclei is produced in the inner body of an ion source-uranium target system. An interhal tungsten filament, coupled to a heater oven with a 20 A current wound around the ion source, produces an inner temperature of up to 2000°C which is necessary for the diffusion of the fission products. Also. this temperature enables the filament to emit electrons and to trigger an arc, which in turn sets the ionization of the atoms inside the source. The ion source system is at 100 kV off ground potential allowing the acceleration of the isotopes which are extracted by means of an extraction power supply. The acceleration voltage and the magnetic field from the mass separator allow one to discriminate the different isotopes. Fig. 1 shows the layout of the NAVE Project and a schematic drawing of the ion source.

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The NAVE assembly includes several power supplies (PS) with different characteristics located throughout the system. Some of the PS are at 100 m wiring distance from the control console. Each PS must be controlled and monitored (output voltage and current in most cases). In addition, alarms such as overtemperatures and overvoltages must be registred and displayed. The common solution for such a system would be a console including all readout, control and alarm parameters of the PS. However, such a console would be very cumbersome and the wiring too bulky, considering that the number of parameters for the whole system is 94. An additional difficulty is the ion source system with its PS floating at 100 kV off ground potential. The technique adopted to solve these problems is a serial data transmission link using a fiber optic cable. It allows an isolated HV control which is conveniently

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handled by a sole cable, which in turn is not interfered by other signals. The layout of the control system is shown in fig. 2. The modular standard CAMAC is used because it is an international standard and is used extensively in other Tandar facilities. A stand-alone crate controller, at the console crate, operates the serial link and consequently controls and reads out the system parameters distributed on the CAMAC modules as shown in figs. 2 and 3. The three crates are linked by U-port adapters CAMAC modules, which translate electrical signals in the crate to optically modulated signals on the fiber optic cable. In each crate there is a crate controller which, under control from the stand-alone processor, manages the corresponding CAMAC modules. The processor periodically polls the parameters through the CAMAC system. These parameters can be analog (voltage, current, temperature, etc.) or digital (on/off status of a PS, alarms, etc.) and are shown on a "page" of a TV B&W monitor.

The operator, using a light pen, can select one of several pages and once in the selected page choose a parameter to be controlled or read out. In the first case he points the light pen to the desired parameter and then to a free assignable shaft-encoder line. Once the assignation is made the parameter follows the shaft encoder action. This is shown in the bottom lines of the page. To read a parameter from the page in an analog format, the operator points at it with the light pen and then to a free assignable meter line. Once the assignation is made the parameter is displayed by the corresponding analog meter. All parameters are displayed in digital form. Also displayed are the status of each device, the alarms and a zone for two assignable shaftencoders and two assignable analog meters. A CRT terminal is used for maintenance and software updating. Figs. 4 and 5 show block diagrams of the control electronics for the ion source system of the NAVE project. Fig. 4 (analog parameters) shows how a series IV.

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of adjustable potentiometers in the signal conditioning block adapt the input parameters amplitudes to the range of the CAMAC ADC. Voltage to frequency and digital to analog converters with optical isolation were used to overcome difficulties such as an off-ground potential filament PS, or an arc PS which must be controlled with isolated circuitry (see figs. 6 and 7). Fig. 5 (digital parameters) shows a similar arrangement with a block named status control/readout whose simplified scheme is shown in fig. 8. All the input/output CAMAC lines are protected against sparks by suitable circuitry for each type of CAMAC module, as shown in fig. 9. Devices described in figs. 4-9 are distributed plug-in cards allocated in a crate, where special care was put in the design of grounding and shielding, in particular the spark protection for the CAMAC modules. An additional protection is achieved by tripolar gas-filled surge arresters and varistors installed on the outputs and power lines of each PS in the ion source system.

3. Autonomous CAMAC crate controller

An autonomous CAMAC crate controller was made for controlling this system. The CPU is an Intel 8085 running with a 10 MHz clock. During operation the parameters are periodically polled through the CAMAC system, and upon operator (light pen) command are

displayed on the standard TV set. With the light pen, the operator can change the page on the TV, assign one parameter to the assignable knob or meter, and control logical parameters such as "on", "off", "increase", etc. The language used for approximately 70% of the software is PLM with the remaining 30% being 8085 Assembler. Central to the system software structure is a "linked list" database which contains identification, location into the pages, type, scale factor, etc., of all the parameters. The database was created and can be periodically updated by and auxiliary program developed for this purpose.

4. Conclusions

The control system is at present partially implemented with only two crates in use: the control console and the ion source crate. From its implementation so far the following conclusions can be made: (1) due to the adoption of the assignable variable technique, a very simple operation of the system is achieved at the control console, (2) implementation by CAMAC standard and a flexible software make the system easily expandable, (3) real time communication allows the system to be controlled without any time delay visible to the operator, and (4) as any processor managed system, operation sequences or files related to specific experiments can be generated for further use.