ISHN Ion Source Control System

M. Eguiraun, ESS Bilbao Consortium

"Choosing National Instruments hardware and LabVIEW proved very useful because it fulfills the control requirements with the ability for quick upgrades in almost every section of the control system."

- M. Eguiraun, ESS Bilbao Consortium

The Challenge:

Developing two different subsystems for controlling and monitoring a Penning-type ion source on a high-voltage platform and integrating it with an Experimental Physics and Industrial Control System (EPICS)-based general control network.

The Solution:

Combining an embedded real-time controller in an NI PXI chassis with field-programmable gate array (FPGA) modules to meet data acquisition and synchronization requirements, and running NI LabVIEW software in a Linux environment for integration with an EPICS network.

Author(s):

M. Eguiraun - ESS Bilbao Consortium
J. Feuchtwanger - ESS Bilbao Consortium
I. Arredondo - ESS Bilbao Consortium
G. Harper - ESS Bilbao Consortium
M. Del Campo - ESS Bilbao Consortium
S. Varnasseri - ESS Bilbao Consortium
J. Jugo - University of the Basque Country
V. Etxebarria - University of the Basque Country

 

The Ion Source Hydrogen Negative (ISHN) project consists of a Penning ion source that delivers up to 65 mA of H- beam pulsed at 50 Hz. This is the first stage in the particle accelerator being developed for the ESS Bilbao project [1]. The ISHN project is a result of several modifications and extensions to the ITUR project [2].

 

We used a diagnostics vessel for beam testing. There are several power supplies for plasma generation and beam extraction, including auxiliary equipment and beam diagnostic devices. The control system implemented in LabVIEW is based on NI PXI hardware. A real-time processor manages source operation and an FPGA performs additional tasks. The control system uses EPICS Archiver and Hypertable database for data logging. Deploying a channel access server in the PXI controller integrates the control system into the EPICS network.

 

 

A Penning-type ion source periodically applies a pulsed discharge (800 μs, 30 A, 50 Hz) to the source’s cathode, generating a mixed plasma of hydrogen gas and cesium steam [3]. Delivered hydrogen applies a pulsed voltage to a piezovalve for 250 μs. Once the plasma is stabilized (∼500 μs later), the system applies a pulsed extraction voltage (300 μs, 12 kV), generating an H-beam.

 

To accelerate the beam, the platform’s high-voltage power supply gives up to 100 kV of energy to the particle beam. In addition, a continuous power supply (600 V and 2 A) conditions the ion source’s electrodes. The main devices required for the source operation are listed in Table 1. Once the beam is extracted, it goes through the diagnostics vessel to measure the ion beam characteristics, including key parameters such as current or emittance, which should fulfill the required specifications. The actual diagnostics are two current transformers (ACCT and DCCT), a Faraday Cup, and a pepper-pot device. Additionally, a quadrupole and a dipole modify the beam shape.

 

 

Control System Overview

Due to the high voltage in the platform, the main system is divided into two control subsystems located at ground and at the platform. Each area has its own operator panel, allowing ion source operation from both control desks, but not simultaneously. Figure 2 shows a schematic diagram of the control system.

 

We based the control system on NI hardware and used an NI PXI-1042Q chassis at the ground and an NI PXIe-1065 chassis,at the platform. They are linked with a dedicated MXI-4 fiber-optic module (NI PXI-8336) so we can treat this two-chassis system as a single element from the point of view of the control designer.

 

The chassis located at ground contains an NI PXIe-8108 real-time controller. It manages cesium boilers and pressure control loops, some data acquisition through other PXI modules (NI PXIe-6124, NI PXI-6289, NI PXI-6511, NI PXI-6512) and the FPGA (NI PXI-7852R), and communication with the operator’s control desk using shared variables and an EPICS server. It also communicates with some power supplies by Modbus/TCP, GPIB, and with a pressure sensor by serial protocol link.

 

The FPGA located on the high-voltage platform chassis (NI PXI-1042) controls diverse elements. It manages the pulse signals for plasma power supplies and H2 supply, generating the pulse diagram. In addition, it manages safety signals to and from plasma power supplies and controls several electrovalves for gas supply and refrigeration of the ion source. The FPGA is also in charge of acquiring voltage and current waveforms from plasma generation power supplies. Furthermore, it measures gas flow rate, ion source temperatures, and other parameters.

 

Additionally, specialized programmable logic controllers (PLCs) manage safety and interlock signals to obtain adequate maneuvers.

 

EPICS Integration

We based the system’s EPICS integration on the LabVIEW Datalogging and Supervisory Control (DSC) Module, which runs on the real-time system in the PXI controller. The parameters published via EPICS are mainly for system configuration and machine operation, along with data acquisition variables.

 

The real-time controller publishes the LabVIEW shared variable data in the EPICS network as process variables. However, since the operator interface runs under Linux and LabVIEW shared variable hosting is not supported on this OS, the real-time controller communicates with the operator interface through EPICS. To do this, we used a CA Lab LabVIEW library [3] which provides VIs to interface EPICS form LabVIEW and can be compiled for a Linux environment.

 

Timing System

To generate the precise timing signal required to operate the different power supplies and auxiliary equipment, we needed a specific hardware configuration. In the current implementation, this is based on the following devices:

  • Berkeley Nucleonics Corporation 575 precision pulse generator
  • NI PXIe-6672 and NI PXI-6651 for routing main timing pulse through PXI chassis trigger
  • NI PXI-7852R FPGA triggered by PXI_Trig0 line, generates triggers and pulses for the H2 supply and plasma generation power supplies
  • NI PXIe-6124 triggered data acquisition, synchronized with extraction power supply

 

 

Operator’s Interface

The system uses two different operator panels, one on the platform computer and one at ground. In the beginning of the ion source operation, the main tasks are performed on the platform because there are some manual procedures. At the same time, the computer located at ground manages data logging and data acquisition from diagnostics, which is one of the main differences between both control applications (see Figure 3).

 

The platform computer runs Windows XP, but the one at ground runs Fedora 14 Linux. This is a specific requirement of the project because the communication to EPICS and related data management (HyperArchiver engine through Hypertable database) is done with required stability through a Linux machine.

 

On the other hand, with the EPICS integration we can perform remote control and monitoring of all published variables across the network. Among other advantages, this facilitates the creation of databases for operational and scientific purposes.

 

Conclusion

The current control system is suitable for managing the ion source, but we made several big changes since beginning this project, including improving system modularization, using Linux, integrating with an EPICS network, and improving timing systems. We expect more changes because this facility tests not only components for accelerator technology, but also control systems. Choosing National Instruments hardware and LabVIEW proved very useful because it fulfills the control requirements with the ability for quick upgrades in almost every section of the control system. Moreover, a very useful set of tools for NI hardware with EPICS networks integration is under continuous improvement.

 

Bibliography

[1] ESS Bilbao homepage, http://essbilbao.org

[2] “Un Banco de Pruebas para Fuentes de Iones de Máxima Fiabilidad” NI Case Study, http://sine.ni.com/cs/app/doc/p/id/cs-13366

[3] D. C. Faircloth et al., “The Front End Test Stand High Performance H- Ion Source at RAL”, Review of Scientific Instruments, Volume 81, Issue 2, 2010.

[4] CA Lab, http://www-csr.bessy.de/control/SoftDist/CA_Lab/

 

Author Information:

M. Eguiraun
ESS Bilbao Consortium

Table 1: Main Devices for Ion Source Operation
Figure 2: Schematic Diagram of ISHN Control System
Figure 3: Main Operator Panel on Linux Host