Developing an Ion Source Control System Using NI LabVIEW, PXI, and CompactRIO

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"We used NI LabVIEW software and NI hardware to successfully build our ECR ion source, which integrates several technologies and protocols. NI products helped us unify everything we needed into a single system without sacrificing the modularity and EPICS integration we required."

- I. Arredondo, Consorcio ESS-Bilbao

The Challenge:
Developing a control and monitoring system of an electron cyclotron resonance (ECR) ion source, taking into account synchronization and DAQ requirements and overcoming the challenges of a high-voltage platform, radio frequency (RF) system tuning, communication with other subsystems, integration into an Experimental Physics and Industrial Control System (EPICS) network, short development time, and a large, diverse development team.

The Solution:
Using the NI LabVIEW Real-Time and LabVIEW FPGA modules along with PXI and NI CompactRIO hardware to build modular subsystems that we can independently control through a single LabVIEW interface to meet all of our requirements and reduce implementation time.

I. Arredondo - Consorcio ESS-Bilbao
M. Eguiraun - Consorcio ESS-Bilbao
D. Piso - Consorcio ESS-Bilbao
M. del Campo - Consorcio ESS-Bilbao
J. Feuchtwanger - Consorcio ESS-Bilbao
G. Harper - Consorcio ESS-Bilbao
J. Bilbao - Consorcio ESS-Bilbao
X. González - Consorcio ESS-Bilbao
L. Muguira - Consorcio ESS-Bilbao
N. Garmendia - Consorcio ESS-Bilbao
P. González - Consorcio ESS-Bilbao
J. Corres - Consorcio ESS-Bilbao
R. Miracoli - Consorcio ESS-Bilbao
S. Varnasseri - Consorcio ESS-Bilbao
J. Jugo - Universidad del País Vasco/ Euskal Herriko Unibertsitatea, España
J. Portilla - Universidad del País Vasco/ Euskal Herriko Unibertsitatea, España
V. Etxebarria - Universidad del País Vasco/ Euskal Herriko Unibertsitatea, España

We developed an ion source hydrogen positive (ISHP) project consisting of an ECR ion source that delivers up to 70 mA of H+ pulsed beam (20 Hz to 50 Hz). An ECR ion source forms plasma-injecting RF microwaves into a vacuum chamber with a proper magnetic field and a gas. Then, the ions of the plasma are extracted by means of an electrical potential difference. The equipment needed to generate the beam is on a high-voltage platform (70 kV) to give the particles initial accelerating potential.

System Description

The platform houses the ion source, the RF system, the control network (CN) and interlock network (IN) controllers, and some auxiliary signals. On the ground, we placed the extraction column, the master CN and IN controllers, the human safety network (HSN) system, and the diagnostics. Some devices are related to two networks, such as the transformer to feed the platform devices (the high-voltage power supply [HVPS]), which delivers 70 kV, and the mechanical grounding arm (MGA), which puts the platform at ground potential for safety.

The ion source is composed of the plasma chamber, the H2 injector, and the extraction column. The plasma chamber has four solenoids to induce a magnetic field that moves using two stepper motors. These solenoids run on four power supplies (10 A, 30 V). The system achieves H2 injection through a mass flow controller connected to a bottle. Finally, the extraction column has a triode system moved by two synchronized stepper motors. An additional 3 kV power supply focuses the extracted beam.

To inject the RF microwaves properly into the plasma chamber, we installed an RF generator, a Klystron linear beam vacuum tube, and an automatic tuner unit (ATU). The RF generator provides a 2.7 GHz microwave amplified by the Klystron, a specialized linear-beam vacuum tube, up to a maximum of 2.5 kW, while the ATU tunes the impedance of the transmitter chain to achieve the proper power delivery into the chamber. The system delivers a control signal to the RF generator for a pulsed beam. The ATU is composed of three stubs moved by three stepper motors. It also includes power sensors, couplers, and specific electronics to measure the incident and reflected power to perform closed loop control.

Control System

Our modular control system includes four almost independent networks with their own technologies: control network, timing and synchronization, interlocks network, and human safety. Their corresponding technologies are PXI and CompactRIO, programmable logic controllers (PLCs), PXI devices, and safety PLCs, respectively. We use EPICS and LabVIEW to centralize the networks at a single station. On another level related to control, there are diagnostics, auxiliary systems (such as vacuum and refrigeration), and data logging. The control system components are the following:

Control Network: We based the control system on NI products (blue elements in Figure 2) using three chassis: an NI PXI-1042Q, NI PXIe-1065, and NI cRIO-9112. To avoid a high-voltage gap, we linked the two PXI chassis with a dedicated NI PXI-8336 MXI fiber-optic module.

The chassis on the ground contains an NI PXIe-8108 real-time controller. It manages an NI PXI-8433/4 RS485 PXI module to control the extraction column motors, the steppers of the plasma chamber (serial TCP/IP), and the NI PXI-7852R FPGA to drive the extraction column power supply, acquire the diagnostics signal, and read the pressure sensors. In addition, it handles the communication with the control PC using shared variables and an EPICS server via the LabVIEW Datalogging and Supervisory Control Module.

The chassis on the platform includes a PXI-7852R FPGA module that generates the pulses (20 µs to 2 ms at 20 Hz to 50 Hz) for the RF generator, implements some digital logic for plasma chamber motors, controls the H2 flow, and manages some timing issues.

CompactRIO handles all of the signals of the RF system, with the exception of the Klystron and the pulses for the RF generator. It acquires the fast signals with the NI 9223 C Series module and the slow signals with the NI 9205 C Series module, and drives the motors with the NI 9403 C Series module. Moreover, it implements an EPICS server to publish all involved signals.

The control PC running Scientific Linux and LabVIEW drives the plasma chamber power supplies (Modbus TCP/IP), manages the Klystron (binary-based serial computer interface [BCIP] through TCP/IP), and monitors the EPICS variables (CA Lab library) published by PXI and CompactRIO. Everything is integrated in a friendly OPI (Figure 3).

The control PC is installed with an alarm system based on CSS to warn the operator in case of emergency.

Timing and Synchronization: To generate the precise timing signal required for the operation, we needed a specific hardware configuration. For our current implementation, we used a GFT9404 eight-channel digital delay generator and an NI PXI-6651 system timing and control module to route the timing pulse through the ground and platform PXI chassis trigger, respectively. We also used the NI PXI-7852R FPGA module triggered by a PXI_Trig0 line to generate pulses for the RF generator.

Interlocks Network: The interlocks network, based on PLCs, is the machine protection system. The communication with EPICS and LabVIEW is performed through Modbus TCP/IP (red in Figure 2).

Human Safety: High-voltage hazards are avoided with a fence surrounding the system. This fence and the devices needed that deliver high voltage are enabled and disabled with a mechanical key system and a safety system composed of SIL3/PLe sensors and PLCs (green and striped in Figure 2).

Flexible Tools, Modular System

We used LabVIEW and NI hardware to successfully build our ECR ion source, which integrates several technologies and protocols. NI products helped us unify everything we needed into a single system without sacrificing the modularity and EPICS integration we required. In the future, the modularity of the system will help us maintain, modify, and upgrade the system.

Author Information:
I. Arredondo
Consorcio ESS-Bilbao

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