12/4/13 3:54 PMIEEE Xplore - HTML View

Pagina 1 di 11http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5948402

Sign Out

Access provided by:Universita degli Studi di Roma LaSapienza

IEEE.org | IEEE Xplore Digital Library | IEEE Standards | IEEE Spectrum | More Sites

First Steps in the FTU Migration Towards a Modularand Distributed Real-Time Control Architecture Basedon MARTeThe Fusion Advanced Studies Torus (FAST) experiment is being proposed by the Italian laboratories as a Europeansatellite Tokamak that will enhance and facilitate the exploitation of ITER like scenarios and technologies. Its size andcomplexity is comparable to the largest fusion machine in the world: JET. As such, its real time control system will haveto meet basic requirements such as a modular and distributed architecture, where different control subsystems can beeasily integrated at different times and can operate either independently or in cooperation with other subsystems.Another important feature, which has to be taken into account, is the transparency regarding both the hardwareinterfacing and the adopted platform. As a test bed, we are currently planning to upgrade the architecture of theFrascati Tokamak Upgrade (FTU) real-time system in order to improve its flexibility and modularity and have decided toadopt the MARTe package to reach our goal. Currently, there are four systems under development at FTU: the LH-Power system; the gas puffing control system; the ODIN Equilibrium Reconstruction system; and the position andcurrent feedback control system (currently in a design phase). This paper will describe the current status and firstresults of the previously referred systems integration.

This paper appears in: Nuclear Science, IEEE Transactions on, Issue Date: Aug. 2011, Written by: Boncagni, L.;Sadeghi, Y.; Carnevale, D.; Mazzitelli, G.; Neto, A.; Pucci, D.; Sartori, F.; Piesco, F.; Sinibaldi, S.; Vitale, V.; Vitelli, R.;Zaccarian, L.; Monaco, S.; Zamborlini, G.

© 2011 IEEE

SECTION I

INTRODUCTION

SECTION II

BASELIB2 AND MARTe

A Tokamak control system should solve different issues, both during the experiment as well as in the configuration phase: it should stabilize the plasma dynamics,

reject disturbances, and generally help in the programming of the experiment as well. Moreover, as experimental Tokamaks evolve throughout their life and

diagnostics and actuators are progressively installed or enhanced, the system should be modular and easily upgradeable. Another requirement for the control system

of a large Tokamak is to be decentralized: thus, a real-time network becomes a necessity.

From the software point of view, the majority of those requirements is satisfied by the MARTe framework [1], which is being used on several fusion devices like JET,

COMPASS, and ISTTOK [2] to tackle different control issues. This framework provides “a clear boundary between algorithms, hardware interaction, system

configuration, leveraging reusability and maintainability” [3]. Moreover, as MARTe can run on many different OSes (mainly Wind River VxWorks, Linux,

Linux/RTAI, SOLARIS, MS Windows, and Mac OS X), the framework greatly helps in the decentralization of the control system. Due to the actual FTU software

environment and in order to be used in conjunction with RTNet, we choose the Linux-RTAI implementation of MARTe.

The first part of this paper describes the MARTe components and how we integrated them into the FTU COntrol and Data Acquisition System (CODAS) [4]. In the

second part, it reports the recent status of all the MARTe projects at FTU.

MARTe is a framework for real-time control system development. It is implemented on the top of a platform-agnostic C++ software library, called BaseLib2, which

hides to the programmer all the OS dependent details and provides tools and classes for the most common problems faced while developing control systems, such as

error reporting and managing, data and configuration parameters access and matrix operations.

BaseLib2 is heavily object-based and has been built from the ground up with flexibility in mind, making it possible to develop applications by juxtaposing objects and

making them cooperate via message passing (a concept taken from the Smalltalk programming language, and reimplemented in C++). This led to the creation of the

Multithreaded Application Realtime executor(MARTe), which basically consists of several objects whose interconnections realize the architecture of a control system.

Abstract Authors Figures Multimedia References Cited By Keywords

12/4/13 3:54 PMIEEE Xplore - HTML View

Pagina 2 di 11http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5948402

SECTION III

MARTe FRAMEWORK AND FTU

Among these objects, it is possible to find service utilities, such as a web server (used to explore the internal structure of the application), as well as the real control

system which, following the same idea of using objects as building blocks of BaseLib2, is made by a series of small components called Generic Application Modules

(GAMs), which exchange data through a Dynamic Data Buffer (DDB), and are otherwise completely independent. The GAMs are sequentially ran by a

RealTimeThread which is usually completely isolated on his own processor or core in order to obtain the best performances with the minimum conceivable latency

and jitter, for instance in the order of hundreds of microseconds in JET's Vertical Stabilisation system [5]. More than one RealTimeThread can be managed by a single

instance of MARTe, each one running its own set of GAMs on a different processor, eventually synchronized by a SynchronizationGAM, which makes MARTe capable

of handling even the most peculiar control system requirements.

In Fig. 1, an example of how a feedback system in the standard block diagram form is translated in MARTe's GAMs/DDB sequential structure is reported.

Fig. 1. Conceptual translation from a standard block diagram to a MARTe application.

Another core object of the framework is the State Machine, which is able to exchange messages with all the other existing objects in order to signal the various stages

of the experiment and allowing the GAMs to run their own initialization code at the correct moment.

The communication with hardware is well contained into the GenericAcquisitionModule (GACQM) interface. These kind of classes are used for data input and output,

and by the External Time Triggering Service to perform the synchronization with the hardware through data polling or interrupts.

The deployment of a MARTe system consists basically in writing the required high-level hardware drivers (i.e., the GACQMs), the control algorithm itself (i.e., the

GAMs), and a configuration file, which is basically a text file with a proprietary structure which tells MARTe what GAMs will be used, and how they will be

interconnected via the DDB.

As of today, in FTU, the software dedicated to the real-time control of plasma current, position, and density (which will be simply called “feedback” in the rest of the

paper) runs in VME standard hardware. There exist two identical feedback stations, the online and the backup one, the only difference being that the last one is not

connected to the actuators.

Table I reports the details of the hardware in use at FTU for the feedback. The C.A.E.N. ADC can be triggered by an external clock ( at maximum) and can be

accessed directly by the XEmbedded XVME-6200 throughout the PCI bus using the Tundra Universe IID chip. A low-level driver for the device already exists, and it is

responsible for the memory mapping of the chip. The driver provides a set of three functions: one is used to wait for the next clock event, one to read from the ADC a

12/4/13 3:54 PMIEEE Xplore - HTML View

Pagina 3 di 11http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5948402

single channel, and the last to write to the DAC a single channel. This low-level driver can be safely used by the high-level GACQM driver for MARTe. The master-clock

and the start gate coming from the plant trigger the acquisition during the Fast Sequence Controller (FSC) phase of the FTU experiments. The Slow Control phase in

FTU (see Fig. 2) is activated by the supervisory level of the CODAS (Prometeo in the following) [4].

Fig. 2. FTU CODAS integration.

TABLE I THE FTU HARDWARE

At the start of each experiment, Prometeo sends the configuration parameter chosen for the current experiment to all systems and diagnostics, then it waits for 120 s

for a positive acknowledgment by the subsystems, and finally starts the Fast Sequence Controller (FSC) phase. During this phase, two hardware gates (synchronized

with the master-clock and its subfrequencies as well) rise up to signal -20 s and -10 s from the plasma zero (i.e., the time instant in which the plasma begins forming).

Each diagnostic can choose which gate and which subfrequency of the master-clock to use to make its own synchronization within the experiment. The feedback

system frequency is 2 kHz, and it waits in an idle state until the second gate raises up before starting the real-time control activities. After the FSC, the Prometeo

system continues its loop, acquiring measures from the subsystems and starting the post elaboration procedures. In the Slow Sequence Controller phase, the messages

Fig. 3. VMEDrv GenericAcqModule class diagram scheme.

12/4/13 3:54 PMIEEE Xplore - HTML View

Pagina 4 di 11http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5948402

SECTION IV

LOWER HYBRID SATELLITE SYSTEMDESCRIPTION

Fig. 4. Deployed LHPP system.

exchanged by Prometeo and other systems are forwarded as TCP messages using a simple string made by a message and some basic information. The configuration

data is shared among nodes via AFS or NFS file systems.

In FTU, MARTe is being deployed using USB pendrives with a live Linux distribution. This allowed to test and deploy different systems without needing to reinstall

anything on the VME stations. Currently the GenericAcquisitionModule for the ADC and DAC, called VMEDrv, is being implemented. During the polling phase, the

VMEDrv resets (see Fig. 3) to zero the software time only if the experiment Start Gate is detected (for safety reason, if not present, the DAC output will be forced to

zero).

The same state machine in use at the JET Tokamak is being used, as the FTU sequence is quite similar. During the development phase, the MARTe Web Server is

being used to simulate the various state changes which happen during a real experiment, while the integration in the real CODAS system is realized by a simple

software named Feed2Marte which translates the Prometeo TCP messages into the corresponding HTTP ones and then forwards them to the MARTe system.

For data retrieval, the same software is being used: In fact, it is possible to retrieve the data collected by the CollectionGAMs using a simple HTTP GET. After

downloading and locally storing (for a finite time) the signals, Feed2MARTe transfers them to the official FTU archive using AFS access or some RPC call (depending

on how it is configured). The integration procedure is still work in progress.

Besides Joule effect, FTU plasmas are generally heated by radio frequencies, which, given the limited accesses, provides the most suitable tools. In particular, the FTU

is equipped with Electron Cyclotron Resonance Heating (ECRH) and Lower Hybrid (LH) systems. In this method, high frequency waves are

delivered via suitable antennas, and a part of the energy is absorbed by the plasma and transformed into heat via resonant modes of ions and electrons (or even hybrid

resonances). When LH heating is active, part of the launched waves are reflected by the plasma boundary. As the amount of reflected power is a convex or quasi-

convex function of the plasma/antenna distance, which can be affected by suitably adjusting the plasma horizontal position, extremum seeking techniques are being

applied [6].

The Extremum Seeking Algorithm requires as an input the fraction of power reflected by the plasma. This is computed as the ratio between the launched power and

the measured reflected power, and averaged among the eight central cells of the antenna (the antenna is made by a grill of 48 cells displaced in four rows of 12 cells

each). Note that, due to physical reasons, the fraction of reflected power is always greater than 5%. In the current FTU environment, this signal is an analog input to

the real-time feedback system that perform the horizontal control, and it is produced by a satellite station based on the VME standard, synchronized with the

experiment and with the main feedback control system. The satellite station is a very simple system that perform real-time calculation of the fraction of reflected

power and writes on a DAC channel the result waveform. For its simplicity, it was the first MARTe test system in the FTU real-time software environment.

The system consisted of one GAM and two IOGAMs to send and receive data from the DAC and ADC (see Fig. 4). LHTubeGAM, the core of the system, has 17 inputs

and 3 outputs. The inputs consists of time, 8 measurements for emitted power and 8 for the reflected power. The time signal is used to sample, for a time interval of a

specific duration, an average of the noise before processing. A different configuration file for debugging the algorithm has also been generated, substituting the ADC

and DAC GAMs with software generated signals taken from the FTU database.

Fig. 5 shows the cycle time (2 kHz) for the system, the reflected, emitted, and coupled power evaluated by the system.

12/4/13 3:54 PMIEEE Xplore - HTML View

Pagina 5 di 11http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5948402

SECTION V

GAS PUFFING

Fig. 5. Cycle time, reflected, emitted and coupled power for the LHPP system.

The goal of this project is to develop a control algorithm for the plasma density in FTU. A similar control system is already implemented in the current feedback, but it

is set up for “fixed flow” (i.e., on/off) piezoelectric valves. Instead, a control algorithm for the new “variable flow” valves is desired and being developed.

The control should be active between -10 and 2 s (where 0 is the previously defined “plasma zero”). From -10 up to 0 s, the control should only act a “camera pre-fill”

following a pressure reference expressed in millibars, while from 0 up to 2 s, it must follow a reference value expressed in . The control must also

guarantee a small overshoot of the real density with respect to the preprogrammed one in order to avoid undesired instabilities, as the valve cannot extract excess gas

from the chamber. In the simulation phase, in order to test the control law, a set of mathematics models reproducing the behavior of the actuator, the chamber

pressure and plasma density evolution has been realized.

A. The MARTe Calibration System

The most important parameters of the model of the valve are its response time, 2 ms in this case, and its static characteristic flow/voltage. To estimate the

flow/voltage characteristic, a test environment was built, together with a MARTe stand-alone system (see Fig. 6) that implement the flow estimation procedure as

described in the following steps:

close the gate;

read initial pressure;

actuate a number of fixed voltage pulses of a fixed time duration on the valve;

read final pressure;

calculate

TeX Source

open the gate;

wait for the decrease of pressure to high vacuum ( millibar);

change the actuation voltage and goto (1).

1 2

3

1)

2)

3)

4)

5)

6)

7)

8)

12/4/13 3:54 PMIEEE Xplore - HTML View

Pagina 6 di 11http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5948402

Fig. 6. Valve's flow evaluated by the MARTe Calibration System.

B. MARTe Simulation of the Control System

The proposed control law uses an anti-windup scheme by taking into account the nonlinearity caused by the saturation of the valve. The Fig. 7 show the online phase

of the MARTe Simulator System. The GasFluxControlGAM estimates the next requested flow for the valve using the error between the reference signal and the

simulated one given in feedback by the plasma model (DCNModelGAM).

To build the nonstationary linear plasma model (2), it was assumed that until the plasma zero is the number of electrons in the vacuum chamber, after the ones

confined in the plasma, is the corresponding electron density , is the chamber volume, or the plasma volume, is the confinement time, and

is the valve flow request.

Fig. 7. Closed-loop simulation in MARTe.

TeX Source

The transfer function of the controller of the system (3) is defined as

TeX Source

4

12/4/13 3:54 PMIEEE Xplore - HTML View

Pagina 7 di 11http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5948402

SECTION VI

REAL-TIME EQUILIBRIUMRECONSTRUCTION-ODIN

and the values for in (5) were chosen using the root-locus method because it led to the absence of overshoot in the control.

The main equation to describe the plasma force balance is the Grad–Shafranov equation:

TeX Source

Fig. 8. The three phases of the development of the RT-ODIN system: debug (a), test with real signals(b), and data transfer via RTNet (c).

Equation (7) is a second-order partial differential equation, where the functions is the plasma pressure and is the current flux function which is related to

poloidal current density in an axial symmetric torus . The magnetic flux can be expanded in a series of toroidal multi-poles, by using the toroidal coordinate system

with the definition of and [7]. According to [7], the solution of the GS equation in toroidal coordinates correspond to

TeX Source

where and are Fock's functions given in terms of half integer order, first degree Legendre functions of the first and second kinds. and are internal and

external moments.

A. MARTe RT-ODIN Test and Development

The ODIN algorithm was decomposed in two GAMs: MomentsGAM and OdinGAM. The former evaluates the internal and external moments; the latter calculates a

least square approximation which fits the magnetic measurements, adjusts the moments according to this approximation, and computes a new guess for until the

difference between two subsequent iterations is less than a specified tolerance over the whole mesh. Finally, it also computes important quantities associated with the

equilibrium, such as the poloidal beta and the internal inductance . The algorithm runs with a cycle time of

The RT-ODIN system is a good example of the flexibility of the MARTe Framework. The two main GAMs of the system, MomentsGAM and OdinGAM, were written

once, debugged in a simulation environment using data stored from previous experiments, and then reused on a VME crate directly connected to the analog inputs

from the plant, as well as on a dedicated PC connected to the main feedback crate via RTNet.

12/4/13 3:54 PMIEEE Xplore - HTML View

Pagina 8 di 11http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5948402

FOOTNOTES

REFERENCES

This work was supported by the European Community within the framework of the ENEA/EURATOM Association on Fusion Research. The views and opinions expressed herein do notnecessarily reflect those of the European Commission.

L. Boncagni, G. Mazzitelli, and V. Vitale are with the EURATOM–ENEA Fusion Association, Frascati Research Centre, Division of Fusion Physics, Rome, Frascati 00044, Italy (e-mail:luca.boncagni@enea.it)

Y. Sadeghi, D. Carnevale, S. Sinibaldi, R. Vitelli, and L. Zaccarian are with the Department of Computer Science, Systems and Production, University of Rome “Tor Vergata,” 00133Rome, Italy (e-mail: ysadeghi@disp.uniroma2.it).

D. Pucci, F. Piesco, S. Monaco, and G. Zamborlini are with the Faculty of Engineering, University of Rome “La Sapienza,” 00185 Rome, Italy.

F. Sartori is with the Fusion for Energy CODAC, 08019 Barcelona, Spain.

A. Neto is with the EURATOM–IST Nuclear Fusion Association, 1049-001 Lisbon, Portugal.

Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org.

Using as feedback, the pressure measure, obtained from a PKR 251 full scale range.

Using as feedback, the measured density, obtained from interferometric measurements.

The test environment consists of a vacuum chamber, a pumping group (rotative plus turbo-molecolar pump), a controllable gate that isolate the chamber from the pumping group, thepiezoelectric valve to characterize plugged to an amplifier driven by the MARTe Calibration System that runs in a PC equipped with a NI 6024e ADC/DAC card.

In FTU, the experimentally estimated major and minor radius of plasma are 0.94 m, 0.27 m, respectively.

1. Marte: A multiplatform real-time framework

A. C. Neto, F. Sartori, F. Piccolo, R. Vitelli, G. D. Tommasi, L. Zabeo, A. Barbalace, H. Fernandes, D. F. Valcarcel and A. J. N. Batista

IEEE Trans. Nucl. Sci., vol. 57, no. 2, pp. 479-486, 2010

Quick Abstract | Show Context | Full Text: PDF

2. A survey of recent MARTe based systems

A. Neto, D. Alves, L. Boncagni, P. J. Carvalho, D. F. Valcarcel, A. Barbalace, G. D. Tommasi, H. Fernandes, F. Sartori, E. Vitale, R. Vitelli and L. Zabeo

IEEE Trans. Nucl. Sci., 2011

Quick Abstract | Show Context | Full Text: PDF

1

2

3

4

SECTION VII

CONCLUSION AND FUTURE WORK

In Fig. 8, the three phases of the evolution of the RT-ODIN system are shown. During development (phase A), a standard PC has been used to test the software, using

a waveform generator to produce the input signal for the ODIN algorithm by reading the FTU signals database. After the system was completely tested and error-free,

the MomentsGAM and ODINGAM were inserted on a MARTe system running on a VME crate connected to the analog inputs from the plant (phase B). The system

was then tested using real experimental data. After this phase, it was realized that, using RTNet, there was not any need to run the system on a VME crate, but that the

input data could be streamed via RTNet from the fast feedback system (running at ) which already had all the needed analog inputs and is being also ported to

MARTe. So a dedicated machine for ODIN was prepared and connected to the feedback system via a standard Ethernet cable (phase C, and current status of the

system), and a specific configuration file was prepared, avoiding the need to buy a new VME crate and to duplicate the input signals. It is important to stress that the

two GAMs where coded only once and never modified during all the tests and that switching between these three deeply different system configurations was just a

matter of modifying a text-only configuration file.

In this work, the essential components needed for a complete integration of the MARTe Framework in FTU have been shown, as well as some smaller MARTe systems

that were developed with the aim of acquiring skill on this environment. These systems are still work in progress; currently, the main objective is to port the actual

feedback control system to the MARTe framework, with the idea of uncovering the main issues arising during the development of a Tokamak Control System using

MARTe, and to check its scalability to larger fusion devices like Fusion Advanced Studies Torus “FAST,” a fusion project recently proposed by the Italian Association

on Fusion for a European satellite Tokamak in support of the ITER program [8].

ACKNOWLEDGMENT

The authors would like to thank the PPCC team for their generous help in carrying out this research.

12/4/13 3:54 PMIEEE Xplore - HTML View

Pagina 9 di 11http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5948402

AUTHORS

3. ATCA control system hardware for the plasma vertical stabilization in the JET tokamak

A. J. N. Batista, A. Neto, M. Correia, A. M. Fernandes, B. B. Carvalho, J. C. Fortunato, J. Sousa, C. Varandas, F. Sartori and M. Jennison

IEEE Trans. Nucl. Sci., vol. 57, no. 2, pp. 583-588, 2010

Quick Abstract | Show Context | Full Text: PDF

4. Ftu operation

B. Angelini

Fusion Sci. Technol., vol. 45, pp. 437-458, 2004

Show Context

5. The PCU JET plasma vertical stabilization control system

F. Sartori, A. Barbalace, A. Batista, T. Bellizio, P. Card, G. D. Tommasi, P. M. Cullen, A. Neto, F. Piccolo, R. Vitelli and L. Zabeo

Fusion Eng. Des., vol. 85, no. 3-4, pp. 438-442, 2010

Show Context

6. A new extremum seeking technique and its application to maximize RF heating on FTU

D. Carnevale, A. Astolfi, C. Centioli, S. Podda, V. Vitale and L. Zaccarian

Fusion Eng. Des., vol. 84, pp. 554-558, 2009

Show Context

7. Analysis of MHD equilibria by toroidal multi-polar expansions

F. Alladio and F. Crisanti

Nucl. Fus., vol. 26, p. 1143, 1986

Show Context

8. The Fusion Advanced Studies Torus (FAST): A proposal for an ITER satellite facility in support of the development of fusion energy

A. Pizzuto

22nd IAEA Fusion Energy Conf., 2008

Show Context

Luca BoncagniNo Bio Available

Yahya SadeghiNo Bio Available

Daniele CarnevaleNo Bio Available

Giuseppe MazzitelliNo Bio Available

Andr NetoNo Bio Available

Daniele Pucci

12/4/13 3:54 PMIEEE Xplore - HTML View

Pagina 10 di 11http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5948402

CITED BY

KEYWORDS

No Bio Available

Filippo SartoriNo Bio Available

Francesco PiescoNo Bio Available

Simone SinibaldiNo Bio Available

Vincenzo VitaleNo Bio Available

Riccardo VitelliNo Bio Available

Luca ZaccarianNo Bio Available

Salvatore MonacoNo Bio Available

Giorgio ZamborliniNo Bio Available

None

IEEE Keywords

Control systems, Hardware, Logic gates, Plasmas, Real time systems, Software, Valves

12/4/13 3:54 PMIEEE Xplore - HTML View

Pagina 11 di 11http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5948402

Sign In | Create Account

IEEE Account

Change Username/Password

Update Address

Purchase Details

Payment Options

Order History

Access Purchased Documents

Profile Information

Communications Preferences

Profession and Education

Technical Interests

Need Help?

US & Canada: +1 800 678 4333

Worldwide: +1 732 981 0060

Contact & Support

About IEEE Xplore | Contact | Help | Terms of Use | Nondiscrimination Policy | Site Map | Privacy & Opting Out of Cookies

A not-for-profit organization, IEEE is the world's largest professional association for the advancement of technology.© Copyright 2013 IEEE - All rights reserved. Use of this web site signifies your agreement to the terms and conditions.

CORRECTIONS

INSPEC: Controlled Indexing

Tokamak devices, real-time systems

INSPEC: Non-Controlled Indexing

European satellite Tokamak, FAST experiment, FTU migration, Frascati Tokamak Upgrade, Fusion Advanced Studies Torus, MARTe package, ODIN Equilibrium Reconstruction system,distributed real-time control architecture, modular control architecture

Authors Keywords

Gas puffing, LHPP, MARTe, real-time control, rt-ODIN

None