Data acquisition and control system for large volume ...

Data acquisition and control system for large volume plasma device G. B. Patel, P. K. Srivastava, L. M. Awasthi, V. P. Anitha, G. Ravi et al. Citation: Rev. Sci. Instrum. 73, 1779 (2002); doi: 10.1063/1.1458046 View online: http://dx.doi.org/10.1063/1.1458046 View Table of Contents: http://rsi.aip.org/resource/1/RSINAK/v73/i4 Published by the AIP Publishing LLC.

Additional information on Rev. Sci. Instrum. Journal Homepage: http://rsi.aip.org Journal Information: http://rsi.aip.org/about/about_the_journal Top downloads: http://rsi.aip.org/features/most_downloaded Information for Authors: http://rsi.aip.org/authors

Downloaded 20 Sep 2013 to 14.139.114.53. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://rsi.aip.org/about/rights_and_permissions

REVIEW OF SCIENTIFIC INSTRUMENTS

VOLUME 73, NUMBER 4

APRIL 2002

Data acquisition and control system for large volume plasma device G. B. Patel,a) P. K. Srivastava, L. M. Awasthi, V. P. Anitha, G. Ravi, P. J. Patel, U. K. Baruah, and S. K. Mattoo Institute for Plasma Research, Near Indira Bridge, Bhat, Gandhinagar-382428, India

共Received 15 October 2001; accepted for publication 7 January 2002兲 This article describes hardware and software solutions to a need which is comprised of 共i兲 acquisition of a large volume of high speed data with multiple time scales, 共ii兲 control of various operational parameters of device and diagnostics, and 共iii兲 processing and management of the acquired data for a large volume plasma device. The solution relies on the base of a VXI bus and uses a standard PC with a Windows 98/NT operating system and C as the programming language. The system is networked with the existing network with the result of allowing a large data storage space of processing facilities from any terminal in the laboratory. © 2002 American Institute of Physics. 关DOI: 10.1063/1.1458046兴

I. INTRODUCTION

supported by various auxiliary facilities. The vacuum system is capable of providing a base pressure ⬃10⫺7 mb and can handle gas throughput of 5 Torr l/s. A large magnetic coil system is provided for producing a uniform magnetic field upto 150 G dc in the whole volume of the device. A power supply system energizes coils, heats filaments or oxide coated cathode, and strikes an arc with arc current up to 4000 A with a 2% shot to shot variation. The system will be augmented by a highly accurate indigenously developed probe drive system which can enable spatial resolution of 10 mm in the x, y, z direction. Total volume to be scanned is (25 ⫻25⫻50) cm3 . The nature of the experiment is such that it requires high sampling techniques as the phenomena of study related to high frequency oscillations. A full understanding is realizable only when topology of the field parameters can be mapped with a high spatial resolution. To achieve this end, there is a need to have not only a drive system which can scan the desired plasma volume, but also to have a matching acquisition which can acquire data at a fast sampling rate, store it in appropriate system, and make use of software programs for efficient data processing and management. In addition, as it is not possible to produce dc plasmas in such a system either because of poor cooling capacity or because of the nature of experiments, the plasma has to be pulsed. The repeatability of the discharge pulse is therefore important and entirely depends upon the control parameters such as arc current, filament heater current, gas throughput, etc. Further, safety of the device requires various parameters to be monitored and interlocked. Another design issue arises purely from various time scales that exist in the system. These scales vary from a few hundred of ms for plasma discharge pulses to a few ns for excitation of high frequency oscillations. Table I gives an account of the experimental requirement with regard to the time scales involved. The maximum sampling rate required is 1 G Sa/s. Hence the data acquisition system has to handle multiple time scales. To get statistically meaningful data, the data acquisition has to be executed in a burst mode of 3–10 pulses in the same plasma discharge pulse. To reduce the campaign time and therefore to obtain stable operation of the

Basic plasma physics experimental devices have grown in status from handling very simple experiments yielding data which can be handled by simple recording systems such as oscilloscopes and recorders to complex experiments, which can be meaningfully understood only when a large volume of data is acquired,1,2 assisted by computers.3 In the past, this need was satisfied by modern and powerful oscilloscopes with a general purpose interface bus for the transport of data. However, such systems cannot provide high throughput. The performance was enhanced by basing the data acquisition system on a VXI interfaced CAMAC4 crate using FORTRAN code and VMS. While this system provided useful assistance in data acquisition, its poor upgradability has been a major concern. Now client CAMAC has given way to VXI. This led to at least an order of magnitude increase in the capability of data transfer rates, as has been demonstrated on a large plasma device 共LAPD兲 by Mandrake and Gekelman.5 However, performance of this system can be further improved by making use of the relational database management system 共RDBMS兲 on network. This results in reduced need for permanent storage systems, ease of operation from any terminal point, and increased capacity of data management.6 The subject matter of this article is to demonstrate that network based data acquisition and database management solution eases operations with regard to acquisition, data processing, and management.7 In the following we shall describe the need for a data acquisition system in Sec. II, hardware configuration in Sec. III, and software developed for this program in Sec. IV. Examples are given to demonstrate the capability of the data acquisition and control system. II. EXPERIMENT AND DATA ACQUISITION AND CONTROL REQUIREMENT

The device8 is shown in Fig. 1. It consists of a double walled cylindrical shell of 3 m length and 2 m diameter. It is a兲

Electronic mail: [email protected]

0034-6748/2002/73(4)/1779/7/$19.00

1779

© 2002 American Institute of Physics


1780

Patel et al.

Rev. Sci. Instrum., Vol. 73, No. 4, April 2002

FIG. 1. Schematic of the large volume plasma device.

cathode of the device during the period of compaign, the plasma discharge frequency must be ⬃1 Hz with a duty cycle of 4 –10 ms ON/1 s OFF. Further, the plasma device has to be prepared for repeating the experiment and the data acquisition has to be armed for the next acquisition. III. DATA ACQUISITION HARDWARE CONFIGURATION

We are using three TVS641 共Tektronix Inc. Make兲 VXI based digitizer modules. These modules have four channels, each with 1 GHz single shot sampling rate. The auto advance acquisition mode 共using segmented memory兲 of this module offers the additional advantage of scaling down the time interval between consecutive pulses, as and when required this module also offers flexibility over triggers 共internal, external, and VXI burst兲, record length, gain, and sampling rate. The VXI mainframe provides power to these modules. All the VXI data acquisition modules and controller module share the single VXI bus. All these modules are controlled by the MXI2 共National Instruments product兲 slot ‘‘0’’ controller which is in turn controlled by a PC add on card. This card is a MXI bus controller and resides on a PCI slot of a standard

computer. This computer controls the whole VXI system. The MXI-2 bus has a throughput of 33 Mbytes/s in block transfer mode and 23 Mbytes/s in sustained mode. Our VXI data acquisition modules are message based. These modules have their own command processing time. The effective transfer rate, which is system dependent, is 500 Kbytes/s in our case, irrespective of the operating system. A. Triggering and data acquisition

The plateau region of 5 ms discharge pulse, where primary and plasma electrons coexist, has a density of ⬃1012 cm⫺3 . At the turn off of the discharge voltage the plasma begins to decay. 400 ␮s after the turn off of the discharge voltage, the plasma is quiescent, devoid of primary electrons and has a density ⬃5⫻1011 cm⫺3 . This regime of the afterglow plasma is suitable for whistler wave excitation.6 Density measurement is carried out by a Langmuir probe. For triggering the wave excitation, a Langmuir probe signal is compared in a comparator circuit. A fast comparator, MAXIM model MAX905, produces a transistor-transistor logic 共TTL兲 signal when density crosses

TABLE I. LVPD diagnostics and sampling rate requirement. Signal Langmuir probe Langmuir probe Langmuir probe Magnet probe Electric dipole probe Diamagnetic probe Emissive probe

Diagnostics

Sampling rate

Record length

steady state density measurement Afterglow density measurement Fluctuation study whistler wave magnetic field electric field measurement beta effect study plasma potential study

250 K sa/s 1 G sa/s 1 G sa/s 1 G sa/s 250 M sa/s 250 K sa/s 250 K sa/s

2 048 30 000 15 000 2 048 2 048 2 048 2 048



Data and control for plasma device

1781

TABLE II. Control and monitoring signals. Signal Pump ready signal from three difstackes Roughing pump valve status Roughing pump valve ON/OFF Baffle valve status of three difstackes pumps Baffle valve of three difstackes pumps ON/OFF Gate valve status of roughing pump Gate valve of roughing pump ON/OFF Status thermal snap switches of three difstack pumps Water flow switches Difstack heater status Penning gauges relay signal Pirani gauges relay signal Ionization gauge relay signal Power supplies’ OFF signal for magnet, filament, and discharge RTD PT-100 signal K-type thermocouples T-type thermocouples

a reference signal. One of the TVS641 modules is triggered by the output signal of a comparator circuit and it raises the VXI backplane TTL trigger line. Remaining modules are triggered from the VXI backplane TTL trigger line. Thus all three modules get triggered at a specific plasma density that can be changed by changing a reference signal, and capture signals for 10 ␮s. B. Burst mode data acquisition operation

In this mode of data acquisition, we capture the signals for the multiple triggers. Data are acquired and stored in the segment of a VXI digitizer module. In any one particular shot the data for 10–15 triggers is acquired every 1 s. Each trigger data is kept in one of the segments of the VXI digitizer module. The trigger data are stored in different segments of memory. These segments are not physical segments, but are logical segments. Finally, all the data are simultaneously transferred to the computer. This burst mode data acquisition is accomplished by using the Auto Advance data acquisition facility of the TVS 641 Tektronix VXI data acquisition module.

Type

No.

digital input digital input digital output digital input digital output digital input digital output digital input digital input digital input digital input digital input digital input digital output analog input analog input analog input

3 3 3 3 3 1 1 3 8 3 3 5 2 3 60 6 4

terface. Datalogger scans all these channels within 2 s. It compares input signals with predefined set limits. Crossing of the set limit by any of the signals produces a TTL pulse. This pulse is isolated using opto-couplers and it drives a relay, which trips the filament and magnet power supply of the system. The vacuum system for LVPD is a complex system with multiple vacuum pumps, requiring a certain fixed procedure of turning ON and OFF and a protocol has to be observed for obtaining the vacuum. These procedures and protocols may change with the experimental condition. Hence there has to be a full online monitoring of the whole vacuum system. The power of all the vacuum pumps is monitored along with the valve position 共open/close兲 with the help of electrical signals obtained from these devices. Other signals from thermal snap switch and pump ready switches are also monitored. Opto-isolaters are put in these monitoring lines to isolate the power side from the monitoring and control side. Signals from the penning, pirani, and ionization gauges are analog output signals. These signals are interlocked with a vacuum control system. All the power supplies are interlocked with vacuum, temperature, and flow signals using the datalogger.

C. Monitoring and control system

The requirements regarding the control and monitoring input/output signals are listed in Table II. In the LVPD, the temperature at various places of the cathode structure, which dissipates about 90 KW, the walls of the chamber, and the magnetic field coils 共180 KW兲 have been continuously monitored. In case of the coils, which are 60 in number, RTDs 共PT-100兲 have been mounted on each, and the temperature is compared with the predefined set limits. The temperature of the hot cathode and chamber wall is monitored with the help of K-type thermocouples. Special thermocouples have been designed for this purpose. These thermocouples are nongrounded, potential free, and vacuum compatible. The vacuum of the chamber is also monitored through the output signal of vacuum gauges. All these signals travel 20 m and terminate at a 96-channel microprocessor based monitoring, logging, and contol system 共datalogger兲 with a computor in-

D. Probe drive control system

A three axes probe drive control system 共PDCS兲 is a recent addition to the LVPD. High accuracy (⬃0.1°), error correction, protection, and flexibility are its main features. Power supplies, motor drives, stepper motors, encoders, limit switches, and a computer with software are the main components of the PDCS. Three 2 N m torque stepper motors are powered by the motor drive. Each motor has a separate drive. A stepper motor has a resolution of 1.8° per pulse, i.e., 200 pulse per revolution, giving an accuracy of 0.1°. Movement of the stepper motors is controlled by the drive. These drives are powered by a separate power supply. The motor drives are microcontrolled and they accept a command from the computer and control the movement of motors. All three motor


1782

Patel et al.


drives are interfaced with each other as well as with the computer through a RS 485 multidrop bus. We are using a RS 485 to RS 232 converter inside the PC which enables us to use a computer standard COM port. A signal from the optical shaft encoder is given back to the motor drive. Whenever a computer gives a command to drive, signals from encoders are monitored. In case of an error, due to jamming of the drive caused by an overload, either a corrective action is taken by the microcontroller or an error is displayed on the screen. Signals from the limit switches are also monitored by the motor drive. They decide the home and end position of our probe drive system. We have developed a digital input/output 共I/O兲 module which is interfaced with the computer through the parallel port. Using this digital I/O module we can interlock the operation of the PDCS with any external signal like temperature, vacuum, etc. Overall operation of the PDCS is controlled by the general purpose computer. We have developed a software using ‘‘C’’ programming language. Our software has the capability to run in slave mode. In slave mode, all the commands to the system are given by the remote computer, which is connected to this local computer through the RS 232 interface. Overall operation of PDCS is controlled by the computer, which provides enough flexibility to change the sequence of operation as per requirements. IV. SOFTWARE SYSTEM

The LVPD software system is modular and distributed, each module performs a specific task. With modular architecture of the software system we can easily modify the code without affecting other modules. This is very important to provide flexibility in the operational sequence of experiments. The LVPD software system consists of a VXI graphics user interface, a database graphics user interface, and a database management system. A. LabWindowsÕCVI

LabWindows/CVI is a software development tool for instrumentation supplied by National Instruments Inc. 共http:// www.natinst.com兲. It is an interactive ANSI C programming environment designed for building virtual instrument applications. It delivers a drag-and-drop editor for building user interfaces, a complete ANSI C environment for building our test program logic, and a collection of automated code generation tools and utilities for building a data acquisition and control system. It provides a hardware interface with GPIB, PXI, VXI, RS 232, etc. It gives high-level hardware interfaces which help to build high-speed, device-independent applications. It is also easy to learn and use in a development environment. B. VXI graphic user interface

An interface must be both intuitive and pleasing to use, allowing the user to focus on the physics of the situation rather than program configuration and mechanics, especially in the case of long data runs. With LabWindow/CVI graphical front panels, a single screen control panel, from which all

FIG. 2. Database graphic user interface.

aspects of the DAQ can be managed, is created. The VXI system is fully controlled by this graphic user interface 共GUI兲. All the parameters for the VXI system like sampling rate, trigger, record length, etc. are controlled using this GUI. As the data is acquired, it is important to allow the user to view what is being acquired. Four channels of data are displayed in each of the three windows enabling the user to assess the data acquired before saving. Further, an additional provision which allows viewing of the latest data of all 12 channels in a single window is also incorporated through locally developed software. A VISA 共virtual instrumentation software architecture兲 is used as a main library of the data acquisition software. A graphic user interface is developed using LabWindows/CVI with a VISA library. Our data acquisition modules are message based and their logical addresses are dynamically configured. Hence knowledge of the hardware details like addressing of control resistor, etc. is not essential. All that is required is to give the command and queries specified by the hardware manufacturer. viPrintf and viRead functions from the VISA library are used to give the command and get the response from the module, respectively. For example, information regarding record length can be obtained using the following sequence of operation. QUERY→‘‘SWEep:POInts?’’ RESPONSE→2048 C. Database graphics user interface

All the experimental parameters like probe position, filament current, discharge current, type of diagnostics, etc. are entered before taking a shot using this GUI. This graphical user interface is developed using Visual Basic 共Fig. 2兲. Due to large volume of data, all the data are stored with the experimental parameters to be used for processing later. GUI also communicates with the COM 共component object model, Microsoft ActiveX Technology兲 object, which has been developed in Visual C⫹⫹. This COM object controls the VXI backplane and transfers the data from the VXI digitizer to the database management system. A GUI gives all the user input data to this object, which stores these pa-




1783

E. COM object

A COM component is developed using Visual C⫹⫹. This COM component reads the data from the VXI module and stores it into the SQL Server. DBLIB is a library supplied with a SQL server. It is used to store the large data in the database. This COM component gives interface to other applications for acquisition. In our case, the COM component is used by Visual basic application. Two main methods have been implemented in COM. They are ‘‘PutInSQLServer’’ which stores the data from the VXI module to the database and ‘‘GetFromSQLServer’’ which retrives perticular shot data. A ‘‘sqlwritetext’’ method of DBLIB is used to store the large data items in the database. FIG. 3. Software architecture.

rameters with the data in the database. Figure 3 shows the interface of various software components. The user can view and retrieve the data for further analysis from the database using this interface software. D. Database management system

We are using SQL 7.0 共Microsoft Product兲 as a database management system on the Windows NT 4.0 operating system. SQL is a relation database management system 共RDBMS兲. This system has been chosen considering the large amount of data (⬃3 GB) to be stored. The data is stored as a binary large object 共BLOB兲 in a text field. A complete design of our database is shown in Table III. We have chosen a SQL because it has a TCP/IP network support, good scalability, and security. Any computer, which has a privilege on the TCP/IP network can access the data from the server. TABLE III. LVPD database design. Table name Shotinfo

Fields Shotnumber 共Integer兲, shotdate 共Date and Time兲, channels 共Byte兲, pulses 共Byte兲, rposition 共Real兲, theataposition 共Real兲, zposition 共Real兲, basepressure 共Real兲, workpressure 共Real兲, gastype共Single Character兲, DPSVoltage 共Real兲, DPSCurrent 共Real兲, MPSVoltage 共Real兲, MPSCurrent 共Real兲, FPSVoltage 共Real兲, FPSCurrent 共Real兲, CathodTemp 共Real兲, MagneticField 共Real兲, Operator 共var Char兲, Remarks 共var Char兲

Channelpara

Shotnumber 共Integer兲, channelid 共Byte兲, diagnosticstype 共4 Char兲, recordlength 共Integer兲, samplingrate 共Long Integer兲, portnumber 共Integer兲

Channeldata

Shotnumber 共Integer兲, channelid 共Byte兲, channeldata 共Text兲, Xoffset, 共Real兲 Xscale 共Real兲, Yoffset 共Real兲, Yscale 共Real兲

Diagnosticsinfo

Diagnostictype 共4 char兲, diagnosticsdescription 共var char兲

V. OPERATIONAL EXPERIENCE

The LVPD, along with the VXI based data acquisition system, has been operational for the last three years. The plug, play nature of the VXI platform provides future expandability in terms of more channels for data acquisition. Due to its open vendor architecture and VISA library, there is no single vendor dependence, making the system highly flexible. Any new operational requirement can be fullfilled in a short time by making a relevant alteration in the software. A. Operational reliability

All the control logic in LVPD are hardwired. The control signals from vacuum system, power supplies, and PDCS are interlocked by various hardware gates, thus providing a high level of reliability. Various test utilities have been developed for the VXI system, where by it is possible to read the data from all the VXI modules memory and display it in graphical form simultaneously. This allows the user to make an online assessment of the shot. A utility program for the database further confirms the proper storage of the shot data. Various features of the SQL server database system like backup and network support allow one to keep the backup of the data on other auxiliary storage as well as on other computers on the network. B. Pitfalls

The vendor has supplied us with drivers for Windows NT as well as Windows 98. Although Windows NT is a more stable system than Windows 98, our system is based on the latter for performance reasons. Previously, we had implemented the whole system on NT, where we faced limitation in speed as our system had a lot of graphic user interfaces. Therefore we switched over to Windows 98. With this, smooth operation of the system is achieved. However, Windows 98 suffers from inherent drawbacks related to stability and security. Occasionally, this leads to difficulties associated with corruption of system files. To overcome this we are planning to use Windows 2000 Profession system for LVPD. Our VXI data acquisition modules have 15 K of record length for 1 G Sa/s and 30 K for less then 1 G Sa/s. This record length size is adequate for normal experiments. For experiments requiring a larger record length it becomes essential to use alternate solutions like usage of a digital storage oscilloscope. A technique has been developed for long


1784

Patel et al.


duration acquisition by triggering all the modules sequentially. By this method, a total 30⫻3⫽90 K of data can be acquired. However, it may be noted that the number of data channels which can be acquired is reduced to 4. Our control system is mainly hardwired and microprocessor based. Though it gives a high level of reliability, it suffers from reduced flexibility. For example, incorporation of an additional requirement is possible only by changing the logic, which necessitates replacement of the PCBs. At present, our data acquisition computer and data base server is on an existing ATM network. Failure of this network results in failure of data recording as well as analysis of stored data. Implementing a local dedicated network could prevent such problems. The fast acquiring/storing efficiency of the system is not being fully utilized presently due to the following existing inadequacies of the LVPD system: The mechanical part of the fully automated LVPD probe drive system mentioned above as well as the proposed large area (1⫻1 m) cathode are at the developmental stage and will be installed soon. The experimental requirements related to plasma production and three-dimensional scanning have, so far, been achieved with the help of alternate solutions. Certain operational limitations of these, which use a mechanical driven probe drive unit and a cathode requiring minor improvization in its cooling arrangements, lead to a present experimental constraint of an increased shot to shot interval. However, to date, we have already acquired ⬇1 GB of data from ⬇10 000 plasma shots.

vides the user a standard interface. Our software can also be made fully compatible with any new controller from any other vendor by making minor changes in the code. We have kept the IEEE 1394 firewire slot ‘‘0’’ controller 共National Instruments Product兲 as a spare and our present code for the MXI-2 controller is fully compatible with it. All the database software has been developed using Visual Basic and Microsoft ActiveX Data Object 共ADO兲. We are using a ODBC driver to connect the database, which makes our software database independent. The database server can be changed without changing our front-end software. As already mentioned, we have already acquired ⬇1 GB of data from ⬇10 000 plasma shots by now. By deploying a network based database management system, we have reduced data processing, retrieval, and analysis time. Since this also offers the flexibility of using any terminal, excessive dependence on a single machine attached with the experimental device is completely eliminated. Further, a web based interface of our data allows users to extract data from outside of our local area network. A PC based probe drive control system allows great flexibility for operation of our probe drive movement. It is possible to interlock the probe drive system with any parameters like temperature, vacuum, etc. By interfacing the PDCS with our data acquisition system it is possible to carry out automatic operation of LVPD. Maximum flexibility has been provided in our existing hardware and software so that we can benefit from future technological developments without increasing our investment.

C. Distinct software features

D. Future upgrades

Using VISA library in software development makes the VXI system plug and play, and hardware independent. LVPD software has been developed using the VISA Library. Following is a small ‘‘C’’ program using the VISA library, which reads and prints an identity of a VXI device at a logic address 2 on the VXI bus. # include 具stdio.h典 # include 具visa.h典 main共兲兵 ViSession rm, instr; char buf关100兴; long count; viOpenDefaultRM 共&rm兲; viOpen共rm,‘‘VXI0::2::INSTR’’,VI – NULL, VI – NULL, &instr兲; viPrintf共instr,‘‘* IND? ’’兲; viRead 共instr, buf, 100, &count兲; printf 共‘‘%s,’’ buf兲; viClose共instr兲; 其 This code offers a lot of flexibility. For example, if there is a requirement of changing the slot ‘‘0’’ controller, we need to change only a single line 共viOpen Statement兲 of the whole code. Further, knowledge of the complete hardware details is not essential. VISA hides all the hardware details and pro-

The system shall be supplemented by another four channel VXI module with the same specifications, for which the order has been placed. To incorporate this module we need to modify our existing acquisition software as well as database design. Accomplishing this, development of a 16-channel data acquisition system is expected to be complete by December 2001. Features of this system shall be enhanced to include a software for online processing of the data as well as utility programs which read the data from the database server, process it, and give us a graphical output. The existing database shall be modified to facilitate storage of processed data. For full automation of the LVPD, a PC based monitoring system shall be provided in which status of all the control signals will be displayed. With a provision of automation in ordering the discharge duty cycle and arming of magnet and filament power, all the operational processes related to LVPD experiments can be made fully automatic and left unattended around the clock.

1

W. Gekelman, H. Pfisteer, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 共1991兲. 2 R. L. Stenzel, Phys. Fluids 19, 857 共1976兲. 3 K. L. Greene and B. B. McHarg, Jr., in Proceedings of the 17th IEEE/ NPSS Symposium on Fusion Engineering 共IEEE, New York, 1997兲, O-12.3.


Rev. Sci. Instrum., Vol. 73, No. 4, April 2002 4

M. Kawai, T. Aoyagi, H. Ooharg, A. Honda, T. Itihi, and M. Kuriyama, in Proceedings of the 17th IEEE/NPSS Symposium on Fusion Engineering 共IEEE, New York, 1997兲, p-16.7. 5 L. Mandrake and W. Gekelman, Comput. Phys. 共Annual Index兲 11 共1997兲. 6 M. Korten, B. Becks, and G. Kemmerling, in Proceedings of the 17th IEEE/NPSS Symposium on Fusion Engineering 共IEEE, New York兲, p-5.5.


1785

7

B. U. Niderost, A. A. Gerritsen, P. C. van Haren, W. Lourens, A. Taal, C. Fuchs, G. Kemmerling, M. Korten, W. Kooijman, A. A. M. Oomens, and F. Wijnoltz, in Proceedings of the 21st Symposium on Fusion Technology 共unpublished兲, p. E-36. 8 S. K. Mattoo, V. P. Anitha, L. M. Awasthi, G. Ravi, and LVPD Team, Rev. Sci. Instrum. 72, 3864 共2001兲.
