Libo,Song xianming, Lili Liuli,Wang minghong,

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Feedback Control
For Plasma Postion in HL-2A

• Libo,Song xianming, Lili Liuli,Wang minghong,
• Fan mingjie, Chen liaoyuan, Yaolieying, Yan
  qingwei

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1. Introduction 2. Requirement 3. System
Overview 4. Program 5. Control Algorithm
6. Test 7. Experimental results 8. Summary
Outline
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Introduction

• HL-2A is a tokamak device with closed
  divertor. It was put into operation at the end of
  2002. But Divertor configuration discharges were
  achieved only after the successful development
  and operation of the horizontal plasma position
  feedback control system (FBCS).
• From the engineering point of view, to
  control the plasma position is to control the
  magnetic field produced by VF and RF, i.e. to
  control the power supple of each coil. This
  paper introduces the hardware configuration,
  program, control algorithm and operational
  results of FBCS.

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2. Requirement

• As HL-2A device itself is a scientific
  experimental device used to study plasma physics.
  The operating mode and parameters of discharge
  themselves need to be tested and summarized. So
  the operation of the FBCS designed for it must be
  adjusted and modified easily in control mode and
  parameters during the tokamak discharges. This is
  a basic requirement for operation of the control
  system. Further, the most important thing is that
  the control system should run steadily in a bad
  environment where has strong magnetic fields.

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3. System Overview

• Because the control system should run
  on real-time and the budget is very limited. The
  industrial computer (IPC) was chosen as
  controller. The hardware of the FBCS is consist
  of IPC and some input /output cards based on ISA
  bus such as A/D, D/A, DI/DO etc, and some
  necessary units such as isolation circuits and
  driving circuits etc. The FBCS must response in
  real time, so the program must be programmed
  under real-time operation system.
• As the FBCS is isolated from other
  systems, so the operation of it is safety. And as
  the watchdog circuit, the power supply of all the
  coils were always guaranteed to work in the
  normal situation. If something wrong happened
  with IPC, no matter for the program or hardware,
  the watchdog will work and preset voltage will be
  output to the thyristor rectifier and let the
  power supply to wok in inverse mode.

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IPC Hardware Configuration
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FBCS System Configuration
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• It is noticed that IPC was programmed
  to be an intelligent controller. It just needs to
  receive commands and control parameters from
  experimental management computer (EMC) through
  ETHERNET. All the commands, parameters and
  discharge waveforms are set or modified or edited
  on EMC according to necessary. The operation is
  very simple and easy. The operator only needs to
  drag and drop the waveform by mouse to get the
  desired waveform.

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4. Program

• Borland C V3.0 was chosen as program
  language under MS-DOS operation system to satisfy
  the need of plasma position real-time control.
  Timer card was programmed in wave generator mode
  at the frequency of 333 Hz, i.e. time interval is
  3 milliseconds. That is the control cycle of
  control system. As we know, when there is an
  interruption signal for a computer, it will cause
  the execution of interruption service routine
  (ISR program). In the ISR program, the following
  tasks will be accomplished 1) acquire signals of
  magnetic probes, 2) calculate the plasma
  position, 3) compare the current plasma position
  with that of formers, through PD controller
  calculating the increase of the control signal of
  VFs power supply. 4) Add the increase calculated
  in step 3 to the preprogrammed data, and then
  send the sum of them to control the VFs power
  supply through DA(PCL-728).

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ISR Flow chart
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5. Control Algorithm

• For easy to control plasma position,
  preprogrammed method and Proportional-Differential
  (PD) controller was adopted together. After
  preprogrammed discharge experiment was
  successful, and the operating experience of the
  discharge accumulated, on the basement of
  preprogrammed discharge, feedback control with
  PD controller was introduced. The PD controller
  is expressed by the following formula

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• a(1)KD/T ,a(2)-K(12D/T), a(3)K(1D/T)
• ( Where K is proportional coefficient ,
• D is differential coefficient,
• T is control cycle)
• dSa(i)(EXP_Data(i)-Data(i))
• (Where EXP_Data is experimental data on
  real-time,
• Data is preprogrammed data,
• d is increase calculated by PD
  controller)
• KoutVSd

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6.Test

• Before tokamak discharge in 2003, a lot
  of tests about character of the power supply of
  every field coil was carried out. This is very
  important and basic step for controlling the
  plasma discharge. Because only the character of
  all the power supply was mastered, the magnetic
  field produced by the corresponding coil can be
  consistent with expected. On the other hand, a
  lot of tests of anti- disturbance and signals
  calibrating were done before formal tokamak
  discharge also.

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7.Experimental results
Plasma position Waveforms contrast between the
first shot of FBCSs operation(1282) and shot
1281 without FBCSs operation under the same
discharge condition.
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Plasma position waveforms under FBCS with
P-controller
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Plasma position waveforms under FBCS with
PD-controller
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Plasma position waveforms contrast among
preprogrammed discharge, FBCSs operation with
P-controller and PD-controller.
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Repeating discharge under FBCS
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8.Summary

• After several shots under difference
  proportional-differential coefficient, the rule
  of the PD controller was mastered. Finally, the
  good repeatability of divertor discharges were
  achieved and the horizontal plasma position was
  controlled as expected.
• Anyway, the FBCSs operation was
  successful for achieving the experimental results
  as expected in 2003.

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Thanks !