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AXISYMMETRIC CONTROLS IN RFX-mod: STATUS AND PERSPECTIVES. M. Barp , R. Cavazzana, G. Marchiori, A. Soppelsa, L. Zanotto. Outline. Feedback Control of Reversal Parameter Optimization of Toroidal Power Supply Control System Feedback Control of Plasma Current

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axisymmetric controls in rfx mod status and perspectives

AXISYMMETRIC CONTROLS IN RFX-mod: STATUS AND PERSPECTIVES

M. Barp, R. Cavazzana, G. Marchiori, A. Soppelsa, L. Zanotto

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

outline
Outline
  • Feedback Control of Reversal Parameter
  • Optimization of Toroidal Power Supply Control System
  • Feedback Control of Plasma Current
  • MHD Equilibrium Codes for Horizontal Equilibrium and Shape Control

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide3
Feedback Control of Reversal Parameter

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

feedback control of reversal parameter
Feedback Control of Reversal Parameter
  • A reliable control of F was missing in RFX-mod:
    • F controlled in “open loop”
    • Control relied very much on the experience of the operator
    • Plasma events had strong impact on the control
  • Reasons for a reliable and precise control:
    • Best performance of RFX-mod at shallow F (-0.05≤F<0)
    • At high current and shallow F, small deviations of Bt(a) are tolerable
    • F positive  loss of RFP configuration and very poor confinement

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

system modeling
System Modeling

General scheme and models

  • Model of the toroidal power supply (both power circuit and control system)
  • Model of the coupling between the toroidal windings and the plasma during the flat-top phase

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

closed control loop

vq

vq*

Closed Control Loop

Feedback controller scheme

vq(t) affected by

plasma reconnection

The reversal parameter control can be reformulated as a control of toroidal edge field at the plasma radius

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

results
Results

Reversal loss

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide8
Optimization of Toroidal Power Supply Control System

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide9

Optimization of Toroidal Power Supply Control System (1)

  • New feed-forward input to the internal controller of the toroidal PS to improve the dynamic performance of the system
  • Proportional and Integral gain optimization

+

+

+

+

Toroidal

inverters

+

-

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide10

Optimization of Toroidal Power Supply Control System (2)

  • Small current unbalances in the toroidal coils give rise to wall mode locking
  • Significant m=0, n=1 mode/field error not adequately corrected
  • A proper controller necessary to drive independently the current in the 12 toroidal coils
    • reduction of field errors and current unbalances
    • m=0 mode control

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide11
Feedback Control of Plasma Current

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide12

Current Controller Limitations (1)

  • Plasma current controller implemented and tested
  • Tuning campaign not completed
  • Controller step response can be optimized
  • Feedback component is a lag compensator, which is affected by the actuators saturations
  • Experimental proposal has been submitted to tune the regulator

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide13

Current Controller Limitations (2)

  • Plasma Current Controller (PCC) increases plasma current independently from plasma resistance
  • High energy deposition on a localized set of tiles
  • Debate whether the machine is protected “by design” against such occurrence or if the PCC should take any action
  • At present PCC switched off if a power threshold is exceeded

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide14

Automatic Ip ramping

Plasma Current 29271

PCAT Voltage 29271

Vmag29271

Vmag estimate 29271

  • Plasma current control based on operator experience
  • Plasma current ramps at the fastest rate without control
  • PCAT unit automatically switched on as soon as their voltage is higher than the voltage drop on the transfer resistor (vm)
  • vm not available in the real-time system but a good estimation can be obtained

Automatic Ip ramping

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide15

MHD Equilibrium Codes

for Horizontal Equilibrium and Shape Control

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide16

Horizontal Equilibrium and Shape Control Codes (1)

  • Reliable MHD Equilibrium code to describe a wide range of plasma equilibria in RFX-mod is needed for engineering applications
  • Static/evolutionary MHD equilibrium
    • free boundary problem (direct problem): determination of the plasma boundary for an assigned set of external currents and JT(y) plasma density profile
    • fixed boundary problem (inverse problem): determination of position and amplitude of external currents for an assigned plasma boundary and JT(y) plasma density profile

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide17

Horizontal Equilibrium and Shape Control Codes (2)

  • Engineering oriented versions (e.g. Proteus, MAXFEA) including realistic description of the conducting structures are essential:
    • Design magnetic winding systems
    • Derive linearized model of the plasma response
    • Test and to assess the performances of plasma magnetic control systems
  • Modified 2D non linear MHD equilibrium code MAXFEA used in RFX-mod to solve particular RFP equilibria

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide18

Horizontal Equilibrium and Shape Control Codes (3)

  • Research activity for a renewed code or a different one to be adapted to RFP discharges, in particular to the shallow F equilibria.
  • Codes needed for:
    • Study of different plasma shape in RFP or Tokamak configuration in RFX-mod
    • Conceptual design of new RFP experimental devices

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives

slide19

Conclusions

  • F-control system has been implemented and tested in 2010. It proved to be a very useful tool in particular at very high plasma current.
  • The optimization of the toroidal power supply control system for the improvement of the m=0 mode control and the reduction of field errors and currents unbalances has been considered.
  • Plasma current control has also been developed in 2010 but not fully tested. It is scheduled in 2011 a campaign to tune the regulator. A new controller for the automatic ramping of the plasma current is under consideration too.
  • The investigation for a new MHD equilibrium codefor horizontal equilibrium and plasma shapeto be used with shallow F is needed.

M. Barp – 08 Feb. 2011 – Axisymmetric Controls in RFX-mod: Status and Perspectives