1 / 23

In the control room: A customer’s perspective on the need and means for control

In the control room: A customer’s perspective on the need and means for control. Marco de Baar Tokamak Physics Group FOM institute for plasma physics. In present fusion experiments…. Control is often used for a wide variety of applications in tokamaks

mendel
Download Presentation

In the control room: A customer’s perspective on the need and means for control

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. In the control room: A customer’s perspective on the need and means for control Marco de Baar Tokamak Physics Group FOM institute for plasma physics M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  2. In present fusion experiments… • Control is often used for a wide variety of applications in tokamaks • Operations control: Shape and position, density, machine integrity,.. • Physics control: Plasma scenarios, MHD, Dynamic fluxes • Physics control (often) is not control in the strict sense. Feed-back loops that are used to • Improve the quality of experiments • Improve the reproducibility of experiments • Improve the discharge performance are often referred to as control M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  3. Fusion Basics • D + T  He (3.5 MeV) + n (14.1 MeV) • This reaction requires • High Ti • High ne • High energy confinement time tE • Moderate He confinement time tHe • In a reactor: • Neutron absorbed in Li mantle for T production • Energetic helium (a-particle) for a-heating • Collisional slowing down time 1 - 4 s! • To achieve these conditions simultaneously: Confine a DT-plasma in a tokamak Control of a wide variety of parameters Observe requirements on power gain factor Q M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  4. ITER operating conditions • ITER is expected to operate at: • Ip~ 15 MA, Bf ~ 5 T • nD ~ nT = 5x1019m-3, • Ti ~ 20 keV • Additional heating for (Core) Control required • Q = PFUS/PADD= 5 – 10 • Pa / PADD = 1 - 2 • va / valfvén ~ 1.3 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  5. Core control challenges • Limited set of actuators • Pa~ Padd • Wide variety of processes and instabilities, most of which are inter connected • To control the processes that are associated with • Operational limits: Avoidance and amelioration of MHD (examples JET and TEXTOR) • Performance: Turbulence and Transport (example JET) • Plasma self heating: a-particles confinement ta ~ tSD • Ash: Core helium concentration nHe/(nD+nT) < 0.15 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  6. Island formation and suppression • Magnetic island with m/n = 2/1 or 3/2 stable in normal conditions • At high pressure non-linear interaction with sawtooth. This is an operational limit. • In JET RTC is used to track the mode-onset in order to study in detail the mode-dynamics • In TEXTOR this non-linearity can be mimicked at low pressure with the DED coils • Non-linear islands can be stabilised with Electron Cyclotron Waves (ECRH). Dedicated actuator in ITER Upper Port Launcher M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  7. Pressure gradient drives non-inductive current jbsOperational limit due to interaction of sawtooth with “seed island” and this current 10 Sawtooth at q= 1/1 Magnetic ‘gong’ Seed-island w> wcrit w/ t [cm/s] Pressure 0 -10 8 cm W [cm] M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  8. n=1n=2 Probing the operational boundary using Control • At high pressure, islands develop. These deteriorate the confinement. • Power ramp-up to drive onset of 2/1 pressure limit • Island onset  power (and hence pressure) ramp down • Complicated mode dynamics: Locking and un-locking of modes • Marginal pressure for onset of m/n=2/1 mode determined Ip = 2.0MA Bt = 2.7T q95 = 4.4 Ha Pmarginal locked mode M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  9. Marginal pressure determined M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  10. Not control in the strict sense • After detection of mode pre-programmed ramp down of the power was initiated • This allowed for • high quality outcome of the experiment • At high reproducibility M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  11. In TEXTOR islands are induced with the Dynamic Ergodic Divertor • 3/1 6/2 or 12/4 mode • DC, AC to 10 kHz Our experiments: • 3/1 mode • Large 2/1 side band • 1 kHz AC M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  12. penetration stabilisation ECE sxr resolution ~2cm Island suppression with localised electron heating ECRH: Electron cyclotron resonant heating BT = 2.25 T; Ip = 300 kA ne = 2.0 1019 m-3 ECRH on “q=2” • 140 GHz, 770 kW M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  13. Not control in the strict sense Real control requires • Model of the non-linear behaviour of the island • Model Electro-mechanical properties of ECHR Launcher • RT-interpretation of island location • Egbert Westerhof and Sante Cirant (tomorrow) M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  14. ‘Advanced modes:’ no sawteeth Sawteeth: Repetitive modification of core profiles ITER workhorse: H-mode High confinement mode Dynamic heat fluxes ITER reference plasma scenario Control of Confinement Mode Local turbulence suppression Instabilities: Driven unstable by free energy Profiles of ne, Ti,e, j, p, nEp M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  15. Turbulent vortices are ‘broken’ and transport reduced Monotonic q profile (~inverse of current profile) Off-axis current drive Reversed q profile Controling Turbulent transport H-Mode Advanced Mode X.Garbet,CEA M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  16. Example advanced scenario Shot 53521 (3.4T/2MA) 90% Non Inductive Current: Bootstrap current ~ 50% Neutral Beam Current Drive ~ 15% LH Current Drive ~ 25% (code CRONOS) M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  17. Reduced turbulence: Steep p gradient Reversed shear by off-axis Current Drive (LHCD) Off-axis current : q-profilemodified Steep p gradient Off-axis (bootstrap) current Non-linear coupling between Current and Pressure Profiles in Advanced Modes Current Diffusion relaxesq(r) to monotonic profile Control of j(r) and p(r) required for advance modes M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  18. a-particles introduce new control issues • Balance ta vs tHe • Control of He recycling? • Sawtooth control for ta • Compatible with non-linear island formation? • How to control ta in discharges without sawteeth? • Collective effect: Energetic particles drive instabilities M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  19. Not control in the strict sense • High degree of self organisation of the plasma and interaction between the profiles • One-way only: Once the current density shaping is lost, almost impossible to re-achieve the target. • Control can be used to coax the plasma in the desired self organised state M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  20. M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  21. Observations • For the burning plasma core control in the strict sense is required • Need to be able to “move the working point around” • Many interacting processes. Can we control a self organizing multi process system with a limited number actuators? • This motivates setting-up an integrated model of the plasma core • Are the models that physicist are working on suited for this task? M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  22. Conclusions • Tokamak Plasma is a complex medium • Instability drive from gradients • P, j, na, Ti, … • Wide variety of control issues: Turbulence, Transport, MHD, dynamic edge fluxes • The control requirements are often conflicting. Limited number of actuators. Limited number of diagnostics • Present experiments start to rely on RTC, but control if often used in a non-strict sense • True Burn control will require control in the strict sense M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

  23. Bf coils For toroidal field Primary P1 For inductive current P2UL and P3UL For plasma shaping P4UL For radial and vertical field Divertor coils D1-4 Exhaust of heat and particles Tokamak Functionality M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08

More Related