Implications of TFTR D-T Experiments for Burning Plasma Program

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					Implications of TFTR D-T Experiments
     for Burning Plasma Program

                 R. J. Hawryluk

       IEA Large Tokamak Workshop (W60)
      Burning Plasma Physics and Simulation

                  Tarragona, Spain

                   July 4-5, 2005
     Thanks for Useful Discussions

M. Bell, R. Budny, R. Goldston, N. Fisch,       N.
Gorelenkov., J. Hosea, C. Kessel, D. Meade, S.
Medley, C. K. Phillips, R. Nazikian,         N.
Sauthoff, S. Scott, C. Skinner, J. Strachan,
E. Synakowski, J. R. Wilson, K. L. Wong,
M. Zarnstorff, and S. Zweben
Presentation reflects my personal
ITER Must Demonstrate Fusion Power Production
    and Make Critical Scientific Contributions

    Today: ~10 MW for ~1 second, gain of < 1
    ITER: 500 MW for 400 seconds, gain > 10
    Power Plant: 2500 MW, continuous, gain > 25
•   Transport and Turbulence: Extend the study
    of turbulent plasma transport to much larger

•   Stability: Extend the understanding of
    pressure limits to much larger plasmas.
•   Energetic particles: Study strong heating by
    fusion products, in new regimes where
    multiple instabilities can overlap.

•   Plasma-boundary interface: Extend the study
    of plasma-materials interactions to much
    greater power and pulse length.
        What Should be the Goals for
          Research Prior to ITER?

 Enable ITER to demonstrate fusion power
 Enable ITER to make the scientific contributions
  needed for Demo.
• Continue to develop the scientific basis for an
  attractive power plant

 Together with the ITER results, this will enable us
  to move forward with Demo
   What are the Implications of the TFTR D-T
Experiments for ITER and Research Prior to ITER?

  • Transport and Turbulence
     – Isotope Effects

  • Stability

  • ICRF Heating

  • Alpha-particle Physics

  • Plasma-boundary Interface
    Global Ethermal Increased, I Decreased
    in Core of DT Supershots Compared to D

                                     2 / s)
                                      (including convection) (m
                                                                                   D                D-T

                                                                                          factor of 2

                                                                                                          P NBI = 18MW
                                                                                                             I p= 1.6MA

                                  tot

                                                                    0.0                       0.5
                                                                                       Minor Radius / a

                                                                              Ethermal <A>0.89±0.1
                                                                              itot  <A>-1.8 ±0.2
•  ni(0)ET i(0) increased by ~55%
  from D to DT
    – Some cases up to 80%
• Enhanced confinement critical
  for fusion power production.                                            S. Scott, M. Zarnstorff
ITG Model with Radial Electric Field
 Reproduced the Ion Temperature

                    •   Maximum linear growth rate
                        decreases with ion mass.

                    •   Er shearing rate increases with T i.

                    •   Radial electric field shear
                        reproduces strong isotope effect in

D. Ernst
             Isotope Effect on Confinement Varied
            Widely Depending on Operating Regime
                         JET H-Mode                                      TFTR

                                                                           <A> 0.85
EDT   -   EDD
   EDD                                            <A>0.3-0.5
   (% )           10        <A>0.16±.06

                                 Elmy        OH      ICRF         NBI      Supershot/
                                                    L-mode      L-mode     High l i     Reverse
                  -10                                                                    Shear

• Challenge to theory and to gyro-Bohm scaling: <A>-0.2
• Recent ITER scaling for ELMy H-mode: Ethermal  <A>+0.19

 S. Scott, S. Sabbagh, C. K. Phillips
     Understanding of Isotope Scaling
          Remains Incomplete
• Depends on operating regime
   – Not consistent with naive turbulence theory scaling
   – What is the role of radial electric field shear in the different regimes?
   – What are the implications for advanced operating modes?
• Power threshold for internal barrier formation increased with
   – Was this a transport effect or a consequence of the beam deposition
     profile being different?
Operational Implications:
• Though TRANSP was used extensively for experimental
   – Existing transport models were inadequate to predict both the
     isotope effect as well as variations in confinement.
• Occurrence of internal transport barriers or unforeseen
  improvements in core confinement occasionally resulted in
    Implications of Transport Studies

• Implications for ITER:
   – Burn control will require controlling the pressure and
     current profile in the presence of dominant alpha heating.
      • Are the required profiles consistent with the underlying
        transport rates?
      • Enhanced confinement at high density is key to optimizing
   – Measure turbulence in ITER low r* regime and
     comprehensive profile and edge diagnostics.
      • Needed to apply the results to different configurations.
• Implications for research prior to ITER:
   – Develop predictive capability beyond empirical scaling
     that has been experimentally established.
   – Develop fluctuation diagnostics for ITER.
   – Develop a deeper understanding of the relationship of
     “wall conditioning” and “plasma performance.”
   – Aggressive goal: control the transport locally????
                   TFTR Stability was Limited by Kink-Ballooning Mode and
                                 Neoclassical Tearing Modes
                                 Experimental Data          MH3D code simulation
                   3.4                                                                      5
                   3.2           ballooning                                                 4


                                                                                   W (cm)
                         5 keV                                                              3

                                                                                            2                      ECE
                   2.8 10 keV
                            Magnetic Axis
                                                                                                        24MW NBI
                   2.4                                                                       3.0            3.5              4.0
                                     180 sec        W. Park, PRL 75 1763 (1995)
                                                                                                                  Time (s)

                     Nonlinear numerical simulations found                                  Theory predicted observed
                     n=1 kink excited local ballooning modes                                amplitudes and growth
                                                                                            rates for neoclassical
                     Kink-ballooning mode limited fusion                                    tearing modes (NTM).
                     power performance.                                                     - NTM were observed to
                                                                                               occur without a seed.
                     E. Fredrickson, Y. Nagayama, W. Park                                       Z. Why? E. Fredricskon
           Implications of Stability Studies
• Implications for ITER:
   – Control tools will be used to both establish and control a burning
      • Are they sufficient?
   – Performance optimization entails increased likelihood of disruption.
   – Disruption mitigation and avoidance is very important.
   – Study of extended MHD effects at low r* will be a major scientific
      • For example NTM, RWM and sawteeth
• Implications for research prior to ITER:
   – Perform assessment of heating and current drive options to optimize
     research and performance capabilities.
   – Develop techniques to modify the pressure and current profile.
   – Develop and test three dimensional nonlinear MHD codes with extended
   – Develop techniques to stabilize sawteeth, NTM and RWM that can be
     applied to ITER.
   – Establish reliable disruption mitigation and avoidance techniques.
       ICRF Successfully Heated D-T Supershot
                 Plasmas in TFTR

        D Ti due to 2nd harmonic                   D Te due to direct electron
        tritium heating                            and 3He minority ion heating

            • Power deposition calculations in good
              agreement with experiment.
G. Taylor, J. R. Wilson, J. Hosea, R. Majeski, C. K. Phillips
    Implications of ICRF Heating and
          Current Drive Studies
• ITER Implications:
   – Fundamental heating and current drive physics for ICRF
     has largely been established for D-He3 minority and
     second harmonic tritium heating experiments.
   – Outstanding technology and coupling issues remain.
• Implications for research prior to ITER:
   – Need to develop predictive tools to design antennae and
     obtain good power coupling.
   – Need to improve performance of couplers and matching
   – Application of mode conversion or IBW to drive currents,
     induce flows or alpha channeling requires further
   Confined Alpha-particle Studies on TFTR were
Confirmatory in Normal Shear (Supershot) Discharges
     Chordal DT neutron emission

                                                                              Measured                                          30                                      90° detector

                                                                                            Alpha collection fraction (x10-9)
                                                                               (neutron                                                                                                         Escaping Alpha
                                                                              collimator)                                                                                                       Detectors
                                                   2.0   beam-beam

                                                                                                                                         Normalized                                                   B
                                                         beam-thermal                                                           10
                                                   1.0    Thermal                                                                6                                                         CL         90   60°

                                                                                                                                 4        First-orbit
                                                                                                                                          loss model
                                                           2.0          2.5     3.0                                              2
                                                                     Radius (m)                                                      0        0.5        1     1.5        2     2.5    3
                                                                                                                                                      Plasma current (MA)

• Alpha birth rate and profile   • Escaping alpha flux at 90o
  were adequately modeled.         detector was consistent with
   - Neutron flux in good          classical first orbit losses
     agreement with calculations
     based on plasma profile in
     normal shear discharges.

R. Budny, L. Johnson                                                                                                                     S. Zweben, D. Darrow
                     Confined Alpha-particle Studies Relied on New
                      Diagnostics Developed for D-T Experiments
                                                                                        Double Charge Exchange
                     106              n                                                 Technique
                                          n                                   r-0
      dn/dE (a.u.)

                                              n                                         He ++ + Li+  He 0 + Li3+
                     105       normalization            n
                                                            n                                   Vpellet
                                                                n   n
                     104       TRANSP/FPPT

                                 Double Charge Exchange
                                 Technique                                               He0
     r-0                   0         1      2      3       4                        5            Cloud
                                 He ++ + Li+  He 0 + Li3+
                                   Alpha energy (MeV)                                                             He++
                                                                                                          Alpha Particles

                                                       Li                                                                   Rapid ash transported
                                   He0                                                                                      from the core to the
 4                   5                             Cloud

V)                                                                  He++
                                                                                                                            edge in supershots.
                                                            Alpha Particles
                         Confined alphas in the                                           Alpha particles were                DHe/D ~ 1
                         plasma core showed                                               well confined.
                                                                                                                               E. Synakowski
                         classical slowing down                                            0 D 0.03 m2/s
                         spectrum .

      R. Fisher, S. Medley, M. Petrov                                                   R. Fonck, G. McKee, B. Stratton
                           Initial Evidence of Alpha-particle Heating

                                                   • Alpha heating ~15% of power
                                                     through electron channel
Te(R) (keV)

                                                   • Plasmas matched for dominant
                                                     Te scaling in D only plasmas.

                                                     - Te(0) E0.5
  Te(DT) - Te(D) (keV)

                                                     - account for the isotope
                                                       effect on confinement

                         G. Taylor, J. Strachan
       MHD Activity can Cause Enhanced
         Transport of Alpha Particles

• Strong toroidal anisotropic loss   •    Sawteeth caused a large radial
  apparent as NTM mode was rotating.      redistribution of alpha
• Enhanced loss also observed due
  - disruptions
  - kinetic ballooning modes, sawteeth
   D. Darrow, S. Zweben              S. Medley, M. Petrov, R. Fisher
                          TAEs Driven by Neutral Beam or ICRF
                       Fast Ions Caused Substantial Fast Ion Losses
                    100.0                                    10 -5
                                - NBI driven TAE
                                - ICRF driven TAE

                                                                     Mode Amplitude [B/B0]
                    10.00                                    10 -6
Loss Fraction (%)

                    1.00                                     10 -7
                               D-T experiments

                    0.10                                     10 -8

                    0.01                                     10 -9
                           1                       5   10   20
                                 Input Power (MW)                                             • ICRF induced TAE with
                                                                                                ripple trapping damaged
• In normal shear D-T                                                                           the vessel during D-T
  discharges, TAE was stable.                                                                   operations.

              E. Fredrickson, K. L. Wong, D. Darrow                                             R. White
      Alpha-particle Physics Studies in Reversed
    Shear Discharges Resulted in New Discoveries.

                               • TAEs redistributed deeply       • Stochastic ripple
 • Alpha-driven TAE              trapped alpha-particles           diffusion affected
   (subsequently                  –Further work required           confinement of
   identified as Cascade            to benchmark models.           deeply trapped
   Modes) were observed.                                           particles
    • Neutron emission in D-T enhanced reverse shear discharges
      disagreed with TRANSP analysis in some shots by factors of 2-3
         –Source of discrepancy was not identified.

R. Nazikian, Z. Chang, G. Fu   S. Medley, M. Petrov, R. Fisher, M. Redi
Implications of Alpha-particle Physics
• Implications for ITER:
   – Nonlinear consequences of alpha heating will be studied
     for the first time.
   – Comprehensive measurements of confined and lost alpha
     particles are critical.
   – Scientific research is paced by diagnostic capabilities as
     well as operating regimes.
      • ITER needs to be flexible to adjust to scientific developments.
• Implications for research prior to ITER:
   – Nonlinear consequences of alpha-particle driven modes
     need to be put on a quantitative basis.
   – Interaction of ripple and alpha-particle driven modes
     needs to be addressed.
   – Develop alpha-particle diagnostics for ITER.
   – Can alpha-particle channeling be experimentally
     established? (See N. Fisch at this meeting and        K.
     L. Wong’s DIII-D papers.)
   Experience with Plasma-Boundary
• “Wall conditioning” and wall coatings were critical
  for enhanced performance in TFTR.
   – Li coatings were crucial for supershot performance.
   – Other experiments exhibit strong dependence of
     performance on wall conditions.
• Design of plasma facing components underwent
  several design iterations prior to D-T.
   – Carbon fiber composite tiles were reliable and effective.
• Tritium retention in graphite is a serious concern.
   – TFTR tiles 16% retention
   – JET 12% retention
   – One year after extensive removal efforts

C. Skinner
        Implications of Experience with
          Plasma-Boundary Interface
• Implications for ITER:
   – If a reliable technique is not developed to remove the tritium from the
     graphite tiles and coatings, it will have devastating operational
   – Need to qualify plasma facing components prior to D-D/D-T operation.
        • Will H operation be sufficient? Are we prepared to resolve this in
          D-D? What should the balance be between H and D operation?
   – What can ITER do to establish the basis for Demo with ~5 times the
     heat exhaust?
• Implications for research prior to ITER:
   – Develop technique to remove the tritium from the plasma facing
      • Increase removal rate by four orders of magnitude.
   – Ascertain whether high-Z materials (with and without coatings) can
     survive the high heat fluxes and long pulses in ITER.
   – Are the E projections for ITER affected by the extensive use of wall
     coatings in present experiments?
   – Develop backup strategy
      • Li divertor??? What else??
Developing the Scientific Basis for a Power Plant is
         the Common Focus of both the
      Ongoing Research Program and ITER

• Current research program will enhance the
  prospects for ITER:
   – Achieving a burning plasma and meeting its
     programmatic goals.
   – Developing the science and technology that will also
     impact a power plant.
• ITER’s success will be measured by:
   – Meetings its programmatic goals.
   – Developing the scientific understanding and making the
     discoveries required to make an attractive power plant.

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