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    Triggered Enhancement Confinement and Pedestal
   Expansion in NSTX: The Enhanced Pedestal H-mode
College W&M
Colorado Sch Mines
Columbia U                                              Culham Sci Ctr
Comp-X               R. Maingi, J.M. Canik               U St. Andrews
General Atomics                                                   York U
INL
Johns Hopkins U
                     S. Gerhardt, S. Kaye,
                                       Columbia U.
                                                               Chubu U
                                                                Fukui U
                                                           Hiroshima U
LANL
LLNL                  and the NSTX team                        Hyogo U
Lodestar                                                        Kyoto U
MIT                                                           Kyushu U
Nova Photonics         MIT PSFC Seminar                 Kyushu Tokai U
                                                                    NIFS
New York U
Old Dominion U
                          Boston, MA                           Niigata U
ORNL                      2 Aug 2010                            U Tokyo
                                                                   JAEA
PPPL
PSI                                                           Hebrew U
Princeton U                                                    Ioffe Inst
Purdue U                                             RRC Kurchatov Inst
SNL                                                              TRINITI
Think Tank, Inc.                                                    KBSI
UC Davis                                                          KAIST
UC Irvine                                                    POSTECH
UCLA                                                              ASIPP
UCSD                                                    ENEA, Frascati
U Colorado                                             CEA, Cadarache
U Maryland                                                   IPP, Jülich
U Rochester                                               IPP, Garching
U Washington                                          ASCR, Czech Rep
U Wisconsin                                                   U Quebec
The Enhanced Pedestal H-mode (EPH) has favorable
 characteristics and improved long pulse prospects
•  Energy confinement in NSTX H-modes is generally 0.8-1.2*
  ITER98y2 scaling

   –  Note that τE increases stronger with Bt and weaker with Ip than 98y2

   –  Several next step ST designs based on ~ 50% higher τE 

•  A transition to a (transiently) improved confinement with
  enhanced H-mode pedestal Te, Ti observed a few years ago

•  Characteristics of EP H-mode

   –  Highest normalized energy confinement of any regime in NSTX, with
     H89P < 3.5 and H98y2 < 1.8

•  Prospects for increasing pulse length

   –  Can be triggered by large ELM or RMP-triggered ELM(!), with pulse
     length < 3 τE (up to 300 msec) observed in 2009

                                  EPH Mode: Maingi                  2 Aug 2010   2
   Transition to an Enhanced Pedestal H-mode
   enables lower pedestal νe,ped * ~ 0.1 in NSTX

                                                                                         6
                                                                                                                                        #117820
                                                                                                                                       LRDFIT06
                                                                                         5




                                                                       ne [101 9m - 3]
                                                                                         4

                                                                                         3

                                                                                         2
                                   PNBI/10 [MW]
                                         1
                                                                                                  t=0.248 sec
                                                                                                  t=0.165 sec
                                                                                   0
                                   EPH-mode
                                       -0.25         -0.2   -0.15     -0.1     -0.05       0      0.05
                         H-mode
                                                 1.2                              R-Rs e p

                                                                                         1

                                                                                 0.8




                                                                       Te [keV]
                                                                                 0.6

                                                           #117820
              0.4
                                                                                                                                        #117820
                                                                                                  t=0.248 sec                          LRDFIT06
                                                                                 0.2              t=0.165 sec
                                                                                    0
                                                                                    -0.25        -0.2   -0.15     -0.1      -0.05      0     0.05
                                                                                  1.4                           R-Rs e p [m]
                                                                                  1.2                                          t=0.245 sec
                                                                                                                               t=0.165 sec
                                                                                         1




                                                                      Ti [keV]
                                                                                  0.8
                                                                                  0.6
•  Note: Pedestal νe* ~ 0.5-1 in H-mode
                                          0.4
                                                                                                                                       #117820
                                                                                  0.2                                                  LRDFIT06

                                                                                         0
                                                                                         -0.25   -0.2   -0.15      -0.1    -0.05       0     0.05
          Maingi, JNM 390-391 (2009) 440
                                                                       R-Rs e p [m]

                                            EPH Mode: Maingi                                                              2 Aug 2010        Page 3
 EPH-mode phases up to several hundred msec
 observed recently (more common with lithium?)
                                                           •  Ip = 0.9 MA,
                                                             PNBI = 3.8 MW

                               PNBI/10 [MW]

                                                           •  WMHD < 350 kJ


                                                           • βN > 6.5


                                                           • τE > 80 msec for
                                                             225 msec

                                                           • H97L < 3 


                                                           • Natural ELM
                                       EPH
                  trigger for EPH

                                                           •  Not sure of termination
Maingi, PRL (2010) at press
                                  event

                                        EPH Mode: Maingi                   2 Aug 2010   4
 Common Enhanced Pedestal H-mode Characteristics


•  A second transition to enhanced confinement and high
   pedestal Te, Ti < 700 eV

   -  Second transition after large ELM, either natural or triggered by 3D
      fields

   -  WMHD ramps ~ linearly in time for ~ 0.1 s, typically dW/dt ~ 0.4*PNBI

   -  HH97L > 2.5, and as high as 3.5 transiently

   -  EP H-mode phase observed during Ip ramp or flat-top


•  Common feature: edge vφ develops large gradient, with a
   large drag, often near the q=3 surface

•  Low loop voltage, high βN (due partly to low pressure
   peaking factor)

     high performance, long pulse candidate

                                EPH Mode: Maingi                  2 Aug 2010   Page 5
Comparison of Standard and EP H-mode evolution


                (a)                 L-H

                                                           • Same Ip, PNBI



                (b)                                        • Higher WMHD
                                                             during EPH


                                                           • Higher H97L
                (c)                                          during EPH


                (d)
                                                    EPH
   • ELM trigger
                                                             for EPH 



  Maingi, JNM 390-391 (2009) 440

                                     EPH Mode: Maingi             2 Aug 2010   Page 6
Comparison of Standard and EP H-mode profiles





                   EPH Mode: Maingi        2 Aug 2010   Page 7
EP H-mode profiles evolved continuously during Ip ramp





                       EPH Mode: Maingi         2 Aug 2010   Page 8
     Enhanced Pedestal H-mode barrier width size
            comparable to gyro-diameter

•  Edge scale lengths for both Ti and nC
   approach the gyro-diameter during EPH-
   mode 


•  Ion gyroradius ρi ~ 0.7 cm relative to |B|,
   owing to combination of local Ti ~ 350 eV
   and and |B| ~ 0.35 T at outer midplane

     Approaching or at the fundamental limit on
      the gradient scale length? 



•  Minimum vφ seems to be in center of
   highest ∇Ti region 


                                                   R. Bell

                              EPH Mode: Maingi               2 Aug 2010   Page 9
                  Changes in vφ accompany high Te,iped in Enhanced
                                  Pedestal H-mode

•  First order radial force balance:                                               20
   Er+vθΒφ=vφΒθ+∇Pc/6eNc
                                                                    (a)                              Er + v θ Bφ
                                                                                   15                                         dP/dr
                                                                                                                              V φ Bθ
•  EPH mode has vφ ~ 0 near                                                        10
   separatrix, probably due to drag




                                                                          [kV/m]
                                                                                    5
   from an island, such that ∇P term                                                0
   dominates vφ over large region
                                                  -5
                                                                                             EPH-mode

•  Large ∇vφ indicative of large Erʼ
                                              -10
                                                                                             #117820@0.225sec
•  vθ negligible (recent measurement)
                                             -15
                                                                                         0         0.2      0.4        0.6       0.8         1
            250                                                                    20
                                                            0.245                            (b)                       Er + v θ Bφ
                                                                                   15
            200                      EPH-mode
              0.225                                                      dP/dr
                                                                                                                       Vφ Bθ
                                                            0.205                  10
 V tor [km/sec]




                                                                          [kV/m]
                                                            0.185
            150                                                                     5

            100                                                                     0

                                                                                    -5
                  50                                                                         Standard H-mode

                                                                                   -10
                           #117820                                                           #117821@0.225sec
                  0                                                                -15
                       0   0.2       0.4    0.6   0.8   1           1.2                  0         0.2      0.4        0.6       0.8         1
                                           ψN                                                                     ψN

                                                            EPH Mode: Maingi                                                   2 Aug 2010   Page 10
Spontaneous EPH-mode also observed during Ip flat-top


        L-H
                              • Same Ip, PNBI



                                          • Lower PNBI


                                          • Higher WMHD
                                            during EPH

                                          • Higher H97L
                                            during EPH

                    EPH


                                          • ELM trigger
                                            for EPH



                       EPH Mode: Maingi          2 Aug 2010   Page 11
3D fields used for ELM pace making may trigger EPH
     during periods when 3D fields switched off




                     EPH





                      EPH Mode: Maingi    2 Aug 2010   12
EPH may occur naturally in recovery period
     following ELM/braking triggers




      EPH





                  EPH Mode: Maingi     2 Aug 2010   13
EPH-mode phase observed for several τE , up to ~
                300 msec
                                              EP H-mode

         PNBI/10 [MW]
                        H-mode 

                                                  separatrix





                   EPH


              t1    t2 

                           EPH Mode: Maingi                     2 Aug 2010   14
Thermal and angular momentum transport reduced
            over outer half of plasma
                         EP H-mode

                         H-mode 





                    EPH Mode: Maingi    2 Aug 2010   15
Spatial extent of significant Er shear region doubled
             in size during EP H-mode

                                  • Ti pedestal height correlates
                                    with edge toroidal rotation
                                    shear 

               H-mode 





             EP H-mode


       EP H-mode

       H-mode 


                                             dvφ/dr[106 sec-1]



                          EPH Mode: Maingi                       2 Aug 2010   16
High βN phase maintained for 2 τE

                                    •  Ip = 0.9 MA,
        PNBI/10 [MW]
                 PNBI = 3.8 MW

                                    •  WMHD ~ 325 kJ


                                    • βN ~ 6.5


                                    • τE > 80 msec for
                                      225 msec

                                    • H97L > 2.5 


                                    • EPH phase is
                                      ELM-free


                 EPH Mode: Maingi                 2 Aug 2010   17
High βpol results in high bootstrap and non-inductive
           fraction (fNI ~ 0.65 from TRANSP)
                                               •  Ip = 0.9 MA,
                                                 PNBI = 3.8 MW

                 PNBI/10 [MW]


                                               • βp ~ 1.5, very high
                                                 for 0.9 MA


                                               • Loop voltage low
                                                 during EPH, due to
                                                 high bootstrap



                                 EPH
          • Very little or no flux
                                                 consumption



                            EPH Mode: Maingi                2 Aug 2010   18
High bootstrap and non-inductive fractions, high
         thermal τE during EPH phase

                                        • fbs between
                                          0.5-0.6, and fNI
                                          between 0.6-0.7





                                        • H98y2 between
                                          1.6 and 1.8, with
                                          τEth between
                                          90-100 msec



                                          S. Gerhardt, S. Kaye

                     EPH Mode: Maingi                       2 Aug 2010   19
Long pulse EPH – density still evolving slowly, Zeff
        rising, but Prad seems reasonable


                      PNBI/10 [MW]





                       EPH Mode: Maingi      2 Aug 2010   20
  EPH-mode would make a decent ASC TSG high
        performance, long pulse target
•  Initiating EPH-mode:

   -  Lithium conditioning for ELM-free conditions

   -  Either fast RMP trigger of a large ELM(5 Hz?), or longer
      RMP pulse with several ELMs: both seem to work

   -  Since density profile control may be important, supersonic
      gas injection (SGI) may provide easier access (longest
      pulse EPH had SGI)

•  Sustaining EPH-mode:

   -  Use β feedback + n=1 feedback to avoid β limit

   -  Pre-program NBI reduction, if needed

   -  Raise Bt or drop Ip or more shaping to delay q0=1
      crossing
                            EPH Mode: Maingi              2 Aug 2010   21
  The Enhanced Pedestal H-mode has favorable
characteristics and improved long pulse prospects
•  EP H-modes occur naturally following large ELMs, or can be
  triggered with 3D fields


•  Recently, EPH phases were obtained during Ip flat-top for
  several τE


•  With the advent of β feedback on NBI and good n=1
  feedback, extending the pulse length and using EPH as a
  high-performance target will be attempted in FY10 in NSTX


  Experiments will be lead by Canik and Gerhardt




                             EPH Mode: Maingi          2 Aug 2010   22
Backup




EPH Mode: Maingi   2 Aug 2010   23
EP H-mode profiles evolve continuously, although
     recovery from trigger takes a little time





                                       • Discharge
                                         had Li
                                         evaporation
                                         to improve
                                         performance
                                         in regular H-
                                         mode 





                    EPH Mode: Maingi         2 Aug 2010   Page 24
EPH-mode can have transient H89P up to 4


            PNBI/10 [MW]
                                               separatrix





                                               134987: t1=0.75

                                               134991: t2=1.0 (EPH) 





                                EPH



                      t1                t2 

                     EPH Mode: Maingi                             2 Aug 2010    25

				
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