View from the US and the DIII-D programme

10_ADASWS_tee-1/25

View from the US and the DIII-D programme

T. E. Evans*General Atomics,San Diego, CA

15th ADAS Workshop3-6 October 2010Armagh, Northern Ireland*In collaboration with:N. H. Brooks, N. Eidietis, D. Humphreys, A. Hyatt,P. Parks, E. Strait, J. Wesley (GA)O. Schmitz (FZ-Jülich)J. Canik, N. Commaux, J. Harris, D, Hillis,T. Jernigan, R. Maingi, M. W. Shafer, E. A. Unterberg (ORNL)D. J. Battaglia (ORNL-ORISE)E. Hollmann, A. James, J. Yu (UCSD)S. Ohdachi (NIFS)A. Wingen (Dusseldorf)

10_ADASWS_tee-2/25

The DIII-D program is strongly focused on addressing ITER urgent issues • Global performance and stability

– Scenario II H-mode startup, core stability and energetic particle physics

– Core fueling, heating and current drive

– Neoclassical tearing mode, sawtooth and resistive wall mode control

– Development of advance inductive operating scenarios (high-N, high-gain)

• Pedestal, scrape-off layer and divertor– L-H power threshold, energy, particle and momentum transport

– ELM stability, suppression and mitigation• Resonant magnetic perturbation (suppression and pacing)

• Pellet pacing

• Off-normal events– Vertical stabilization

– Disruption mitigation• Thermal quench

• Non-axisymmetic currents and vessel forces (i.e., halo currents)

– Runaway electron generation, control and suppression

10_ADASWS_tee-3/25








• Pellet pacing





10_ADASWS_tee-4/25

Two sets of non-axisymmetric coils produce a variety of RMPs in DIII-D

• The 4-turn C-coil and single-turn upper/lower I-coil can be configured for n=3 RMP experiments or n=1 field-error correction

10_ADASWS_tee-5/25

3D magnetic perturbations split the separatrix into a homoclinic (self-intersecting) tangle

2 unstable branches

exit the X-point

as

2 stable branches

enter the X-point

as

• 3D perturbations cause the separatrix to bifurcate into stable and unstable invariant manifolds

Axisymmetric(no 3D perturbations)

Non-axisymmetric(with 3D perturbations)

Homoclinic tangle produced by DIII-D I-coil RMP fields

T. E. Evans, et al., J. Physics: Conf. Ser., 7 (2005) 174

10_ADASWS_tee-6/25

Stochastic field lines formed by n=3 RMPs intersect divertor targets through homoclinic tangle lobes

• I-coil perturbations create stable and unstable invariant manifolds

– Field lines escape though lobes formed by the manifolds

M. W. Shafer (ORNL)

+ BT- BT

132731:2750

1.0 1.5 2.0 2.5 R(m)

1.0 1.5 2.0 2.5 R(m)

-300 -200 -100 0 (deg)

0 100 200 300 (deg)

1.0

0.5

0.0

-0.5

-1.0

1.0

0.5

0.0

-0.5

-1.0

I-Coil current = 4.1 kA (n=3)

Z (m)

1.38

1.36

1.34

1.08

1.06

1.04

1.02

R (m)

10_ADASWS_tee-7/25

Peak divertor heat flux bifurcates due RMP fields during ELM suppression

• Split heat flux peaks are consistent with vacuum field line calculations of magnetic footprint patterns on the divertor target plates

10_ADASWS_tee-8/25

ELM suppression correlated with a reduction in peak p

Expectation based on quasilinear transport theory:

stochastic layer reduces peak p and shifts it inward

• Experimental data has outward shifted p peak rather than inward

• High-resolution ne and Te pedestal profiles diagnostics are being developed

Theory Experiment

10_ADASWS_tee-9/25

• He-I line ratio technique: basic approach

• Application to H-mode plasmas

• Assessment of feasibility for DIII-D using existing hardware:He-I intensity examples post-boronization residual helium

He-I intensity examples from post-helium glow residual helium neutrals

He-I intensity examples from low order He gas puffing into far SOL

• Proposed He-I line ratio setup for DIII-DUpgraded filterscope system for ne(r,t), Te(r,t) and simultaneous nn(r,t) measurement

Proposed set of helium gas capillaries for SOL characterization

Modeling effort for adaptation of collisional radiative model for H-mode application

He-I line ratio electron density and temperature diagnostic for DIII-D

10_ADASWS_tee-10/25

Based on ne and Te dependence of the atomic level population densities in both spin systems

• Suitable transitions:

31D 21P @ 1=667.8 nm

31S 21P @ 2=728.1 nm

33S 23P @ 3=706.5 nm

ne(r,t)

Te(r,t)

Maximum of normalized population density at

lower Te for triplet system

Comparison yields Te sensitivity

Electron temperature Te sensitivity

Employ ratio of levels predominantly depopulated by (a) collisions and (b) spontaneous radiation

Electron density ne sensitivity

(Result of different rate coefficients for spin forbidden transitions)

Comparison yields ne sensitivity

Hintz E and Schweer B 1995 Plasma Phys. Control. Fusion 37 A87

10_ADASWS_tee-11/25

Proposed DIII-D system based on TEXTOR He beam implemnetation

667.8 nm

728.1 nm

706.5 nm

ne(r,t)

Te(r,t)

670.8 nm ne(r,t)

Range of wavelengths

Accessible quantities

Standard system characteristics:• time resolution: > 100Hz• digital resolution: 12 bit or higher• spatial resolution: 15 cm coverage (0.7 < < 1.1) with r=1.2mm • He gas puff capability (rate needed < 8 x 1018 s-1)• Lithium oven for beam attenuation on Lithium as ne reference

O. Schmitz et al. PPCF 50 (2008) 115004

10_ADASWS_tee-12/25

Atomic data and Collisional Radiative Model (CRM) need to be optimized for H-mode conditions

Need to determine if He line intensities provide sufficient signals-to-noise levels in H-mode SOL plasmas

Analysis needs to be pushed

beyond actual boundaries for

good H-m

ode measurem

ents

We are aiming at ne and Te measurements in the SOL radial up to the separatrix under H-mode conditions at different poloidal

positionsUse line ratio technique for 2D imaging and as divertor diagnostic

• Te lower than reference measurements with increasing heating

• at low ne<1.0 1018 m-3, relaxation issues

Improve atomic data

Include high energy states by cascading and bundled solutions

Develop fast algorithm for automated non-stationary solution

Develop fast algorithm for automated non-stationary solution

Include beam geometry and change in velocity distribution into CRM

10_ADASWS_tee-13/25

Proof-of-concept testing done with existing hardware

Midplane filter scope system

• One channel equipped with He-I filters and PMT

Divertor video cameras

• He-I filters on cameras•tanTV captured two lines simultaneously

MDS spectrometer

• Check carbon background for He-I lines used

tanTV view

DiMES TV views

10_ADASWS_tee-14/25

Residual helium after boronization gives sufficient signal for ~15 discharges

706.5nm728.1nm

667.8nm

Signal from residual helium after boronization only, no puffing!

Discharge #15 after boronization recoveryDecays slowly but not sufficient for quantitative evaluation by CRM

How much gas injection do we need for a robust signal?

10_ADASWS_tee-15/25

Helium images of the divertor provide high-resolution profiles of magnetic footprints

15

Strong density and temperature dependence of level populations makes He attractive for imaging purposes

Camera views can be used as two dimensional ne and Te monitors in the divertor if calibrated

667.8nm2

1Strike line striation due to n=1 LM during TBM application observed in high contrast

10_ADASWS_tee-16/25

Mid-plane filterscope system has sufficient signal when a low-flow He puff is introduced in the SOL

Signal from residual helium glow discharge

Signal from 0.2 torr-L-s-

1 helium gas puff into far SOL

Signals from chord 6 at separatrix

Midplane filterscope system

Residual helium gas from glow discharge is marginal but a small He puff sufficient for ne and Te measurement

16

10_ADASWS_tee-17/25

An H-mode relevant collisional radiative model is being developed for the proposed He beam system

Population density ni is established by:

• radiative transitions to and from other levels with Einstein coefficient Aij

• electron impact excitation and de-excitation with rate coefficient qej->i=<e

j->i v> and qei->j=<e

j->j v>• ion impact excitation and de-excitation with rate coefficient qi

j->i=<ij->i v> and qi

i->j=<ii->j v>

• electron and ion impact ionization with rate coefficients Sei and Si

i

Same processes included but improvement towards H-mode challenges:

• Including pseudo states to calculate rate coefficients for high n levels

• Atomic data manufactured in particular for He problem with comparison to experiment

• Introduced linearization method for time dependent CRM solution to overcome relaxation issues

• Include line of sight effects of diagnostic setup for net line emission correction due to ionization

Further improvement ongoing but readily available for basic studies

J. M. Munoz Burgos, O. Schmitz, S. D. Loch and C. P. Balance, paper in process

10_ADASWS_tee-18/25

The proposed DIII-D He beam system will use proven nozzle technology

Design is based on a local gas puff with direct tangential/perpendicular views

Strong active and therefore localized signalWell defined beam geometry and velocity distributionPulsed system possible for optimized background subtraction

Standard TEXTOR nozzle

• 340 micro tubes• 210 µm diameter each

• beam with +/- 10 degree divergence

• 30 mm in length

• thermal velocity (1.4-1.6 km s-1)• puff rate 0.3-4.0 1018 He atoms s-1

• local beam density 0.2-2.0 1017 at. m-3

• effect on local plasma parameters negligible (<5%)

DiMES

10_ADASWS_tee-19/25

Additional poloidal locations are being evaluated as an upgrade option

System I: HFS and LFS profile diagnostic

System II: UD and LD ne and Te diagnostic

System III: DiMES capillary

DiMES

• 1 filter scope system, 12 radial chords, Dr=3 mm with 2 mm spot size• automated view adjustment to one of six puff locations• tangential view with radial fine adjustment

• 2 filter scope systems – one in each divertor

• automated view adjustment to one of six puff locations

• 12 radial chords, Dr=3 mm with 2 mm spot size

• tangential view with radial fine adjustment

• 1 filter scope system

• 1 additional channel observation of DiMES sample (PPI)

• 2-3 channel observation from UD on capillary

10_ADASWS_tee-20/25

A soft X-ray imaging system is being designed to study magnetic islands in DIII-D L- and H-modes

• Ohmic & L-Mode magnetic islands images agree with vacuum field modeling

– Better validity for vacuum field modeling– Are islands screened in diverted H-mode plasmas?

• Visible diagnostics restricted to LCFS-PSI region

CIII ImageInner Wall

Poincaré Plot TEXTOR

Tore Supra

Visible light

TRIPND

Schmitz et al. RMP Workshop (2008)Schmitz et al. RMP Workshop (2008)

Evans et al. PoP (2002)Evans et al. PoP (2002)

10_ADASWS_tee-21/25

The proposed DIII-D system is largely based on the LHD SXR imaging system design

• Pinhole/Foil with Fiber image guide to fast camera

– Tangential View

• Analysis uses tomographic inversion with regularization techniques

– SVD used to isolate core modes

Ohdachi, et al, Plasma Science Tech. (2006).Ohdachi, et al, Plasma Science Tech. (2006).

10_ADASWS_tee-22/25

O. Schmitz et al. PPCF 50 (2008) 115004

The design and installation of DIII-D SXR imaging system is constrained by port structures & TF coil locations

• Relies on efficient scintillator with high resolution: CsI:Tl

• Sensitivity: ~ 0.11 e-/ 1 kev X-ray– Scintillator Efficiency, Light

Coupling Losses, Detector Efficiency

Tangency Plane

Pinhole

CsI:Tl Scintillator

10_ADASWS_tee-23/25








• Pellet pacing





10_ADASWS_tee-24/25

Runaway Electron (RE) current decay may be related to multi-step ionization energy loss • RE beam position controlled

to avoid wall contact

• Understanding the physics of the natural decay phase may be important for mitigating RE beams in ITER

• avalanche process inhibited due to E < Ec?

• RE beam instabilities?

• RE energy loss due to background impurity ionization processes?

• Cross sections needed for mono-energetic MeV electron inner shell ionization and radiation processes

10_ADASWS_tee-25/25

Summary and conclusions

• DIII-D program focused on ITER urgent issues– Advanced diagnostic development for boundary control with

3D magnetic perturbation fields• High-resolution He-I beam system for edge profile analysis

• Soft x-ray imaging system for studying 3D lobe structures and magnetic islands in L- and H-mode

– Develop ELM suppression approachs for ITER

– Runaway electron beam physics• Develop an understanding of RE beam generation and decay

processes

• Develop RE beam control and mitigation approach

• Progress is being made on developing CRM analysis tools and specifying atomic data needs

10_ADASWS_tee-26/25

DIII-D

Documents

View from the US and the DIII-D programme