nstx-u team ideas for jrt15

NSTX-U Team Ideas For JRT15NSTX-U Team Ideas For JRT15

Stefan (for Mario Podesta)Active Members of MS, ASC, T&T, WEP TSGs

and the NSTX Research Team

HellPPPL

12/10/2013

NSTX-UNSTX-U Supported by

Culham Sci CtrYork U

Chubu UFukui U

Hiroshima UHyogo UKyoto U

Kyushu UKyushu Tokai U

NIFSNiigata UU Tokyo

JAEAInst for Nucl Res, Kiev

Ioffe InstTRINITI

Chonbuk Natl UNFRI

KAISTPOSTECH

Seoul Natl UASIPP

CIEMATFOM Inst DIFFER

ENEA, FrascatiCEA, Cadarache

IPP, JülichIPP, Garching

ASCR, Czech Rep

Coll of Wm & MaryColumbia UCompXGeneral AtomicsFIUINLJohns Hopkins ULANLLLNLLodestarMITLehigh UNova PhotonicsORNLPPPLPrinceton UPurdue USNLThink Tank, Inc.UC DavisUC IrvineUCLAUCSDU ColoradoU IllinoisU MarylandU RochesterU TennesseeU TulsaU WashingtonU WisconsinX Science LLC

NSTX-UNSTX-U DIII-D/NSTX-U Collaboration-Fest– JRT2015 Ideas, Gerhardt (12/10/201#)

“Impact of broadened current and pressure profiles on tokamak plasma confinement and stability”

Conduct experiments and analysis to quantify the impact of broadened current and pressure profiles on tokamak plasma confinement and stability. Broadened pressure profiles generally improve global stability but can also affect transport and confinement, while broadened current profiles can have both beneficial and adverse impacts on confinement and stability.

This research will examine a variety of heating and current drive techniques in order to validate theoretical models of both the actuator performance and the transport and global stability response to varied heating and current drive deposition.


Suggested Interpretation From NSTX-U Discussion

• Do our H&CD (and momentum) actuators operate the way we thing they should?

• Given actuator performance, what is the transport response?

• Given actuator performance and the transport response, how can we use actuators to optimize the global stability?

The questions form a hierarchy, but are independently addressable.


Six NB Sources With a Range of Rtan Allow Flexibility in the Locations of Driven Current and Torque

fGW~1

fGW~0.55

110 cm120 cm 130 cm

50 cm60 cm

70 cm

110 cm

120 cm 130 cm

50 cm60 cm

70 cm

fGW~1

fGW~0.55110 cm

120 cm

130 cm

50 cm60 cm

70 cm

110 cm120 cm

130 cm50 cm60 cm 70 cm

Torque Profiles

NBCD Profiles


Do our H&CD (and momentum) actuators operate the way we think they should?

• In the absence of *AE and EPMs, verify that the beam physics is (neo)classical.– Quantify the dependence of prompt loss on Rtan as expected from NUBEAM

– Validate classical slowing down for the full range of Rtan.

• Assess the range in key parameters (fast, Vfast/VA,…) where the *AE and EPMs can be avoided.

• Improved modeling for HHFW/MHFW coupling– interactions with fast ions– SOL physics

Tests of reduced “kick” model for NUBEAM/TRANSP

shaded: exp’tsymbols: model

NSTX#139048

• Validate reduced models for *AE induced transport.– 1.5-D QL model– “Kick” model being implemented in

NUBEAM


Given actuator performance, what is the transport response?

• Study the dependence of transport on qmin.

– As qmin is increased at fixed q95, will the global confinement degrade?

• Attempt to control the rotation gradient inside the pedestal by varying the NB torque.– Which modes will respond to the changes in the rotation gradient?

• Does the large momentum input generate significantly large polodial variations of the impurities, and can this be modeled?


Given actuator performance and the transport response, how can we use actuators to optimize the global stability?

• Study the ability of the H&CD actuators to reliably maintain li low enough for robust vertical control.

• Core kink/tearing physics:– Study increment of qmin above 1 required to avoid onset of core 1/1

activity in cases with “hybrid-like” current profiles.– Explore ability of momentum actuators to (simultaneously?) modify the

magnetic & rotation shear at the q=2 surface.• Use resistive DCON.

• RWM– Assess role of changes in the mode-particle resonances due to

changes in the pressure profile.– Examine how anisotropies in the fast particle distribution function can

impact RWM kinetic stabilization physics.• Vary the fast ion distribution function with the different sources.


Backup

These were the slides presented by different people at the brainstorming meeting


WEP contributions target characterization of [new] actuators, model validation

9

This research will examine a variety

of heating and current drive

techniques

in order to validate theoretical

models of both the actuator

performance

and the transport and global

stability response to varied heating

and current drive deposition.


NSTX-U can contribute with studies of NBIand NBI+HHFW/MHFW experiments

• Actuators are complementary to NBI+ECH on DIII-D

• Restrict to flat-top phase• Characterization of 2nd NBI line part

of FY15 Research Milestone R15-2– Specific targets for JRT: effects of

NBI parameters on q profile, rotation, *AE stability

• NBI+rf scenario of interest for ITER– Unique (US) capability for NSTX-U– Look at effects on JNI (through

heating -> boostrap)– Will ITER-relevant MHFW conditions

be achievable in FY15?

10



techniques...

New 2nd NBIPresent NBI


Model development and validation is high priority for FY13-15; excellent progress made

11



techniques



performance ...

> Complementary to NBI+ECH on DIII-D> Characterize new NBI line (R15-2)> Study NBI+rf scenarios

• Validation of classical NUBEAM/TRANSP foreseen (R15-2) as “baseline capability”

• New capabilities in NUBEAM/TRANSP will enable more accurate simulations - “Kick” model for NUBEAM being

developed- Improved computation of fast ion-

related quantities (e.g. JNB, torque) when instabilities are present

Tests of reduced “kick” model for NUBEAM/TRANSP

shaded: exp’tsymbols: model

NSTX#139048



12



techniques



performance




> Complementary to NBI+ECH on DIII-D> Characterize new NBI line (R15-2)> Study NBI+rf scenarios> Validation of NUBEAM/TRANSP> Validation of reduced models> Improved HHFW/MHFW modeling capabilities

• Reduced models for fast ion transport by *AEs [, kinks, NTMs] being developed/validated (R14-2)- Critical Gradient (1.5D-QL) model- “Kick” model for NUBEAM

• Improved models also being developed for HHFW/MHFW- Awaiting for new data for extensive validation- Will apply to NBI+rf scenarios

• Modeling work exploits synergy with DIII-D and collaborators



13



techniques



performance




> Complementary to NBI+ECH on DIII-D

> Characterize new NBI line> Study NBI+rf scenarios

> Validation of NUBEAM/TRANSP> Validation of reduced models> Improved HHFW/MHFW modeling

capabilities

> Apply reduced models for fast ion transport

> Apply improved models for NBI+HHFW/MHFW


T&T TSG Experimental Ideas

• NSTX-U will have a set of experimental knobs to vary/control pressure and current profiles – Two NBIs (6 independent sources), HHFW, 3D coils and lithium

deposition• Different pressure and current profiles from using a subset of the 6 NBI

sources

• Heating/current drive from HHFW with NBI or used independently

• 3D coils used to modify rotation profile coupled with NBI

• Different profiles with/without lithium

– Need to identify ways to decouple pressure and current profile variations

• Different time scales of pressure and current profile relaxation

• HHFW in heating mode


T&T TSG Experimental Ideas• Some first year T&T researches to support the FY15 JRT

– qmin dependence of confinement with fixed q95

• DIII-D observation of degraded confinement with broader current profile and with q95 fixed

– BT, Ip and collisionality scalings with different NBI source combinations and HHFW

• Try to decouple pressure and current profile effects

• 3D coils to modify rotation profile

– Lithium scan to vary pressure and current profile • Need to assess the coupling between pressure and current profile

– Lithiated and non-lithiated plasma comparison• Confinement and pressure profiles are known to be different between the

cases from NSTX experiments


What was done…

• ISOLVER-TRANSP– Scale existing electron density profiles, use Zeff=2 to derive ion density

profiles.

– Use Chang-Hinton model for ion transport, scale electron temperature to give a desired H98 or HST.

– NUBEAM for the beam heating, torque, and current drive.

– ISOLVER to compute self-consistent internal equilibrium

– Run simulations long enough that the simulations reach steady state, and only use the steady state part of the solution.

• Stand-alone ISOLVER– Used input pressure and current (ff’) profiles from various NSTX shots.

• Range of shots taken to give a wide range in li.

– Auto-generate thousands of equilibria with different shapes to look for trends in the PF requirements.


For Relaxed Scenarios, the Thermal Pressure Peaking Strongly Impacts the Equilibrium Parameters

1.0 MA, 1.0 T, Pinj=12.6 MW, near non-inductive

1.6 MA, 1.0 T, Pinj=10.2 MW, partial inductive

1.2 MA, 0.55 T, Pinj=12.4 MW, high T

All: fGW=0.7, H98y,2=1

• Concerns: n=0 stability and control (VDE, boundary) and n=1 (core kink/tearing)

• Regardless of the target, too much thermal pressure peaking will drive li too high.

– And values above 2.3 will probably be unacceptable for n=0 (next slide)

– (note, li reaches approximate steady state faster than qmin).

• When pushing to higher IN (or lower q95), broader thermal profiles will allow the final qmin to equilibrate above 1.


Vertical Stability May Provide Limitations on Global Stability With Narrower Profiles

• Use stand-alone ISOLVER simulation of NSTX-U• Scan many values of , , dr-sep, for each of a large number of

profile shapes.• Plot the PF-3 to PF-5 ratio for all the cases

Empirically, IPF-3U/IPF-5<0.25 Leads to a VDE.

(These had ~9 kA of PF-5 Before the VDE)

Vertical Control Good

Vertical Control Bad


Rules For NBCD…

• Call the sources by the tangency radius– 50 cm: old source C– 60 cm: old source B– 70 cm: old source A– New beams at 110 cm, 120 cm, 130 cm

• Highest core NBCD efficiency:– 110 cm, 120 cm

• Highest mid-radius NBCD efficiency: – 130 cm

• Lowest total NBCD efficiency: 50 cm– Then 60 cm, then 70 cm

• Want to maximize NBCD?– Use 110 cm, 120 cm, 130 cm– But will be dominant in the core.

• Want to minimize NBCD?– use 50 cm, 60 cm

• Want to raise qmin with 4 sources?– use 50, 60, 70, 130

• Want to lower qmin with 4 sources?– use 60, 70, 110, 120

fGW~1

fGW~0.55110 cm

120 cm

130 cm

50 cm60 cm

70 cm

110 cm120 cm

130 cm50 cm60 cm 70 cm


At BT=0.75 T, Significant Variation in the Current Profile May be Possible: fGW=0.7

4 Source Combinations at Fixed Current IP=800kA, fGW=0.74 4 Source Combinations at 100% NI Fraction


At BT=0.75 T, Significant Variation in the Current Profile May be Possible: Varying fGW

4 Source Combinations at Fixed Current IP=800kA, fGW=0.74

4 Source Combinations at Fixed Current IP=800kA, fGW=0.6


A Small Amount of Fast Ion Diffusion Might Be Good!


It MAY be Possible to Generate Large Changes in the Rotation Profiles

fGW~1fGW~0.55

110 cm120 cm 130 cm

50 cm60 cm

70 cm

110 cm

120 cm130 cm

50 cm60 cm

70 cm

• Details of torque profile depend on the density.

• No predictions yet, because so validated momentum transport model.– But note that I Goumiri has a very simple control-oriented model that could be used for

prediction soon.


Optimized Equilibrium For Maintaining High T

(At BT=0.55 T, How Can the Plasma Current Be Maximized with qmin>1?)

Target Equilibria:BT=0.55 T, IP=900-1100 kA

=2.9-2.9N=5.2-5.9, T=18-22%

qmin=1.2, tflat-top>>CR

Can only work for broad thermal profiles


Key Experimental Questions

• Can we use variations in the beams to control qmin?

• How does the transport change with qmin?

– Does transport get worse as qmin increases at fixed q95?

• Can we use the available current drive actuators to maintain profiles consistent with vertical and n=1 stability?

• Can we systematically change the rotation shear at the mid-radius/edge (not pedestal) to assess changes in confinement?

• Can we optimize the NBCD, profiles, and plasma shape to maximize N at low-q95?

– Same as asking what is the highest T that we can operate at for longer than a few CR?


“Broadened pressure profiles generally improve global stability”

NSTX disruptivity

NSTX-U projected ideal stability


Focus on:

•details of plasma at pressure peaking / current peaking/broadening disruptive limits, and how to avoid such limits (previous slide)

•the impact of broadened current and pressure profiles on stability in plasmas that are close to being fully non-inductive

•pressure peaking / current profile data in light of a plasma under active MHD control

•how these zeroth order parameters can be influenced by more modern hypotheses – e.g. kinetic stabilization

•different dependencies not explicitly stated in the JRT15: the effect of rotation, q, anisotropic EP distribution…

MS TSG suggestions for the direction of the JRT15


Pressure profile effects kinetic stability by changing the location of mode-particle resonances

Example: ITER case with ITB:Strong internal gradients create large ω*

— Cause difference between ωφ and ωEXB.— Enables resonance with precession drift of trapped thermal ions if ωφ is low.

Strong gradients

dashed lines = “standard” ITER advanced scenario


“Validate theoretical models of… global stability response to varied heating and current drive deposition”

Anisotropy of EPs can effect stability and we plan to study this in NSTX-U

injection pitch χ0

~NSTX~NSTX

Contours of γτw with isotropic thermal particles + anisotropic EPs: fluid correction and δWK

Fluid + Kinetic Effects


Study of classical and neoclassical tearing mode stability vs. pressure gradient and q-shear

• Classical and neoclassical tearing modes can be more important in NSTX-U, despite the favorable Glasser and curvature effects, due to high pressure and bootstrap current fraction

• Study on classical tearing mode – Can be destabilized by both pressure and current broadening– Resistive DCON can be used to more precisely estimate classical tearing mode index

′ and can be compared with experiments △

• Neoclassical tearing mode (NTM)– In low aspect ratio, neoclassical and resistive interchange effects can be comparable– Depending on (p′/q′) and (p′/q′)2, respectively, and thus can be further destabilized if

current broadening leads to q-shear reduction

• Study can be extended onto rotational-shear stabilization as shown in NSTX

nstx-u team ideas for jrt15

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