# Presentation: 603201

## NCSX Research

**M.C. Zarnstorff**
*Princeton Plasma Physics Laboratory*
**NCSX PAC-7**
**13 July 2004**

## Outline

- NCSX mission and research issues
- Expected research phases & topics
- Required capabilities and R&D
- Team Preparation

## NCSX Design Goals: Combine Best Features of Stellarators & Tokamaks

- Use flexibility of 3D plasma shaping to combine best features of stellarators and tokamaks, synergistically, to advance our understanding of both
- Stellarators:  *Externally-generated helical fields;  steady-state compatible;  robust stability, generally disruption free.*
- Tokamaks:  *Excellent confinement; low aspect ratio – affordable; self-generated bootstrap current and flows*
- Transport Optimization:  Quasi-axisymmetry
- (Boozer,1983) Orbits & collisional transport depends on variation of  |B| within flux surface, not the vector components of B !
- (Nührenberg) If  |B| is symmetric in flux coordinates, get confined orbits like tokamak
- 	   transport very similar to tokamaks,  undamped rotation

## NCSX Research Mission

**Acquire the physics data needed to assess the attractiveness of**
**compact stellarators; advance understanding of 3D fusion science.**
- (FESAC-99 Goal)
**Understand...**
- Pressure limits and limiting mechanisms in a strongly shaped 3D plasma
- Effect of 3D magnetic fields on disruptions
- Reduction of neoclassical transport by quasi-symmetric design.
- Confinement scaling with quasi-symmetry; transport barrier formation and reduction of turbulent transport by flow shear control with 3D field.
- Equilibrium islands and tearing-modes, including effects of magnetic shear, seed perturbations and ion-kinetics
- Effect of stochasticity and 3D shaping on the SOL plasma and power and particle exhaust methods.  Compatibility with good core confinement.
- Energetic-ion stability and confinement in 3D magnetic fields
**Demonstrate...**
- Conditions for high- disruption-free operation
- High pressure, good confinement, compatible with steady state

## NCSX Will Have Broad Impact

- NCSX will make strong contributions to the scientific issues facing MFE:
- (in terms of the Priorities Panel’s Topical Questions)
- _T1.How does magnetic structure impact confinement?_  What is the effect of 3D shaping on confinement?  Shear?  Is quasi-axisymmetry effective? How does it differ from axisymmetry?
- _T2.What limits maximum pressure?_   Can 3D shaping increase the  limit?  Is reversed shear beneficial?  What are the limiting mechanisms with 3D fields and how can they be controlled?
- _T3.External control and self organization_  How does 3D shaping affect self-organization of profiles? How high a bootstrap fraction is controllable? Under what conditions are disruptions eliminated?
- _T4.Turbulent transport_  How is turbulent transport affected by 3D shaping?  Does reversed shear help stabilize turbulence in 3D?  How does electron transport depend on local shear and curvature?
- _T5 Electromagnetic fields and mass flow generation_  How does flow damping affect zonal flows and turbulence stabilization?  Can transport barriers be accessed with quasi-symmetry?
- _T6.Magnetic field rearrange and dissipate_  How do shear, pressure, seed perturbations, and ion kinetics affect NTM onset and saturation,in detail?
- _T9.How to interface to room temperature surroundings?_  How is the SOL and interface affected by stochasticity and 3D shaping?  Can the interface and exhaust be improved using 3D effects?
- _T11.Electromagnetic waves interacting with plasma_  How do RF waves interact with plasma in 3D?
- _T12.High-energy particles interacting with plasma_  How does 3D shaping affect energetic-ion instabilities?  Can they be stabilized?  Can orbit losses of energetic ions be controlled in 3D?
- _T15.How to heat, fuel, confine steady-state or pulsed plasmas?_  How can we control and fuel a 3D plasma?  How much control is required?  How can we diagnose the plasma state in 3D?

## NCSX Has Many Unique Physics PropertiesNeed to explore experimentally

- NCSX Has Many Unique Physics PropertiesNeed to explore experimentally

- R/a=4.4
- Strong shaping  ~1.8, ~1
- No need for external current drive
- Designed to have good flux surfaces               at high- and low-
- ‘Reversed shear’ for stability
- Passively stable at =4.1% to kink,    ballooning, vertical, Mercier,              neoclassical-tearing modes
- Stable for   6% by adjusting coil currents

-  LHD & W7AS operate well above their linear instability threshold
-  What will be the  limit for NCSX ?

## Very good Quasi-Axisymmetry: Very Low effective ripple

- New stellarator global scaling finds E ~ [eff(=2/3)]–0.4!   NCSX eff(=2/3) ~ 0.002!
- Low eff gives low flow-damping; control of Er , flow-shear stabilization;      persistent zonal flows
- Reversed shear should stabilize turbulent transport, via drift precession reversal
- Does NCSX confinement act like historical stellarators or tokamaks or ??
- Local transport mechanisms?

- H.Yamada,
-  J.Harris et al
-  EPS 2004

## HSX Quasi-helical symmetry: 

- HSX Quasi-helical symmetry:
- Less flow damping, Goes faster for Less Drive

-  Flow driven by biased probe
-  Quasi-symmetry can be spoiled by powering auxiliary coils (Mirror mode)

## NCSX will be a Flexible Experiment

- Variations from coil currents

- Wide range of 3D shaping flexibility, for control of physics properties
- 9 independent field coil currents
- B  2 T
- Separate trim coils for control of resonant islands and edge shape
- Solenoid for control of toroidal current
- NBI power up to 6MW                   (1.5MW initial)
- ICRF power up to 6MW
- ECH power up to 3MW
- Robust divertor configuration, using flux expansion in elongated cross-section
- Full set of diagnostics planned

- Shear scan

- increased
- & reduced

- iota

- eff   (%)

- •

- ref

- •

- eff scan

## NCSX Research will proceed in Phases 

- 1.  Initial operation  -  warm field map, first plasma
- 2.  Magnetic Configuration Mapping  (cryogenic)
- 3.  1.5MW Initial Experiments
- 4.  3MW Heating
- 5.  Confinement and High Beta -  (~6 MW)
- 6.  Long Pulse – (pumped divertor)
- Diagnostic & facility upgrades throughout to match research goals
- Phases 3 - 5 may last multiple years.
- Expect 18 run weeks in FY09

**NCSX Research will proceed in Phases**** **

## Research Goals of the Initial Phases 

- Magnetic Configuration Mapping
- Document vacuum flux surface characteristics
- Document control of vacuum field characteristics using coil current
- 1.5MW Initial Experiments
- Explore and establish plasma operating space
- Characterize low-power confinement, stability, and operating limits
- 3MW Heating
- Characterize confinement and stability at moderate power, and their dependence on plasma 3D shape
- Test plasma stability at moderate , dependence on 3D shape
- Investigate local transport and effects of quasi-symmetry
- Characterize SOL properties for different 3D geometries, prepare for the first divertor design.
- Explore ability to generate transport barriers and enhanced confinement regimes.

## Initial Phases

| (1)  Initial Testing   (pre-CD4) |  |  | Capabilities | Measurement Requirements |
| --- | --- | --- | --- | --- |
|  | Map flux surfaces (room temperature)
- Assess alignment of coils |  |  | Electron-beam mapping apparatus |
|  | First plasma; exercise coil set & supplies 
- Ip > 25 kA  (cryogenic) |  | Ohmic | Plasma current
External Magnetic diagnostics |
|  | Checkout initial magnetic diagnostics |  | 150 bake | Plasma / wall imaging |
|  | Checkout vacuum diagnostics |  |  |  |
|  | Initial wall conditioning |  |  |  |
|  |  |  |  |  |
|  |  |  |  |  |
|  |  |  |  |  |
| (2) Magnetic Configuration Mapping |  |  |  |  |
|  |  | Map flux surfaces (cryogenic) |  | Electron-beam mapping apparatus |
|  |  | Verify coil-flexibility characteristics |  |  |
|  |  | Verify iota and QA |  |  |
|  |  | Test trim coils |  |  |
|  |  |  |  |  |
|  |  |  |  |  |

- [   Indicates high priority ]

## Research Areas for(3) 1.5MW Initial Experiments

| Topic |  | Heating | Measurement Requirements |
| --- | --- | --- | --- |
|  | Plasma control, plasma evolution control | B=1.2 T | Plasma shape and position |
|  |  | 1.5MW NBI |  |
|  | Global confinement & scaling, effect of 3D shaping
Effect of plasma current | Partial PFCs | Plasma stored energy
Core Te, Ti |
|  | Density limit & mechanisms | GDC | Ne profile
Total Prad
Impurity sources &concentrations |
|  | Current-driven kink stability |  | Low (m,n) MHD  (< 50kHz) |
|  | Vertical stability
Alfvenic mode stability |  |  |
|  |  |  |  |
|  | Effect of low-order rational surfaces on flux-surface topology
Effect of shear on NTM stability |  | Flux surface topology |
|  |  |  |  |
|  | Effect of contact location on plasma plasma performance Control of plasma contact location |  | PFC temperature 
Hydrogen recycling |

- [   Indicates high priority ]

## Research Areas for(4)  3MW Heating

| Topic |  | Capabilities | Measurement Req. |
| --- | --- | --- | --- |
|  | Plasma and shape control, diagnostic validation | B = 2T | Core Te, Ti, Prad profiles |
|  | Test of kink & ballooning stability at moderate beta | 3MW NBI | Tor. & pol. rotation profiles |
|  | Effect of shaping on MHD stability & disruptions | Full liner | Iota profile |
|  | Initial study of Alfvenic modes with NB ions | 350 bake | Er profile |
|  | Confinement scaling |  | Fast ion losses |
|  | Local transport & perturbative transport measurements |  | Ion energy distribution |
|  | Effect of quasi-symmetry on confinement and transport |  | First wall surf. temperature |
|  | Density limits and control with auxiliary heating |  | High frequency MHD |
|  | Use of trim coils to minimize rotation damping & islands |  | Edge neutral pressure |
|  | Blip meas. of fast ion confinement and slowing down |  | SOL temp. & density |
|  | Initial attempts to access enhanced confinement |  | Zeff, Impurity profiles |
|  | Pressure effects on surface quality |  | Flux surface structure |
|  | Controlled study of NTMs using shear variation & trim coils |  |  |
|  | Wall coatings with aux. Heating |  |  |
|  | Plasma edge and exhaust characterization, w/ aux. heating |  |  |
|  | Attempts to control wall neutral influx |  |  |
|  | Wall biasing effects on edge and confinement |  |  |
|  | Low power RF loading and coupling studies (possible) |  |  |

- [   Indicates high priority ]

## Diagnostic Upgrades Provide Needed Measurements 

- Upgrading the diagnostics will continue throughout Research Program
-   Initial (MIE) diagnostics:
-  Ex-vessel magnetic diagnostics (trapped in structure)
-  Diagnostics needed for initial research phases:
- 	Rogowskii loop
- 	Fast Camera
- 	e-beam mapping apparatus
-  Design integration for all planned diagnostics included
-   See B. Stratton’s talk for diagnostics development plan
-   Details of development plan (and research plan) will evolve
-  as NCSX research team assembles
-  as collaboration opportunities are developed

## Equipment Upgrades are Also Necessary

- Major elements				              Phase
-   Plasma facing components and divertors
-  partial liner					3     Oct. 08
-  full liner, with some plates			4     Aug. 09
-  divertor					5     Aug. 10
-   Heating systems
-  second NB-line 				4     Aug. 09
-  RF or further NBI				5     Aug. 10
-   Power supplies
-  all 9 field-coil circuits + trim coils 		3     Oct. 08
-  full field                                          		4     Aug. 09
-  Data acquisition and control
-  acquisition upgrades along with diagnostics
-  pre-programmed WFs			3     Oct. 08
-  initial feedback control			4     Aug. 09

-  Priorities will be set in response to research results

## Long-term developments preparing for research
Ongoing:
Assembly of NCSX Research Team
Physics design and requirements for diagnostics   (Stratton, Lazarus)
Edge Modeling; Physics design and requirements for PFCs 								(Mioduszewski)
Preparation for field mapping (e-beam) 		(Fredrickson)

To start later:
Equilibrium reconstruction analysis
Development of feedback control strategies
Development of comprehensive analysis capability (similar to TRANSP).
Pre-conceptual design of RF test antenna.

- Ongoing:
- Assembly of NCSX Research Team
- Physics design and requirements for diagnostics   (Stratton, Lazarus)
- Edge Modeling; Physics design and requirements for PFCs 								(Mioduszewski)
- Preparation for field mapping (e-beam) 		(Fredrickson)
- To start later:
- Equilibrium reconstruction analysis
- Development of feedback control strategies
- Development of comprehensive analysis capability (similar to TRANSP).
- Pre-conceptual design of RF test antenna.

**NCSX Research Preparation**

## NCSX will be operated as a National & International Collaboration, similar to NSTX
Integrated team, including members from many institutions
Open participation by members, open access to data.

Will hold Research Forums in FY2005/06  to
Identify groups interested in developing needed diagnostics
Nucleate the research team 
Form initial working groups  (4 – 6)
Develop prioritized research plans
Opportunities for collaboration
Plan required resources 
Diagnostics, equipment upgrades, researchers

Preparatory activities  (early FY05)
Work to attract best people to participate
Ensure participation of adequate expertise to achieve goals

- Integrated team, including members from many institutions
- Open participation by members, open access to data.
- Will hold Research Forums in FY2005/06  to
- Identify groups interested in developing needed diagnostics
- Nucleate the research team
- Form initial working groups  (4 – 6)
- Develop prioritized research plans
- Opportunities for collaboration
- Plan required resources
- Diagnostics, equipment upgrades, researchers
- Preparatory activities  (early FY05)
- Work to attract best people to participate
- Ensure participation of adequate expertise to achieve goals

**Preparation of NCSX Research Team**

## DOE funding of collaborations on NCSX will be similar to NSTX
Independently reviewed proposals
3-year proposal cycle
Input via Program Priorities letter, identifying
Research topics expected to have high priority, and
Topics thought to be most appropriate for new collaboration
            e.g. not duplicating existing hardware or ongoing work
However, all topics will be open for collaboration proposals

Expect call for first round of diagnostic proposals in FY06
For funding starting in FY06/07
Additional calls for diagnostic and participation proposals in FY07 and FY08

- Independently reviewed proposals
- 3-year proposal cycle
- Input via Program Priorities letter, identifying
- Research topics expected to have high priority, and
- Topics thought to be most appropriate for new collaboration
-             e.g. not duplicating existing hardware or ongoing work
- However, all topics will be open for collaboration proposals
- Expect call for first round of diagnostic proposals in FY06
- For funding starting in FY06/07
- Additional calls for diagnostic and participation proposals in FY07 and FY08

**Participation by Reviewed Proposals**

## Conclusions

**Conclusions**

- NCSX is an exciting opportunity for unique fusion-science research.
- Have developed outline plans for
- Research program
- Required diagnostic and equipment upgrades
- Preparatory research
- Preparation of the research team
- Ask your advice on
- Research priorities
- Pace of research and upgrades
- Preparatory activities and Research Forum

## 4. Confinement and High Beta

| Topic |  | Upgrade | Measurement Requirements |
| --- | --- | --- | --- |
|  | Stability tests at  >~ 4% | 6 MW | Core fluctuations & turbulence |
|  | Detailed study of  limit scaling | total | Core helium density |
|  | Detailed studies of beta limiting mechanisms | Divertor | Divertor Radiated power profile |
|  | Disruption-free operating region at high beta |  | Divertor recycling |
|  | Active mapping of Alfvenic mode stability (with antenna) |  | Divertor target Te, ne profiles |
|  | Enhanced Conf.:  H-mode; Hot ion regimes; RI mode; pellets |  | Divertor target temperature |
|  | Scaling of local transport and confinement |  |  |
|  | Turbulence studies |  | Divertor impurity concentration |
|  | Scaling of thresholds for enhanced confinement |  |  |
|  | ICRF wave propagation, damping, and heating (possible) |  |  |
|  | Perturbative RF measurements of transport (possible) |  |  |
|  | Divertor operation optimized for power handling and neutral control |  |  |
|  | Trace helium exhaust and confinement |  |  |
|  | Scaling of power to divertor |  |  |
|  | Control of high beta plasmas and their evolution |  |  |

## 5. Long Pulse

| Topic |  | Upgrades | Measurement Requirements |
| --- | --- | --- | --- |
|  |  |  |  |
|  | Long pulse plasma evolution control | Long pulse  | More detailed divertor profiles |
|  | Equilibration of current profile | Divertor pumping |  |
|  | Beta limits with ~ equilibrated profiles | 12 MW? |  |
|  | Edge studies  with 3rd  generation PFC design, pumping |  |  |
|  | Long-pulse power and particle exhaust handling with divertor pumping |  |  |
|  | Compatibility of high confinement, high beta, and divertor operation |  |  |