# Presentation: 471494

## Gary Taylor

presented on behalf of the
NSTX Research Team

- Gary Taylor
*presented on behalf of the*
- NSTX Research Team

**Non-Inductive Operation****5-Year Research Plan**

*NSTX Program Advisory Committee Meeting*
*(PAC-14)*
*January 21-22, 2003*

## Solenoid-Free Initiation & Non-Inductive Plasma Sustainment for  pulse > skin are Major Goals for the NSTX Program

- Spherical torus (ST) plasmas need auxiliary current drive (CD)
- Solenoid-free ST operation may be achieved by a diverse combination of CD tools
- This talk reviews the status & proposed 5-year research
-     plans for three of these tools:
*	**	**- High Harmonic Fast Waves (HHFW)*
*	**	**- Electron Bernstein Waves (EBW)*
*	**	**- Coaxial Helicity Injection (CHI)*

## HHFW, EBW, and CHI Science All Contribute toSolenoid-Free Startup Strategy

- T = 30 ∆t > E
- N = 5: > no wall limit
- HH = 1
- JNI > 60%, ∆t ~ skin
-   Non-solenoid startup demo

- T = 40%, N = 8
- ∆t >> E , HH = 1.4
- JNI ~ 100%, ∆t > skin
- Solenoid-free up to high p

- 40% T
- ∆t >> skin
- N = 8
- HH = 1.4
- 70% JBS

- FY02         03           04          05          06         07          08         09

- HHFW heating & CD
- EBW emissions

- EBW CD 1 MW

-  3 MW

- Real-time HHFW
- heating & phasing

- CHI

- Couple to ohmic

- CHI + Non-inductive ramp up

- HHFW CD - local J, ∆J

*Optimize *
*non-solenoid  operations*

**Notes:**
3 kG, 1 MA is the baseline case (Menard). What drove this scenario to 1 MA was at first arbitrary. We need higher kappa to reduce qedge. Q(0) less than 2 leads to lower with-wall limit, which yields the low li requirement. Q profile, combined with p®, leads to perceived li requirement (pressure driven kink stability). Different bootstrap can change li...betan of 8 and beta-t requirement driven by demand for bootstrap current fraction...

## Non-inductive Current Ramp Up Has Three Phases, Each Requiring Different Current Drive Tools

**Startup: 0 -> 150 kA**
- - *CHI the primary tool at present (maybe EBW later)*
**Initial ramp up: 150 -> 500 kA:**
- - *HHFW, EBW, bootstrap*
*- Research can be performed with an ohmic startup*
*- PF induction -  scenarios also being assessed*
**Final ramp to flattop:**
- - 500 -> 800+ kA: NBI CD, bootstrap current overdrive
- Each phase can be studied separately; combining all three will be a control challenge

## HHFW Research

## 
High  scenarios demand on- and off-axis current drive to complement bootstrap and neutral beams

A form of RF-driven current is also required for solenoid-free ramp-up

Lower hybrid and conventional electron cyclotron CD (ECCD) cannot be used in high  plasmas

HHFW in high  plasmas has strong single pass absorption on electrons that potentially results in desired off-axis deposition

- High  scenarios demand on- and off-axis current drive to complement bootstrap and neutral beams
- A form of RF-driven current is also required for solenoid-free ramp-up
- Lower hybrid and conventional electron cyclotron CD (ECCD) cannot be used in high  plasmas
- HHFW in high  plasmas has strong single pass absorption on electrons that potentially results in desired off-axis deposition

**HHFW Provide a Tool for Electron Heating and CD ****in High ******** ST Plasmas**

## HHFW 5-Year Research Goals 

- HHFW-assisted startup
- Pressure profile modification
- HHFW CD-assisted discharge sustainment
- Use HHFW, with other tools, for pulse > skin operation

## Status of HHFW Research

## Uses TFTR ICRF hardware
f = 30 MHz, D = 9-13
6 MW from 6 transmitters 
Pulse length up to 5 s
12 Element antenna 
Active phase control 
Wide range of wave spectra
		- kT = ± (3-14) m-1
		- variable during shot

- f = 30 MHz, D = 9-13
- 6 MW from 6 transmitters
- Pulse length up to 5 s
- 12 Element antenna
- Active phase control
- Wide range of wave spectra
- 		- *k**T** = ± (3-14) m**-1*
- 		- *variable during shot*

**Flexible System for High Power HHFW Heating ****and CD System Operational on NSTX**

-  Digital phase feedback system sets phase between straps
-  Antenna utilizes BN insulators to minimize RF sheaths

**B**

## HHFW Primarily Heats Electrons, as Expected from Theory

- No evidence for direct thermal ion heating; heats NBI ions
- Confinement consistent with ITER scalings:
*     **L-Mode: ITER97L*
*     **H-Mode ITER98Pby2*

## Some HHFW-Heated Discharges Exhibit Behavior of Internal Transport Barrier

**Some HHFW-Heated Discharges Exhibit Behavior of Internal Transport Barrier**

-  Te increases strongly
-   inside half radius
-  Density profile doesn’t
-   show change
-  Ti (0) rises with Te(0)
***e* progressively
-    decreases with time
-    in the central region

- Prf = 2.5 MW
- Ip = 800 kA

- Te
- (keV)

- 0

- 5

- 0.4

- 1.4

- R (m)

## Less Loop Voltage to Maintain IP With Co Phasing; Magnetic Signal Analysis Estimates Icd = 110 kA (0.05 A/W) 

- HHFW On

- Loop
- Voltage
- (V)

- 0

- 1.0

- TIME (s)

- 0.6

- 0.2

- kT = ±7 m-1

- V = 0.23 V

- Counter-CD
- (1.1 MW)

- Co-CD
- (2.1 MW)

-  TORIC Icd = 95 kA (0.05 A/W) *(Bonoli, MIT)*
-  CURRAY Icd = 162 kA (0.08 A/W) *(T.K. Mau, UCSD)*

## CD Efficiency Consistent with DIII-D & TFTR CD Experiments

-  Operation at increased
-   Te required to meet
-   NSTX goals:
-       - *More RF power *
*        **and improved *
*        **confinement regime*
*        **should allow this*

-  Trapping significantly reduces HHFW-driven current:
- 	- *Diamagnetic effects at high **** may*
*             **reduce trapping*

*C. Petty et al., Plasma Physics and Controlled Fusion ****43**** (2001) 1747*

## Codes Predict Strong Electron Damping, as Seen in Experiments

**Codes Predict Strong Electron Damping, as Seen in Experiments**

- HPRT

- 2.1 MW
- Co-Phasing

- 2

- Pe
- (MW/m3)

-  Excellent agreement between ray
-   tracing codes for HHFW CD
-   experiments
-  Full-wave codes predict similar
-   deposition to ray tracing codes
-  Full-wave kinetic models predict no
-   significant IBW mode conversion
-  More numerical studies to determine
-   if IBW conversion is important at
-   higher B and/or ion 

- 

- 

- 0.8

- 1/2

**CURRAY**

- HPRT

## Evidence Seen for HHFW Interactions with Energetic Beam Ions, as Predicted

- B0=4.5 kG
- B0=4.0 kG
- B0=3.5 kG

- beam injection
- energy

- B0=4.5 kG
- B0=4.0 kG
- B0=3.5 kG

**NBI**

**HHFW**

- NPA

**Evidence Seen for HHFW Interactions with Energetic Beam Ions, as Predicted**

- Tail reduced at lower B, higher 
- 	*-**	**Larger ****e** promotes greater off-axis electron absorption*
*      **reducing power available to centralized fast ion population*

**ln (flux / Energy****1/2****)**

## High  Poloidal H-Mode Plasmas Provide Excellent Candidate for Long Pulse Sustainment

-  Vloop ~ 0
-  ~ 40% bootstrap
-   fraction

## HHFW 5-Year Research Plan

## 2003-4: Test Physics of HHFW Heating & CD

*- Couple HHFW into double null; so far studied limiter and *
*  **single null, but highest **** achieved in double null*
*- Study effect of density on HHFW heating; wider range of *
*  **densities due to improved fueling & wall conditioning*
*- HHFW-only H-mode access & couple HHFW into NBI H-mode*
*- Early HHFW heating; modify internal inductance, reduce volt-   *
*  **sec consumption and increase q(0)*
*- HHFW heating efficiency with strong NBI; study dependence *
*  **on target **** and density *
*- Measure J(R) with CIF MSE during HHFW CD *

## - Couple HHFW into CHI startup

*- Couple HHFW into CHI startup*
*- HHFW heating with CHI to develop bootstrap current*
*- HHFW CD with CHI *
*- HHFW handoff to NBI*
*- Feedback control HHFW heating to maintain J(R) & P(R)*
*- Dependence of CD efficiency on power, n**e**,T**e** and phasing*
*- Study reduction in off-axis CD efficiency due to trapping and   *
*  **increase in CD efficiency at high ***
*- Feedback antenna phasing on MSE J(R) & rtEFIT*
*- Test fully non-inductive steady state operation*

**2005-6: HHFW & CHI, Long Pulse HHFW & ********J Feedback **

## 2005-6: HHFW System Technical Improvements

**2005:**
*- Possibly modify HHFW antenna to be double-end fed to *
*  **reduce voltage for same power *
**2006:*** *
*- If asymmetry in launch spectrum remains a problem for CD, *
*  **may tilt antenna straps*

## - HHFW with full feedback control of phase using MSE LIF 

*- HHFW with full feedback control of phase using MSE LIF *
*  **diagnostic to obtain real time J(R) & P(R)*
*- HHFW-assisted ramp to high ****pol*
* **Use HHFW to optimize flux consumption in high *
*  **performance plasmas*

**2007-8: HHFW Heating & CD Control of P(R) & J(R) and Flux Consumption Optimization  **

## EBW Research

## EBWs May Enable Local Heating, CD and Te(R,t) Measurements on ST Plasmas

- EBWs propagate when pe >> ce and strongly absorb at EC resonances, allowing local EBW heating, CD and Te(R,t) radiometry
- Local EBW heating and CD may be important for non-inductive startup and MHD suppression in an ST
- EBWs can couple to electromagnetic waves near the upper hybrid resonance (UHR) that surrounds ST plasmas

**Notes:**
Electron Bernstein waves may enable local heating, current drive and electron temperature profile measurements in high beta, spherical torus plasmas where we can’t use conventional electron cyclotron heating, current drive and radiometry because the electron plasma frequency is much bigger than the electron cyclotron frequency.

Electron Bernstein waves can propagate when the electron plasma frequency is much greater than the electron cyclotron frequency and they are strongly absorbed near electron cylotron resonances, so EBW radiometer  

The study of EBW emission can yield important information about the viability of EBW heating and current.

## EBW 5-Year Research Goals 

- Efficient coupling of X- and/or O-mode to EBWs
- Control spatial location where EBW heats electrons
- Demonstrate EBW-assisted non-inductive startup, alone or in combination with HHFW and/or CHI
- Suppress neoclassical tearing modes with EBW heating and/or CD
- Install ~ 1 MW by 2006, ~ 3 MW by 2007

## Status of EBW Research

## EBW Experiments on CDX-U and NSTX Have Focused on Maximizing EBW Conversion to X-Mode (B-X)

- Measurement of B-X emission evaluates the efficiency of the X-B process for heating and CD
- If *L**n** *is short at the UHR, EBW can tunnel to the fast X-mode:
*              **- EBW to X-mode conversion efficiency (C**BX**)*
*                **very sensitive to L**n*

- Mode conversion to the O-mode (B-X-O) also possible; studied on W7-AS and MAST

**Notes:**
One important characteristic of the mode-converted EBW emission is the degree of localization of the emission source with respect to the major radius.

In order to determine the EBW source localization, we perturbed the CDX-U plasma temperature profile with a sequence short gas puffs. The modulation in the edge density and temperature was measured by a Langmuir probe (shown in green in the schematic cross section). The evolution of the edge electron temperature is shown here by the upper green plot. During a sequence of similar discharges the EBW radiometer receive frequency was scanned and the time of peak EBW radiation temperature,Trad, was measured. An example of the EBW Trad evolution is shown in red in the lower plot.

## Need CBX > 80% for Viable EBW Heating and CD System on NSTX

- Measured *C**BX* < 5% for
-     NSTX L-Mode plasmas,
-     10-15% during H-Modes
- On CDX-U, local limiter shortened *L**n*  to 0.7cm, increasing *C**BX* to > 95%, in agreement with theory
- Reproduce CDX-U experiments with local limiter on NSTX this year, for both B-X and B-X-O conversion

## Experiment on NSTX Using HHFW Antenna Tiles to Shorten Ln Increases CBX  from 10% to ~ 50% 

*EBW Emission Frequency = 11.6 GHz*

-   Will attempt similar experiment with
-    O-Mode antenna next year

**Notes:**
Plotting the evolution of the EBW Trad at one emission frequency you can see that the emission level increases by about a factor of three at the L-H transition. Above I show the evolution of the Demission, you can see the sudden drop in recycling at the L to H transition. At the time shown by the vertical red line we acquired the density and temperature profile with a Thomson scattering system. Trad/Te increased to 15% at the L-H transition and gradually decreased to 10% as the edge recycling increased. At the time the Thomson scattering data was taken the density scale length at the upper hybrid resonance was about one centimeter implying a mode conversion efficiency of 11%, in good agreement with the Trad/Te value.

## Modeling Indicates Highly Localized EBW CD

- Use GENRAY ray tracing and CQL3D Fokker-Planck codes
- Greatest radial access for fundamental EBW

*1 MW, 14.5 GHz RF at 5**o** above mid-plane, -0.1 < n**//  **< 0.1, **** = 20% *
*CD efficiency = 0.065 A/W, n**eo** = 3x10**19** m**-3**, T**eo** = 1keV*

**Notes:**
For viable mode-converted EBW heating and current drive or for an EBW Te diagnostic it is essential to optimize and define Ln at the upper hybrid resonance. On CDX-U, we plan to use a multi-tipped Langmuir probe to continuously measure Ln at the antenna location. On NSTX, we will use microwave reflectometry to measure Ln. We are also going to use local limiters to define Ln at the EBW antenna on CDX-U.

## Status of EBW RF Source Technology

- Bo ~ 0.4-0.5 T NSTX plasma operation requires fundamental EBW RF source at ~ 15 GHz
- No long pulse, high power ~ 15 GHz sources available
- Develop new megawatt level ~ 15 GHz tube:
- 	   - *MIT proposed 800 kW tube with ~ 50% efficiency*,
-          *estimates 18-24 month development*
- 	   - *Need request for cost & schedule quote in 2003*

**Notes:**
For viable mode-converted EBW heating and current drive or for an EBW Te diagnostic it is essential to optimize and define Ln at the upper hybrid resonance. On CDX-U, we plan to use a multi-tipped Langmuir probe to continuously measure Ln at the antenna location. On NSTX, we will use microwave reflectometry to measure Ln. We are also going to use local limiters to define Ln at the EBW antenna on CDX-U.

## EBW Launcher Design Presently Undefined

- Need well defined n// spectrum, good focusing and
-     some beam steering
- Use either focusing mirrors or phased 4-8 element array
- Polarization control by external waveguide or grooved mirrors
- Use local limiter to steepen *L**n* at the mode conversion layer for both X-B and O-X-B launch

**Notes:**
For viable mode-converted EBW heating and current drive or for an EBW Te diagnostic it is essential to optimize and define Ln at the upper hybrid resonance. On CDX-U, we plan to use a multi-tipped Langmuir probe to continuously measure Ln at the antenna location. On NSTX, we will use microwave reflectometry to measure Ln. We are also going to use local limiters to define Ln at the EBW antenna on CDX-U.

## EBW 5-Year Research Plan

## 2003-5: Establish Conditions for Efficient Coupling to EBWs and Model EBW CD

**2003: ***Complete GENRAY/CQL3D scoping study for NSTX*
-         - *Include relativistic effects in EBW propagation & damping*
*        *
*        **- Are edge parametric instabilities for EBW heating?*
-         - *Request quote for ~ 1 MW, 15 GHz tube*
-         - *MAST to test O-X-B heating*
**2004-5:** *Obtain ≥ 80% B-X and/or B-X-O conversion on NSTX*
-         -* Complete 1-3 MW, 15 GHz EBW system design*
-         - *Include radial transport in CQL3D CD modeling*
-         - *Begin to install of 1 MW, 15 GHz system*

## 2006-8: Demonstrate Local EBW Heating, CD, Startup & NTM Suppression with 3 MW EBW System 

**   ****2006:** *Complete 1MW, 15 GHz EBW system*
* *
-            -* Demonstrate EBW coupling with ~ 1 MW, 15 GHz*
-            - *Study spatial control of EBW electron heating*
**2007-8: ***Begin experiments with 1-3 MW, 15 GHz*
-            - *Demonstrate radial control of local EBW CD*
-            - *EBW plasma startup*
-            - *NTM suppression by EBW heating and/or CD*

## CHI Research

## 
CHI creates plasma current without a solenoid and drives it to a level where other tools can take over

CHI has potential to control edge current profile during the sustained discharge phase

May induce edge plasma rotation to sustain an edge transport barrier

May control scrape off layer flows

High power density presents technical challenges

- CHI creates plasma current without a solenoid and drives it to a level where other tools can take over
- CHI has potential to control edge current profile during the sustained discharge phase
- May induce edge plasma rotation to sustain an edge transport barrier
- May control scrape off layer flows
- High power density presents technical challenges

**CHI May Enable Non-Inductive ST Plasma Startup **

## CHI 5-Year Research Goals 

- Demonstrate transfer of a CHI produced plasma to the central solenoid:
-         - *Handoff CHI startup initially to inductive and *
*          **later to non-inductive CD system*
- Provide edge current during sustained non-inductive operation
- 3D MHD studies and measurement simulations to form a physics-based understanding of CHI and how it might extrapolate
*Strong collaboration with HIT-II (Univ. of Washington)*

## Status of CHI Research

## Simple Description of CHI Start-up 

- Expect reconnection to redistribute edge current to interior, forming closed surfaces

- Absorber

## Produced 400kA Plasma with 14x Current Multiplication

- Evidence for *n=1* MHD, consistent with flux closure
- B-field pickup coils and soft X-rays indicate large scale reconnection activity
- Need feedback control to stabilize CHI-produced discharge

- 0

- 100

- 200

- 300

- Time (ms)

## Technical Problems Have Limited CHI Operational Space

- Arcs across absorber gap on nearly all CHI shots
- Arcs external to vacuum vessel also occur
- Hardware upgrade to address absorber arc problem
- Old absorber uses short insulator length and no PF coils
- New absorber has longer insulator and stray field reducing coils

## Recent Work on HIT-II Demonstrates Short-Pulse CHI and Induction can be Coupled

- New CHI startup tested on HIT-II uses transient (< 50 ms) pulse:
-     - *Successful handoff to inductive  *
*      **operation*
*    *
*    *- *Reduced V-s consumption*
*          *
*    **-  **Reproducible discharges with   *
*       **record currents on HIT-II*
- Will be tested on NSTX this year

- Injector Voltage (kV)

- Injector Current (kA)

- Plasma Current (kA)

- Radiated Power (MW)

- Electron Density (1019m-3)

- 0

- -2

- 25

- 0

- 150

- 0

- 0

- 1

- 0

- 4

- Time (ms)

- 0

- 25

***HIT - II***

## CHI 5-Year Research Plan

## 2003: Test CHI Physics

-  Study handoff of CHI startup to inductive plasma
-  Explore new short pulse startup scenario
-  Develop tools for steady state operation
-  Reestablish CHI startup to ~ 300 kA and investigate
-   new absorber performance

## 2004-5: Optimize CHI, Test Edge CHI CD and Absorber Field Nulling

-  Couple CHI startup to heating and non-inductive current
-   drive methods, including assist from outer PF coils
-  Establish edge CHI CD in an already established discharge
-   and investigate effect of CHI on edge flows and rotation
-  Establish preferred method for CHI startup (transient versus
-   steady state)
-  Implement absorber field nulling

## 2006-8: Integrate CHI with Other Non-Inductive CD Tools & Optimize Edge CHI CD for Long Pulse

-  Demonstrate hand-off of CHI plasma to solenoid-free CD
-   system, ramping to high poloidal 
-  Detailed MSE J(R) measurements of CHI discharges
-  Understand processes that lead to flux closure and
-   mechanisms that sustain closure
-  Investigate edge CHI current drive in high , high bootstrap,
-   steady-state discharges

## HHFW, EBW and CHI May Provide Tools to Enable Solenoid-Free NSTX Operation at High 

**HHFW:**
-  Strong electron heating; evidence for CD & NBI ion interaction
-  5-yr goal: HHFW-assisted startup, current sustainment and
-   pressure profile modification
**EBW:**
-  With limiter, *C**bx*> 95 % on CDX-U, ~ 50% on NSTX
-  Install 1-3 MW EBW system in 2006-7
-  5-yr goal: EBW startup & MHD suppression
**CHI**:
-  Produced 400kA CHI plasma on NSTX , improved short pulse
-   CHI tested on HIT II
-  5-yr goal: optimize CHI startup, edge current drive & rotation

## HHFW/EBW Tools

***IPPA: 5 year***

***IPPA: 10 yr***

- MSE CIF

*MSE CIF*

*MSE LIF (J, E**r**, P);polarimetry*

*Feedback with MSE, heating, CD, rtEFIT*

*CHERS 18 ch*

*MPTS 20 ch, 60 Hz*

*MPTS Upgrades*

*Edge Reflectometry*

*Fluctuations & wave deposition*

*HHFW Phase Control*

*7 MW NBI,*
*6 MW HHFW*

*Upgrade HHFW Feed*

*HHFW Strap*
*Reorientation*

*1 MW EBW                         3 MW EBW*

*7 MW NBI,*
*3 MW HHFW*

*CHERS 51 ch*

***HHFW/EBW Tools***

***HHFW/EBW Physics***

*HHFW heating : density, configuration dependence  6 MW HHFW, with NBI*

*HHFW CD V**loop*

*HHFW CD measure ∆J*

*HHFW CD, long pulse, ∆J feedback*

*HHFW:*****
*feedback with heating, CD*

*HHFW wave/particle interactions*

*EBW emissions & coupling*

*EBW  CD, NTM Control, Startup*

*CHI & HHFW    CHI, HHFW, NBI Ramp to high ****p*

*Optimize*
*Startup   *

*HHFW and P(r) modification*

## CHI Tools

***IPPA: 5 year***

***IPPA: 10 yr***

- MSE CIF

*MSE CIF*

*MSE LIF (J, E**r**, P);polarimetry*

*Feedback with MSE, heating, CD, rtEFIT*

*CHERS 18 ch*

*MPTS 20 ch, 60 Hz*

*MPTS Upgrades*

*Edge Reflectometry*

*Fluctuations & wave deposition*

*HHFW Phase Control*

*7 MW NBI,*
*6 MW HHFW*

*Upgrade HHFW Feed*

*HHFW Strap*
*Reorientation*

*1 MW EBW                         3 MW EBW*

*7 MW NBI,*
*3 MW HHFW*

*CHERS 51 ch*

***CHI Tools***

***CHI Physics***

*Transient CHI startup & hand-off to OH*

*Test steady-state CHI*

*Investigate new absorber performance*

*Optimize edge CD for high ****, long pulse experiments*

*Demonstrate coupling of non-inductive CD to CHI plasma*

*Demonstrate *
*edge CHI CD*

*Absorber*
*field nulling*