# Presentation: 534772

## EBW & HHFW Research (Including EBW Collaborations with MAST & PEGASUS)

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

*NSTX Program Advisory Committee Meeting*
*(PAC-19)*
*February 23, 2006*

## Outline

*   **NSTX EBW Research (including MAST & P**EGASUS** )*
*   **NSTX HHFW Research*
*   **Summary*

**Notes:**
EBW current drive is potentially critical to sustained operation of a high beta Spherical Torus plasma

Electron Berstein waves may provide critical off-axis current at high  to optimize the current density profile & suppress deleterious MHD

Electron Bernstein wave heating & current drive may also assist non-solenoid plasma startup

We are using mode-converted thermal electron Bernstein wave emission  to measure the electron temperature profile and to investigate coupling of electron Bernstein wave to electromagnetic waves, near the plasma edge

Next year, we aim to demonstrate greater than 80% EBW mode conversion with either an X-mode antenna viewing normally to the plasma magnetic field or an obliquely viewing, O-mode antenna

We are also modeling EBW coupling, power deposition and current drive efficiency in support of a planned multi-megawatt EBW heating & current drive system for NSTX 

## NSTX EBW Research

*(including MAST & P**EGASUS**)*
* **EBW research is directed towards...*

**Notes:**
EBW current drive is potentially critical to sustained operation of a high beta Spherical Torus plasma

Electron Berstein waves may provide critical off-axis current at high  to optimize the current density profile & suppress deleterious MHD

Electron Bernstein wave heating & current drive may also assist non-solenoid plasma startup

We are using mode-converted thermal electron Bernstein wave emission  to measure the electron temperature profile and to investigate coupling of electron Bernstein wave to electromagnetic waves, near the plasma edge

Next year, we aim to demonstrate greater than 80% EBW mode conversion with either an X-mode antenna viewing normally to the plasma magnetic field or an obliquely viewing, O-mode antenna

We are also modeling EBW coupling, power deposition and current drive efficiency in support of a planned multi-megawatt EBW heating & current drive system for NSTX 

## EBWCD Needed to Sustain  > 20 % Non-Inductive NSTX Plasmas

*Deposition similar for *
*14 GHz & 28 GHz and ****~ 20-40%*

*CQL3D/GENRAY*

- NSTX
- Bt(0) = 3.5 kG

-  *Need ~100 kA RFCD between ****= 0.4 & ****= 0.8;  *
*  **CD localization is not critical** *

- Current
- Density
- (A/cm2)

***EBWCD Needed to Sustain ************ > 20 % Non-Inductive ******NSTX Plasmas***

-  *Need resilient coupling *
*  **to EBWs** **for viable **  EBWCD scheme*

-  *Large trapped particle  *
* **fraction on low field side  *
* **enables off-axis Ohkawa ** EBWCD*

*G. Taylor et al., Phys. Plasmas ****11****, 4733 (2004)*

## Strong Diffusion Near Trapped-Passing Boundary EnablesEfficient Ohkawa EBWCD 

***Strong Diffusion Near Trapped-Passing Boundary Enables******Efficient Ohkawa EBWCD***** **

*Contours of Quasilinear RF Velocity *
*Space Diffusion Operator*

*GENRAY/CQL3D*

**Notes:**
We are using the GENRAY ray tracing code combined with the CQL3Dquasi-linear bounce-averaged Fokker-Planck code to mode EBW deposition and current drive efficiency.

Here are results for a 1 MA, Bt=0.35 T, beta=40% equilibrium.

Here is a plot of the ECE resonance frequency from the fundamental to fourth harmonic versus major radius. There is a significant magnetic field well at high beta and radial access is best between the fundamental and second harmonic. 

For a 14 GHz launch frequency and a B-X-O oblique launch from an antenna 60 degrees below the mid-plane, we see on this inset plot from GENRAY that there is radially localized deposition on the Doppler-down shifted second harmonic at rho~0.7 on the outboard side of the axis.

This is the calculated EBW-driven current density from CQL3D. We calculate 44kA/MW, with the current density locally peaked near rho of 0.7 

## 
Synergistic bootstrap current results from EBW-induced pitch angle scattering into trapped electron population

Radial diffusion broadening is marginally important for  = 40% case:  ~ 0.05 @ ~ 0.7

CD modeling assuming diffusion constant in velocity space, being performed for range of NSTX conditions

*R.W. Harvey & G. Taylor, Phys. Plasmas ****12****, 051509 (2005)*

-  NSTX  = 40%, PEBW = 1 MW, Co-EBWCD

*GENRAY/CQL3D*

*Synergistic bootstrap current results from EBW-induced pitch angle scattering into trapped electron population*
*Radial diffusion broadening is marginally important for **** = 40% case:  ****~ 0.05 @ ****~ 0.7*
*CD modeling assuming diffusion constant in velocity space, being performed for range of NSTX conditions*
* *

* **CQL3D being upgraded to improve radial transport calculation, i**ncluding **   **possible self-consistent anti-pinch effect of Ohkawa EBWCD & its effect on **   bootstrap current*

**Notes:**
EBW current drive is potentially critical to sustained operation of a high beta Spherical Torus plasma

Electron Berstein waves may provide critical off-axis current at high  to optimize the current density profile & suppress deleterious MHD

Electron Bernstein wave heating & current drive may also assist non-solenoid plasma startup

We are using mode-converted thermal electron Bernstein wave emission  to measure the electron temperature profile and to investigate coupling of electron Bernstein wave to electromagnetic waves, near the plasma edge

Next year, we aim to demonstrate greater than 80% EBW mode conversion with either an X-mode antenna viewing normally to the plasma magnetic field or an obliquely viewing, O-mode antenna

We are also modeling EBW coupling, power deposition and current drive efficiency in support of a planned multi-megawatt EBW heating & current drive system for NSTX 

## Measured 80% B-X-O Coupling in L-Mode Edge Plasmas, Consistent with Modeling

*G. Taylor et al.**, **Phys. Plasmas ****12****, 052511 (2005) *
*J. Preinhaelter et al., AIP Proc. ****787****, 349 (2005)*

* **3-D ray tracing & full wave*
*  **EBW mode conversion model *
*  **using EFIT magnetic equilibrium*
*  **& Thomson scattering T**e** & n**e** *

- f =16.5 GHz

- NSTX Shot 113544

- Frequency = 16.5 GHz, Bt(0) = 4.5 kG

**Notes:**
EBW current drive is potentially critical to sustained operation of a high beta Spherical Torus plasma

Electron Berstein waves may provide critical off-axis current at high  to optimize the current density profile & suppress deleterious MHD

Electron Bernstein wave heating & current drive may also assist non-solenoid plasma startup

We are using mode-converted thermal electron Bernstein wave emission  to measure the electron temperature profile and to investigate coupling of electron Bernstein wave to electromagnetic waves, near the plasma edge

Next year, we aim to demonstrate greater than 80% EBW mode conversion with either an X-mode antenna viewing normally to the plasma magnetic field or an obliquely viewing, O-mode antenna

We are also modeling EBW coupling, power deposition and current drive efficiency in support of a planned multi-megawatt EBW heating & current drive system for NSTX 

## ~ 30% B-X-O Coupling in H-Modes Consistent with Collisional 3fce EBE Damping at Upper Hybrid Layer

***~ 30% B-X-O Coupling in H-Modes Consistent with Collisional 3f******ce****** EBE Damping at Upper Hybrid Layer***

- Trad ~ Te(R=1m)

- Measured Trad
- Simulated Trad with Zeff = 3 at UHR
- Simulated Trad with Zeff = 5 at UHR
- Simulated Trad with no EBW damping at UHR

- Trad(keV)

- 1000

- Time (s)

- Shot = 117970
- f = 25 GHz

- 0

- 0

- 0.6

*T**e**~ 20 eV at UHR, near foot of **  H-mode pedestal*
* **EBW collisional damping sensitive **  to Z**eff** for T**e **< 30 eV*
* **Measured T**rad** behavior consistent **  with EBE only from 3f**ce **off-axis*

* **Li conditioning may significantly improve B-X-O **  coupling from H-modes by increasing T**e** at UHR *

- Trad ~ Te(R=1.3 m)

**Notes:**
EBW current drive is potentially critical to sustained operation of a high beta Spherical Torus plasma

Electron Berstein waves may provide critical off-axis current at high  to optimize the current density profile & suppress deleterious MHD

Electron Bernstein wave heating & current drive may also assist non-solenoid plasma startup

We are using mode-converted thermal electron Bernstein wave emission  to measure the electron temperature profile and to investigate coupling of electron Bernstein wave to electromagnetic waves, near the plasma edge

Next year, we aim to demonstrate greater than 80% EBW mode conversion with either an X-mode antenna viewing normally to the plasma magnetic field or an obliquely viewing, O-mode antenna

We are also modeling EBW coupling, power deposition and current drive efficiency in support of a planned multi-megawatt EBW heating & current drive system for NSTX 

## Remotely-steered B-X-O Antennas, Covering 8-40 GHz, will Test EBW Coupling Efficiency Predictions from Models 

*M. Carter*
*ORNL*

*AORSA-1D*
*NSTX **** = 40%*
*B**t**(0) = 3.5 kG*
*f = 28 GHz**** ***

***Remotely-steered B-X-O Antennas, Covering 8-40 GHz, will Test EBW Coupling Efficiency Predictions from Models ***

-  *Experiments will study **  L- & H-mode plasmas   *
* **and effect of Li pumping*
* **on EBW edge coupling*

-  *Scanning frequency & antenna viewing angle *
*  **provides key information on angle of peak  *
*  **EBW coupling & emission polarization*
* *
* **EBW coupling study critical for assessing *
*  **technical feasibility of EBWCD in FY06*
* **Supports EBW T**e**(R,t) diagnostic development*

- npol

- ntor

- 0.6

- 0.6

- -0.6

- -0.6

## MAST EBW Collaboration

* **EBWCD benchmarking between **GENRAY/CQL3D **& BANDIT *
*  **shows reasonably good agreement for **** = 40% NSTX case:*
*	**- both predict Ohkawa EBWCD, peaked at r/a ~ 0.7*
*	**- BANDIT: 26 kA/MW, GENRAY/CQL3D: 37 kA/MW*
*	**- BANDIT includes EBW coupling at UHR, GENRAY did not*
* *
*	**- In 2006, will include EBW coupling in GENRAY *
-  *28 GHz EBW I**p** initiation/ramp-up system will be tested on MAST **  in late 2006 (installation in summer 2006):*
*              **- collaborate with 28 GHz startup/ramp-up experiments in 2006-7*
*	** **- possible 28 GHz B-X-O experiments in 2007-8*
* **B-X-O coupling measurements from spinning mirror EBE diagnostic   **  (March 2006) will **contribute to FY06 decision on technical feasibility of **  EBWCD on NSTX*

**Notes:**
EBW current drive is potentially critical to sustained operation of a high beta Spherical Torus plasma

Electron Berstein waves may provide critical off-axis current at high  to optimize the current density profile & suppress deleterious MHD

Electron Bernstein wave heating & current drive may also assist non-solenoid plasma startup

We are using mode-converted thermal electron Bernstein wave emission  to measure the electron temperature profile and to investigate coupling of electron Bernstein wave to electromagnetic waves, near the plasma edge

Next year, we aim to demonstrate greater than 80% EBW mode conversion with either an X-mode antenna viewing normally to the plasma magnetic field or an obliquely viewing, O-mode antenna

We are also modeling EBW coupling, power deposition and current drive efficiency in support of a planned multi-megawatt EBW heating & current drive system for NSTX 

## 2.45 GHz EBW Experiments on PEGASUS will Study Coupling, Propagation, Heating & CD

***2.45 GHz EBW Experiments on P******EGASUS****** will Study Coupling, Propagation, Heating & CD***

-  *Existing 2.45 GHz *
*  **PLT equipment to be*
*  **used for 0.9 MW*
*  **EBW system*
* **Demonstrate EBW *
*  **coupling at significant  *
*  **power via O-X-B & X-B*
* **Study nonlinear EBW *
*  **coupling effects *
* **Validate ray tracing, *
*   **demonstrate electron *
*   **heating*
* **Measure EBWCD *

##  Initial modeling completed for PEGASUS 2.45 GHz EBW heating  
      & CD system for Irod = 90-150 kA

		- CD efficiency ~ 20-25 kA/MW ; 
		- Fisch-Boozer CD dominates on axis for Irod = 90-150 kA
		- Irod ~ 210-240 kA may allow dominant off-axis Ohkawa CD 

200-400 kW EBW experiments could begin on PEGASUS in 2008-9          

* **Initial modeling completed for P**EGASUS** 2.45 GHz EBW heating  *
*      **& CD system for I**rod **= 90-150 kA*
*	**	**- CD efficiency ~ 20-25 kA/MW ; *
*	**	**- Fisch-Boozer CD dominates on axis for I**rod **= 90-150 kA*
*	**	**- I**rod** ~ 210-240 kA may allow dominant off-axis Ohkawa CD *
*200-400 kW EBW experiments could begin on P**EGASUS** in 2008-9 **         *

***Near Midplane EBW Launch Provides Significant EBW Electron Heating & Current Drive Near Axis***

## EBW Models & Emission Coupling Studies on NSTX Being Significantly Improved in FY06

***EBW Models & Emission Coupling Studies on NSTX ******Being Significantly Improved in FY06***

* **NSTX & MAST EBW emission studies will contribute to FY06 technical*
*  **assessment of EBWCD:*
*	**- NSTX remotely steered antennas will study B-X-O*
*               **coupling from L- & H-mode & effect of Li conditioning *
*	**- MAST spinning mirror diagnostic will study B-X-O coupling*
*  **2.45 GHz EBWCD modeling of P**EGASUS* plasmas *at I**rod **> 200 kA to    *
*   **identify scenarios with dominant Ohkawa CD*
* **CQL3D/GENRAY modeling of EBE from non-thermal electron distributions*
* **Include EBW mode conversion model in GENRAY*
* **Benchmark CQL3D/GENRAY(with EBW MC) & BANDIT for NSTX cases*
* **Improve user interface to "Prague" EBW emission modeling code *
* **CQL3D/GENRAY EBWCD calculations assuming constant diffusion in *
*  **velocity space (consistent with TCV results) for a range NSTX conditions  *

**Notes:**
New EBW emission antennas installed in NSTX for Te(R) and coupling measurements in 2004: 
          - Demonstrate > 80% EBW coupling

Oblique, near-circularly polarized, launcher for efficient EBW coupling; resilient to changes in edge density gradient & field pitch

Modeling indicates, efficient, off-axis current drive up to  = 40%:efficient off-axis, Ohkawa, CD

~ 3 MW EBW system planned to provide ~100kA off-axis EBW CD on NSTX by 2008

## EBW Priorities for FY 2007-2008

*Complete detailed study of EBE coupling with NSTX remotely steered antennas*
*Collaborate with 28 GHz startup/ramp-up experiments in 2006-7*
*	**& possibly 28 GHz B-X-O experiments in 2007-8*
*Upgrade radial transport calculation in the CQL3D*
*Examine possible role of self-consistent anti-pinch effect in Ohkawa EBWCD and its effect on bootstrap current*
*Analytical study of EB**WCD** **and scenarios for optimizing the current drive efficiency*
*Possible collaboration on NSTX ~1 MW, 28 GHz EBW experiments*
*Implement ~ 400 kW, 2.45 GHz EBW heating & CD capability on P**EGASUS*

## NSTX HHFW Research

* **HHFW research is directed towards... *

**Notes:**
EBW current drive is potentially critical to sustained operation of a high beta Spherical Torus plasma

Electron Berstein waves may provide critical off-axis current at high  to optimize the current density profile & suppress deleterious MHD

Electron Bernstein wave heating & current drive may also assist non-solenoid plasma startup

We are using mode-converted thermal electron Bernstein wave emission  to measure the electron temperature profile and to investigate coupling of electron Bernstein wave to electromagnetic waves, near the plasma edge

Next year, we aim to demonstrate greater than 80% EBW mode conversion with either an X-mode antenna viewing normally to the plasma magnetic field or an obliquely viewing, O-mode antenna

We are also modeling EBW coupling, power deposition and current drive efficiency in support of a planned multi-megawatt EBW heating & current drive system for NSTX 

## HHFW Power Modulation Experiments Show Decreasing RF Absorption with Decreasing k//

| k//(m-1) | % Power absorbed |
| --- | --- |
| 14 | 80 |
| +7 | 70 |
| -7 | 55 |
| +3 | < 20 |

* **Parametric decay into surface waves may explain some of **  the power absorption dependence on k**//*

***HHFW Power Modulation Experiments ******Show Decreasing RF Absorption with Decreasing k*****//**

## Ion heating through parametric decay was observed in 2004 & confirmed with improved time resolution in 2005

Waves in the surface can cause power deposition in sheaths and in the plasma periphery through collisions

*Ion heating through parametric decay was observed in 2004 & confirmed with improved time resolution in 2005*
*Waves in the surface can cause power deposition in sheaths and in the plasma periphery through collisions*

-     *For lower k**// **, fast waves propagate at lower density and reach**     much higher **k**** at a given density *
*   **Wave fields in the edge are enhanced at lower k**//  **and should **     contribute to greater power loss via parametric decay, sheath**     damping & collisions*

***Possible HHFW Power Loss in Plasma Edge ******via Parametric Decay & Waves in the Periphery***

## Parametric Decay Accounts for Significant Fraction of RF Power Losses at k|| = 14 m-1 & -7 m-1  

-    *16% @ k**||** = 14 m**-1**, 23% @ k**||** = -7 m**-1*
* **Represents lower limit estimate of power loss by this process*

*  **Significant RF power required to sustain large temperature difference **  between edge ions and electrons*

***Parametric Decay Accounts for Significant Fraction of RF Power Losses at k******||****** = 14 m******-1****** & -7 m******-1****** ****** ***

## Fast Wave Propagation Begins at Lower Density at Lower k||

- k|| = 3m-1
-          7m-1
-  14m-1

-    *Density onset is function **    of ~** **B*k**||**2** *
*   **Propagation is very close  *
*    **to wall at 7 m**-1** and on the   **    wall at 3 m**-1*
*   **Losses in surface should **    be higher for lower k**||** *
*   **Strong motivation for **    antenna modification to*
*    **provide 14 m**-1** directed**    launch*

***Fast Wave Propagation Begins at Lower Density at Lower k******||***

- B = 4.5kG

- k

- 0

- 60

- ne [x 1012 cm-3]

- 0

- 5

## PDI instability observed at 4.5 kG, PDI should be weaker at higher magnetic field

Onset density for propagation of HHFW is approximately
    proportional to magnetic field at a given k|| :

		- waves propagate further from plasma edge at higher field

Wave propagation into core faster with increased magnetic field:
		- surface fields decrease with increasing magnetic field

In 2006 will measure HHFW power loss properties as function of magnetic field at constant q:

		- New RF probes will detect waves propagating in periphery

		- Important for projections to the higher field regime of 
         ITER & ST CTF; even 5-10% loss significant with ~ 20 MW 
		  RF power

*Onset density for propagation of HHFW is approximately*
*    **proportional to magnetic field at a given k**||** :*
*	**	**- waves propagate further from plasma edge at higher field*
*Wave propagation into core faster with increased magnetic field:*
*	**	**- surface fields decrease with increasing magnetic field*
*In 2006 will measure HHFW power loss properties as function of magnetic field at constant q:*
*	*
*	**	**- New RF probes will detect waves propagating in periphery*
*	**	**- Important for projections to the higher field regime of *
*         **ITER & ST CTF; even 5-10% loss significant with ~ 20 MW *
*	**	**  **RF power*

***Higher Magnetic Field****** ******Should Yield Higher HHFW Heating Efficiency***

## This Year Early Solenoid-Free IP Ramp-up Experiments using HHFW Heating will Benefit from Antenna Voltage Feedback

* **New antenna voltage feedback **  algorithm to reduce RF power **  as voltage on antenna increases *

***This Year Early Solenoid-Free I******P****** Ramp-up Experiments using HHFW Heating will Benefit from Antenna Voltage Feedback***

- IP = 300 kA, k|| = 7 m-1 co-CD
- IP = 250 kA, k|| = 14 m-1 heating

- Time (s)

- 0.6

- 0

* **Need to avoid RF tripping for **  14 m**-1** to get relaxation*

* **14 m**-1** shows robust H-mode*
*   **7 m**-1** does not*

## Magnetic field dependence of RF power loss, PDI ion heating and surface wave propagation & damping

If reversed Bt & Ip campaign, will conduct HHFW experiment to elucidate coupling physics using reversed fields

Effect of Li on HHFW antenna coupling

Non-inductive current ramp up using HHFW

Heat CHI discharges with HHFW

Early HHFW heating to reduce volt-seconds consumption in a long pulse discharge

*If reversed B**t** & I**p** campaign, will conduct HHFW experiment to elucidate coupling physics using reversed fields*
*Effect of Li on HHFW antenna coupling*
*Non-inductive current ramp up using HHFW*
*Heat CHI discharges with HHFW*
*Early HHFW heating to reduce volt-seconds consumption in a long pulse discharge*

***HHFW Experiments in 2006 Continue Exploring Coupling Physics & Application of HHFW to ST’s***

## HHFW Priorities for FY 2007-2008

*** ***
*HHFW applications during current ramp-up phase of discharge:*
*Bridge gap between CHI initiation and NBI heating to high performance*
*Improve understanding and performance of HHFW power coupling to the core plasma:*
*Modify antenna to provide directed spectra at 14 m**-1 **for better CD efficiency (depending on results from FY2006 studies) and for higher power operation*
*HHFW system will support driven CAE mode studies*
*Use improved coupler for HHFW-CD applications*