# Presentation: 501585

## Electron Bernstein Wave Physics on NSTX

**Electron Bernstein Wave Physics on NSTX**

_**G. Taylor**_**, J.B. Caughman, M.D. Carter, S. Diem, **
**P.C. Efthimion, R.W. Harvey, J. Preinhaelter, **
**J.B. Wilgen, A. Bers, T.S. Bigelow, J. Decker,**
**R.A. Ellis, N.M. Ershov, E. Fredd, J. Hosea, **
**F. Jaeger, A.K. Ram, D.A. Rasmussen, **
**A.P. Smirnov, J. Urban, J.R. Wilson**
**47****th**** APS – DPP Meeting**
- Oct 24-28, 2005
- Denver, Co.

***Culham Sci Ctr***
***U St. Andrews***
***York U***
***Chubu U***
***Fukui U***
***Hiroshima U***
***Hyogo U***
***Kyoto U***
***Kyushu U***
***Kyushu Tokai U***
***NIFS***
***Niigata U***
***U Tokyo***
***JAERI***
***Hebrew U***
***Ioffe Inst***
***RRC Kurchatov Inst***
***TRINITI***
***KBSI***
***KAIST***
***ENEA, Frascati***
***CEA, Cadarache***
***IPP, J******ü******lich***
***IPP, Garching***
***ASCR, Czech Rep***
***U Quebec***

***College W&M***
***Colorado Sch Mines***
***Columbia U***
***Comp-X***
***General Atomics***
***INEL***
***Johns Hopkins U***
***LANL***
***LLNL***
***Lodestar***
***MIT***
***Nova Photonics***
***New York U***
***Old Dominion U***
***ORNL***
***PPPL***
***PSI***
***Princeton U***
***SNL***
***Think Tank, Inc.***
***UC Davis***
***UC Irvine***
***UCLA***
***UCSD***
***U Colorado***
***U Maryland***
***U Rochester***
***U Washington***
***U Wisconsin***

## EBWCD Can Stabilize and Sustain Non-Inductive High  Spherical Torus (ST) Plasmas

***EBWCD Can Stabilize and Sustain Non-Inductive ******High ************ Spherical Torus (ST) Plasmas***

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

-  *Large trapped particle fraction on low field side of STs enables efficient *
*  **off-axis Ohkawa EBWCD for 14-28 GHz EBWs *

- NSTX,  ~ 40%, Bt(0) = 3.5 kG

*CQL3D/GENRAY*

- Total

- Bootstrap

- NBCD

- J//
- (A/Wb)

- 0

- 106

- 0

- 1

- 0.5

*C. Kessel, Invited Talk UI2.00004, Fri AM*

- RFCD

***T****okamak *
***S****imulation *
***C****ode*

-  *Need resilient coupling to EBWs *

- NSTX
- Bt(0) = 3.5 kG

-  *Need ~100 kA of I**p **driven by RF between ****= 0.4 & ****= 0.8 *

*G. Taylor, et al., Phys. Plasmas 11, 4733 (2004)*
*A.K. Ram, Invited Talk QI1.00001, Thurs AM*

- Parallel
- Current
- Density
- (arb. Units)

- Current
- Density
- (A/cm2)

- 

## Measured 24-32 GHz EBW Emission this Yearto Assess EBW Coupling Efficiency

*J. Caughman**, Poster RP1.00039 Thurs PM*

***Measured 24-32 GHz EBW Emission this Year******to Assess EBW Coupling Efficiency***

-  *AORSA-1D full wave code predicts efficient EBW coupling at ~ 28 GHz *
*  **into** **** **~ 40% NSTX plasmas via oblique O-X-B launch (n**//** ~ ± 0.5) *
* **EBW coupling efficiency sensitive to edge conditions; EBW emission *
*  **studies can assess EBW coupling efficiency:*
*	**- cannot test parametric decay or ponderomotive effects** *

*M. Carter*
*ORNL*

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

**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 

## Measured 80% EBW Coupling at 16-18 GHz via B-X-O Coupling Last Year, 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 

## Evolution of Measured 24-32 GHz EBW Emission Similar to Simulation, but Trad ~ 2-4 Times Smaller

**Notes:**
A normally viewing X-mode , with radially adjustable carbon limiters, has been installed in NSTX. 

This antenna has been designed to achieve > 80% EBW coupling. A similar antenna design achieved almost 100% EBW coupling on CDX-U
Two years ago

An obliquely viewing , X-mode antenna, with stepped boron nitride wedge, has also been installed between the straps of the HHFW antenna on NSTX

We are also planning to install an obliquely viewing, quad-ridged, antenna viewing the plasma through a vacuum window, to study the polarization of the oblique EBW emission

## Measured Trad at 25 GHz Comes from Both 2fce Near Axis, & 3fce Off-axis; Harmonic Mix Sensitive to EBW n//

***Measured T******rad****** at 25 GHz Comes from Both 2f******ce ******Near Axis, ******& 3f******ce ******Off-axis; Harmonic Mix Sensitive to EBW n******//***

* **Radial access between*
*  **2f**ce** & 3f**ce** sensitive to*
*  **EBW n**//** due to EC  *
*  **resonance Doppler*
*  **broadening*

*J. Preinhaelter** Poster RP1.00038 Thurs PM*

- EBW Ray Tracing

**Notes:**
A normally viewing X-mode , with radially adjustable carbon limiters, has been installed in NSTX. 

This antenna has been designed to achieve > 80% EBW coupling. A similar antenna design achieved almost 100% EBW coupling on CDX-U
Two years ago

An obliquely viewing , X-mode antenna, with stepped boron nitride wedge, has also been installed between the straps of the HHFW antenna on NSTX

We are also planning to install an obliquely viewing, quad-ridged, antenna viewing the plasma through a vacuum window, to study the polarization of the oblique EBW emission

## Collisional Loss at Upper Hybrid Resonance (UHR) May Explain Low Measured EBW Trad

*T**e** ~ 10 - 30 eV near UHR*
* **Collisional losses can be *
*  **significant for T**e **< 30 eV*
* **EBW conversion efficiency *
*  **sensitive to Z**eff** at low T**e*
* **Large uncertainty in Thomson*
*  **scattering T**e** near UHR:*
*      **- few **data points available *
*         **near UHR for simulation*
* **Measured emission polarization *
*  **consistent with simulation*

- Measured Trad
- Simulated Trad with Zeff = 0 at UHR
- Simulated Trad with Zeff = 3 at UHR
- Simulated Trad with Zeff = 5 at UHR

- Shot = 117970
- Frequency = 25 GHz

- Measured
- Emission
- Polarization
- (Epara/Eperp)

- Trad(keV)

- Polarization
- From
- Simulation

- 1000

- Time (s)

**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 

## Off-Axis RF CD Critical to Sustained High  ST Operation 

*  **EBWCD efficiently generates** **needed** **off-axis current*
*  **Efficient EBW coupling predicted via oblique O-mode launch*
*  **EBW **emission used to test coupling predictions on NSTX*
*  **Radial access between 2f**ce **& 3f**ce **sensitive** **to EBW n**//  **spectrum*
*  **When T**e **< 30 ev at UHR collisional losses may reduce EBW *
*   **coupling efficiency:*
*	**- more significant issue for coupling between f**ce** & 2f**ce*

**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

## Future Work

-  *Remotely-steered 8-18 GHz & 18-40 GHz B-X-O antennas being*
*  **installed on NSTX for next run campaign*
* **Detailed study of EBW B-X-O coupling in L-mode & H-mode*
* **Integrate GENRAY/CQL3D EBW modeling into TRANSP & evaluate *
*  **effect of transport on EBWCD*
* **EBWCD benchmarking between **GENRAY/CQL3D **& BANDIT *
*  **(Culham, UK) began earlier this year for **** = 40% NSTX plasma :*
*	**- BANDIT & GENRAY predict **Ohkawa EBWCD at r/a ~ 0.7*
*	**- **BANDIT: 26 kA/MW  *
*	**- GENRAY/CQL3D: 37 kA/MW *
*	**- Further work needed to refine benchmarking*

**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