# Presentation: 070035

## XP 825 & 835

***Culham Sci Ctr***
***U St. Andrews***
***York U***
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***U Tokyo***
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***Ioffe Inst***
***RRC Kurchatov Inst***
***TRINITI***
***KBSI***
***KAIST***
***ENEA, Frascati***
***CEA, Cadarache***
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***IPP, Garching***
***ASCR, Czech Rep***
***U Quebec***

***College W&M***
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***New York U***
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***Think Tank, Inc.***
***UC Davis***
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***U Washington***
***U Wisconsin***

**P. M. Ryan (ORNL)**
**for the NSTX Wave-Particle Interaction Team*** *
- NSTX Results Review
- PPPL August 7, 2008

**XP 825 & 835**
**Heating and CD Phase Scans in L-Mode and H-mode Deuterium Plasmas**

## HHFW Operation in 2008

- The HHFW system was in use for 20 days during the run and supported 10 individual XPs.
- There were two full days and three half days of HHFW antenna conditioning with plasma under MP-26 in 2008.
- Plasma conditioning both before and after the introduction of Li.
- Vacuum conditioning in the evenings before extended HHFW operation.
- This conditioning enabled the HHFW system to operate reliably in supporting the NSTX experimental program.
- Two and a half days were devoted to HHFW XPs
- One and a half days to XP825 (HHFW Heating of L-Mode Deuterium Plasmas).
- One day to XP835 (HHFW Heating of H-Mode Deuterium Plasmas)
- Some of the best HHFW results came while providing rf heating support to experiments in the Wave-Particle Interaction and other Topical Science Groups.

## Heated D, He Plasmas to 5 keV with 3.1 MW of k|| = 14 m-1(XP821 - High-k Scattering - Mazzucato)

**Heated D, He Plasmas to 5 keV with 3.1 MW of k****||**** ****= 14 m****-1****(XP821 - High-k Scattering - Mazzucato)**

## XP825 - HHFW Heating/CD Phase Scans in Deuterium L-mode Plasmas

- _Motivation_:
- Determine if the improvements in power coupling in helium plasmas arising from increased field (5.5 kG) and lower edge density operation could be carried over to deuterium plasmas.
- _Objectives_:
- Keep edge density low enough to prevent wave propagation near the wall.
- Determine heating efficiency dependency on wavenumber (inverse wavelength).
- Determine current relaxation time with time-resolved MSE measurements of HHFW driven current (by moving NBI blips in time)
- One day with NBI and no LITER.
- Half day with LITER and no NBI

## NSTX HHFW Antenna Array Toroidal Spectrum Highly Directional For Phase Shifts of ±30o, ±90o and ±150o

- Straps in each loop fixed at 180o out of phase.
- Phase between adjacent loops easily adjusted between 0o to 180o.
- Full 12-element array operation for  = ±30o, ±90o, ±150o.
- Large B pitch affects wave spectrum in plasma core.

**B**

**I****P**

- HHFW antenna extends toroidally 90o

- Power (A.U.)

- -150o

- -90o

- -30o

- Co-CD
- spectra

## Previous Operation in He Showed Heating Efficiency Maintained for ≥ -90o (k ≥ - 8 m-1) at B = 5.5 kG 

**Previous Operation in He Showed Heating Efficiency Maintained for ********≥ -90****o**** (k******** ≥ - 8 m****-1****) at B******** = 5.5 kG **

- Heating efficiency at strap-to-strap antenna phase,  = - 30o approximately half the efficiency at  = - 90o

- B= 5.5 kG, Ip = 0.6 MA

## XP825 - Phase scan showed strong dependence of HHFW heating on k|| in L-mode deuterium plasmas

-   Array phase shift scanned from -180o to -30o, in 30o increments (128657,61-63,65-66)
-   Behavior of electron profiles in D plasmas comparable to results for helium plasmas

- HHFW

- NBI

## k|| Dependence of HHFW Heating Efficiency in D2 Similar to He Plasmas

**Stored energy (total and electron)**

- WEF

- WELEC

- HHFW

- NBI

**Heating efficiency drops for |********| < 60o**

**time = 0.38 s**

## Heating in D Plasma at 3 m-1 Seen After Li Wall Conditioning

- First observation of core heating in D plasmas for k|| = 3 m-1 ( = -30o)
- LITER evaporation rate of 20 mg/mn was used to reduce edge density

- HHFW

- Wmhd

- Te(0)

## XP835 - Heating and CD Phase Scans in NB Deuterium H-mode plasmas

**Motivation:**
- Develop operational techniques for employing HHFW in H-mode plasmas.
- Determine HHFW power channels in H-mode (core electron heating, damping on fast ions, edge plasma heating).
- Observe HHFW operation during ELMs.
**Method:**
- HHFW into NBI-established H-mode
- Advantage of constant plasma load.
- Loading/antenna protection trade-off with plasma gap.
- NBI-triggered H-mode transition during HHFW operation.
- Controllable H-L transition time?
- Reduce load transition with array phasing or plasma gap.
- HHFW-driven H-mode (future work)

## HHFW Heating of NBI-Driven H-mode Plasmas

- XP 413 (2004 - LeBlanc) HHFW was not able to heat core of NBI H-mode plasma
- First evidence of heating NBI H-mode plasmas came during XP829 (Magnetic Shear Effects on Transport - H. Yuh)

## Recently Measured Core HHFW Electron Heating in Deuterium NBI H-Mode Plasma

**Recently Measured Core HHFW Electron Heating in Deuterium NBI H-Mode Plasma**

- Experiments starting to study HHFW coupling into deuterium H-modes

## Core electron heating observed for -150o phasing Lower efficiency for -90o phasing.

**n****e**

**T****e**

**I****p**

**HHFW**

**NB**

**T****e**

**P****e**

**n****e**

- 20 mg/min Li evaporation plus He glow discharge between shots was needed to heat

## Summary of HHFW H-mode operation

- 130313

- 130314

- 130315

- Low plasma loading at large gaps (6-7 cm for -150o and 8-9 cm for -90o) limited power to 2 MW. Strap upgrade for 2009 should help with this.
- Operation at -150o generally ELM-free.
- Operation at -90o frequently had ELMs during the RF.
- ELMs often tripped the RF off. The data obtained during this operation will help with the design of an ELM dump.
- Plasma would go into H-mode before the NBI trigger, tripping the RF due to mismatch on load transition.

- -90o Phasing