V. A. Soukhanovskii1

Acknowledgements: M. G. Bell2, R. Kaita2, H. W. Kugel2, R. Raman3, A. L.

Roquemore2

1 Lawrence Livermore National Laboratory, Livermore, CA2 Princeton Plasma Physics Laboratory, Princeton, NJ

3 University of Washington, Seattle, WA

NSTX Results Review23 July 2007Princeton, NJ

H-mode fuelling optimization using supersonic gas jet - XP 742

summary

Supported byOffice ofScience

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ2 of 10

SGI on NSTX: placement and control elements

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ3 of 10

SGI head is a densely packed apparatus

• Shroud: CFC and ATJ graphite• Gas valve: Veeco PV-10

piezoelectric type, dthroat=0.02”,

typical opening time1-2 ms, driving voltage 150 V• Thermocouples in shroud and in

gas valve• Two magnetic pick-up coils on

shroud front surface for Bz, Bt

measurements• Three magnetic pick-up coils in

shielded box inside shroud for Bz ,

Br and magnetic fluctuations

measurement• Langmuir probe: flush-mounted

design, dtip= 1.75 mm, I-V

recorded at 5 kHz, -50 < V < 50

• Nozzle: True de Laval geometry, L = 23.4 mm, dthroat = 0.01”

• Can handle 100 PSI (5000 Torr) without change

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ4 of 10

FY 2007 SGI Upgrades are motivated by fueling results obtained with SGI in 2004-

2006 Results from 2005-2006 experiments:

Reliable H-mode access and low power threshold (< 2 MW NBI) in SGI-fueled H-mode discharges

Progress has been made in development of SGI-fueled H-mode scenario with reduced (up to 20) high field side fueling rate

SGI-fueled double-null H-mode plasmas demonstrate different ELM character (type III ELMs vs small and type I ELMs)

SGI flow rate < 65 Torr l / s Measured fueling efficiency 0.1 - 0.4

SGI Upgrade program includes:

Independent gas handling system (D2, other gases, e.g. He, CD4)

Increase SGI plenum pressure from 2500 to 5000 Torr Multi-pulse capability» Density feedback with SGI using Plasma Control System

In blue: ready in FY 2007

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ5 of 10

Both physics and engineering benefits were expected from 2006-2007 SGI

upgrades

Improvements implemented in 2007

Derived benefit

Increased plenum pressure to 100 PSIA (5000 Torr) (previously limited to 50 PSIA (2500 Torr))

1. Increase flow rate x 22. Possibly increase

penetration3. Improve fueling scenario

flexibility, density control

Independent gas handling system

Inject other than D2 gases,

such as He, N2 and CD4

Upgrade software to multi-pulse capability

Improve fueling scenario flexibility, density control

Increase plenum volume (SGI reservoir)

Reduce flow rate dependence on pressure drop

Density feedback with SGI using Plasma Control System(future)

Density control with SGI

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ6 of 10

Supersonic gas jet does not perturb plasma edge

Example frames from fast unfiltered camera movies: (a) SGI-U in NSTX vacuum vessel, (b) SGI-U interacting with edge MHD mode, (c) and (d) SGI-U injecting deuterium into 6 MW NBI-heated H-mode plasma

During supersonic gas injection• SGI Langmuir probe does not typically show much Te reduction or Isat increase • Magnetic sensors do not show any EM perturbations

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ7 of 10

Reduced density H-mode plasmas obtained

HFS Plenum:1100 Torr500 Torr400 Torr300 Torr

Reduced H-mode density x 2-2.5 Peak Te increased from 800 eV to 1-1.4 keV Midplane neutral pressure decreased

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ8 of 10

Plasma edge density profiles show clear increase due to high-pressure jet

Reduced HFS flow rate by x 3 (plenum pressure from 1100 Torr to 500 Torr

SGI-U gas jet operated at 5-7 cm from plasma separatrix

Injection pulses result in pedestal density increase, SOL density same

Analysis of 2007 data is in progress to determine fueling efficiency of high-pressure SGI fueling

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ9 of 10

Favorable comparison of SGI and LFS injector obtained

» SGI-fueled shots have higher “flattop” density» However, during gas flow density is higher for LFS gas injector» SGI-deposited particles penetrate deeper? Higher containement time?

SGI+HFSSGI at 198 cm+HFSLFS+HFS

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ10 of 10

• SGI-Upgrade commissioned for plasma operations

High-pressure SGI fueling efficiency high High-pressure SGI pulses do not lead to H-L transitions Most productive is probably use of many short pulses Particles appear to be deposited in (pre)-pedestal region Particle confinement time low, particles are quickly lost from

deposition region

• SGI-fueled reduced density H-mode scenario obtained

Reduced HFS gas flow rate by up to x 3.8 (to ~ 10 Torr l / s (?)) Density decreased by x 2 SGI-fueled H-mode density can be increased to match HFS-

fueled reference shot However, at low HFS fueling and pulsed SGI, dN/dt is still not

zero

XP 742 conclusions