V. A. Soukhanovskii 1 Acknowledgements: M. G. Bell 2, R. Kaita 2, H. W. Kugel 2, R. Raman 3, A. L. Roquemore 2 1 Lawrence Livermore National Laboratory, Livermore, CA 2 Princeton Plasma Physics Laboratory, Princeton, NJ 3 University of Washington, Seattle, WA NSTX Results Review 23 July 2007 Princeton, NJ H-mode fuelling optimization using supersonic gas jet - XP 742 summary Supported by Office of Science

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ 2 of 10 SGI on NSTX: placement and control elements

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ 3 of 10 SGI head is a densely packed apparatus Shroud: CFC and ATJ graphite Gas valve: Veeco PV-10 piezoelectric type, d throat =0.02”, typical opening time 1-2 ms, driving voltage 150 V Thermocouples in shroud and in gas valve Two magnetic pick-up coils on shroud front surface for B z, B t measurements Three magnetic pick-up coils in shielded box inside shroud for B z, B r and magnetic fluctuations measurement Langmuir probe: flush-mounted design, d tip = 1.75 mm, I-V recorded at 5 kHz, -50 < V < 50 Nozzle: True de Laval geometry, L = 23.4 mm, d throat = 0.01” Can handle 100 PSI (5000 Torr) without change

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ 4 of 10 FY 2007 SGI Upgrades are motivated by fueling results obtained with SGI in  Results from 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  SGI Upgrade program includes: Independent gas handling system (D 2, other gases, e.g. He, CD 4 ) 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, NJ 5 of 10 Both physics and engineering benefits were expected from 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 2 2.Possibly increase penetration 3.Improve fueling scenario flexibility, density control Independent gas handling system Inject other than D 2 gases, such as He, N 2 and CD 4 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, NJ 6 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 T e reduction or I sat increase Magnetic sensors do not show any EM perturbations

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ 7 of 10 Reduced density H-mode plasmas obtained HFS Plenum: 1100 Torr 500 Torr 400 Torr 300 Torr Reduced H-mode density x Peak T e increased from 800 eV to keV Midplane neutral pressure decreased

V. A. Soukhanovskii, NSTX Results Review, 23 July 2007, Princeton, NJ 8 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, NJ 9 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+HFS SGI at 198 cm +HFS LFS+HFS

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