PERSISTENT SURVEILLANCE FOR PIPELINE PROTECTION AND THREAT INTERDICTION

1. Long term monitoring of DIII-D wall conditions following a boronization W.P. Westa, M. Grothb, A.W. Hyatta, G.L. Jacksona, M.R. Wadea And the DIII-D Team aGeneral Atomics b LLNL Presented at the DSOL ITPA Meeting Toronto November, 2006 PERSISTENT SURVEILLANCE FOR PIPELINE PROTECTION AND THREAT INTERDICTION

2. Motivation: Reduce frequency of boronizations • Each boronization cost manpower and run time • ~ 1 full day of plasma operation required to desorb embedded helium from a fresh BZN film • Several person-days of engineer/technician time required • Long pulse, high duty cycle, superconducting devices not amenable to frequent boronizations • Previous typical plasma-time between BZNs on DIII-D ~ 103 s. • On next generation tokamaks (East, K-Star, ITER) this is the order of a fresh BZN between every (or a few) discharge. • Advent of strong divertor pumping on DIII-D leads to indications that mean time between boronizations might be extended • BZN/3 weeks was like an apple a day • Little or no effects on plasma ops if a BZN was skipped.

3. Tools for evaluating need for BZN • A daily reference shot (DRS) was devised to monitor long term changes in parameters that reflect wall conditions. • Spectroscopy • Impurity influx/content • Zeff, Radiaited Power • Gas Balance Measurements • Fueling • Exhaust • Recycling • Density Rise/Loss • High performance discharges were repeated after a long campaign without BZN. • Fusion Gain (bN*H89/q952) • H89 • Neutron production

4. Daily reference shot (DRS) provides relevant data under consistent operating conditions • Shot taken as first shot each morning • Also serves as a check on beam duct conditioning • High d, LSN shape compatible with most commonly used f-coil patch panels • Not compatible with USN patch panel=>skip those days • Three phases in shot • L-mode during rampup and early flat-top • Slow beam power ramp until an L-H transition is followed by an ELM-free period • Final period of increased beam power to induce ELMing H-mode phase. • A total of 40 usable shots obtained over a 3 month operating period.

5. DRS L-mode database indicates a minor upward trend in core impurities 6800 Plasma-seconds between BZN events • Edge lines indicate no long term trend in influx at midplane • CVI CX and NiXXV lines indicate some upward trend in core impurities • Visible Bremsstrahung and O VIII CX show no long term trend

6. DRS H-mode database shows no clear trend in edge or core impurities • Edge lines indicate no long term trend in influx at midplane • CVI CX and NiXXV lines: possible slight upward trend in core impurities • Visible Bremsstrahung and O VIII CX show no long term trend

7. Advanced tokamak (AT) and hybrid discharges show no degradation in performance across 2006 campaign • High performance hybrid and AT discharges were occasionally repeated throughout campaign. • Discharges repeated just before and after last BZN. • Just before last BZN, seven strongly-pumped hybrid discharges were sequentially repeated without helium glow discharge cleaning between each discharge. • No degradation in performance (H89, G=bNH89/q952, neutron production) was observed. • Hybrid discharges were very repeatable without between shot helium glow.

8. Up to 5800 plasma-seconds since last BZN, AT discharges keep on performing • Shot 126472 taken after 5800 plasma.seconds of operation • 122 major disruptions since BZN on June 10th • Shot 126763 taken after 320 plasma.seconds of operation • Taken after BZN on September 16 • Performance very repeatable

9. AT fusion gain, carbon fraction, and neutron production constant across campaign • These high b AT discharges extrapolate well to the ITER Q=5 steady state scenario • Nickel, a very minor player in contamination, increases with total operation time after BZN

10. Hybrid performance constant over several discharges with no between shot helium glow • These performance levels are typical of hybrid shots throughout the 2006 campaign. • Strong pumping is key to maintaining good graphite wall conditions (R. Maingi, et al., Fusion36, (1996) 245)

11. Discussion: High performance more robust with graphite walls compared to high Z metal walls • Tokamaks with metal walls require routine BZN for high performance • C-MOD with molybdenum walls (Lipschultz, PSI 2006) • AUG with mostly tungsten walls (Neu and Kallenbach, PSI 2006, Hefei) • Both cases routine boronizations are required to reduce high Z contamination and associated high radiated power in attempts to produce high performance discharges. • DIII-D used mostly beam heating, C-Mod mostly RF heating • On C-Mod parasitic effects of RF power used for plasma heating is found to be a source of plasma contamination by Mo. • On AUG, similar effects are seen, yet central RF heating also has been used to reduce W contamination of the core plasma.

12. Conclusions • In DIII-D with an all graphite wall and strong divertor pumping capability, we have demonstrated the ability to reproduce ITER relevant high-performance discharges over 6000 plasma-seconds of operation with no intervening boronizations or bakes. • Over a short period (~ 50 plasma-seconds) the ability to maintain hybrid operation without between shot helium glow discharge cleaning has been demonstrated. • Multi-phase daily reference shots are useful in assessing long term trends in wall outgassing/pumping and wall impurity sources.

13. DRS provides data on wall release of deuterium and impurity line emission • More wall release means less gas input needed to reach programed density • More wall release tends to increase dne/dt in ELM free phase and increase density at first ELM • More wall release tends to increase pumping plenum pressure early in shot

14. DRS wall source indicators shown no strong trend throughout 2006 campaign • Net density rise and peak rate of rise constant across campaign • Caveat: Particle balance may be dominated by large gas input during l-mode phase • ELMing H-mode radiated power and PRAD relatively constant throughout campaign

15. Hybrid performance constant throughout campaign and without between shot glow • bN, H89, and fusion gain maintained over 5800 plasma seconds without BZN • Performance and density maintained over seven sequential shots with no between shot helium glow conditioning

16. Spectroscopic and performance data from many shots used to assess effect of wall conditions • Data from every plasma shot has a lot of scatter • 1600 discharges (8000 plasma-seconds) with a wide variety of operating parameters • Daily reference shot data shows specific long term trends under well controlled conditions • 40 discharges with repeated operating parameters • Reproduction of specific high performance discharges • Advanced tokamak and hybrid discharges with high bN and high H-factor chosen for demonstration. • 3 months, ~1400 discharges, 6800 plasma-seconds between BZNs.