Some Observations on Disruptions in CY 2007 Run
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Transcript of Some Observations on Disruptions in CY 2007 Run
Some Observations on Disruptions in CY 2007 Run
Stefan Gerhardt
1720 Discharges From CY07 In Database
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Halo Currents
Two Pearson CTs on buss work to the “McBride” switch…current from inner to outer vessel
Vertical Motion Flux Difference (EFIT usually bad during quench)
Radiated Power: BolometersPlasma Current: RogowskiEquilibrium: EFIT01
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Not All Shots “Disrupt” (I)
Typical IP Ramp Rate: 107 A/s
Non-Disruptive Shots Well Centered At Start of Ramp-Down
Not All Shots “Disrupt” (II)
Typical IP Ramp Rate: 107 A/s
Halo Currents Reduced for Slower Ramping Shots
Fast Current Quenches (“Disruptions”) Scattered Throughout Campaign or XPs
• Previous Data Includes quench on Ramp-Up, or at very low current.
• Restrict Analysis to:
– Current at Quench > 600 kA
– Time of Quench > 150 msec
Disruptivity:# With Quench Rate >2.5x107
# of Shots in That XP
XPs have Vastly Different “Disruptivity”
704: Ext. Perturb.
738: Lithium Powder
702: RFA Optimization
711: High q brkdwn.
727: Stab. Lim. High IN
742: SGI
728: RWM Stab.729: n=3/n=1
737: Ion Power Balance
723: Mom. Conf.
724: NICD @ high q
708: Div. Ht. Flx. Red.
744: BEAP
746: ELM Characterization
741: BAAE706: Beta Sup. Alfven Casc.
Radiated Power Varies Greatly Among Within and Among XPs
Max Prad=Maximum value of Total Radiated Power.
Prad at Max(Wtherm)= Total Radiated Power at time of maximum stored energy.
High Radiated Power in Many Cases Before
LITER
• LITER XP 719 Began on April 20th
•First Shot ~123469
Max Prad=Maximum value of Total Radiated Power.
Prad at Max(Wtherm)= Total Radiated Power at time of maximum stored energy.
XPs With Highest Radiated Powers
718: Li Pellets
702: RFA Optimization
729: n=1/n=3.
701: n=1 & 3 Error Fields
737: Ion Power Balance
745: ELM Severity and Transport
707: MHD Induced Fast Ion redistribution
Highest Disruptivity Does Not Lead to Highest Radiated Power
max(Prad)=Maximum value of Total Radiated Power in a single shot<…>=Average over all shots in an XP
Caveat: Thermal Quench Could More Relevant
• Current quench (this presentation) is of concern due to forces (eddy currents, halo currents)
• Thermal quench releases the plasma thermal stored energy in ~1msec…often after substantial thermal energy is more slowly lost.
• Poorly diagnosed in NSTX…use Wtherm just before disruption.
<Stored Energy Before Disruption> <Peak Stored Energy>
Conclusions
• Many disruptive XPs related to MHD studies, but not always.
• XPs with highest Prad are not the most disruptive.
• Additional thermal quench info would be more useful than current quench…Important for disruption studies…we need a fast IR camera.
So If it isn’t Disruptions, what else?
• Inner & Outer Gap?
• Confinement (correlation with tau from efit)?
• Consider only Discharge with >3.5 MW NBI at time of Max Stored Energy
Many Other Items Systematically Vary Among XPs