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