# Presentation: 268664

##                                            Supported by   

**R. Raman, B.A. Nelson, D. Mueller, T.R. Jarboe, M.G. Bell et al.,**
**University of Washington**
**Princeton Plasma Physics Laboratory**

**NSTX FY08 Results Review**
**August 6-7, 2008 (PPPL)**

***College W&M***
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***Think Tank, Inc.***
***UC Davis***
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***Culham Sci Ctr***
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***Ioffe Inst***
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***TRINITI***
***KBSI***
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***ASIPP***
***ENEA, Frascati***
***CEA, Cadarache***
***IPP, J******ü******lich***
***IPP, Garching***
***ASCR, Czech Rep***
***U Quebec***

**                                           ****Supported by   **

## Transient CHI: Axisymmetric reconnection leads to formation of closed flux surfaces

***Transient***** CHI: Axisymmetric reconnection leads to formation of closed flux surfaces**

- Demonstration of closed flux current generation
- Aided by gas and EC-Pi injection from below divertor plate region
- Demonstration of coupling to induction (2008)
- Aided by staged capacitor bank capability

## FY08 Result: Proof-of-Principle Demonstration of Coupling a CHI Started Discharge to Induction 

**FY08 Result: Proof-of-Principle Demonstration of Coupling a CHI Started Discharge to Induction **

- 8 Total days: 	2 days – commissioning & conditioning
- 			2 days – Testing without Cryo pumping capability
- 			4 days – Full capability
- March 10: Commissioned new CHI hardware
- 	- Staged capacitor bank operation
- 	- Fast voltage monitoring system
- March 11: Conditioned the lower divertor plates
- 	- Operated in stuffed injector mode
- 	- Conducted first D2GDC (in recent history)
- March 12: First day of main XP
- 	- Inductive discharge development that had reduced CS pre-charge
- 	- Started CHI discharge with some pre-charge in CS
- 	- Reproduced good Te CHI discharges with zero CS pre-charge
- 	- Saw first evidence for coupling to OH (good Te and ne signals)

## CHI Started Discharges after Inductive Coupling Transition into H-mode and are more reproducible with Li Conditioning

- March 31: Inductively coupled discharges reach 180kA and reach Te ~100eV
- April 9: Inductively started discharges reach Ip = 600kA and Te = 500eV
- 	- Used position feedback control to increase current
- June 2,3: Operated without Cryo Pumping and without Boronization
- 	- Vessel base pressure ~10x higher than usual (4 x 10-7 Torr)
- 	- June 2- Tested CHI discharge formation in He & then switched to D2 plasmas, Ip ~400kA in poor reproducibility discharges
- 	- June 3 - First use of Li evaporation for CHI
- 	- Discharges became reproducible and reached Ip ~600kA
- 	- Tested use of HHFW for heating during the coupling phase to induction
- July 8: Used Cryo pumping and 10mg/min Li evaporation
- 	- Central electron temperature reached 1keV
- 	- Ip reached 725kA, discharges transitioned into H-modes
- 	- Discharges with 2min HeGDC + 6min Li were more reproducible than Li-only cases

## March 12: First Evidence of CHI Coupling to Induction

**March 12: First Evidence of CHI Coupling to Induction**

- Final four shots coupled to induction
- Te and ne (from Thomson) showed plasma to be resting on outer vessel during inductive phase
- Later confirmed by EFIT
- On last shot increased vertical field moved plasma further inboard verifying Thomson and EFIT results

## March 31: Demonstrated First Good Coupling of CHI Produced Discharge to Induction (in NSTX)

**March 31: Demonstrated First Good Coupling of CHI Produced Discharge to Induction (in NSTX)**

- Started with Final discharge from March 12
- Used 7.5kJ of capacitor bank energy to initiate CHI discharge
- Used pre-programmed PF coil currents to maintain equilibrium
- Discharges >40ms were ramping up in Ip but vertically unstable

## CHI started discharge couples to induction and transitions to an H-mode demonstrating compatibility with high-performance plasma operation

**CHI started discharge couples to induction and transitions to an H-mode ****demonstrating compatibility with high-performance plasma operation**

- Te & Ne from Thomson
- Ti from CHERS
-  Central Te reaches 800eV
-  Central Ti > 700eV
- Note the broad density
- profile during H-mode phase

- Discharge is under full plasma equilibrium position control
- Loop voltage is preprogrammed

**CHERS:      R. Bell **
**Thomson:  B. LeBlanc**

## Discharges with Li Conditioning are More Reproducible and reach Higher Currents after Inductive Coupling

**Li makes breakdown more reproducible and the improvements are due to reduced recycling (similar to the effect of Ti-gettering on HIT-II)**

## Need auxiliary heating or metal divertor plates to compensate for increased radiated power with more capacitors

**Need auxiliary heating or metal divertor plates to compensate for increased radiated power with more capacitors**

**128400: 5mF (7.6kJ)**
**128401: 10mF (15.3kJ)**
**129402: 15mF (22.8kJ)**

**Plasma Current**

- Low-z impurity radiation increases with more capacitors
- High Te in spheromaks (500eV) obtained with metal electrodes
- Test with partial metal outer divertor plates during FY09
- Reverse TF polarity to make outer vessel cathode
- Upper divertor radiation also increases with more capacitors
- Need to reduce absorber arcs
- Absorber field nulling coils to be used during FY09
- Assess benefits 	of partial metal plates + Absorber coils
- Discharge clean divertor with high current DC power supply
- Use 350kW ECH during FY11

## First Demonstration of  Compatibility of CHI with High-Performance Inductive Operation in a Large ST

**First Demonstration of  Compatibility of CHI with High-Performance Inductive Operation in a Large ST**

**Transient CHI is a proven method to generate closed flux (160kA to date)**
**Startup & inductive coupling at 100kA demonstrated on NSTX & HIT-II**
**CHI initiated and inductively ramped current reached 700kA in H-mode**
**Peak Te ~0.9keV obtained in discharges coupled to induction**
**Need to reduce Low-Z impurity radiation to increase current**
**Electrode conditioning to be improved for FY09**
**Reduce absorber arcs using Absorber PF coils**
**Use outer metal divertor plates needed for Liquid Li system**
**Beyond 2009**
**350kW ECH + higher power HHFW will help considerably**
**Results from metal outer plate tests during 2009 will provide additional data on effect of Low-Z impurities**
**Higher voltage needed to increase startup current**
**Higher TF will increase current multiplication factor**

**Closed flux startup currents of about 500kA is possible in NSTX through hardware improvements (not a physics limitation) **