# Presentation: 578320

## Solenoid-free inductive start-up with an outboard field-null and HHFW

***Columbia U***
***Comp-X***
***General Atomics***
***INEL***
***Johns Hopkins U***
***LANL***
***LLNL***
***Lodestar***
***MIT***
***Nova Photonics***
***NYU***
***ORNL***
***PPPL***
***PSI***
***SNL***
***UC Davis***
***UC Irvine***
***UCLA***
***UCSD***
***U Maryland***
***U New Mexico***
***U Rochester***
***U Washington***
***U Wisconsin***
***Culham Sci Ctr***
***Hiroshima U***
***HIST***
***Kyushu Tokai U***
***Niigata U***
***Tsukuba U***
***U Tokyo***
***Ioffe Inst***
***TRINITI***
***KBSI***
***KAIST***
***ENEA, Frascati***
***CEA, Cadarache***
***IPP, J******ü******lich***
***IPP, Garching***
***U Quebec***

**J. Menard, M. Ono (PPPL)**
**W. Choe (KAIST)**
**Y. Takase (U Tokyo)**
**O. Mitarai (****Kyushu Tokai U)**
**NSTX XP Review**
**Princeton Plasma Physics Laboratory**
**Princeton, NJ****February 11, 2005**

## Solenoid-free tokamak formation in NSTX

- Pre-ionize plasma near RF antenna with ECH + 400kW HHFW, nD2 = 1-210-5 Torr
- Create high-quality field-null with 5-15 loop-volts at antenna	- So far, *require E****B****/B**P** > 0.1kV/m* *over substantial plasma volume*
- Have created 20kA plasmas that terminate near center-stack

## Thomson measurements consistent with plasma motion and peaked pe profiles

- Thomson Te < 35eV and camera images consistent with lack of burn-through 
**need more plasma heating power:**
- More HHFW power during breakdown
- Higher VLOOP – keep plasma outboard
- EBW power could be very helpful

## Camera images and reconstructions show plasmas are born on LFS and have an inward radial trajectory

- LRDFIT code used for reconstructions
- IVessel  10  IP
- Careful control of BZ after breakdown helped raise IP from 10kA to 20kA
- More BZ evolution optimization possible

- 114405

## PF coil programming changes to be tested:

- Decrease PF3 after t=0
- Elongates plasma and reduces dBz/dR  enhanced radial stability
- Modest reduction in VLOOP
- If radial position evolution improves, increase PF5 ramp-rate after t=3ms
- Assess trade-off between higher VLOOP and larger BZ
- Increase PF2 after t=0
- Maintains reduced dBz/dR profile while further increasing elongation and BZ

## Shot Plan for 1.5 days

**First run day**
- Reproduce shot 114405 which achieved 20kA plasma current                  **(4 shots)**
- Decrease PF3 current after t=-3ms to reduce dBZ/dR and increase        **(8 shots) **
- For discharge with highest current and longest period near antenna, increase HHFW power incrementally to measure plasma response to higher PRF    **(8 shots)**
- XMP to commission higher-power HHFW pre-ionization is a prerequisite
- Try 750kW, 1MW, 1.25MW, 1.5MW
- Scan VF ramp-rate following improved position control heating.                **(6 shots)**
- Assess impact of higher elongation by adding PF2 current ramp               **(4 shots)**
**Second 1⁄2 run day**
- Study the field null quality requirements for successful breakdown**          (15 shots)**
- 	Start from most successful (highest IP) discharge achieved above:
- Scan TF in 0.25kG decrements below 3kG until plasma initiation fails
- Increase DC PF2U and 2L currents in 0.5kA increments until plasma initiation fails