# Presentation: 532243

## OH-Solenoid free plasma startup program plans on NSTX for the Fy 04 to 08 period

- University of Washington, Seattle
**For the NSTX National Team**
**DOE Review of**
**NSTX Five-Year Research Program Proposal**
- June 30 – July 2, 2003

***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***

- NSTX 5yr plan

- Solenoid-free startup

## NSTX has an important focus on solenoid-free plasma startup research

- The development of methods for solenoid-free current initiation will improve the prospects of the ST as a fusion reactor
- Advanced tokamak designs (ARIES-AT and RS) assume no central solenoid
- NSTX is focused on solenoid-free plasma startup research
- NSTX program addresses IPPA goal 3.2.1.4 for the ST which states: *“Characterize the integration of noninductive plasma startup via magnetic reconnection such as using Coaxial Helicity Injection (CHI) with other noninductive and inductive current drive techniques. Investigate a number of noninductive techniques to start and to increase the plasma current in ST plasmas while at the same time minimizing magnetic flux and helicity injection.”*

- NSTX 5yr plan

- Solenoid-free startup

## Goal is to demonstrate in 5yrs solenoid-free plasma startup method(s)

- Dedicated experiments
- Development of theory to analyze the results and extrapolate techniques to future device
- Upgrades to facility capabilities to explore new techniques and to optimize the most promising concepts
- NSTX is pursuing several solenoid-free plasma start-up concepts
- Coaxial Helicity Injection research (CHI)
- Outside PF coil induction
- EBW/HHFW research (described separately)

- Initiate solenoid-free plasma currents, couple to non-inductive CD methods
- and ramp-up to high beta, high bootstrap current fraction discharges

- NSTX 5yr plan

- Solenoid-free startup

## Simple description of CHI start-up

- Expect reconnection processes to redistribute edge
- current to the interior, forming closed flux surfaces

- NSTX 5yr plan

- Solenoid-free startup

## Obtained 390kA with current multiplication of 14 in 330ms long discharges (steady-state CHI)

- Evidence for good *n=1* oscillations deemed necessary for flux closure
- ESC and EFIT reconstructions consistent with but not conclusive of flux closure

- NSTX 5yr plan

- Solenoid-free startup

## Theory status

- MFIT code used in control room
- (M. Schaffer, GA)
- ESC adapted for CHI discharge reconstructions
- (L. Zakharov, PPPL)
- EFIT also adapted for CHI
- (M. Schaffer, L. Lao, GA)
- Work in progress to use TSC
- (S.C. Jardin, PPPL)
- Work initiated on using CHIP (3DMHD) to understand CHI physics
- (X. Tang, LANL)

- NSTX 5yr plan

- Solenoid-free startup

## Joint effort with HIT-II resulted in development of a new CHI startup method (transient CHI)

- CHI started discharges coupled to and improved the performance of inductive discharges
- Saved volt-seconds
- CHI started discharges much more robust and less sensitive to wall conditions
- CHI started discharges produced record plasma currents on HIT-II (265kA)

- NSTX 5yr plan

- Solenoid-free startup

## New revised thinking for CHI research on NSTX

- Decouple plasma startup and steady-state current sustainment objectives
- Use ***transient CHI*** for plasma startup
- Use ***steady-state CHI*** for edge current drive
- 	CHI capability enables edge biasing studies
- Edge current profile modification
- Favorably modify edge SOL flows
- Induce edge rotation

- NSTX 5yr plan

- Solenoid-free startup

## Fy 04-06 CHI Research Plan

- FY04: Transfer transient CHI plasma to the PF system
- Commission new absorber (field nulling requirements)
- FY05: Transfer transient CHI plasma to non-inductive CD system
- Increase current levels produced by  transient CHI
- Reestablish 300kA steady-state discharge
- FY06: Establish transfer of CHI to non-inductive CD system and establish edge current drive
- Investigate SOL effects
- Establish preferred method for startup

- NSTX 5yr plan

- Solenoid-free startup

## Fy 07-08 CHI Research Plan

- FY07: Flux closure studies in steady-state CHI
- Profile measurements using MSE and dynamo probe
- Mechanisms leading to flux closure
- FY08: Use methods developed for volt-seconds savings to help high performance discharges
- Use CHI in conjunction with other CD methods
- Improve performance of fully non-inductive discharges via CD and SOL modifications

- NSTX 5yr plan

- Solenoid-free startup

## Plasma Start-up Using Outer Poloidal Field Coils

**Outer PFs have been used to start-up the plasma:**
- • MAST (START) - poloidal field coils + radial compression
- • JT-60U -  Aggressive application of rf heating and current drive

**Three exciting new approaches for outer PF start-up are explored:***** ***
- # I. Outer PF ramp from near zero flux and current.  Use variety of non-inductive current drive for ramp-up assist (HHFW, NBI, BS, etc. )
- # 2. Approach based on the JT-60U experience.  Strong heating & CD for initiation and ramp-up could relax the Lloyd condition.
- # 3. Error field minimization to satisfy the “Lloyd condition” for plasma start up with strong preionization, ET·BT / BP ≥ 0.12  kV/m achieved while retaining as much flux as possible for subsequent current ramp .

- NSTX 5yr plan

- Solenoid-free startup

## PF-only scenario development for NSTX

- Circuit equation solver
- Coils and conducting structures
- Eddy currents accounted
- No plasma equilibrium
- Plasma modeled by passive coils
- Distribution of “plasma” coils
- Variable resistivity profile in space
- 	but constant in time
- Model selected to reproduce 1MA NSTX plasma (~70eV equivalent Te)

- Analysis by Menard’s LRDIAG

- NSTX 5yr plan

- Solenoid-free startup

## #1. Outer-PF ramp from near zero current/flux

- Higher IP possible with additional current drive:  RF, NBI, BS?
- Initial simulations show core back-EMF – current hole?

- NSTX 5yr plan

- Solenoid-free startup

## # 2.  Different scenarios modeled

-       Outboard X-point                      Scenario 2 (JT-60U-like)

- •   Requires strong plasma source (HHFW/ECH)
- Ip ~ 650 kA may be possible

- Ip = 550 kA may be possible

- NSTX 5yr plan

- Solenoid-free startup

## #3. Creation of high quality field null possibleby energizing the presently unused PF 4

- Flux contours

- Lloyd’s condition, with strong pre-ionization, ET·BT / BP ≥ 0.12  kV/m satisfied in a significant volume

- 20 kA

- - 20 kA

- 2.8 kA

- Analysis by W. Choe: NULLB code

- NSTX 5yr plan

- Solenoid-free startup

## Time-dependent calculation with vacuum vessel eddy currents included

- Coil current

- Flux vs. t (at 1.4 m)

- • Significant V-S is available for current ramp-up.
- • Plasma equilibrium and stability at the time of breakdown needs to be checked carefully.
- • Full ramp-up scenario will require bi-polar PF 5.  But initial breakdown experiment to ~100 kA should be possible with the existing power supplies.

- Loop voltage

- 13%

- NSTX 5yr plan

- Solenoid-free startup

## FY 03-08 plans for plasma startup by PF induction

- NSTX 5yr plan

- Solenoid-free startup

## Non-inductive plasma startup program plan

- NSTX 5yr plan

- Solenoid-free startup

## 5yr plan allows for a demonstration of solenoid-free plasma startup on NSTX

- Transient CHI: simple method demonstrated on HIT-II
- Advantage of non transient PF coil currents
- Steady state CHI: potential to optimize the edge region in sustained non-inductively driven discharges
- Plasma startup using outside PF induction: potential to produce MA level startup currents in large STs
- A test of this concept is planned on NSTX

- NSTX 5yr plan

- Solenoid-free startup

## Demonstration of flux closure in a CHI produced discharge on HIT-II

- Plasma current persists after the injector current has been reduced to zero

- NSTX 5yr plan

- Solenoid-free startup

## Highest ever plasma current on HIT-II (265kA) obtained using CHI start-up

- No transient coil currents
- Discharges initiated & maintained in diverted configuration
- CHI is more tolerant to field errors
- Discharges can be initiated when -VLoop is applied to CHI

- NSTX 5yr plan

- Solenoid-free startup