Merging Start-up and Sustainment Experiments on UTST

15th Intl. Workshop on Spherical Tori 2009, Madison, WI, Oct. 22, 2009

T. Yamada1, R. Imazawa2, S. Kamio1, R. Hihara1, K. Abe1,M. Sakumura1, Q. H. Cao1, H. Sakakita3, H. Koguchi3, S. Kiyama3,

Y. Hirano3, T. Oosako1, H. Kobayashi1, T. Wakatsuki4, B. I. An4,Y. Nagashima1, M. Inomoto1, A. Ejiri1, Y. Takase1 and Y. Ono1

1Graduate School of Frontier Sciences, The University of Tokyo2Graduate School of Engineering, The University of Tokyo

3National Institute of Advanced Industrial Science and Technology4Graduate School of Science, The University of Tokyo

Outline

• Overview of the UTST experiment• Recent progress of the UTST experiment

290-ch. simultaneous measurement PF + Acceleration coils Neutral Beam Injection

• Summary

Overview of the UTST experiment

Objective of the UTST Plasma

UTST (Kashiwa campus)

(Hongo campus)

TST-2 (Takase-Ejiri Lab.)

RF heatingtechnique

Mergingtechnique

NB injectionfrom AIST

Generating a High ST By magnetic reconnection, the magnetic field energy is converted to the plasma kinetic energy, and the plasma is increased up to 50%.

Two Merging STs

Double Null Merging (DNM) Method

At UTST, DNM start-up is performed by outer PF coils.

Null-points formedPF

Ion heating byMagneticReconnection

PF coils generate plasmas

High ST

Merging

The UTST Plasma Merging Device

2 m

0.7 m

ACC2 (4 turns)

EF2 (8 turns)

PF3 (3 turns)

ACC1 (4 turns)

PF1 (8 turns)

Washer gun(for pre-ionization)

PF2 (3 turns)

EF1 (8 turns)

CS (95 turns)

TF (8 turns)

Pickup coil array Bt: 64 channels Bz: 64 channels

PF4 (8 turns)

Pickup coil array Bt: 81 channels Bz: 81 channels

Typical Discharge of the UTST Plasma

Gas (H2) AnodeCathode

Plasma

WashersInsulator

Washer gun is used for pre-ionization.

Two main discharge scenarios.

a. DNM start-up discharge (PF).

b. DNM start-up + CS assist discharge (PF + CS).

Seed plasma in a spiral magnetic field.

TF (/turn) EF (/turn)

Washer gun

PF (/turn)

Plasma current (CW)

a. PF discharge

Plasma current up to 40 kA was obtained by DNM method, by using PF coils.

b. PF+CS discharge

TF (/turn) EF (/turn)

Washer gun

PF (/turn)

Plasma current (CW)

CS (/turn)

curr

ent[

kA]

Plasma current reached 170 kA by using the CS coil to assist the DNM start-up (PF) discharge.

Recent progress of the UTST experiment

1. Two-dimensional Pickup Coil Arrays

Glass tube

drrBz2

zrBr

2

1

Bj 0

1

dt

d

rEt

2

1

BjP

By using Bt and Bz pickup coil arrays, many variables can be calculated.

An Example of poloidal flux, , produced by EF coils, measured by the pickup coils.

Pickup coil array Bt: 64 chs. Bz: 64 chs.

Pickup coil array Bt: 81 chs. Bz: 81 chs.

Expansion of the digitizer made it possible to measure all the 290 channels simultaneously.

Improvement of the measurement

z

t

z

t

B

B

B

B~

~

cossin

sincos

cos

1

Bz and Bt are reconstructed by

Precision of Bz and Bt measurement has been improved.

and are measured by generating toroidal or vertical magnetic fields.

Good agreement between Bz with Bt and Bz w/o Bt.

a. Results on PF discharge

Fast camera images

Two STs are merged together to form a single ST

(Movies)

b. Results on PF + CS discharge

4.70 ms 4.71 ms 4.72 ms 4.73 ms 4.74 ms

Fast camera images

The merged plasma reached up to 170 kA.

(Movies)

To be reported in APS DPP, PP8.00099 (Atlanta, GA).

2. PF discharge + Acceleration coils

ACC2

ACC1

By using acceleration coils on PF discharge, current sheet was observed.

Acceleration coils increase the plasma merging speed.

Current sheet ?!

PF + CS + ACC is under preparation.

3. Neutral Beam Injection

160 mm

NB's acceleration electrode(concave type, F = 1250 mm)

UTST

NB

A general view of the experiment device

Neutralizationchamber

Jointed to UTSTIon source

10 ms500 kW

Neutral beam power

Neutral Beam Injection

focus

NBUTST

Top view of NB and UTST

Fast camera imagePlasma current

Test of the neutral beam device and test injection into the UTST device have been finished.

Higher density will be required for effective results.

• Plasma startup by double null merging method was successfully observed in the UTST plasma merging experiment. Plasma current up to 40 kA was achieved, and the merging of magnetic surfaces was observed.

• With CS assist, plasma current reached 170 kA.

• By using Acceleration coils, current sheet was observed.

• Neutral beam injection has just started.

Summary

• Pre-ionization at the upper region is needed for balancing STs.

• Power supplies to the coils will be increased.

• More diagnostics.

Future Works