Research on High-Beta Plasmas
Based on Two-Fluids Relaxation Theory

OGAWA Yuichi
High Temperature Plasma Center, The University of Tokyoe-mail: ogawa@plasma.q.t.u-tokyo.ac.jp

andHIMURA Haruhiko1), HIROTA Makoto1), HORI Dan1), ITOH Atsushi2),
KONDOH Shigeo1), MORIKAWA Junji, NAKASHIMA Chihiro2),
NIHEI Hitoshi2),NUMATA Ryusuke1), OHHASHI Manabu1),
OHKUNI Kohtaro, OHSAKI Shuichi1), SAITOH Haruhiko1),
SHATASHVILI Nana, VOLPONI Francesco1), WAKABAYASHI Hidenori1)
and YOSHIDA Zensho1)
High Temperature Plasma Center, The University of Tokyo,1) School of Frontier Sciences, The University of Tokyo2) School of Engineering, The University of Tokyo

Acknowledge for Profs. T. Mito and Yanagi in NIFS

Exploration of new relaxation states
for high beta plasmas

ULQ

REPUTE‑1
Taylor State
・Current (electron fluid)
・Low(zero) beta plasmas

High β

Proto‑RT

S‑RT

MahajanーYoshida theory
・Two fluids (electron & ion)・Ultra high beta plasmas

Concept for Confining a New High Beta Plasma@ Internal Ring Device* toroidal flow velocity : Vt = Er/Bp(Er ~ const. , Bp ~1/r )@ Non-neutralized Plasma* Injection of electrons through separatrix* Orbit loss of high energy electrons

VtOrbit loss
ErBp
Injection ofElectrons

１―
Bp〜ｒ

ExB

Vt＝ ――2Bβ Value
V2+ β =const.
RadiusA Bird’s-eye view of an internal coil device
with an superconductor floating coil
( Superconductor Ring Trap : S-RT)

Basic research for fusion plasmas− with internal ring devices −Multipole
LevitronSpherator

Confinement
Min-B
Magnetic shear

Contemporary Research
Relaxation physics in fusion plasmas(high beta configurations)●Two-fluids (electron and ion) relaxation(ref. S.M. Mahajan and Z. Yoshida, Phys. Rev. Lett., 81 (1998) 4863.)

ーー＞S-RT(Superconducting-Ring Trap)：the Univ. of Tokyo●Kinetic relaxation under µ and J conservation(ref. A. Hasegawa, et al., Nucl. Fusion, 30 (1990) 2405.)−−＞LDX（Levitated Dipole Experiment)：MIT/Columbia

Research on Two-fluid Relaxation
With an Internal Ring Device,
exploring a new high beta plasma

S-RT
・ PoP Experiment
・ Floating Ring Coil・ Rc=40cm,Ic=500kAT
・ (Proposal)

1600

Mini-RT

Proto-RT

1200

・ Normal conductor Coil・ Rc=30cm,Ic=10kAT・Operating for high beta study

・High Tc Floating Coil・Rc=15cm,Ic=50kAT・Under Construction

FB-RT・ Feedback Study
・ High Tc coil・ Rc=4cm,Ic=2.6kATExpected Plasma Parameters in the S-RT Device@ Radial Electric Field Err r
E×B
VP =B22Vp   + β = const.
VA ∴ Er (V / m) =andB2µ 0ni miβ

@ Plasma non-neutralityr e ∆n∇⋅E =ε0∴ ∆n =ε0 Ee a

@ Plasma parameters
β(%)
100 %
100 %
10 %Density
Temperaturen = 1018 m-3
T = 12 keVn = 1019 m-3
T = 1.2 keVn = 1018 m-3
T = 1.2 keV

RadialElectric Field : ErNon-neutrality∆n/n

220 kV/m

2.4X 10-5

69 kV/m

0.08X 10-5

69 kV/m

0.76X 10-5

( at Bp = 0.1 T and a = 0.5 m )@ Energy confinement timerequired for above-mentioned plasma parameters

P=Wp
τE∴ τ E = 120 m sec

at

β = 100%,

P = 100kWCharacteristics of Mini-RT
High Tc Superconductor (HTS) Floating Coil

Advantages
High operation temperature：20 K - 40 K
High heat capacity yields a long time
operationNo liquid helium : small refrigerator, easymaintenanceDisadvantages
Critical current density is not so large.
Decay of permanent current due to a flow
resistance

Persistent Current Switch (PCS) by HTS
No induction coilCurrent lead with less heat input

Removable current lead
Removable transfer tube

Specification of a floating coil
62

R150

Coil casing
HTS coil

Radiation
PCS Shield

Current lead
Transfer tube

Major/minor radii

150 mm / 28 mm

Total coil current

50 kA

HTS tape

BSCCO-2223

Operation current

115 A

Operation temperature

20 K – 40 K

Critical current, 77K s. f.

108 A

Stored energy

600 JInductance0.09 H

Max. magnetic field

Bx:0.57 T,
By:0.75 T

Total weight20 kg

Current decay time

174hr (20 K)

Fabrication of the HTS coil for the Mini-RT device

Winding of the HTS coil
Ag-sheathed Bi-2223 tape
( 4.3 mm × 0.26 mm)I(coil) = 117 A
I(total) = 50 kAturns

Persistent Current Switch
Ag-sheathed Bi-2223 tapewith 0.3wt% Mn
RΩ(turn off) = 0.27 Ω

the Floating Coil(mock-up)
R = 15 cm
Weight = 20 kg

Development of the Persistent Current Switch (PCS)_____________________________________________
Cable Type
Cable Width / Thickness
Silver Ratio
Winding Method
Cable Length
Critical Current (77K, self-field)
Turn-off ResistanceHeater(Ag-0.3wt%Mn sheathed) Bi-2223
3.8 / 0.26 mm
1.9Bifilar
21.24 m53 A
0.27 Ω
φ0.5 mm Manganin

10

Voltage (mV)

1

TPCS = 77 K (LN2 cooled)I c (1 µV/cm) = 69.4 A

Voltage vs. current curve measured
for the HTS-PCS cooled by liquid
nitrogen. Two curves determinedby the n-value of 12 and 15 areindicated by dashed lines.

0.10.01n = 120.001
n = 150.0001
10100Current (A)Critical Current (A)500
400PCS (bifilar winding)

Dependence of the measured
critical current on the PCStemperature. Critical current for astraight sample is deduced for thepresent conductor based on theempirical scaling.

300
200
100010Straight Cable Data

2030

40

5060

Temperature (K)7080

Levitation Experiment of HTS coil

Laser & Detector

Levitation of a HTS coil
(The coil position is artificially changed, so as to examine
the dynamic response of the HTS coil.
The levitation more than 4 minutes has been demonstrated .)(a)Experimental Data
100-10050

100150200250300

Time(s)

0.4

0.2

0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Time(s)(b)Calculation Result
0.4

0.2

0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Time(s)Summary@ A new relaxation state based on two-fluids plasma theory
has been proposed by Mahajan-Yoshida, and a possibility
for confining high-beta plasmas has been pointed out.
@ To explore this new relaxation state experimentally, atoroidal device with an internal coil is suitable, where thestrong plasma flow in the toroidal direction is induced by E×B drift by introducing a radial electric field. Since theE × B flow velocity increases as the minor radius isincreased, the high-beta plasma could be confined at thecore region.
@ A torus device with a floating superconductor coil, called
S-RT, is proposed, and the engineering design andexpected plasma parameters are discussed.
@ A device with a normal conductor, called Proto-RT, hasbeen constructed, and the build-up of plasma potential up
to ~ 1 keV has been achieved.
@ A small-scale torus device with a high temperature
superconductor (HTS) coil, called Mini-RT, are underconstruction. This is a first challenge to explore afeasibility of HTS coils for fusion plasma devices.
@ Persistent Current Switch (PCS) with the HTS tape has
been developed for the Mini-RT device. A miniature
HTS coil have been successfully levitated within an
accuracy of 20~30 micrometers.