(1)Title

Physics of High Pressure Helicon Plasma

and Effect of Wavenumber Spectrum

Interdisciplinary Graduate School of Engineering Sciences, Kyushu Univeristy, Japan Shunjiro SHINOHARA

Scientific Center Institute for Nuclear Research, Kiev, Ukraine Konstantin SHAMRAI

1. Introduction

� High Density Plasma Source cf. Plasma Application Studies � Study on Helicon Source (Physics)

Critical Issues: Plasma Generation Mechanism & Application Comparison: Experiment & Computation Future Plan: Large & Small Volume Plasmas

2. Experimental Setup + Theory

� Large Diameter Plasma Device � Antenna Structure � Theoretical Model (TG Wave: Mode Conversion)

3. Results

� Good Agreement between Experimental Results and Computed Ones Based on H-TG Model

Antenna Loading , Power Absorption, Wave Structures TE-H Model: Poor Agreement

� Future Plan Small & Large Plasmas

3. Summary

(2)Intro

Introduction � Importance of High Density Plasma Source Plasma Processing, Accelerator, Laser, Confinement Devices

…. � Study on Helicon Source (Physics) e.g., Diameter 5 - 45 cm [1-5], Change of Antenna Spectra [6-9]

� � Critical Issues Plasma Generation Mechanism, Density Jump, Control of

Discharge and Optimization ..... Application �

� Control of Discharge Regime and Wave Structures

Comparison: Experiment & Computation 1) Antenna Spectra (2 Loops, Current Direction) 2) Magnetic Field (0 - 1000 G) 3) RF Input Power (� 3 kW) 4) Pressure (Ar : 6, 51 mTorr) � Antenna Loading & Density Jump, Wave Structures Power Absorption (Bulk & Edge) cf. TG Wave (Mode Conversion) � Future Plan (Large & Small Volume)

References [1] S. Shinohara, Y. Miyauchi and Y. Kawai, Plasma Phys. Control. Fusion 37

(1995) 1015. [2] S. Shinohara, Y. Miyauchi and Y. Kawai, Jpn. J. Appl. Phys. 35 (1996) L731. [3] S. Shinohara, S. Takechi and Y. Kawai, Jpn. J. Appl. Phys. 35 (1996) 4503. [4] S. Shinohara, Jpn. J. Appl. Phys. 36 (1997) 4695. [5] S. Shinohara, S. Takechi, N. Kaneda and Y. Kawai, Plasma Phys. Control.

Fusion 39 (1997) 1479. [6] S. Shinohara, N. Kaneda and Y. Kawai, Thin Solid Films 316 (1998) 139. [7] S. Shinohara and K. Yonekura, Plasma Phys. Control. Fusion 42 (2000) 41. [8] S. Shinohara and K. P. Shamrai, ibid. 42 (2000) 865. [9] K. P. Shamrai and S. Shinohara, Phys. Plasmas 8 (2001) 4659.

Schematic View of Experimental Device

Axial Magnetic Field Coils

To Pump

170 cm

Ar Gas B

Magnetic Probe

80 cm

Magnetic ProbeLangmuir Probe

Loop Antenna

Microwave Interferometer

z0

20 cm

Chamber(Yoko)M

Schematic View of Antenna Structures

(a) Parallel Current (b) Anti-Parallel Current

d = 1 cm

L = 2 cm

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0

kz (cm-1 )

Parallel

Anti-Parallel

Power Spectra of Antenna Wavenumber j (kz)2

(d = 1 cm, L = 2 cm)

AntennaMM

(5)thmodelM.doc

THEORETICAL MODEL H-TG Model cf. Ez = 0 (TE-H Model)

Maxwell Equations c∇×E = iωB

c∇×B = − iωD + 4πiaδ(r − r0)

Boundary and Joining Conditions Et(z = R, L) = 0 { }Et 0rr = = 0, { }Bt 0rr = = 4πia/c

Antenna Current and Fields ia = Σ ik zsinkzz

kz = lzπ/(R−L), lz = 1,2 … lzmax E = Σ (E⊥sinkzz + z Ezcoskzz)

B = Σ (B⊥coskzz + z Bzsinkzz)

Permittivity Tensor K1 = 1 − ωγω

γω2ce

2e

2e

2pe

− −

γω

ω

i2

2pi ,

K2 = )( 2

ce2e

2ce

2pe

ωγωω

ωω

− , K3 = 1 +

)()/(i1)(11

ee2De

2 ξγωνξ

w

w

rk z −−

Collisions and Landau Damping γe,i= 1+i(νe,i/ω), νe= νen+νei , ξ = ωγe/kzvTe

Plasma Load Impedance Zp = − [4π2r0(R−L)/c] Σ |ikz/Ia|2�θ(r = r0)

Plasma Density Profile n (r) = n0 – (n0 – nedge) ( r / r0 )2 _______________________________________________________________________________________

Ref.: K. P. Shamrai, V. P. Pavlenko and V. B. Taranov: Plasma Phys. Control. Fusion 39 (1997) 505. K. P. Shamrai and S. Shinohara: Phys. Plasmas 8 (2001) 4659.

ra

Ia2

za

CFCFm=0 antenna

Double

Rd

b

PlasmaVacuum

Ia1

r0 zL

Fig.1(a,b)(51mT,para/anti,H)M

109

1010

1011

1012

1013

1014 1000 G

650 G500 G300 G

50 G30 G

100 G

(a) Parallel

109

1010

1011

1012

1013

1014

10 100 1000

Pin (W)

1000 G

650 G

500 G 300 G

100 G 50 G30 G

(b) Anti-Parallel

[ Electron Density as a Function of Input Power ]P = 51 mTorr

Lower Wave Number Spectrum Part and/or Lower Magnetic Field is Necessary for Obtaining High Density Plasma with Low RF Power

(Experiment)

2Loop(AP).G4M3m

[ Plasma Density ne as a Function of Pressure P ]

Lower Wavenumber Spectrum Part is Necessary

for Plasma Initiation in Lower Pressure Range

10 10

10 11

10 12

10 13

10 14

0.001 0.01 0.1

P (Torr)

L = 1.5 cm

2 cm

4 cm7.5 cm

15.5 cm

OscillationO (10 12 cm -3 )

L: Distance between Two Loop Antennae with Opposite Current Directions

(8)PoP_colorM(13,18,20) 13

[ Fractions of Total Power Absorbed ] (Calculation)

(a) Under Antenna Region (4 cm

l ), (b) Edge Layer (∆∆r =2 mm),

(c) Edge Layer of Under Antenna Region

Role of TG Wave, Mode Converted from Helicon Wave (Edge, Downstream, High B0)

(9)PoP_colorM(13,18,20) 18

[ Comparison: Measured and Computed Resistances ]

H-TG Model: Good Agreement

(ICP) nedge = 0.5 (PC)

1.0 (AC)

----------------------------- nedge = 0.5 (PC)

1.0 (AC)

nedge = 0.2 (PC)

(10)PoP_colorM(13,18,20) 20

[ Comparison: Measured and Computed B z Profiles ]

H-TG Model: Good Agreement

PAr = 51 mTorr, B0 = 300 G

Before Density Jump After Density Jump

(11)PoP_f11M.doc

[ Power Absorption Profiles (mW/cm3) in log Scale ] PAr = 6 mTorr, ne = 2 × 1012 cm-3, B0 = 100 G, Parallel Currents (1 A each)

(Calculation)

(a) H-TG Model Uniform Plasma

(b) H-TG Model Non-Uniform Plasma (nedge = 0) -----------------

(c) TE-H Model

Uniform Plasma

- 4 0

- 3 0

- 2 0

- 1 0

0

zHc mL0.5

11.5

22.5

rHc mL0

1

- 4 0

- 3 0

- 2 0

- 1 0

0

zHc mL0

1

- 4 0

- 3 0

- 2 0

- 1 0

0

zHc mL0.5

11.5

22.5

rHc mL0

1

- 4 0

- 3 0

- 2 0

- 1 0

0

zHc mL0

1

- 4 0

- 3 0

- 2 0

- 1 0

0

z Hc mL0 . 5

11 . 5

22 . 5

rHc mL- 2

- 1

0

- 4 0

- 3 0

- 2 0

- 1 0

0

z Hc mL- 2

- 1

0

(12)Large Diameter

[ Large Volume Plasma Production by Helicons ]

Sh [ Kyushu Univ. ]

Large Diameter Plasma: 45 cmφφ, 170 cml, 2 kG 3 - 15 MHz, 5 kW, Spiral Antenna (4 Turns, 18 cmφφ)

Cusp, Divergent & Convergent Fields (Uniformity, Wave Studies)

(Present: BaO Discharge) [ Institute of Space & Astronautical Science ]

Device for High Density Plasma Production: 75 cmφφ, 490 cml, 2 kG

Plan: 1.8 - 30 MHz, 1 kW (or more), Spiral Antenna (5 Turns, 22 cmφφ) Production of Target Plasma (Space and Basic Fields), Profile Control Plasma Propulsion (cf. Muses C (Asteroid): 2002~), Wave Studies

------------------------------ cf. UCLA (Wave Studies) ‘LAPD’ by Gekelman (80 cmφφ�1,800 cml )

Large Linear Plasma Device by Stenzel (150 cmφφ�250 cml )

(13)SMALL _M0.doc

[ Small Source ] Initial Data

Single-Loop m = 0 Antenna in the Midplane

Calculation: L = 4 cm; r0 = 2 cm; ra = 2.2 cm; Te = 4 eV; f = 100 MHz (f / fce = 0.36 for B0 = 100 G)

(a) (ICP)

---------------------------------------

(b) (c)

[ Plasma Loading Resistance vs. Plasma Density ]

(14)Concl

Summary Comparison between Experiment and Computation Future Plan: Large and Small Sources

High Pressure (6, 51 mTorr) Antenna Spectra (2 Loops�Same & Opposite Directions)

f = 7 MHz, B = 0 - 1000 G cf. 4 Loops

Mode Conversion (Helicon & TG Waves) Bulk & Edge

(Results� � Good Agreements were found Between Experiment and

Computation Results (H-TG Model) on Antenna Loading, Density Jump and Wave Structures under Various Parameters.

High Pressure, High Field, Opposite Current Directions � High Threshold Power for Density Jump

� With the Increase in the Magnetic Field, Density and Edge Density Ratio, Larger Antenna Loading and Enhanced Edge Absorption (TG Wave, z Direction), and Absorption Spectra with Higher kz Component were Found (Computation).

� Absorption near Antenna Region Increased with Density, but Decreased with the Magnetic Field (Computation).

� Effects of Pressure and Antenna Spectra were also Investigated (Computation).

� The H-TG Model is Better to Explain Obtained Results than the

TE-H Model.

Future Plan

� Studies on Large & Small Diameter Plasmas for Basic and Plasma Propulsion Studies were Discussed Shortly.