Physics of High Pressure Helicon Plasma and Effect of Wavenumber Spectrum

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1 (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. 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 ( Loops, Current Direction) ) Magnetic Field ( 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) [] 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) [4] S. Shinohara, Jpn. J. Appl. Phys. 36 (1997) [5] S. Shinohara, S. Takechi, N. Kaneda and Y. Kawai, Plasma Phys. Control. Fusion 39 (1997) [6] S. Shinohara, N. Kaneda and Y. Kawai, Thin Solid Films 316 (1998) 139. [7] S. Shinohara and K. Yonekura, Plasma Phys. Control. Fusion 4 (000) 41. [8] S. Shinohara and K. P. Shamrai, ibid. 4 (000) 865. [9] K. P. Shamrai and S. Shinohara, Phys. Plasmas 8 (001) 4659.

3 Chamber(Yoko)M Microwave Interferometer Loop Antenna To Pump 0 z Ar Gas B Magnetic Probe Magnetic Probe Langmuir Probe 80 cm 0 cm Axial Magnetic Field Coils 170 cm Schematic View of Experimental Device

4 AntennaMM d = 1 cm L = cm (a) Parallel Current (b) Anti-Parallel Current Schematic View of Antenna Structures Parallel Anti-Parallel k z (cm -1 ) Power Spectra of Antenna Wavenumber j (k z ) (d = 1 cm, L = cm)

5 THEORETICAL MODEL H-TG Model cf. E z = 0 (TE-H Model) (5)thmodelM.doc L CF Vacuum Plasma r 0 Double CF m=0 antenna d r a z a R z I a1 I a b Maxwell Equations c E = iωb c B = iωd + 4πi a δ(r r 0 ) Boundary and Joining Conditions E t (z = R, L) = 0 Antenna Current and Fields { } r = = 0, { } Et r0 i a = Σ i k z sink z z Bt r = r0 = 4πi a/c k z = l z π/(r L), l z = 1, l zmax E = Σ (E sink z z + ẑ E z cosk z z) Permittivity Tensor pe e K 1 = 1 ω ω ce K =, K 3 = 1 + ω( ω γ ω ce ) B = Σ (B cosk z z + ẑ B z sink z z) ω ω γ pe e γ e ce ω ω ω pi 1 1 w( ξ) r 1 i( ν e / ωγ ) w( ξ ) Collisions and Landau Damping γ e,i = 1+i(ν e,i /ω), ν e = ν en +ν ei, ξ = ωγ e /k z v Te Plasma Load Impedance Z p = [4π r 0 (R L)/c] Σ i kz /I a θ(r = r 0 ) Plasma Density Profile n (r) = n 0 (n 0 n edge ) ( r / r 0 ) 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 (001) k z De γ e i,

6 Fig.1(a,b)(51mT,para/anti,H)M [ Electron Density as a Function of Input Power ] P = 51 mtorr (Experiment) G (a) Parallel G G 50 G 300 G 500 G 650 G (b) Anti-Parallel 30 G 50 G 100 G 650 G G 300 G 1000 G P in (W) Lower Wave Number Spectrum Part and/or Lower Magnetic Field is Necessary for Obtaining High Density Plasma with Low RF Power

7 Loop(AP).G4M3m [ Plasma Density n e as a Function of Pressure P ] Lower Wavenumber Spectrum Part is Necessary for Plasma Initiation in Lower Pressure Range cm 15.5 cm cm 4 cm L = 1.5 cm Oscillation O (10 1 cm -3 ) P (Torr) L: Distance between Two Loop Antennae with Opposite Current Directions

8 (8)PoP_colorM(13,18,0) 13 [ Fractions of Total Power Absorbed ] (Calculation) (a) Under Antenna Region (4 cm l ), (b) Edge Layer (Dr = mm), (c) Edge Layer of Under Antenna Region Role of TG Wave, Mode Converted from Helicon Wave (Edge, Downstream, High B 0 )

9 (9)PoP_colorM(13,18,0) 18 [ Comparison: Measured and Computed Resistances ] H-TG Model: Good Agreement (ICP) n edge = 0.5 (PC) 1.0 (AC) n edge = 0.5 (PC) 1.0 (AC) n edge = 0. (PC)

10 (10)PoP_colorM(13,18,0) 0 [ Comparison: Measured and Computed B z Profiles ] H-TG Model: Good Agreement P Ar = 51 mtorr, B 0 = 300 G Before Density Jump After Density Jump

11 (11)PoP_f11M.doc [ Power Absorption Profiles (mw/cm 3 ) in log Scale ] P Ar = 6 mtorr, n e = 10 1 cm -3, B 0 = 100 G, Parallel Currents (1 A each) (Calculation) (a) H-TG Model Uniform Plasma rhcml zhcml (b) 1 H-TG Model Non-Uniform Plasma (n edge = 0) rhcml zhcml (c) 0 TE-H Model Uniform Plasma rhcml zhcml

(1)Large Diameter [ Large Volume Plasma Production by Helicons ] Sh [ Kyushu Univ.

cm f ) Cusp, Divergent & Convergent Fields (Uniformity, Wave Studies) (Present: BaO

Production: 75 cm f, 490 cm l, kg Plan: 1.

12 (1)Large Diameter [ Large Volume Plasma Production by Helicons ] Sh [ Kyushu Univ. ] Large Diameter Plasma: 45 cm f, 170 cm l, kg 3-15 MHz, 5 kw, Spiral Antenna (4 Turns, 18 cm f ) Cusp, Divergent & Convergent Fields (Uniformity, Wave Studies) (Present: BaO Discharge) [ Institute of Space & Astronautical Science ] Device for High Density Plasma Production: 75 cm f, 490 cm l, kg Plan: MHz, 1 kw (or more), Spiral Antenna (5 Turns, cm f ) Production of Target Plasma (Space and Basic Fields), Profile Control Plasma Propulsion (cf. Muses C (Asteroid): 00~), Wave Studies cf. UCLA (Wave Studies) LAPD by Gekelman (80 cm f 1,800 cm l ) Large Linear Plasma Device by Stenzel (150 cm f 50 cm l )

13 (13)SMALL _M0.doc [ Small Source ] Initial Data Single-Loop m = 0 Antenna in the Midplane Calculation: L = 4 cm; r 0 = cm; r a =. cm; T e = 4 ev; f = 100 MHz (f / f ce = 0.36 for B 0 = 100 G) (a) (ICP) (b) (c) [ Plasma Loading Resistance vs. Plasma Density ]

14 (14)Concl Summary Comparison between Experiment and Computation Future Plan: Large and Small Sources High Pressure (6, 51 mtorr) Antenna Spectra ( LoopsSame & Opposite Directions) f = 7 MHz, B = 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 k z 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.

The low-field density peak in helicon discharges

The low-field density peak in helicon discharges PHYSICS OF PLASMAS VOLUME 10, NUMBER 6 JUNE 2003 Francis F. Chen a) Electrical Engineering Department, University of California, Los Angeles, Los Angeles, California 90095-1597 Received 10 December 2002;