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Plasma and fusion science : from fundamental research to technological applications / edited by B. Raneesh, PhD, Nandakumar Kalarikkal, PhD, Jemy James and Anju K. Nair.
Includes bibliographical references and index.
Issued in print and electronic formats.
ISBN 978-1-77188-453-2 (hardcover).--ISBN 978-1-315-36594-7 (PDF) 1. Plasma (Ionized gases). 2. Nuclear fusion. 3. Controlled fusion. I. Raneesh, B., editor II. Kalarikkal, Nandakumar, editor III. James, Jemy, editor, IV. Nair, Anju K., editor
Title: Plasma and fusion science : from fundamental research to technological applications / editors, B. Raneesh, PhD, Nandakumar Kalarikkal, PhD, Jemy James and Anju K. Nair
Description: Oakville, ON ; Waretown, NJ : Apple Academic Press, [2017] | Includes bibliographical references and index.
Identifiers: LCCN 2017027546 (print) | LCCN 2017030738 (ebook) | ISBN 781315365947 (ebook) | ISBN 9781771884532 (hardcover : alk. paper) | ISBN 1771884533 (hardcover : alk. paper) | ISBN 1315365944 (eBook)
LC record available at https://lccn.loc.gov/2017027546
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1. Plasma Treatment of Powder and Granulates......................................... 3
Petr Špatenka, Taťana Vacková, and Zdeňka Jeníková
2. Plasma Dynamical Devices: Review of Fundamental Results and Applications ....................................................................................... 17
Alexey Goncharov
3. Conceptual Design of a Permanent Ring Magnet-Based Helicon Plasma Source ............................................................................ 31
Arun Pandey, Dass Sudhir, M. Bandyopadhyay, and A. Chakraborty
4. Solitary Wave Solutions of Modified Kadomstev-Petviashivili
Equation for Hot Adiabatic Dusty Plasma Having Non-Thermal Ions with Trapped Electrons ........................................... 47
Apul Narayan Dev, Rajesh Subedi, and Jnanjyoti Sarma
5. Global Transition from Drift Wave Dominated Regimes to Multi-Instability Plasma Dynamics and Simultaneous Formation of a Radial Transport Barrier .............................................. 67
Saikat Chakraborty Thakur, Christian Brandt, and George R. Tynan
6. Magnetic Drift and Its Effect on Cross-Field Diffusion Process .......... 93
P. Hazarika, B. K. Das, M. Chakraborty, and M. Bandyopadhyay
7. On the Effect of Base Pressure upon Plasma Containment ............... 109
G. Sahoo, R. Paikaray, S. Samantaray, P. S. Das, J. Ghosh, and A. Sanyasi
8. Ion-Acoustic Dressed Solitons in Electron-Positron-Ion Plasma with Nonisothermal Electrons ................................................. 123
Parveen Bala and Tarsem Singh Gill
9. Arbitrary Amplitude Kinetic Alfvén Solitary Waves in a Plasma with Two-Electron Temperatures ............................................ 143
Latika Kalita
10. Nonlinear Dust Kinetic Alfvén Waves in a Dust–Ion Plasma with Ions Following q-Non-Extensive Velocity Distribution .............. 159
M. K. Ahmed and O. P. Sah
11. Study Generation of Pulsed High Current with Aluminum Electrolytic Capacitor ............................................................................ 177
Pankaj Deb and Anurag Shyam
12. Effect of Radio Frequency Power on Magnetron Sputtered TiO2 Thin Films ............................................................................................... 185
R. Satheesh, S. Sankar, and K. G. Gopchandran
PART II: SPACE AND ATMOSPHERIC PLASMA ................................... 203
13. Stability of Kinetic Alfvén Wave (KAW) in a Cometary Plasma with Streaming Electrons and Protons ................................................. 205
G. Sreekala, Sijo Sebastian, Manesh Michael, E. Savithri Devi, C. P. Anilkumar, and Chandu Venugopal
14. External Magnetic Field Effect on Absorption of Surface Plasma Waves by Metal Nano-Particles ............................................................ 219
Deepika, Prashant Chauhan, Anshu Varshney, D. B. Singh, and Vivek Sajal
15. Plasma Waves Beyond the Solar System .............................................. 231
Vipin K. Yadav and Anil Bhardwaj
16. Jeans Instability of a Self-Graviatating Viscous Molecular Cloud Under the Influence of Finite Electron Inertia, Hall Effect, Fine Dust Particles, and Rotation ......................................................... 243
D. L. Sutar and R. K. Pensia PART III: NUCLEAR FUSION ....................................................................
17. Structural Fabrication: Study of Infrastructure Facilities Required to Convert Concept to Reality ..............................................
Gautam R. Vadolia
18. DAC-Controlled Voltage Variable RF Attenuator for Generating RF Pulses of Different Shapes and Amplitudes for ICRH System .................................................................................... 285
Manoj Singh, H. M. Jadav, Ramesh Joshi, Sunil Kumar, Y. S. S. Srinivas, S. V. Kulkarni, and RF-ICRH Group
19. Investigation of the Effect of Thermal Cycle on SS/CRZ Brazed Joint Sample .............................................................................. 307
K. P. Singh, Alpesh Patel, Kedar Bhope, S. Belsare, Nikunj Patel, Prakash Mokaria, and S. S. Khirwadkar
20. Design and Test Results of a 200 kV, 15 mA High Voltage DC Test Generator ........................................................................................ 321
S. Amal, Urmil M. Thaker, Kumar Saurabh, and Ujjwal K. Baruah
21. Design, Development, and Testing of Water-Based Co-Axial Blumlein Pulse Generator ..................................................................... 339
Sanjay Singh, S. P. Nayak, Ashutosh Jaiswar, T. C. Kaushik, and Satish C. Gupta
22. Optimization of MgB2-Brass Joint Resistance for SST-1 Superconducting Magnet Current Leads ............................................ 347
Upendra Prasad, V. L. Tanna, and S. Pradhan
23. Studies on Effect of Gaseous Quenching Media on Performance of Electrically Exploded Foils ............................................................... 359
S. P. Nayak, Ankur Chowdhury, M. D. Kale, T. C. Kaushik, and Satish C. Gupta
24. Particle Acceleration by Whistler Pulse in High
Punit Kumar, Abhisek Kumar Singh, and Shiv Singh
25. Generation of Terahertz Radiations by Flat Top Laser Pulses in Modulated Density Plasmas .............................................................. 385
Divya Singh and Hitendra K. Malik
26. Surface Modification of High Density Polyethylene and Polycarbonate by Atmospheric Pressure Cold Argon/Oxygen Plasma Jet ..................................................................... 397
R. Shrestha, J. P. Gurung, A. Shrestha, and D. P. Subedi
27. Optical Imaging of SST-1 Plasma .........................................................
Manoj Kumar, Vishnu Chaudhary, Chestaparmar, Ajai Kumar, and SST-1 Team
28. Pulsed Electrical Exploding Wire for Production of Nanopowders ...................................................................................... 419 S. Borthakur, N. Talukdar, N. K. Neog, and T. K. Borthakur
ABOUT THE EDITORS
B. Raneesh, PhD
Assistant Professor, Department of Physics, Catholicate College, Pathanamthitta, Kerala, India
Dr. B. Raneesh, PhD, is currently an Assistant Professor in the Department of Physics, Catholicate College, Pathanamthitta, Kerala, India. His current research interests include nanomultiferroics, metal oxide thin films, plasma science, and electron microscopy. He has published many research articles in peer-reviewed journals and co-edited one book. Dr. Raneesh has received his MSc and MPhil degrees from Bharathiyar University, Coimbatore, India, and PhD in physics from Mahatma Gandhi University, Kerala, India.
Nandakumar Kalarikkal, PhD
Director, International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kerala, India
Dr. Nandakumar Kalarikkal, PhD, is the Director of the International and Inter University Centre for Nanoscience and Nanotechnology as well as an Associate Professor in the School of Pure and Applied Physics at Mahatma Gandhi University, Kerala, India. His current research interests include synthesis, characterization, and applications of various nanostructured materials, laser plasma, and phase transitions. He has published more than 80 research articles in peer-reviewed journals and has co-edited seven books. Dr. Kalarikkal obtained his Master’s degree in physics with a specialization in industrial physics and his PhD in Semiconductor Physics from Cochin University of Science and Technology, Kerala, India. He was a postdoctoral fellow at NIIST, Trivandrum, and later joined Mahatma Gandhi University, Kerala, India.
x About the Editors
Jemy James, MSc
International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala, India
Mr. Jemy James obtained his Integrated MSc degree in photonics from Cochin University of Science and Technology, Kochi, Kerala, India. He is currently pursuing his PhD program in International and Inter University Centre for Nanoscience and Nanotechnology at Mahatma Gandhi University, Kottayam, Kerala, India. His current research interests include laser plasma and polymer nanocomposites.
Anju K. Nair, MPhil
Research Scholar, International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala, India
Ms. Anju K. Nair is currently a Research Scholar in the International and Inter University Centre for Nanoscience and Nanotechnology at Mahatma Gandhi University, Kottayam, Kerala, India. Her current research interests include graphene-based hybrid structures for sensing applications. She received her MSc and MPhil degrees in physics from Mahatma Gandhi University, Kerala, India.
LIST OF CONTRIBUTORS
M. K. Ahmed
Department of Physics, Birjhora Mahavidyalaya, Bongaigaon – 783380, Assam, India, E-mail: mnzur_27@rediffmail.com
S. Amal
Institute for Plasma Research (IPR), Bhat, Gandhinagar, Gujarat – 382428, India, E-mail: amal@ipr.res.in
C. P. Anilkumar
Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Krishnapuram, Tirunelveli, Tamil Nadu – 627011, India, E-mail: cvgmgphys@yahoo.co.in
Parveen Bala
Department of Mathematics, Statistics & Physics, Punjab Agriculture University, Ludhiana –141004, India, E-mail: pravi2506@gmail.com
M. Bandyopadhyay
ITER-India, Institute for Plasma Research, A-29, GIDC, Electronic Estate, Sector-25, Gandhinagar –382025, Gujarat, India, E-mail: mbandyo@yahoo.com
Ujjwal K. Baruah
Institute for Plasma Research (IPR), Bhat, Gandhinagar, Gujarat – 382428, India
S. Belsare
Divertor and First Wall Technology Development Division, Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
Anil Bhardwaj
Space Physics Laboratory (SPL), Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram –695022, Kerala, India
Kedar Bhope
Divertor and First Wall Technology Development Division, Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
S. Borthakur
Centre of Plasma Physics, Institute for Plasma Research, Sonapur, Kamrup, Assam – 782402, India
T. K. Borthakur
Centre of Plasma Physics, Institute for Plasma Research, Sonapur, Kamrup, Assam – 782402, India, E-mail: tkborthakur@yahoo.co.uk
Christian Brandt
Center for Energy Research, University of California at San Diego, San Diego, CA 92093, USA
A. Chakraborty
ITER-INDIA, Institute for Plasma Research, Bhat, Gandhinagar 382428, Gujrat, India, E-mail: arun.chakraborty@iter-india.org
M. Chakraborty
Centre of Plasma Physics-Institute for Plasma Research, Nazirakhat, Sonapur – 782402, Kamrup, Assam, India, E-mail: monojitc@yahoo.com
Vishnu Chaudhary
Institute for Plasma Research, Gandhinagar – 382428, India
Prashant Chauhan
Department of Physics and Material Science and Engineering, Jaypee Institute of Information Technology, Noida – 201307, UP, India, E-mail: prashant.chauhan@jiit.ac.in
Ankur Chowdhury
Applied Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai – 400085, India, E-mail: ankurc@barc.gov.in
B. K. Das
Centre of Plasma Physics-Institute for Plasma Research, Nazirakhat, Sonapur – 782402, Kamrup, Assam, India, E-mail: bdyt.ds@rediffmail.com
P. Das
Ravenshaw University, Cuttack, Odisha – 753003, India
Pankaj Deb
Energetics and Electromagnetics Division, Bhabha Atomic Research Centre, IDA Block B, 4th Cross Road, Autonagar, Visakhapatnam – 530012, India, E-mail: pankajdeb24@gmail.com
Apul Narayan Dev
Centre for Applied Mathematics and Computing, Siksha 'O' Anusandhan University, Khandagiri, Bhubaneswar – 751003, India, E-mail: apulnarayan@gmail.com
E. Savithri Devi
School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam – 686560, Kerala, India
J. Ghosh
Institute for Plasma Research, Bhat, Gandhinagar, Gujarat – 382428, India
Tarsem Singh Gill
Department of Physics, Guru Nanak Dev University, Amritsar – 143005, India, E-mail: tarsemgill50@gmail.com
Deepika Goel
Department of Physics and Material Science and Engineering, Jaypee Institute of Information Technology, Noida – 201307, UP, India, E-mail: deepika7nov@yahoo.co.in
Alexey Goncharov
Institute of Physics NAS of Ukraine, Kiev, 03650, Ukraine, E-mail: gonchar@iop.kiev.ua
K. G. Gopchandran
Associate Professor, Department of Optoelectronics, University of Kerala, Kariavattom, Thiruvananthapuram, India, E-mail: satheeshr83@gmail.com
RF-ICRH Group
Institute for Plasma Research, Bhat, Gandhinagar – 382428, India, E-mail: parihar@ipr.res.in
Satish C. Gupta
Applied Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai – 400085, India, E-mail: satish@barc.gov.in
J. P. Gurung
Department of Natural Science, Kathmandu University, Dhulikhel, Nepal
P. Hazarika
Centre of Plasma Physics-Institute for Plasma Research, Nazirakhat, Sonapur – 782402, Kamrup, Assam, India, E-mail: hazarikaparismita@rediffmail.com
H. M. Jadav
Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
Ashutosh Jaiswar
Applied Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai – 400085, India, E-mail: ashuj@barc.gov.in
Zdeňka Jeníková
Czech Technical University of Prague, Faculty of Mechanical Engineering, Department of Materials Engineering, Karlovo náměstí 13, CZ-120 00 Prague, Czech Republic, E-mail: Zdenka.Jenikova@fs.cvut.cz
Ramesh Joshi
Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
M. D. Kale
Applied Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai – 400085, India, E-mail: kalemd@barc.gov.in
Latika Kalita
Department of Mathematics, Kamrup Polytechnic, Baihata Chariali, Kamrup, Assam, India, E-mail: latika84k@rediffmail.com
T. C. Kaushik
Applied Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai – 400085, India, E-mail: tckk@barc.gov.in
S. S. Khirwadkar
Divertor and First Wall Technology Development Division, Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
S. V. Kulkarni
Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
Ajai Kumar
Institute for Plasma Research, Gandhinagar – 382428, India
Manoj Kumar
Institute for Plasma Research, Gandhinagar – 382428, India, E-mail: mkg.ipr@gmail.com
Punit Kumar
Department of Physics, University of Lucknow, Lucknow – 226007, India, E-mail: punitkumar@hotmail.com
Sunil Kumar
Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
Hitendra K. Malik
Department of Physics and Electronics, Rajdhani College, University of Delhi, New Delhi – 110015, India
List of Contributors
Manesh Michael
School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam – 686560, Kerala, India
Prakash Mokaria
Divertor and First Wall Technology Development Division, Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
S. P. Nayak
Applied Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai – 400085, India, E-mail: spnayak@barc.gov.in
N. K. Neog
Centre of Plasma Physics, Institute for Plasma Research, Sonapur, Kamrup, Assam – 782402, India
R. Paikaray
Christ College, Cuttack, Odisha – 753001, India
Arun Pandey
ITER-INDIA, Institute for Plasma Research, Bhat, Gandhinagar – 382428, Gujarat, India, E-mail: arun.pandey@ipr.res.in
Chesta Parmar
Institute for Plasma Research, Gandhinagar – 382428, India
Alpesh Patel
Divertor and First Wall Technology Development Division, Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
Nikunj Patel
Divertor and First Wall Technology Development Division, Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
R. K. Pensia
Department of Physics, Govt. Girls College, Neemuch (M.P.), 458441, India
S. Pradhan
Institute for Plasma Research, Bhat, Gandhinagar, India
Upendra Prasad
Institute for Plasma Research, Bhat, Gandhinagar, India, E-mail: upendra@ipr.res.in
O. P. Sah
Department of Physics, Birjhora Mahavidyalaya, Bongaigaon – 783380, Assam, India, E-mail: opbngn@gmail.com
G. Sahoo
Stewart Science College, Cuttack, Odisha – 753001, India, E-mail: gsahoo@iopb.res.in
Vivek Sajal
Department of Physics and Material Science and Engineering, Jaypee Institute of Information Technology, Noida – 201307, UP, India, E-mail: vsajal@rediffmail.com
S. Samantaray
Ravenshaw University, Cuttack, Odisha – 753003, India
S. Sankar
Assistant Professor, Department of Physics, S. N. College, Chathannur, Karamkode (P.O.), Kollam, India
List of Contributors
A. Sanyasi
Institute for Plasma Research, Bhat, Gandhinagar Gujarat, 382428, India
Jnanjyoti Sarma
Department of Mathematics, R. G. Baruah College, Guwahati – 781025, Assam, India, E-mail: jsarma_2001@yahoo.com
R. Satheesh
Assistant Professor, Department of Physics, S. V. R. NSS College, Vazhoor, T. P. Puram (P.O.), Kottayam, India
Kumar Saurabh
Institute for Plasma Research (IPR), Bhat, Gandhinagar, Gujarat – 382428, India
Sijo Sebastian
School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam – 686560, Kerala, India
A. Shrestha
Department of Natural Science, Kathmandu University, Dhulikhel, Nepal
R. Shrestha
Department of Physics, Basu H.S.S./Basu College, Kalighat, Byasi, Bhaktapur, Nepal, E-mail: rajendra.ts2002@gmail.com
Anurag Shyam
Energetics and Electromagnetics Division, Bhabha Atomic Research Centre, IDA Block B, 4th Cross Road, Autonagar, Visakhapatnam – 530012, India
Abhisek Kumar Singh
Department of Physics, University of Lucknow, Lucknow – 226007, India
D. B. Singh
Laser Science and Technology Center, Metcalfe House, New Delhi – 110054, India, E-mail: dbsingh2@rediffmail.com
Divya Singh
Department of Physics, PWAPA Laboratory, Indian Institute of Technology, New Delhi – 110016, India, E-mail: divyasingh1984@gmail.com
K. P. Singh
Divertor and First Wall Technology Development Division, Institute for Plasma Research, Bhat, Gandhinagar – 382428, India, Tel.: +91-79-2396-2107; E-mail: kpsingh@ipr.res.in
Manoj Singh
Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
Sanjay Singh
Applied Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai – 400085, India, E-mail: sanjay@barc.gov.in
Shiv Singh
Department of Physics, University of Lucknow, Lucknow – 226007, India
Petr Špatenka
Czech Technical University of Prague, Faculty of Mechanical Engineering, Department of Materials Engineering, Karlovo náměstí 13, CZ-120 00 Prague, Czech Republic, E-mail: Petr.Spatenka@fs.cvut.cz
G. Sreekala
School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam – 686560, Kerala, India
Y. S. S. Srinivas
Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
D. P. Subedi
Department of Natural Science, Kathmandu University, Dhulikhel, Nepal
Rajesh Subedi
Department of Science and Humanities, College of Science and Technology, Rinchending, Phuentsholing – 450, Bhutan, E-mail: rajesh@cst.edu.bt
Dass Sudhir
ITER-INDIA, Institute for Plasma Research, Bhat, Gandhinagar 382428, Gujarat, India, E-mail: dass.sudhir@iter-india.org
D. L. Sutar
ResearchScholar Mewar University Gangrar, Chittorgarh, 312901, Rajasthan, India, E-mail: Devilalsutar833@gmail.com
N. Talukdar
Centre of Plasma Physics, Institute for Plasma Research, Sonapur, Kamrup, Assam – 782402, India
V. L. Tanna
Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
SST-1 Team
Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
Urmil M. Thaker
Institute for Plasma Research (IPR), Bhat, Gandhinagar, Gujarat – 382428, India
Saikat Chakraborty Thakur
458, EBU-II, CER – UCSD, 9500 Gilman Drive, Mail Code 0417, La Jolla, CA 92093, USA, E-mail: saikat@ucsd.edu
George R. Tynan
Center for Energy Research, University of California at San Diego, San Diego, CA 92093, USA
Taťána Vacková
Czech Technical University of Prague, Faculty of Mechanical Engineering, Department of Materials Engineering, Karlovo náměstí 13, CZ-120 00 Prague, Czech Republic, E-mail: Tatana.Vackova@fs.cvut.cz
Gautam R. Vadolia
Institute for Plasma Research, Near Indira Bridge, Bhat, Gandhinagar – 382428, Gujarat, India, E-mail: gautamv@ipr.res.in
Anshu Varshney
Department of Physics and Material Science and Engineering, Jaypee Institute of Information Technology, Noida – 201307, UP, India, E-mail: anshu.varshney@jiit.ac.in
Chandu Venugopal
School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam – 686560, Kerala, India
Vipin K. Yadav
Space Physics Laboratory (SPL), Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram –695022, Kerala, India, E-mail: vipin_ky@vssc.gov.in
LIST OF ABBREVIATIONS
AO analog output
APPJ atmospheric pressure plasma jet
ASME American Society of Mechanical Engineers
BHEL Bharat Heavy Electricals
BRFST Board of Research for Fusion Science and Technology
CCD charge couple device
CCP capacitive coupled plasma
CCU camera control unit
CMERI Central Mechanical Engineering Research Institute
CMTI Central Manufacturing Technology Institute
CNM cold neutral medium
CPS compact plasma system
CSDX Controlled Shear De-correlation eXperiment
DA dust acoustic
DAQ data acquisition
DC direct current
DIA dust ion acoustic
DM de-mineralized
DO digital output
DPD double plasma device
EAWs electron-acoustic waves
EEC electrically exploded conductor
EEF electrically exploded foil
ESCA electron spectroscopy for chemical analyses
ESL equivalent series inductance
FLR finite Larmor radius
FTL flat top laser
FWHM full width at half maximum
GL Gaussian laser
GUI graphical user interface
HCG hot coronal gas
List of Abbreviations
HDPE high density polyethylene
HEAT helicon electrodeless advanced thruster
HIM hot ionized medium
HIP hot isostatic press
HV hardness value
HV high voltage
IASs ion-acoustic solitons
IASWs ion acoustic solitary waves
IAW ion-acoustic wave
ICE International Cometary Explorer
ICP inductively coupled plasma
IMD internal Mg diffusion
IPM interplanetary medium
IPR Institute for Plasma Research
ISM interstellar medium
ITER International Thermonuclear Experimental Reactor
KASWs kinetic Alfvén solitary waves
KdV Schamel Korteweg-de Vries
KH Kelvin-Helmholtz
LHe liquid helium
LIF laser-induced fluorescence
LPA low power amplifier
LTD linear transformer drivers
MAW magnetoacoustic waves
MITL magnetically insulated transmission lines
mK-P modified Kadomstev-Petviashivili
MW microwave
NBI neutral beam injector
NDT non-destructive testing
OD outer diameter
PC personal computer
PC polycarbonate
PE polyethylene
PEEW pulsed electrical exploding wire
PFC plasma facing component
PFN pulse forming network
xviii
List of Abbreviations
PU polyurethane
QHD quantum hydrodynamic
R&D research and development
RDW resistive drift wave
RF radio-frequency
RPT reductive perturbation technique
RRR residual resistance ratio
RT Rayleigh Taylor
SC superconductor
SEM scanning electron micrographs
SOL scrape-off-layer
SP Sagdeev potential
SPS spark plasma sintering
SPW surface plasma waves
SS stainless steel
SWs solitary waves
TCT thermal cyclic test
TDE time delay estimation
TMF transverse magnetic field
UT ultrasonic testing
VIM vacuum induction melting
VPS vacuum plasma spraying
WIM warm ionized medium
WKB Wentzel-Kramers-Brillouin
WNM warm neutral medium
XRD x-ray diffractometer
PREFACE
Recently, plasma science and nanotechnology have attracted the attention of researchers because of the enormous applications of these techniques in the modern world to create novel power sources and devices that have unique applications. Plasma is often called as “the fourth state of matter,” along with solid, liquid, and gas. Plasma science is the study of the ionized states of matter. Most of the observable matter in the universe is in the plasma state. Because plasmas are conductive and respond to electric and magnetic fields, and can be efficient sources of radiation, they are usable in numerous applications where such control is needed or when special sources of energy or radiation are required. Much of the understanding of plasmas has come from the pursuit of controlled nuclear fusion and fusion power, for which plasma physics provides the scientific basis.
This book is the collection of peer-reviewed papers presented at the 29th National Symposium Plasma Science & Technology and International Conference on Plasma and Nanotechnology (PLASMA-2014) held in Kottayam, India. In fact, this edited book showcases the research of an international roster of scientists and students. The conference was organized by International and Interuniversity Centre for Nanoscience & Nanotechnology at Mahatma Gandhi University, Kottayam, Kerala. The conference had over 500 delegates from all over the world—good representation from France, Slovenia, Australia, USA, Netherlands, Germany, Iran, Sweden, Spain, and Italy; and as well as a substantial number of eminent Indian scientists. The conference was designed so as to generate excellent opportunities for international researchers interested in plasma science and technology to meet and discuss issues related to current developments in the field of power generation. The goal of the conference emphasizes interdisciplinary research on plasma science and nanotechnology.
This volume, Plasma and Fusion Science: From Fundamental Research to Technological Applications collects together a selection of 29 papers presented during the conference. The papers include a wide variety
of high attractive topics in the plasma science with emphasis on basic plasma physics, computer modeling for plasma, exotic plasma (including dusty plasma), industrial plasma applications, laser plasma, nuclear fusion technology, plasma diagnostics, plasma processing, pulsed power, space astrophysical plasma, and plasma and nanotechnology. In this important work, an excellent big team of international experts provide an exploration of the emerging plasma science that are poised to make the plasma technology to become a reality in the manufacturing sector. We trust that this special issue will stimulate new ideas, methods, and applications in the field of plasma science and technology.
We would like to thank all who kindly contributed their papers for this issue and the editors of Apple Academic Press for their kind help and co-operation. We are also indebted to the Apple Academic Press editorial office and the production team for their assistance in the preparation and publication of this issue.
PART I BASIC PLASMA
CHAPTER 1
PLASMA TREATMENT OF POWDER AND GRANULATES
PETR ŠPATENKA, TATANA VACKOVÁ, and ZDE NKA JENÍKOVÁ
Czech Technical University of Prague, Faculty of Mechanical Engineering, Department of Materials Engineering, Karlovo Námě stí 13, CZ-120 00 Prague, Czech Republic, E-mail: Petr.Spatenka@fs.cvut.cz, Tatana.Vackova@fs.cvut.cz, Zdenka.Jenikova@fs.cvut.cz
The cold plasma surface modification is a low-cost and highly effective technology for influencing surface properties of polymers without altering the bulk material. Prevalent industrial applications for surface modification
of bulk polymers—for example, packaging foils, headlights, or automobile bumpers preceding metallization—are frequently used. But for many other different applications, such as basic construction materials, synthetic polymer fillers, agriculture, pharmaceutical, cosmetic, paintings, and food industry polymer the materials are required in the form of granules or powder. The worldwide annual production of all kinds of granules and powders reaches approximately 10 billion metric tons [1]; nevertheless, the plasma modification of polymer powders has not found plenty of applications as modification of flat bulk polymers. This is due to the problems connected with (i) three-dimensional geometry of powders, (ii) their large surface area, and (iii) the aggregation phenomenon; and therefore, there is a necessity of solid mixing of treated powder.
The reactors designed for plasma powder treatment can be divided into three main groups. The first one is based on an application of mechanical mixture of the powder. As an example, a radio-frequency (RF) plasma reactor consisting of a large rotating and rocking Pyrex glass vacuum chamber can be mentioned. The RF power is coupled with a coil or clamshell electrode arrangement. Batches of several thousands of rubber parts—for example, intended for the pharmaceutical industry—are loaded into the reactor in this process. The uniformity of the surface modification is assured by the motion of the reactor while the batch is treated in a propylene-helium mixture [2, 3]. Another type of reactors used for the mechanical mixing is described elsewhere [4]. The RF or microwave (MW) antennas are placed on the top of the plasma reactor and the system employs continuous mixing during the treatment process. This is accomplished by a mixer arranged inside a tubular stainless steel reactor. One batch contains up to 70 kg of polyethylene powder.
The second group is based on a vertical tubular plasma reactors. The polymer powder is gravity-fed in a continuous stream through the RF plasma zone from a hopper at the top to a collecting bin at the bottom [3, 5]. Such a system was proposed to improve properties of thermoplastic polymer matrix composites. The treatment conditions are fixed and therefore they could be applied for only one type of material. One of the treatment objectives is to incorporate a few atomic percent of chemically bonded oxygen into particles surface. The efficiency of the plasma modification in this type of reactor is approximately 50 kg/h for the particles with diameter of 60 μm on average.
The third group, plasma fluidized bed techniques, is one of the most frequently reported laboratory-scale method [6]. The principle of the reactor is porous plate placed on the reactor bottom on which the powder is spread and the working gas is injected through the porous reactor bottom. Subsequently, the gas passes through a bed of the powder. When the gas flow increases above the critical flow rate the drag on the individual powder particle increases. As a result, the powder starts to move and becomes suspended into the fluid. This state is called fluidization.
Application of low-temperature atmospheric plasma was also demonstrated by several authors. Hladík et al. [7] and Píchal et al. [8] employed dielectric barrier discharge for treatment of polyethylene (PE) particles. The particles passed an approx. 25 cm long channel for several times. They demonstrated hydrophility saturation after 20 transitions of the powder through the plasma channel. Based on electron spectroscopy for chemical analyses (ESCA) they proved incorporation of hydroxyl polar groups on the PE polymer chain. Gilliam et al. [9] treated poly(methylmethacrylate) and polypropylene in the downstream of a low-temperature plasma torch. They proved significant hydrophility enhancement of the both polymers. Addition of 10 g/min of water flow into the torch resulted in subsequent decrease of the measured contact angle from 110° to 100°. Spillmann et al. [10] presented a sophisticated device based on inductively coupled discharge excited in fluidized bed reactor. This type of reactor was used by Roth et al. [11] for powder encapsulation by SiO2. The reactor operates with a capacity of 2 kg/hour.
Most of the published papers describe laboratory-scale experiments, where the portion of treated material is of several tens of grams. For real applications, the industrial/scaled-up devices with a capacity at least of some hundreds kilograms per day are necessary. The objective of this chapter is to analyze the conditions for the powder treatment in industrialscale application, to present an industrial scale reactor, and to demonstrate some examples of plasma treated powder applications.
1.2 THEORETICAL BACKGROUND
A powder represent a body with a very large total surface area in comparison with bulk materials or foils. To ensure treatment of the whole surface
of each particle, the whole particle should be in contact with plasma (or more precisely with radicals produced by plasma). Two methods are usually applied—mechanical mixing and fluidized bed reactor. A mechanical mixing is convenient for the larger particles; with lowering particle diameter fluidization is necessary. A detailed calculation can clarify the limits of the mechanical mixing.
Assuming free packing of the powder particles in a container, the particles do not fill the whole container volume. A quantity of the powder can be characterized by a filling factor. The filling factor is defined as a ratio of volume summation of all powder particles in the container to the container volume. Provided the density of the particles is constant, the filling factor F can be expressed as:
F = Vpowder/Vbox = mpowder/mbulk
where Vpowder and Vbox are the volumes of powder in container, respectively; mpowder and mbulk are the masses of powder of a bulk body occupying the whole container volume, respectively. Typically, the filling factor varies between 0.45–0.64 [12]. The total number of all powder particles N in the container can be determined as:
N = (Vbox F)/(4/3 πR3)
where R is the particle diameter. The total surface area Stotal of particles present in the container can be then expressed as a multiple of the total number of powder particles N and the surface area of a powder particle Sparticle:
It follows that the total surface area increases with the particle diameter decrease. Thus, reduction of the particle diameter results in increase of the treated total surface area. Consequently, it leads to a prolongation of the process time. Application of the fluidized bed reduces the filling factor. This leads to the reduction of the total powder amount in the
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hair, stuff her fingers down his neck, pluck off ruthlessly the finest blossoms from his favourite plants, throw his pet books recklessly on the floor, thereby breaking their backs, scribble over his carefully written Latin exercise, and yet he could not find the heart to be angry with her.
"When could Father be home, if he comes?" asked Forbes, after a few moments pause.
"He might be here by Christmas," answered Geoffrey. "Poor Father! He must know by this time," he added, seating himself again by the fire. "Mr. Hodson telegraphed to him last night."
"Nurse says we needn't go back to school till after Christmas," remarked Jack, "We shall have a jolly long holiday."
"Jolly!" exclaimed Geoffrey, looking up in surprise,—then he remembered that Jack was only seven years old.
CHAPTER
Had the inhabitants of Hazelbury seen the Rev. Claude Hodson on a certain winter's afternoon about a fortnight after the events recorded in the last chapter took place, crawling about the floor of his sitting room on all fours, minus a coat, but with a rug thrown across his back, and roaring in imitation of some wild beast, they would scarcely have recognised him as their quiet and grave young curate.
With children, he felt thoroughly at ease, and specially with his little friends the Fortescues. Nothing gave him greater pleasure than to have all four of them to spend the afternoon with him and to stay to tea.
Mrs. Fortescue had always been very kind to him, and he had felt less shy with her than with most people.
Thinking that the young man must be lonely, she had allowed the boys to run in and out of his rooms on their half holidays, at his request, and thus a warm friendship was formed between them.
The table was pushed to one side, its former contents cleared quite away, next Sunday's sermons among them.
During Mrs. Fortescue's last illness, no one could have been more tender to and sympathizing with the children than he was, and it was to him that Geoffrey had gone at once when the end came. "Mr. Hodson," he had said, looking up at him with tearless eyes, but with a pale face, "Mother has gone."
For the minute Claude was quite silent, and then he did, what to him was the only possible thing he could do under the circumstances.
"Let us pray, Geoff," he had said in a low voice, and though no word was uttered aloud by either of them, they knelt silently together, Claude's hand resting tenderly on the boy's shoulder.
Geoff did not cry. His breath came quick and short for a few minutes, and then he grew calm. From that day their friendship was sealed.
On this particular afternoon of which I write, the Curate was in his element. He had invited his little friends to tea and had resolved to do what he could to cheer them up and to make them happy, and he certainly had succeeded.
Game after game they had played, turning everything in his room upside down.
The table was pushed to one side, its former contents cleared quite away, next Sunday's sermons among them, for the Vicar was away from home, and the preaching therefore devolved on the Curate.
Dodie was sweeping about the room, with the table cloth tied round her waist, forming a long train behind her, and an antimacassar thrown over her head for a veil, and the Curate himself amidst the shrieks of his little friends, was
prowling about the floor, supposed to be a wild beast, trying to catch the children one by one.
Everything was in wild confusion, and Mrs. Green, the landlady, hearing the merriment from her dull little parlour at the back of the house, could not resist giving a peep into her lodger's room, to see a bit of the fun.
At the sight of her at the door, Claude sprang up from his humiliating position, and wiping the heat from his brow, said:
"I'm afraid Mrs. Green that we are making an unearthly noise, you've not a bad head to-day, I trust."
"Bless you, no Sir," said Mrs. Green, laughing, "It does one's heart good to see them enjoying themselves, poor little dears. I like a noise, it's cheery. 'Why Sally,' my husband has said many a time to me, when I've complained of the quiet of the country, 'I do believe,' says he, 'you'd like to live in an Inn, where people are always going and coming. One day, says he, when my ship comes in, I'll buy a Hotel at Yarmouth or Margate or some such place, and then you'll have as much noise as you like.'"
"You've had enough noise I expect for one day, any way," said Claude, suddenly becoming conscious that he was standing talking to his landlady in his shirt sleeves, and turning round to hunt for his coat among the confusion.
"Well as I tell you Sir, I like it, it's cheerful. Now that's what I like to think about Heaven," continued Mrs. Green, who at the slightest show of interest on the part of her listener, was inclined to become garrulous. "We shan't have no dull back parlours there I take it, not seeing a soul from one day to another, all shut up by ourselves like. We shall always be coming across new people there, and there'll be plenty to
see and to hear. Think of old Rachel, Sir, her as lives at the bottom of the hill all by herself. She don't see a fresh face from one week's end to another. What a nice change it'll be for her now, that's to say if ever she gets there. I'm afraid she ain't fit for Heaven yet from all I hear."
The children interrupted in their game stood staring at the intruder, somewhat indignantly, while Dodie administered sundry impatient thumps on Claude's back.
"I must say," added Mrs. Green, "that that daughter of hers behaves shameful. Ever since she married the man Jones she has quite neglected her poor old mother, and if ever she gives her anything, you may be quite sure it ain't fit to eat, something they can't eat themselves because it's turned."
"What!" cried Geoffrey. "Does she do that to her own Mother?"
"You may well cry out, Master Geoff, it's a wicked shame, and I tell you Sir," she added, turning to Claude, "mark my word, if that woman don't manage somehow to get the Christmas Charities this year, even though her own old Mother has to go without."
"Come, come, Mrs. Green," expostulated Claude, "She's not quite so base as that, I hope. However I'll have an eye on her at Christmas; and now," he added, as Dodie's thumps became more violent, "do you think you could let us have tea? It's early I'm afraid, but we're all hungry. Is it too early?"
"Bless you no Sir,—not if you want it. I'm always willing to do what I can to make you comfortable. 'Sally,' my husband used to say to me when I had troublesome lodgers, 'don't you mind being put about a bit, keep a cheerful countenance my girl,' and so I've always tried to do Sir, and
though the kitchen fire is a bit low as I didn't know you'd be wanting tea quite so early, I'll make it up at once Sir, and tea will be ready in a few minutes."
And Mrs. Green hurried off with a good-natured smile on her face, thinking to herself, "Who wouldn't be obliging to such a nice young gentleman, I should like to know—such a quiet lodger too—so different from my last party. I sometimes wish he'd make a little more noise, that I do; it 'ud be more cheerful. But there now, it isn't his way. Bless me! Flow those dear children are enjoying themselves," as a fresh peal of laughter found its way down into the kitchen.
Nurse's hair would have stood up on end, if half an hour afterwards she had looked in, and seen the zest with which the three boys tucked in to the apricot jam and currant cake, which their host brought out of his cupboard.
Geoffrey perhaps fared the worst of the three, for a great deal of his time was spent in looking after Dodie, tying on her bib, cutting her bread and butter into tempting little shapes, so as to take off her attention from the currant cake, which he knew she must not eat, giving her tiny little portions of his own jam on her bread and butter to taste.
He would not let anyone do anything for her but himself, and no mother could have been more careful of her.
"Mr. Hodson," said Forbes, when after tea they put on their hats and jackets most unwillingly to go, "will you take us one day into Ipswich to get our Christmas presents? It's three weeks to Christmas now, and Nurse won't let us go alone, though of course Geoff could take care of us. Mother used always to let him go into the town alone."
"I want to get heaps of presents," said Jack, tugging away at his boots breathlessly, "there's Nurse, and James, and
Ann, and Geoff of course, and the others, I don't think I can buy mine all in a day."
"I wouldn't tell a lie if I were you," said Geoff, "it's very mean to tell a lie."
"Well, you'll have to, that's all," said Forbes, "and we mustn't forget Father's present, at least I suppose he'll be with us then. We've had a telegram to say he is coming soon, and he'll send another when it's quite decided. Do you think you could take us, Mr. Hodson?"
Claude promised he would do what he could, and then Dodie was put into her little mail cart, which of course Geoff drew himself, and their friend saw them safely home.
Nurse met them at the door.
"It's wonderful kind of you Sir to have them," she said, lifting Dodie out of the cart and giving her a hearty kiss, "I hope they've all been good," then, as Claude made his escape, after assuring her it had been quite as much pleasure to him to have them, as it was for them to come, Nurse made her way up into the nursery, seated herself in her large chair by the fire, and began to take off Dodie's gloves. But Dodie was tired, perhaps from over excitement, and was not inclined to sit still, and finally ended in crying, as the string of her little cape had got into a knot, and took nurse some time to undo.
"Where's her doll?" said Nurse, "run and fetch it, there's a good boy, it'll stop her crying."
Forbes went to the cupboard to look for it, but it was not there. He hunted all over the nursery, but it was no where to be found. After a long search, he went down into the schoolroom, and to his astonishment found it hidden away behind the curtain, with its face not only cracked, but looking as if it had been melted in the fire. Forbes ran upstairs two steps at a time, as he held out the doll for Nurse to see; Jack, who was on the floor reading a book by
the light of the fire, looked up and turned very red, while Dodie, catching sight of her disfigured doll, set up a lusty scream, and was a long time before she would be comforted, in fact not till Forbes had carried the doll out of the room, having beckoned to Jack to follow him.
They met Geoffrey on the stairs.
"What's the matter with Dodie?" he asked.
Forbes explained the mysterious finding of the doll, and the three went back into the schoolroom to see the exact spot.
"Who could have done it?" murmured Jack.
"That's just it," answered Forbes, "we must find that out of course, it was hidden away on purpose."
"Could Dodie have broken it herself?" suggested Jack.
"Dodie! Of course not, why you saw yourself how scared she was at the sight of it. I suppose Jack—" Forbes hesitated and looked down at his little brother, who turned again very red.
"Jack," said Geoffrey gravely, "you know something about it, did you do it?"
"I? No! of course not, I don't know anything about it," stammered Jack.
"I wouldn't tell a lie if I were you," said Geoff, "it's very mean to tell a lie."
"It isn't a lie," said Jack angrily, "I tell you I don't know who did it."
"I do," retorted Forbes, "so there's an end of it," and he was just about to leave the room when he felt a sharp kick on his ancle, and turned round to see Jack's face crimson with rage and his small hands clenched.
"Oh, that's it, is it?" said Forbes coolly, and being a much stronger boy than Jack, had him down on the ground in a moment of time, and held him there saying, "I shan't let you go till you've confessed that you're a wicked little liar."
Geoffrey here interfered.
"Come Forbes, that isn't fair," he said, "he's a little chap, and besides we have no right not to believe him. Let him go, there's a good fellow."
But it was not till Forbes had administered a certain amount of corporal punishment on the offender that he let him go, and saw him make his way upstairs sobbing.
Jack did not however, for a wonder, go straight to Nurse, but hid himself on the floor in a dark corner of the night nursery.
There huddled poor little Jack, with a great burden on his conscience. He had told a lie—a direct lie—and he had told it twice, and yet he felt he could never confess that he was the guilty one. They would never forgive him for spoiling Dodie's doll, and they would always look down upon him for telling a lie about it. Jack sat and cried all by himself in the dark, and did not move from his corner till nurse herself came up an hour afterwards with Dodie in her little nightdress in her arms. It was only on putting the candle on the chest of drawers that she discovered Jack.
"Why my beauty!" she cried, laying Dodie down and turning towards Jack, "What's the matter, eh? Has anyone been
unkind to you?"
And taking him on her knee, she kissed him and smoothed his hair, and rocked him in her kind old arms, in great distress at finding him crying in the dark.
"He's thinking about his poor dear Mamma, I do believe, bless him," she thought to herself, as Jack still sobbed, giving no explanation of his tears; then aloud she said, "if you're a good boy, you shall have a bit of cake for supper. Leave off crying, there's a darling, while I tuck Dodie up, and then I'll tell you a story by the nursery fire."
So Jack went down into the nursery, with the lie still on his conscience, and looking very shamefaced. It was true he was able to enjoy the large slice of currant cake which an hour or two afterwards Nurse gave him, for Jack could enjoy cake under almost any circumstances, but he did not enjoy meeting Forbes' eyes fixed upon him, after taking an unusually large mouthful.
Forbes and Geoff were eating the usual supper of bread and butter by the table, and neither of them could quite make out what Jack had done to deserve an extra treat in the way of cake, and to be allowed to eat it by the fire, notwithstanding the crumbs which fell on the carpet, and against which Nurse as a rule waged war.
That look of Forbes, however, almost choked Jack. He was eating the last mouthful, but I do not think he could have eaten another, certainly not with Forbes' eyes upon him.
He was glad when it was time to go to bed. He went up to Geoffrey who kissed him as usual, but Forbes waved him away, and Jack stumbled out of the nursery with his eyes full of tears, and feeling himself to be the meanest little wretch alive.
Jack slept in a bed in the night nursery, in the opposite corner to Dodie's crib, which was close beside Nurse's big bed, and as a rule, he fell asleep the moment his head touched the pillow, but tonight he could not sleep. He lay awake, longing to hear Nurse's step on the stair outside, he longed for the comfort of her motherly presence. When, however, she came up at last, Jack, afraid lest she should ask him questions, feigned to be asleep at first, and then when she had smoothed his pillow and tucked him up for the night, he opened his eyes, and amused himself by watching her shadow on the ceiling as she moved about the room. But this amusement soon came to an end, before long he saw her blow out the candle, and heard her get into bed, and all was still.
Then Jack's burden, in the silence and dark, grew so heavy and large that he could bear it no longer, and sitting up in bed, he cried out "Nurse! Nurse!"
In a moment the candle was lit again, and Nurse by his side.
"What is it, dearie?" she asked, putting her arms round him. "Have you had a bad dream, dear heart?"
"I've told a lie," sobbed Jack. "It was me that spoilt Dodie's doll, I was pretending to ha-ha-hang her for fun, and she dropped and br-br-broke her face, and I tried to mend it, so that no nobody should know. I broke it, and I thought the fire would make the cr-cr-crack all right again, but it diddid-didn't, it made it worse. So I hid it away in the sch-schschoolroom, and I have told two lies to Geoff and Forbes, and I don't think God will ever forgive me, and Forbes will ha-ha hate me."
"You're a good boy to tell me," said nurse, "and don't you cry no more, there's a darling. You just tell God about it. You may get out if you like, and kneel down now and pray, and I'm certain sure that if you are really sorry, the good God will forgive you," and kind old Nurse wiped away a tear or two herself, and after tucking him up in bed again, and kissing him, she knelt down by her own bedside to pray for her boy.
Jack confessed to Forbes next morning, and the latter gave him a slap on the back, saying:
"That's right old boy, stick to the truth though another time, that's all."
CHAPTER III.
PREPARING FOR CHRISTMAS.
According to his promise Mr. Hodson arranged an afternoon on which to take the three boys into Ipswich.
They started early in the afternoon in high spirits. The sky was a clear blue with white billowy clouds sailing slowly
across it, and the air was cold and crisp. The river which they passed on their way to the town had caught the colour of the sky, and one or two little white sailed boats were reflected on its waters, while in the distance a large ship with red sails was slowly making its way against wind and tide.
Geoffrey was the only one of the three boys whose thoughts were full of anything except the shops which they were nearing, and the presents they were about to buy. He could not but remember that the chief excitement in past years of buying Christmas presents was over, that the best present of all would not be wanted. How gladly would he have parted with all his little savings if only he could buy his Mother a present once again. He felt he would willingly give her all he possessed.
Afraid as he was of giving people trouble himself, he was quite aghast at the way the boys insisted upon having the counter strewn with various articles.
He had noticed the thought of his Mother cross Forbes' mind that morning too. Just before they had started the latter had been counting out his money, and arranging how much he could spend on each person, when suddenly he came to a full stop, and looking up at Geoffrey in whose eyes the one word "Mother" seemed to Forbes to be so evidently written, he had flushed crimson, and had to bite his lips to prevent tears coming.
That Forbes was constantly thinking of his Mother, Geoffrey was sure, but it surprised him to find how seldom the thought of her seemed to cross Jack's mind. Nurse apparently filled her place to him completely, and Geoffrey recognised none of the "Mother hunger" in his little brother, from which he suffered so much himself.
Even Dodie seemed to remember her more than Jack, for often in her sleep, when she stirred she would murmur "Mammie." It always gave Geoff a strange sensation when he heard this, and he liked to fancy that in some way or other, his Mother watched over his little sister and talked to her in her dreams.
Geoffrey was the only one of the three boys who was silent, as he walked by the side of Mr. Hodson to the town, his hands deep in his pockets, but his silence was more than made up for by the lively chatter of his two brothers.
The shops looked very tempting, decorated as they were for Christmas, and the town was full of people. Claude Hodson found he had given himself a task when he had promised to take his little friends shopping. It was the first experience of shopping with children, and before the afternoon was over, he fervently hoped it would be the last.
Afraid as he was of giving people trouble himself, he was quite aghast at the way the boys insisted upon having the counter strewn with various articles for them to look at, often without deciding to buy any of them. It never struck them that they were giving trouble, or that they were making their kind friend feel supremely uncomfortable. Jack was the most undecided of the three as to what to buy. He would change his mind a dozen times before he settled upon anything. Every fresh thing he saw he wanted, and liked better than the last.
Forbes, on the other hand, was the most unprincipled in the matter of giving trouble, and his remarks about the different articles covered Claude Hodson with confusion more than once. "Why that isn't worth a shilling," he would say, "it's nothing of a knife, only two blades! I got a much better one last year for sixpence!" or "Haven't you any better sticks than this? These are no good at all, I want a regular wopper you know, one that I could knock a fellow down with if he attacked us."
"I say, Forbes," said Jack, as they neared home, "I'll show you your present, if you'll show me mine?"
But if Jack was the most undecided, and Forbes the most inconsiderate of people's feelings, Geoffrey was certainly the hardest to please, as he made up his mind beforehand exactly what he wanted, and would scarcely be satisfied with anything short of it. Among the many things he wanted was a doll for Dodie, as like as possible to the one his Mother gave her, which Jack had spoilt. This doll must, he explained, have light hair and blue eyes, and its head must be turned a little to the right. Mr. Hodson's spirits sank when he heard the minute description Geoffrey gave of the doll, and knew that when he had once set his heart on a thing, he would hunt till he found it, if he could.
"I promised Dodie I'd get her one as like the other as possible," he explained to Mr. Hodson, who mildly hinted that he must be quick, as it was getting late, "and of course, I mustn't break my promise. I'm sure I've seen a doll very like it, somewhere. You don't mind me trying a little longer do you?"
At last Claude had to remonstrate, and Geoff had to give up the idea of finding a doll with a turned head,—he found one, however, with blue eyes and golden hair, and hoped that Dodie would be satisfied with it. He had anyhow kept his promise, and tried hard to find one like her broken favourite.
So at last, with their pockets stuffed out and their arms full, they turned homewards to Mr. Hodson's great relief, and soon they left the lights of Ipswich behind them, and were plodding quickly towards Hazelbury, through the dusk.
"I say Forbes," said Jack, as they neared home, "I'll show you your present, if you'll show me mine."
Jack was tired, and they had both lagged behind the others.
