Report from MeVArc 2013 CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
Stands for - Me chanisms of V acuum Arc s • Focuses on the fundamental physics of vacuum arcs – our main performance limitation in CLIC. • Theory, simulation and experiments. • Multi-disciplinary - material science, surface physics, plasma physics, high-voltage systems, radio frequency, etc. • Multi-project – accelerators (rf (even a little superconducting), kickers ), fusion, vacuum interrupters, satellite ion thrusters, fast switches CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
Fourth in series: • 2012, hosted by Sandia Laboratory https://www.regonline.com/builder/site/Default.aspx?EventID=1 065351 • 2011, hosted by University of Helsinki http://beam.acclab.helsinki.fi/hip/mevarc11/index.php • 2010, hosted by CERN http://indico.cern.ch/event/75380/ • 2013, hosted by us and held from 4-7 November in Chamonix http://indico.cern.ch/event/246618/overview • 2015, to be hosted by University of Helsinki CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
We now have contact with another bi-annual workshop series ISDEIV (International Symposium on Discharges and Electrical Insulation in Vacuum), and had good participation from them. We will alternate years with them from now on. Personal opinion now. We had around 55 participants. Some loss of US participation due to government shut-down. CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
Primary organizers were me and Alexia. My sincere thanks to her for her incredible efficiency! Big efforts also from Flyura Djurabekova (University of Helsinki), Matt Hopkins (Sandia Laboratory) and Sergio Calatroni (CERN). Plus lots of background help from all the CERN-based students! Thanks, thanks, thanks! CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
I will now review of content and ideas. Emphasis on newcomers and other areas. Broad, fast brush overview from presentations. We also had a half day poster session. Very good format for medium sized workshops. No rf today although a ½ day was spent at the workshop. CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
Modeling Approaches to Vacuum Arc Plasma Michael Keidar Mechanical & Aerospace Engineering The George Washington University In collaboration with: I. I. Beilis, R.L. Boxman, M.B. Schulman, E. Taylor, P. Slade, T. Zhuang, A. Shashurin, Acknowledgement: NSF, NASA, AFOSR M icro p ropulsion and N anotechnology L aboratory ( MpNL )
Micro-cathode arc thruster (µCAT)
Schematic of the μCT Feed Mechanism Isolation Material Magnetic Core Coil Anode Spring Cathode Isolator
The Free Bounda The Free Boundary Model ry Model • Assumptions – Steady-state, fully ionized, collision dominated, quasi-neutral plasma n j B m v v k Z T T – Anode acts as a passive current and particle i i i i e i n n collector kT n j B – e j E v B Cathode spots act as source of plasma at a i e n en specified jet angle and velocity n v 0 – Cathode spots evenly distributed (no arc i constriction) within a circular area j 0 – Magnetized electrons, unmagnetized ions E – External magnetic field purely axial and uniform, self field purely azimuthal 2 3 j j e kN V T 3 k T kT div ( j ) P div ( V ) • e e e e e Numerical methods 2 e – Iterative scheme for solving for the potential r 0 B r j r d r – Implicit second-order accuracy method to z r calculate the velocity, current density, and density 0 from the potential V V V V n • 1 n Two approaches: V 2 – V self consistent solution 2 n 1 ( ) V – voltage is set by high-current column 10 Keidar et al, J. Phys. D , 1996
Comparison with Experiment anode cathode Experiment: V.M. Khoroshikh, Sov. Phys. Tech. Phys., 33(6) 723 (1988) 11 Keidar, J. Appl. Phys . 1998; Rev. Sci. Instr . 2000
INITIATION of EXPLOSIVE ELECTRON EMISSION PULSES – ECTONS as INITIATION of VACUUM DISCHARGE STAGES – the BREAKDOWN, the SPARK, and the ARC J v pl Mikhail M Tsventoukh Lebedev Physical Institute of the Russian Academy of Science Gennady A Mesyats and Sergey A Barengolts Lebedev and Prokhorov Institutes of the RAS
RECENT INTEREST FOR ARCING IN FUSION Two reasons for recent interest in arcing and, in general, in collective plasma-surface interactions Large transient energy flux ( ~1 Surface fine structure, i.e. MW/cm 2 ) due to ELMs W-deposited films (edge localized modes) (ASDEX-Upgrade tiles) Layers of W-fuzz Liquid Li films on a capillary structure MAST ( megaamp. spherical tokamak )
INITIATION BY PLASMA ACTION For plasma: 10 20 cm -3 , 4 eV new explosion within t ~ 10 ns has been shown numerically Numerical modeling has been performed for the plasma action onto the wall having a microprotrusion with taking into account - thermo-field-emission, T - 2D thermal balance, 2 c div gradT grad - heating by incident plasma, t - sheath properties T grad ( T ) q q j e i e TF [ Uimanov 2003 IEEE Trans Plas Sci 31 822; Barengolts, Mesyats, Tsventoukh grad div 0 2008 JETP 107 1039 ] T grad ( ) e j i e TF
INITIATION BY PLASMA ACTION explosive overheating of a surface microprotrusion by volume Joule energy release, whereas the surface fluxes likely being balanced
‘FINE - STRUCTURE’ EFFECT on ARCING A new power threshold q > q 0 ~200 MW/cm 2 q threshold,1 << q 0 Within factor 2 of our S c limit ! Film- structure of surface absorbs the incident energy ( positive ) The condition for explosive electron emission (arcing) arise at a lower power threshold ( negative )
MeVArc 2013 1D PIC/DSMC computer modeling of near- cathode plasma layers and expansion of cathode plasma flare of vacuum arc cathode spot Dmitry L. Shmelev Institute of Electrophysics UB RAS, Ekaterinburg, Russia 106 Amundsen St., Ekaterinburg, 620016, Russia ------------------------------------------------------------------------------------------------- e-mail: shmelev@iep.uran.ru 17
1D3V PIC/DSMC model of cathode layer Problem geometry Calculation domain - 5 µm e Plasma e Ghost cell with a Cu parameters a obtained by Cathode i extrapolation e Collisions from the gap a fixed T c i U 0 voltage Flux of the atoms from the cathode is P ( T ) 0 nv calculated according to Hertz-Knudsen a 2 m T approximation a 0 Flux of the electron is calculated W , , , nv D E W N W T d according to Murphy and Good approx. e 0 W a D. Shmelev, shmelev@iep.uran.ru 18 18 Institute of Electrophysics UB RAS
1D3V PIC/DSMC model of cathode layer Results T c =4100 K, U 0 =15 V. Ions Electrons Distribution of particles Atoms returned to cathode Cathode sheath is collisional layer for ions D. Shmelev, shmelev@iep.uran.ru 19 19 Institute of Electrophysics UB RAS
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
CLIC Meeting, 7 March 2014 Walter Wuensch, CERN
Early signals of breakdown through Stochastic modeling Yinon Ashkenazy & Michael Assaf Racah Institute of Physics, Hebrew University, Jerusalem, Israel
Dislocation mediated – self organized criticality Single crystal micro-pillar compression: Dislocation mediated intermittent flow - size effects, hardening. Dislocation density inside a plane as a controlling parameter. Direct quantitative analysis of strain bursts (~20 micron). Intermittency characterized by a universal Power law burst PDF Acoustic emissions: Similar + space and time coupling between events (Weiss & Marsan, Scjence 2003 ) Earthquakes show similar PDF and spatio-temporal correlation (Kagan, Geopgysical J. (2007) Uchic, Shade & Dimiduk, Annual Review of Materials Research (2009). Dimiduk, Woodward, LeSar & Uchic : “Scale -Free Intermittent Flow in Crystal Plasticity.” Science (2006) 1188.
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