Accelerator Technology RECFA report 2017 HIP Kenneth sterberg
Accelerator Technology RECFA report 2017 HIP Kenneth Österberg, Helsinki Institute of Physics and Department of Physics, University of Helsinki, Finland
Overview Introduction Accelerator technology @ HIP Multiscale physics modelling of breakdown Module, RF structures & manufacturing Summary Compact Linear Collider (CLIC) Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 2
CLIC Finland Finnish CLIC activity initiated by industry request 15 years ago First copper fatigue & high precision manufacturing 10 years ago started activity on high precision assembly & mechanical modelling @ HIP 8 years ago started activity on multiscale physics modelling of breakdown @ HIP 5 years ago started activity on development of diagnostics methods for CLIC RF structures Last years extending activities beyond CLIC Mainly based on external funding (EU, Academy of Finland, CERN, private foundations etc. . ) Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 3
Accelerator technology @ HIP Multiphysics simulations of Materials for accelerator technology Flyura Djurabekova onset of vacuum electrical breakdowns 2 staff, 2 Post-docs, 7 Ph. D students (9. 6 FTE) Multiphysics simulations of vacuum electrical breakdowns Thesis (since 2010): 4 Ph. D (1 female), 7 MSc (2 female) & 4 BSc Publications (since 2010): 28 in refereed journals & 3 in conf. proc. Modules, structures & manufacturing Markus Aicheler 3 staff & seniors, 3 Ph. D students (4. 3 FTE) CLIC RF structure & module assembly Diagnostics of CLIC RF structures Thesis (since 2010): 7 MSc eng. (1 female) & 2 BSc Publications (since 2010): 5 in ref. journals & 13 conf. proc. or similar Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 4
CLIC accelerating structure (AS) 11. 994 GHz X-band Outside Inside 6 mm diameter beam aperture, 25 cm long The high field leads to ‘classic’ vacuum breakdown: v field emission; v neutral copper emission; v plasma formation; v k. A currents; v collapse of fields. Beam kicked, luminosity or emittance reduced Without well-developed theoretical understanding of the breakdown process, difficult to find a solution Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 5
Multiscale modelling of breakdown F. Djurabekova Model: Results: Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 6
Research highlights 1 F. Djurabekova Main outcome: breakdown behavior of different materials correlated with dislocation activity. E. g. undersurface void which breaks through surface, when high electric field applied to surface (“catastrophic” growth of a protrusion, see video below) [A. S. Pohjonen, S. Parviainen, T. Muranaka, and F. Djurabekova, J. Appl. Phys. 114, 033519 (2013)]) Direction of applied electric field Side slice of the system Accelerator technology, RECFA, 19. 5. 2017 the top view K. Österberg 7
8 2 / 1 / 2 0 2 2 Research highlights 2 F. Djurabekova Dislocation motion strongly related to crystal structure of metals. w dislocations most mobile in FCC & least in HCP crystal structures. Dislocation-based model to explain breakdown rate dependence on accelerating gradient, empirically described by ~E 30 law. A. Descoeudres, F. Djurabekova, and K. Nordlund, DC Breakdown experiments with cobalt electrodes, CLIC-Note 875 (2009). (After A. Descoeudres et a. in [Phys. Rev. ST Accel. Beams 12, 092001 (2009) ]) K. Nordlund and F. Djurabekova, Phys. Rev. ST-AB 15, 071002 (2012). Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 8
Research highlights 3 F. Djurabekova Dislocation-mediated mechanisms confirmed @ CERN: copper, initially harder, conditioned faster than copper thoroughly annealed in a certain thermal cycle, i. e. conditioning = hardening! w Below: hard copper conditions much faster than soft copper as function of number of short pulses. [A. Korsbäck, W. Wuensch, F. Djurabekova et al. , to be published] Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 9
1 2 / 0 1 / 2 0 2 2 Current activities Surface diffusion under electric fields F. Djurabekova Recently tip growth on metal surface been shown by applying simultaneously fs-laser & large electric bias. [H. Yanagisawa, F. Djurabekova et al. , Applied Physics Letters: Photonics 1, 091305 (2016), ] May be relevant for CLIC, local heating combined with pulsed electric field. Develop model to simulate diffusion process under electric field. Implement dipole moment of surface atoms affecting diffusional jumps of surface atoms via gradient of electric field, present near sharp surface features. Result shows that growth occurs above local fields of ~1. 8 x 1010 V/m, corresponding to applied fields of 6 GV/m. Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 10
Future plans F. Djurabekova Recently, started performing electrical breakdown experiments with a fixed gap setup to better employ potential of existing infrastructure at Department of Physics’ Accelerator Laboratory. Plan to use available Tandem accelerator to modify electrode surfaces to investigate it’s ability to withstand high electric fields. Establish collaboration Fixed gap system for with other groups @ HIP breakdown experiments to enhance microscopy analysis of studied structures. Currently strong collaboration with CERN, Hebrew University of Jerusalem, Tartu University and Uppsala University. Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 11
Load effect on stripping foils @ FAIR F. Djurabekova Best candidates for charge stripping foils: different carbon ones. To reduce effect of foil material on incoming heavy ion beam, density of charge stripping foils must be kept very low. Develop models to describe interaction of fast heavy ions on electronic structure of stripping foils. Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 12
Module & RF structures for CLIC M. Aicheler Assembly & precision manufacturing of CLIC module & RF structures (co-leading CLIC prototype module assembly) Diagnostics for CLIC RF structures (material analysis, internal geometry measurement, …) Close links to Finnish high precision manufacturers Me. Chan. ICs – FP 7 IAPP project 2010 -14 for knowledge exchange on high precision manufacturing between Finnish companies and CERN. Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 13
CLIC module assembly m assembly of repeatable 2 m long sections of CLIC M. (“CLIC Aicheler module”) needed to achieve required luminosity. Integration of subsystems & constant interaction with them. Design, modelling and assembly of CLIC module prototypes to test solutions & viability. New test programme starting 2017. CTF 3 CLEX module CLIC lab module Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 14
RF structure internal geometry 1 E. Haeggström & K. Österberg Need to verify m precision of RF structure also after assembly. Developing Fourier domain short coherence interfermometry (FDSCI) method for non-contact measurement at m precision. Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 15
RF structure internal geometry 2 E. Haeggström & K. Österberg Precision & method proven [R. Montonen et al. , Appl. Opt. 54, 4635 (2015)]. Currently working on probe head alignment & stability. Also applicable for roughness measurement [R. Montonen et al. , Opt. Exp. 25, 12090 (2017)] that is important RF structure operation. 50 mm End face of the prism provides reference reflection for interferometry 5 mm Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 16
Dynamic vacuum measurement E. Haeggström & K. Österberg Simulations predict outgassing from CLIC AS during RF pulse to be below levels that might affect the beam significantly. To verify predictions, develop method to measure small changes of gas quantity. Also interesting for understanding breakdowns. First tests at CERN fixed gap system for breakdown experiments. lamp on Lamp On Light in Light out? PMT 1 7 of Accelerator technology, RECFA, 19. 5. 2017 Absorption Spark break down ~40 000 x Larger than Lamp K. Österberg 17
Acoustic microscopy of Cu samples E. Haeggström & K. Österberg Measure elasticity of Cu samples after RF pulsing or breakdown. Material elasticity related to bulk & shear modulus. Light 0. 1 mm Ultrasound Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 6. 3. 201 1 8 18
Other activities & proposals M. Aicheler, K. Österberg Flask project: design & construction of movable radiation shielded manipulator for highly active Super-FRS beam-line components. Contributing to design & manufacturing development. Proposal of beam instrumentation related activity in close collaboration with CERN BE/BI group. Thermo accoustic cooling of rest gas ionization monitor based on TIMEPIX chip placed directly in vacuum chamber. Transferring CLIC expertise to FELs. Part of Xb. FEL proposal (http: //xbandfel. web. cern. ch/) for engineering and manufacturing. CERN Accelerator School 2018 (beam instrumentation) in Finland C Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 19
Summary Accelerator technology activities @ HIP give important contributions to R&D of CLIC and high gradient accelerators. Improved physics understanding breakdown in CLIC AS structures has led to improved design & performance. w CLIC module prototyping program important for feasibility and cost. w Novel RF structure diagnostics methods show interesting potential w Expanding accelerator activities @ HIP beyond CLIC Desire to continue to contribute to high energy frontier accelerator R&D. Accelerator technology, RECFA, 19. 5. 2017 K. Österberg 20
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