Download or read book RF Breakdown in Accelerator Structures written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Plasma spots are known to form at field emission sites in regions of high dc or rf electric field. Several mechanisms for the formation of plasma spots in an rf field have been proposed, and one such mechanism which fits experimental data is presented in this paper. However, a plasma spot by itself does not produce breakdown. A single plasma spot, with a lifetime on the order of 30 ns, extracts only a negligible amount of energy from the rf field. The evidence for its existence is a small crater, on the order of 10 [mu]m in diameter, left behind on the surface. In this paper we present a model in which plasma spots act as a trigger to produce surface melting on a macroscopic scale (≈ 0.1 mm2). Once surface melting occurs, a plasma that is capable of emitting several kiloamperes of electrons can form over the molten region. A key observation that must be explained by any theory of breakdown is that the probability of breakdown is independent of time within the rf pulse breakdown is just as likely to occur at the beginning of the pulse as toward the end. In the model presented here, the conditions for breakdown develop over many pulses until a critical threshold for breakdown is reached.
Download or read book A Plasma Model for RF Breakdown in Accelerator Structures written by and published by . This book was released on 2000 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: A plasma model is presented for the formation of cathode spots and subsequent crater development near field emission sites on a copper surface in the presence of a strong dc electric field. Adding to previously published models, we propose that the two-stream plasma instability relates the plasma density to its dimensions. Arguments are presented that suggest that the formation and dynamics of such plasma spots are essentially the same phenomenon for both dc and rf fields. A consequence for accelerating structures is that, when such plasma spots are present, they erode the copper surface at a rate on the order of 300 micrograms per Coulomb of ion bombardment current. This erosion rate can have a measurable effect on the rf properties of an accelerating structure after processing at high gradients for a few hundred hours.
Download or read book Frequency and Pulse Length Scaling of RF Breakdown in Accelerator Structures written by and published by . This book was released on 2002 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: The plasma spot model predicts that small areas of plasma on the order of 10 microns in diameter form in regions of intense electric field near the iris tips of accelerator structures. These plasma spots act as a dc current source, injecting both electrons and ions into the rf field. The model suggests that an observable breakdown event will occur when electrons, extracted from the spot and accelerated, absorb energy faster than it can be supplied by the rf source. The resulting field collapse, which can occur during processing as the gradient is increased, is not an ultimate limit on accelerating gradient. It is conjectured that surface melting, due to electron back-bombardment at the emitting site, leads to a pseudospark-like discharge which limits the gradient and can produce massive surface damage. Using a statistical model, the dependence on frequency and pulse length of the probability of triggering a plasma spot is examined.
Download or read book Field Emission and Rf Breakdown in High gradient Room Temperature Linac Structures written by and published by . This book was released on 1997 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this article is to serve as a tutorial review on the subject of field emission and rf breakdown in high-gradient room-temperature accelerator structures and associated devices. The need to understand and control these two phenomena has become increasingly important because of the prospect of using high-gradient structures in future linear colliders. Electron field emission creates so-called dark current which parasitically absorbs rf energy, causes radiation, backgrounds, and possibly wakefields; it seems to be the precursor of rf breakdown, possibly in combination with local outgassing and plasma formation. In turn, rf breakdown limits the operation of accelerators and can cause irreversible damage to their physical structures. Research on these topics is interesting and challenging because it involves a mixture of disciplines such as surface physics, metallurgy, fabrication technologies, microwaves, beam dynamics and plasmas. This review consists of four parts: (1) field emission under dc, enhanced and rf conditions; (2) experimental set-ups; (3) prebreakdown stage--dark current and radiation; (4) experimental observations and analysis of rf breakdown. The review ends with conclusions and an outline of work that remains to be done.
Download or read book Investigations on rf breakdown phenomenon in high gradient accelerating structures written by Jiahang Shao and published by Springer. This book was released on 2018-01-19 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book mainly focuses on the experimental research of rf breakdown and field emission with novel methods, including triggering rf breakdown with high intensity laser and pin-shaped cathodes as well as locating field emitters with a high resolution in-situ imaging system. With these methods, this book has analyzed the power flow between cells during rf breakdown, observed the evolution of field emission during rf conditioning and the dependence of field emission on stored energy, and studied the field emitter distribution and origination. The research findings greatly expand the understanding of rf breakdown and field emission, which will in turn benefit future study into electron sources, particle accelerators, and high gradient rf devices in general.
Download or read book High Gradient RF Breakdown Studies written by Lisa Leanne Laurent and published by . This book was released on 2002 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Plasma based Accelerator Structures written by and published by . This book was released on 1999 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: Plasma-based accelerators have the ability to sustain extremely large accelerating gradients, with possible high-energy physics applications. This dissertation further develops the theory of plasma-based accelerators by addressing three topics: the performance of a hollow plasma channel as an accelerating structure, the generation of ultrashort electron bunches, and the propagation of laser pulses is underdense plasmas.
Download or read book High Energy Density and High Power RF written by Steven H. Gold and published by American Inst. of Physics. This book was released on 2003-12-04 with total page 474 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the sixth in a series of international workshops on high-power and high-energy density microwave devices for accelerator, plasma physics, and defense applications. Past workshops were held in Dubna, Montauk, Hayama, Pajaro Dunes, and Snowbird. The theme is research and development of techniques to increase microwave energy density and peak power in active and passive microwave devices and components ranging from L-band to W-band. The scope of this workshop has now been broadened to include radar and high power microwave (HPM) systems, space exploration, neutron sources, and even plasma heating and current drive in controlled thermonuclear fusion research.
Download or read book RF Linear Accelerators written by Thomas P. Wangler and published by John Wiley & Sons. This book was released on 2008-03-03 with total page 476 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dieses einschlägige Lehrbuch, entwickelt auf der Grundlage der Ausbildung an der US Particle Accelerator School, schließt eine Lücke in der verfügbaren Literatur zum Thema Hochfrequenz-Linearbeschleuniger, kurz RF-Linac. Nach einer Erläuterung der naturwissenschaftlichen Grundlagen und der neuesten technologischen Eckdaten stellt diese zweite Auflage neueste RF-Linacs, spezialisierte Systeme, Systeme mit Supraleitern und verschiedene Spezialverfahren vor. Übungsaufgaben an den Kapitelenden erleichtern das Einprägen und das Nacharbeiten von Vorlesungen.
Download or read book Frontiers Of Accelerator Technology Proceedings Of The Joint Us cern japan International School written by Melvin Month and published by World Scientific. This book was released on 1999-03-23 with total page 875 pages. Available in PDF, EPUB and Kindle. Book excerpt: The motivation to conceive and build accelerators comes from a most fundamental need of man — to understand and control the world around us. With beams and their associated accelerators, scientists and engineers can gain understanding of the nature of matter and modify matter, which is not possible by other means. The areas already influenced by the developments in accelerator technology are high energy and nuclear physics, atomic and molecular physics, condensed matter physics and the biological sciences. There are also a growing number of applications in medicine and industry.This book summarizes all the currently available knowledge on the rf technology driving the development of particle beams for science, medicine and industry. It is a unique collection of information on this technology.
Download or read book Advanced Accelerator Concepts written by Manoel Conde and published by American Institute of Physics. This book was released on 2006-12-13 with total page 952 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lake Geneva, Wisconsin, 10 - 15 July 2006
Download or read book Some Problems on Rf Breakdown in Room Temperature Accelerator Structure a Possible Criterion written by and published by . This book was released on 1986 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The discussion is confined to high gradient, room-temperature accelerators which have clean well-finished cavity surfaces and good vacuum conditions. Breakdown-initiating mechanisms due to ''cold'' field electron emission occurring at isolated sites on broad-area cavity surfaces, where the field is enhanced, are described. The influences of an alternating field and transition time tunneling are taken into account. The thermal instability resulting in vacuum voltage breakdown is hypothesized to derive a new criterion for room-temperature accelerator structure. 18 refs., 5 figs. (DWL).
Download or read book Industrial Accelerators and Their Applications written by Robert Wray Hamm and published by World Scientific. This book was released on 2012 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt: This unique new book is a comprehensive review of the many current industrial applications of particle accelerators, written by experts in each of these fields. Readers will gain a broad understanding of the principles of these applications, the extent to which they are employed, and the accelerator technology utilized. The book also serves as a thorough introduction to these fields for non-experts and laymen. Due to the increased interest in industrial applications, there is a growing interest among accelerator physicists and many other scientists worldwide in understanding how accelerators are used in various applications. The government agencies that fund scientific research with accelerators are also seeking more information on the many commercial applications that have been or can be developed with the technology developments they are funding. Many industries are also doing more research on how they can improve their products or processes using particle beams
Download or read book Self mapping the Longitudinal Field Structure of a Nonlinear Plasma Accelerator Cavity written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The preservation of emittance of the accelerating beam is the next challenge for plasma-based accelerators envisioned for future light sources and colliders. The field structure of a highly nonlinear plasma wake is potentially suitable for this purpose but has not been yet measured. Here we show that the longitudinal variation of the fields in a nonlinear plasma wakefield accelerator cavity produced by a relativistic electron bunch can be mapped using the bunch itself as a probe. We find that, for much of the cavity that is devoid of plasma electrons, the transverse force is constant longitudinally to within ±3% (r.m.s.). Moreover, comparison of experimental data and simulations has resulted in mapping of the longitudinal electric field of the unloaded wake up to 83 GV m-1 to a similar degree of accuracy. Lastly, these results bode well for high-gradient, high-efficiency acceleration of electron bunches while preserving their emittance in such a cavity.
Download or read book RF Breakdown in High Vacuum Multimegawatt X Band Structures written by and published by . This book was released on 2004 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: Increasing the power handling capabilities of rf components is an important issue for the design of rf accelerators and rf sources. RF breakdown is a phenomena that limit the high power performance. A major concern is the damage that can occur in rf components from breakdown. To better understand this damage, we have studied rf breakdown in a rectangular waveguide experimentally and theoretically. The breakdown process in a waveguide is both easier to measure and simulate than breakdown in a complex geometry such as an accelerating structure. We used a particle tracking code and a Particle-In-Cell code to model the breakdown behavior. Models developed for the waveguide were applied to the breakdown in accelerating structures. RF breakdown in traveling wave and standing wave accelerating structures was simulated. We compare the experimental data with results of the simulations for the accelerating structures.
Download or read book Advanced Accelerator Concepts written by Vitaly Yakimenko and published by American Inst. of Physics. This book was released on 2004-12-14 with total page 1056 pages. Available in PDF, EPUB and Kindle. Book excerpt: These proceedings cover new developments for a number of the most advanced methods for acceleration of heavy ions, protons, electrons and positrons.
Download or read book A Theory for the RF Surface Field for Various Metals at the Destructive Breakdown Limit written by and published by . This book was released on 2007 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: By destructive breakdown we mean a breakdown event that results in surface melting over a macroscopic area in a high E-field region of an accelerator structure. A plasma forms over the molten area, bombarding the surface with an intense ion current ((almost equal to) 108 A/cm2), equivalent to a pressure of about a thousand Atmospheres. This pressure in turn causes molten copper to migrate away from the iris tip, resulting in measurable changes in the iris shape. The breakdown process can be roughly divided into four stages: (1) the formation of ''plasma spots'' at field emission sites, each spot leaving a crater-like footprint; (2) crater clustering, and the formation of areas with hundreds of overlapping craters; (3) surface melting in the region of a crater cluster; (4) the process after surface melting that leads to destructive breakdown. The physics underlying each of these stages is developed, and a comparison is made between the theory and experimental evidence whenever possible. The key to preventing breakdown lies in stage (3). A single plasma spot emits a current of several amperes, a portion of which returns to impact the surrounding area with a power density on the order 107 Watt/cm2. This power density is not quite adequate to melt the surrounding surface on a time scale short compared to the rf pulse length. In a crater field, however, the impact areas from multiple plasma spots overlap to provide sufficient power density for surface melting over an area on the order of 0.1 mm2 or more. The key to preventing breakdown is to choose an iris tip material that requires the highest power density (proportional to the square of the rf surface field) for surface melting, taking into account the penetration depth of the impacting electrons. The rf surface field required for surface melting (relative to copper) has been calculated for a large number elementary metals, plus stainless-steel and carbon.
