Arnold Vlieks

Bio: Arnold Vlieks is an academic researcher from Stanford University. The author has contributed to research in topics: Particle accelerator & Klystron. The author has an hindex of 16, co-authored 93 publications receiving 843 citations. Previous affiliations of Arnold Vlieks include University of California, Davis.

High-gradient electron accelerator powered by a relativisitic klystron.

Abstract: We have used relativistic klystron technology to extract 290 MW of peak power at 11.4 GHz from an induction linac beam, and to power a short 11.4-GHz high-gradient accelerator. We have measured rf phase stability, field emission, and the momentum spectrum of an accelerated electron beam. An average accelerating gradient of 84 MV/m has been achieved with 80 MW of relativistic klystron power.

Active high-power RF pulse compression using optically switched resonant delay lines

Abstract: We present the design and a proof of principle experimental results of an optically controlled high-power RP pulse-compression system. In principle, the design should handle a few hundreds of megawatts of power at X-band. The system is based on the switched resonant delay-line theory [1]. It employs resonant delay lines as a means of storing RF energy. The coupling to the lines is optimized for maximum energy storage during the charging phase. To discharge the lines, a high-power microwave switch increases the coupling to the lines just before the start of the output pulse. The high-power microwave switch required for this system is realized using optical excitation of an electron-hole plasma layer on the surface of a pure silicon wafer. The switch is designed to operate in the TE/sub 01/ mode in a circular waveguide to avoid the edge effects present at the interface between the silicon wafer and the supporting waveguide; thus, enhancing its power handling capability.

The Next Linear Collider Test Accelerator

Abstract: During the past several years, there has been tremendous progress on the development of the RF system and accelerating structures for a Next Linear Collider (NLC). Developments include high-power klystrons, RF pulse compression systems and damped/detuned accelerator structures to reduce wakefields. In order to integrate these separate development efforts into an actual X-band accelerator capable of accelerating the electron beams necessary for an NLC, we are building an NLC Test Accelerator (NLCTA). The goal of the NLCTA is to bring together all elements of the entire accelerating system by constructing and reliably operating an engineered model of a high-gradient linac suitable for the NLC. The NLCTA will serve as a testbed as the design of the NLC evolves. In addition to testing the RF acceleration system, the NLCTA is designed to address many questions related to the dynamics of the beam during acceleration. In this paper, we will report on the status of the design, component development, and construction of the NLC Test Accelerator. >

Breakdown phenomena in high power klystrons

Abstract: In the course of developing new high-peak-power klystrons, high electric fields in several regions of these devices have become an important source of vacuum breakdown. In addition, a renewed interest in breakdown phenomena for nanosecond-pulse, megavolt-per-centimeter fields has been sparked by recent work in the area of gigawatt RF sources. The most important regions of electrical breakdown are in the output cavity gap area, the RF ceramic windows, and the gun ceramic insulator. The experiments and results on the breakdown in these regions are discussed, as well as the solutions to alleviate this breakdown problem. >

Breakdown phenomena in high-power klystrons

Abstract: In the course of developing new high-peak-power klystrons, high electric fields in several regions of these devices have become an important source of vacuum breakdown. In addition, a renewed interest in breakdown phenomena for nanosecond-pulse, megavolt-per-centimeter fields has been sparked by recent work in the area of gigawatt RF sources. The most important regions of electrical breakdown are in the output cavity gap area, the RF ceramic windows, and the gun ceramic insulator. The experiments and results on the breakdown in these regions are discussed, as well as the solutions to alleviate this breakdown problem. >

Naturalness, weak scale supersymmetry, and the prospect for the observation of supersymmetry at the Fermilab Tevatron and at the CERN LHC

Abstract: Naturalness bounds on weak scale supersymmetry in the context of radiative breaking of the electroweak symmetry are analyzed. In the case of minimal supergravity it is found that for low $\mathrm{tan}\ensuremath{\beta}$ and for low values of fine-tuning $\ensuremath{\Phi},$ where $\ensuremath{\Phi}$ is defined essentially by the ratio ${\ensuremath{\mu}}^{2}{/M}_{Z}^{2}$ where $\ensuremath{\mu}$ is the Higgs mixing parameter and ${M}_{Z}$ is the $Z$ boson mass, the allowed values of the universal scalar parameter ${m}_{0},$ and the universal gaugino mass ${m}_{1/2}$ lie on the surface of an ellipsoid with radii fixed by $\ensuremath{\Phi}$ leading to tightly constrained upper bounds $\ensuremath{\sim}\sqrt{\ensuremath{\Phi}}.$ Thus for $\mathrm{tan}\ensuremath{\beta}l~2(l~5)$ it is found that the upper limits for the entire set of sparticle masses lie in the range $l700 \mathrm{GeV} (l1.5 \mathrm{TeV})$ for any reasonable range of fine-tuning $(\ensuremath{\Phi}l~20).$ However, it is found that there exist regions of the parameter space where the fine-tuning does not tightly constrain ${m}_{0}$ and ${m}_{1/2}.$ Effects of nonuniversalities in the Higgs boson sector and in the third generation sector on naturalness bounds are also analyzed and it is found that nonuniversalities can significantly affect the upper bounds. It is also found that achieving the maximum Higgs boson mass allowed in supergravity unified models requires a high degree of fine-tuning. Thus a heavy sparticle spectrum is indicated if the Higgs boson mass exceeds 120 GeV. The prospect for the discovery of supersymmetry at the Fermilab Tevatron and at the CERN LHC in view of these results is discussed.

Flashover of insulators in vacuum: review of the phenomena and techniques to improved holdoff voltage

Abstract: Reviews surface flashover of insulator, primarily in vacuum, although some comments are made about the effect of ambient gases on surface flashover. It presents theoretical mechanisms of surface flashover and pertinent experimental results. The holdoff voltage of insulators depends upon many insulator parameters, such as material, geometry, surface finish, and attachments to electrodes, but also on the applied voltage waveform (duration, single pulse or repetitive), the process history of the insulator operating environment, and previous applications of voltage. Several suggestions are made regarding choice of the material, geometry, and processing when selecting an insulator for a particular application. Some specific techniques for improving the holdoff voltage of insulators are recommended. >

New local field quantity describing the high gradient limit of accelerating structures

Abstract: A new local field quantity is presented which gives the high gradient performance limit of accelerating structures due to vacuum rf breakdown. The new field quantity, a modified Poynting vector ${S}_{c}$, is derived from a model of the breakdown trigger in which field emission currents from potential breakdown sites cause local pulsed heating. The field quantity ${S}_{c}$ takes into account both active and reactive power flow on the structure surface. This new quantity has been evaluated for many X-band and 30 GHz rf tests, both traveling wave and standing wave, and the value of ${S}_{c}$ achieved in the experiments agrees well with analytical estimates.

High-Power Multimode X-Band RF Pulse Compression System for Future Linear Colliders

Abstract: We present a multimode $X$-band rf pulse compression system suitable for a TeV-scale electron-positron linear collider such as the Next Linear Collider (NLC). The NLC main linac operating frequency is 11.424 GHz. A single NLC rf unit is required to produce 400 ns pulses with 475 MW of peak power. Each rf unit should power approximately 5 m of accelerator structures. The rf unit design consists of two 75 MW klystrons and a dual-moded resonant-delay-line pulse compression system that produces a flat output pulse. The pulse compression system components are all overmoded, and most components are designed to operate with two modes. This approach allows high-power-handling capability while maintaining a compact, inexpensive system. We detail the design of this system and present experimental cold test results. We describe the design and performance of various components. The high-power testing of the system is verified using four 50 MW solenoid-focused klystrons run off a common 400 kV solid-state modulator. The system has produced 400 ns rf pulses of greater than 500 MW. We present the layout of our system, which includes a dual-moded transmission waveguide system and a dual-moded resonant line (SLED-II) pulse compression system. We also present data on the processing and operation of this system, which has set high-power records in coherent and phase controlled pulsed rf.