42 Matching Results

Search Results

Advanced search parameters have been applied.

Multimoded Compact Delay Lines for Applications in High Power RF Pulse Compression Systems

Description: Pulse compression systems for future linear colliders, such as NLC and JLC, involve hundreds of kilometers of waveguide runs. These waveguides are highly overmoded to reduce the rf losses. Reducing the length of these waveguide by loading them with irises increase the losses of the system. Also, loading makes the waveguide depressive, and rf pulse shapes get distorted. In this paper we present a novel idea for utilizing the waveguides several times by using different modes. All the modes being used have low-loss characteristics. We describe mechanically simple mode transducers that switch the propagation mode from one configuration to another with no observable dispersion. We compare our theoretical designs with experimental data.
Date: July 11, 2005
Creator: Tantawi, S. G.
Partner: UNT Libraries Government Documents Department

On the RF Distribution System for a Set of Standing-Wave Accelerator Structures

Description: In this paper, we study the RF feeding system for a set of standing-wave accelerator structures. To avoid the initial reflections produced by the structures, sometimes these structures are fed in pairs through a four-port 3-dB Hybrid. We present an extension to this system for an arbitrary number of accelerator structures and show it is always possible to cancel the reflection back to the source. The necessary and sufficient condition for this to happen depends only on the spacing between accelerator structures. In this system, the structures are not fed in a binary hierarchal system, rather in series with a set of directional couplers designed to bleed off an equal amount of power to each accelerator structure in the set. We study the sensitivity of such a system to errors resulting from the differences in accelerator structures spacing. We also study the sensitivity of the system to component imperfections, such as the finite directivity of the directional couplers, and the residual reflections from the loads that are attached to these couplers. We also study the system under fault conditions, such as a breakdown in an accelerator structure or a feed waveguide.
Date: September 28, 2006
Creator: Tantawi, Sami G.
Partner: UNT Libraries Government Documents Department

Active RF Pulse Compression using Electrically Controlled Semiconductor Switches

Description: In this paper, we will present our recent results on the research of the ultra-fast high power RF switches based on silicon. We have developed a switch module at X-band which can use a silicon window as the switch. The switching is realized by generation of carriers in the bulk silicon. The carriers can be generated electrically or/and optically. The electrically controlled switches use PIN diodes to inject carrier. We have built the PIN diode switches at X-band, with <300ns switching time. The optically controlled switches use powerful lasers to excite carriers. By combining the laser excitation and electrical carrier generation, significant reduction in the required power of both the laser and the electrical driver is expected. High power test is under going.
Date: January 30, 2008
Creator: Guo, J. & Tantawi, S. G.
Partner: UNT Libraries Government Documents Department

Development of Ultra-Fast Silicon Switches for Active X-Band High Power RF Compression Systems

Description: In this paper, we present the recent results of our research on the high power ultra-fast silicon RF switches. This switch is composed of a group of PIN diodes on a high purity SOI (silicon on oxide) wafer. The wafer is inserted into a cylindrical waveguide under TE01 mode, performing switching by injecting carriers into the bulk silicon. Our current design use a CMOS compatible process and the device was fabricated at SNF (Stanford Nanofabrication Facility). This design is able to achieve sub-100ns switching time, while the switching speed can be improved further with 3-D device structure and faster circuit. Power handling capacity of the switch is at the level of 10MW. The switch was designed for active X-band RF pulse compression systems--especially for NLC, but it is also possible to be modified for other applications and other frequencies such as L-band.
Date: February 22, 2006
Creator: Guo, J. & Tantawi, S. G.
Partner: UNT Libraries Government Documents Department

Compact X-band high power load using magnetic stainless steel

Description: We present design and experimental results of a high power X-band load. The load is formed as a disk-loaded waveguide structure using lossy, Type 430 stainless steel. The design parameters have been optimized using the recently developed mode-matching code MLEGO. The load has been designed for compactness while maintaining a band width greater than 300 MHz.
Date: May 1, 1995
Creator: Tantawi, S.G. & Vlieks, A.E.
Partner: UNT Libraries Government Documents Department

Distributed Bragg Coupler for Optical All-dielectric Electron Accelerator

Description: A Bragg waveguide consisting of multiple dielectric layers with alternating index of refraction provides confinement of a synchronous speed-of-light mode with extremely low loss. There are three requirements in designing input coupler for a Bragg electron accelerator: side-coupling, selective mode excitation, and high coupling efficiency. We present a side coupling scheme using a Bragg-grating-assisted input coupler to address these three requirements. Side coupling is achieved by a second order Bragg grating with a period on the order of an optical wavelength. The phase matching condition results in resonance coupling thus providing selective mode excitation capability. We demonstrate a non-uniform distributed grating structure generating an outgoing beam with a Gaussian profile, therefore, increasing the coupling efficiency.
Date: September 30, 2005
Creator: Zhang, Z.; Tantawi, S.G.; Ruth, R.D. & /SLAC
Partner: UNT Libraries Government Documents Department

Distributed Grating-Assisted Coupler for Optical All-Dielectric Electron Accelerator

Description: A Bragg waveguide consisting of multiple dielectric layers with alternating index of refraction becomes an excellent option to form electron accelerating structure powered by high power laser sources. It provides confinement of a synchronous speed-of-light mode with extremely low loss. However, laser field can not be coupled into the structure collinearly with the electron beam. There are three requirements in designing input coupler for a Bragg electron accelerator: side-coupling, selective mode excitation, and high coupling efficiency. We present a side coupling scheme using a distributed grating-assisted coupler to inject the laser power into the waveguide. Side coupling is achieved by a grating with a period on the order of an optical wavelength. The phase matching condition results in resonance coupling thus providing selective mode excitation capability. The coupling efficiency is limited by profile matching between the outgoing beam and the incoming beam, which has normally, a Gaussian profile. We demonstrate a non-uniform distributed grating structure generating an outgoing beam with a Gaussian profile, therefore, increasing the coupling efficiency.
Date: September 23, 2005
Creator: Zhang, Z.; Tantawi, S.G.; Ruth, R.D. & /SLAC
Partner: UNT Libraries Government Documents Department

Design of Compact Multi-Megawatt Mode Converter

Description: Experience gained during recent operation of high power 11.424 GHz rf sources for accelerators led to new, more strict requirements on system components. One of the basic components of such a system is a mode converter that transforms the rectangular waveguide mode into the TE{sub 01} mode in circular waveguide. With such a converter, it is possible to minimize the use of WR90 rectangular waveguide which was shown to be a weak part of the previous system at power levels higher than 100 MW and pulse lengths on the order of a microsecond. We used several methods to design a mode converter with extremely low parasitic mode conversion and compact size. These methods employ HFSS[4] and include multi-parameter searches, concurrent optimization with a mode-matching code Cascade[2], cascading of resulting S-matrices, and tolerance analysis using perturbation techniques. This report describes the design methods and presents results.
Date: March 21, 2006
Creator: Dolgashev, V.A.; Tantawi, S.G.; Nantista, C.D. & /SLAC
Partner: UNT Libraries Government Documents Department

CLIC RF High Power Production Testing Program

Description: The CLIC Power Extraction and Transfer Structure (PETS) is a passive microwave device in which bunches of the drive beam interact with the impedance of the periodically loaded waveguide and generate RF power for the main linac accelerating structure. The demands on the high power production ({approx} 150 MW) and the needs to transport the 100 A drive beam for about 1 km without losses, makes the PETS design rather unique and the operation very challenging. In the coming year, an intense PETS testing program will be implemented. The target is to demonstrate the full performance of the PETS operation. The testing program overview and test results available to date are presented.
Date: November 2, 2011
Creator: Syratchev, I.; Riddone, G.; /CERN; Tantawi, S.G. & /SLAC
Partner: UNT Libraries Government Documents Department

Development of a Multi Megawatt Circulator for X Band

Description: Research is in progress on a TeV-scale linear collider that will operate at 5-10 times the energy of present-generation accelerators. This will require development of high power RF sources generating of 50-100 MW per source. Transmission of power at this level requires overmoded waveguide to avoid breakdown. In particular, the TE{sub 01} circular waveguide mode is currently the mode of choice for waveguide transmission at Stanford Linear Accelerator Center (SLAC) in the Multimode Delay Line Distribution System (MDLDS). A common device for protecting an RF source from reflected power is the waveguide circulator. A circulator is typically a three-port device that allows low loss power transmission from the source to the load, but diverts power coming from the load (reflected power) to a third terminated port. To achieve a low loss, matched, three port junction requires nonreciprocal behavior. This is achieved using ferrites in a static magnetic field which introduces a propagation constant dependent on RF field direction relative to the static magnetic field. Circulators are currently available at X-Band for power levels up to 1 MW in fundamental rectangular waveguide; however, the next generation of RF sources for TeV-level accelerators will require circulators in the 50-100 MW range. Clearly, conventional technology is not capable of reaching the power level required. In this paper, we discuss the development of an X-Band circulator operating at multi-megawatt power levels in overmoded waveguide. The circulator will employ an innovative coaxial geometry using the TE{sub 01} mode. Difficulties in maintaining mode purity in oversized rectangular guide preclude increasing guide area to allow increasing the power level to the desired 50-100 MW range. The TE{sub 01} mode in circular waveguide is very robust mode for transmission of high power in overmoded waveguide. The mode is ideal for transmission of high power microwaves because of its ...
Date: March 24, 2008
Creator: Neilson, J.; Ives, L. & Tantawi, S. G.
Partner: UNT Libraries Government Documents Department

Design and Test of a 100MW X Band TE01 Window

Description: Research at Stanford Linear Accelerator Center (SLAC) is in progress on a TeV-scale linear collider that will operate at 5-10 times the energy of present generation accelerators. This will require development of high power X-Band sources generating 50-100 MW per source. Conventional pillbox window designs are capable of transmitting peak rf powers up to about 30 MW, well below the desired level required for the use of a single window per tube. SLAC has developed a 75 MW TE{sub 01} window [1] that uses a 'traveling wave' design to minimize fields at the window face. Irises match to the dielectric window impedance, resulting in a pure traveling wave in the ceramic and minimum fields on the window face. The use of the TE{sub 01} mode also has zero electric field on the braze fillet. Unfortunately, in-band resonances prevented this window design from achieving the desired 75MW power level. It was believed the resonances resulted from sudden steps in the circular guide to match the 38mm input diameter to the overmoded (TE{sub 01} and TE{sub 02} mode propagating) 65 mm diameter of the window ceramic. Calabazas Creek Research Inc. is currently developing a traveling wave window using compact, numerically optimized, parabolic tapers to match the input diameter of 38mm to the window ceramic diameter of 76mm (Figure 1). The design is projected to handle 100 MW of pulse power with a peak field at the window face of 3.6 MV/m. Cold test of the window has shown the return loss to be better than -25 dB over a 100 MHz bandwidth and to be resonance free (Figure 2). The window is scheduled for high-power testing in July 2003 at the SLAC.
Date: March 24, 2008
Creator: Neilson, J.; Ives, L. & Tantawi, S. G.
Partner: UNT Libraries Government Documents Department

Reduced field TE{sub 01} X-Band traveling wave window

Description: The RF electric field is reduced by more than a factor of two using a pair of symmetrically located irises in a new type of klystron window operating in the TE{sub 01} mode at X-Band. The advantages of this window over the usual TE{sub 01} half-wave resonant window are discussed as well as theory and operating results. Ultra high purity alumina formed by the HIP process is used. This window has been successfully tested at 100 MW with a 1.5 microsecond RF pulse width and is being used on the XL series klystrons.
Date: December 31, 1995
Creator: Fowkes, W.R.; Callin, R.S.; Tantawi, S.G. & Wright, E.L.
Partner: UNT Libraries Government Documents Department

Status of High Power Tests of Normal Conducting Single-Cell Structures

Description: We report the results of ongoing high power tests of single-cell standing wave structures. These tests are part of an experimental and theoretical study of rf breakdown in normal conducting structures at 11.4 GHz. The goal of this study is to determine the maximum gradient possibilities for normal-conducting rf powered particle beam accelerators. The test setup consists of reusable mode launchers and short test structures powered by SLACs XL-4 klystron. The mode launchers and structures were manufactured at SLAC and KEK and tested at the SLAC klystron test laboratory.
Date: November 4, 2011
Creator: Dolgashev, V.A.; Tantawi, S.G.; /SLAC; Higashi, Y.; Higo, T. & /KEK, Tsukuba
Partner: UNT Libraries Government Documents Department

High Power Tests of Normal Conducting Single-Cell Structures

Description: We report the results of the first high power tests of single-cell traveling-wave and standing-wave structures. These tests are part of an experimental and theoretical study of rf breakdown in normal conducting structures at 11.4 GHz. The goal of this study is to determine the gradient potential of normal-conducting rf-powered particle beam accelerators. The test setup consists of reusable mode converters and short test structures and is powered by SLAC's XL-4 klystron. This setup was created for economical testing of different cell geometries, cell materials and preparation techniques with short turn-around time. The mode launchers and structures were manufactured at SLAC and KEK and tested in the SLAC Klystron Test Lab.
Date: November 7, 2007
Creator: Dolgashev, V.A.; Tantawi, S.G.; Nantista, C.D.; /SLAC; Higashi, Y.; Higo, T. et al.
Partner: UNT Libraries Government Documents Department

Waveguide Structures for RF Undulators with Applications to FELs and Storage Rings

Description: RF undulators, suggested a long time ago, have the advantage of fast dynamic control of polarization, undulator strength and wavelength. However, RF undulators require very strong RF fields in order to produce radiation of the same order as conventional static devices. Very high power RF energy confined inside a waveguide or a cavity can provide the necessary RF fields to undulate the electron beam. However, the wall losses in the waveguide should be low enough to make it practically feasible as a CW or quasi CW undulator and, hence, competitive with static devices for applications to storage rings and FELs. Here we present various waveguide structures such as smooth walled and corrugated walled waveguides and various RF modes. We will show that there are some advantages in operating with higher order modes and also with hybrid modes in the corrugated guide. We will show that the RF power requirement for some of these modes will permit a quasi CW operation of the undulator, thus permitting its operation in a storage ring.
Date: November 2, 2011
Creator: Yeddulla, M.; Geng, H.G.; Huang, Z.; Ma, Z.; Tantawi, S.G. & /SLAC
Partner: UNT Libraries Government Documents Department

Damping Effect Studies for X-band Normal Conducting High Gradient Standing Wave Structures

Description: The Multi-TeV colliders should have the capability to accelerate low emittance beam with high rf efficiency, X-band normal conducting high gradient accelerating structure is one of the promising candidate. However, the long range transverse wake field which can cause beam emittance dilution is one of the critical issues. We examined effectiveness of dipole mode damping in three kinds of X-band, {pi}-mode standing wave structures at 11.424GHz with no detuning considered. They represent three damping schemes: damping with cylindrical iris slot, damping with choke cavity and damping with waveguide coupler. We try to reduce external Q factor below 20 in the first two dipole bands, which usually have very high (R{sub T}/Q){sub T}. The effect of damping on the acceleration mode is also discussed.
Date: August 3, 2009
Creator: Pei, S.; Li, Z.; Tantawi, S.G.; Dolgashev, V.A.; Wang, J. & /SLAC
Partner: UNT Libraries Government Documents Department

RF Breakdown in Normal Conducting Single-Cell Structures

Description: Operating accelerating gradient in normal conducting accelerating structures is often limited by rf breakdown. The limit depends on multiple parameters, including input rf power, rf circuit, cavity shape and material. Experimental and theoretical study of the effects of these parameters on the breakdown limit in full scale structures is difficult and costly. We use 11.4 GHz single-cell traveling wave and standing wave accelerating structures for experiments and modeling of rf breakdown behavior. These test structures are designed so that the electromagnetic fields in one cell mimic the fields in prototype multicell structures for the X-band linear collider. Fields elsewhere in the test structures are significantly lower than that of the single cell. The setup uses matched mode converters that launch the circular TM{sub 01} mode into short test structures. The test structures are connected to the mode launchers with vacuum rf flanges. This setup allows economic testing of different cell geometries, cell materials and preparation techniques with short turn-around time. Simple 2D geometry of the test structures simplifies modeling of the breakdown currents and their thermal effects.
Date: February 22, 2006
Creator: Dolgashev, V.A.; Nantista, C.D.; Tantawi, S.G.; /SLAC; Higashi, Y.; Higo, T. et al.
Partner: UNT Libraries Government Documents Department

Investigations into Cost Reductions of X-band Instrumentation

Description: The prohibitive costs of commercial test equipment for making fast and accurate pulsed phase and amplitude measurements at X-Band result in decreased productivity due to shortages of shared equipment across the test laboratory. In addition, most current set-ups rely on the use of pulsed power heads which do not allow for the measurement of phase thereby limiting the flexibility of available measurements. In this paper, we investigate less expensive in-house designed instrumentation based upon commercial satellite down converters and widely available logarithmic detector amplifiers and phase detectors. The techniques are used to measure X-Band pulses with widths of 50 ns to 10's of usec. We expect a dynamic range of 30-40 dB with accuracies of better than +/- 0.1 dB and +/- 1 degree of phase. We show preliminary results of the built and tested modules. Block diagrams of the down conversion scheme, and the architecture of a multi-signal X-band RF monitor and measurement system is illustrated. Measured results, and possible modifications and upgrades are presented.
Date: May 15, 2009
Creator: Van Winkle, D.; Dolgashev, V.A.; Fox, J.D.; Tantawi, S.G. & /SLAC
Partner: UNT Libraries Government Documents Department

Design of a multi-megawatt x-band solid state microwave switch

Description: The authors present design methodology for high power microwave switches. Among all possible applications for such a switch they emphasize the design parameters for application to the pulse compression system associated with the Next Linear Collider (NLC). The switch is based on the excitation of a plasma layer within a silicon wafer by either a laser or an electron beam. They investigate problems associated with high power operation of such a switch. Mainly, they explore solutions to the problems of thermal runaway, avalanche breakdown, photo-emission, and secondary emission. Different design methodologies are presented.
Date: July 1, 1995
Creator: Tantawi, S.G.; Lee, T.G.; Ruth, R.D.; Vlieks, A.E. & Zolotorev, M.
Partner: UNT Libraries Government Documents Department