Stripline Electrodes Research Articles

Reduction of beam induced RF-heating in the horizontal stripline kicker at the TPS

In preparation for 500 mA operation at the Taiwan Photon Source (TPS), we redesigned the horizontal stripline kicker for the beam feedback system to gain a smaller loss factor with higher shunt impedance. We introduced ground fenders (see figure 1) to this new design which resulted in the reduction of the loss factor and substantial increase of the kicker shunt impedance. The transverse profile of the kicker electrodes was matched to the racetrack beam pipe in the straight sections to minimize broadband impedance. The ground fenders can reduce the leakage of image currents through the gaps between the two strip line electrodes and also help to achieve a better impedance matching for the TEM modes in the transmission lines formed by the stripline electrodes and beam pipe in the kicker. The RF design and analysis of trapped resonant modes in the kicker were simulated by the 3-D electromagnetic code GdfidL [1]. Results of the RF design and analysis of trapped resonant modes will be discussed together with analytical estimates of coupled bunch instabilities at a beam current of 500 mA.

A Novel Non-Linear Strip-Line Kicker Driven by Fast Pulser in Common Mode

The next generation storage ring-based light sources adopt multi-bend achromat lattices to achieve a low emittance. The dynamic apertures of these machines are usually less than 10 mm so that the traditional pulsed local bump injection is difficult to achieve. Off-axis injection with a pulsed multipole or a non-linear kicker could be a viable solution which requires a moderate dynamic aperture of a few mm. In this paper, a novel non-linear kicker design is presented. Unlike pulsed sextupole or nonlinear kicker magnet, the nonlinear kicker we proposed is a traveling wave kicker with 2 strip-line electrodes driven by a nanosecond-level fast pulser in common mode. The disturbance to the stored beam is minimal since the perturbation is limited to the target bunch alone.

One-dimensional magneto-hydrodynamic simulation of the magnetic drive isentropic compression experiments on primary test stand

The 10 MA primary test stand (PTS), the most powerful pulse power generator in China, is used to obtain isentropic compression of Al samples under a pressure of about 100 GPa. The high performance of laser-triggered gas switches enables the precise synchronization of the 24 modules according to the required timing sequence. This advantage makes the PTS a very good platform for dynamic material compression with fundamental capability of pulse shaping. Tens of isentropic compression experiments have been conducted on the PTS, among which two distinct loading profiles were designed and used to obtain distinct compression processes. The first current, which is used to obtain a shockless compression, has a relatively smooth rise, and the rise-rate keeps almost constant during the 400 ns-long compression. The second current shape has a mild rise but a sharp ends, which is designed to make an artificial turn-point in the velocity history, which is helpful for the numerical code verification. The current profile, as well as the sample thickness, is optimized by a one-dimensional magneto-hydrodynamic (1D MHD) code MADE1D coupled with a full circuit model for the PTS. The equation of state and conductivity model used here have a wide coverage in the density, temperature and pressure range. The strength of material and its constitution model are also taken into consideration to simulate the elastic and plastic flow of metal at relatively low pressure and temperature. Compared with the experimental results, the simulated velocity at the sample/window interface is found to agree well with the measurement for most of the cases. This suggests that the MHD simulations with the circuit model are able to reflect the main process of the loading history, and help to analyze and elucidate the phenomena contributing to the compression. It shows that the current waveform is one of the most important factors that affect the loading process. For the PTS and strip-line electrodes it uses, a current rise ratio less than 15 kA/ns helps to obtain a smooth off-Hugoniot pressure rise. The temperature rise due to the pdV work is very small, and most of the sample material, except those in the skin layer where current passes through, keeps solid during the compression. However, for a current rises at 40 kA/ns or more, the ramp loading wave could be sharpened into a shock within the sample thicker than 1.2 mm. Based on the PTS flexibility of pulse shaping, a wide range of desired load processes can be gained by designing and controlling the load current and sample thickness precisely.

A new measurement method for electrode gain in an orthogonally symmetric beam position monitor

The new beam position monitor (BPM) system of the injector at the upgrade project of the Hefei Light Source (HLS II) has 19 stripline beam position monitors. Most consist of four orthogonally symmetric stripline electrodes. Differences in electronic gain and mismachining tolerance can cause changes in the beam response of the BPM electrodes. This variation will couple the two measured horizontal positions, resulting in measuring error. To alleviate this effect, a new technique to measure the relative response of the four electrodes has been developed. It is independent of the beam charge, and the related coefficient can be calculated theoretically. The effect of electrode coupling on this technique is analyzed. The calibration data is used to fit the gain for all 19 injector beam position monitors. The results show the standard deviation of the distribution of measured gains is about 5%.

Optical efficiency enhancement methods for terahertz receiving photoconductive switches

Abstract We improve the efficiency of THz receiving photoconductive switches by improving the conversion of the optical pump to signal current. This is achieved by both optimizing the incident excitation beam polarization and spatial profile of excitation. Due to boundary conditions of the electric field at the electrode edge, a nanometer-sized polarization-dependent shadow is created in the substrate at the electrode edge where most picosecond lifetime photocarriers are collected. This edge effect is further harnessed by elongating the excitation beam next to the stripline electrode. The effects of excitation beam polarization and spatial profile were experimented with InGaAs/InAlAs quantum-well-based photoconductive switch. In both cases notable enhancement in the signal is observed—30% with polarization optimization and up to 100% with beam elongation. Both techniques preserve the pulse quality and are applicable with readily available optical elements.

Characteristic analysis of coupled transmission lines in stripline-type beam position monitor

Signal transmission characteristics in stripline electrodes of a stripline-type beam position monitor (BPM) are discussed on the basis of a coupled-mode analysis in electromagnetically coupled transmission lines. The physical prospect in the calibration procedure of stripline electrodes is improved in terms of signal transmission characteristics in the frequency domain. It is demonstrated that in the signal transmission with electromagnetic coupling between the stripline electrodes, the magnetic- and electric-coupling parameters play an important role depending upon the spatial configuration and mechanical structure of the stripline electrodes. In this report, a theoretical analysis, and experimental investigation into signal transmission characteristics and performance in a standard stripline-type BPM are described in detail on the basis of a coupled-mode analysis in uniform transmission lines.

Multibunch beam extraction using the strip-line kicker at the KEK Accelerator Test Facility

The International Linear Collider (ILC) damping ring (DR) injection and extraction kickers have a very special role: the bunch spacing 189--480 ns is compressed to 3--9 ns when injected into the DR and then decompressed to 189--480 ns when leaving the DR. The kickers act as a bunch-by-bunch beam manipulator to compress and decompress the bunch spacing into/from the DR. They require a fast rise/fall time (3--9 ns) and a high repetition rate (6--2 MHz). Among the candidate technologies, the multiple strip-line kicker system is the most likely to realize the specifications for the ILC reference design. A beam extraction experiment with a prototype strip-line kicker has been carried out at the KEK Accelerator Test Facility (ATF). The kicker is composed of two units of 60-cm-long strip-line electrodes. The multibunch beam (30 bunches spaced at 5.6 ns) stored in the DR was extracted successfully with a bunch spacing of 308 ns. The measured stability of the kick angle was $3.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. Some, but not all, parameters of the tested kicker meet the ILC-DR injection/extraction kicker requirements.

Electron cloud detection and characterization in the CERN Proton Synchrotron

We describe a dedicated electron cloud experiment which was installed in the CERN Proton Synchrotron in 2007. The setup comprises shielded button-type pickups, a fast vacuum logging, a dipole magnet, and a stripline electrode to experimentally verify the beneficial effect of electron cloud clearing. The electron cloud effect was observed within the last milliseconds before ejection of the nominal LHC proton beam consisting of 72 bunches with 25 ns spacing. Measurements of electron flux at the wall and vacuum pressure are presented for a set of magnetic fields and bias voltages on the clearing electrode, showing that efficient electron cloud suppression can be obtained for appropriate clearing voltages but revealing an unexpectedly complex dependence on magnetic field and voltage.

Development of a 3 ns rise and fall time strip-line kicker for the International Linear Collider

The kicker systems for the damping rings (DR) of the International Linear Collider (ILC) assume the use of multiple units of strip-line electrodes and fast pulse power supplies for beam injection and extraction. The design of the DR with a 6.7 km circumference requires the kicker system to have a 3 ns (or 6 ns) rise and fall time and a 6 MHz (or 3 MHz) repetition rate. The development of a single unit of a kicker system having such a performance was carried out at KEK-ATF DR. A system to improve the rise and fall time of the kick field by combining two opposite-sign pulses was developed. A rise time for the kick field of less than 3 ns is achieved using this technique.

New energy-spread-feedback control system using nondestructive energy-spread monitors

A new energy-spread feedback control system using nondestructive energy-spread monitors has been developed in order to control and stabilize the energy spreads of single-bunch electron and positron beams in the KEKB injector linac. A well-controlled feedback system has been successfully working in daily operation not only for keeping the injection rate higher along with the beam-orbit and energy-feedback control system, but also for reducing the background level to the KEKB collider experiment. The energy spreads of the injection beams have been well stabilized within $0.33\ifmmode\pm\else\textpm\fi{}0.01%$ and $0.50\ifmmode\pm\else\textpm\fi{}0.02%$ ($0.55\ifmmode\pm\else\textpm\fi{}0.06%$) for the electron beam and the first (second) bunch of the high-current primary electron beam for positron production at the $180\ifmmode^\circ\else\textdegree\fi{}$ arc, respectively, and within $0.39\ifmmode\pm\else\textpm\fi{}0.01%$ ($0.36\ifmmode\pm\else\textpm\fi{}0.03%$) for the first (second) bunch of the positron beam at the end of the injector linac through the energy-spread feedback control system under the nominal operation condition. In this report we describe in detail the energy-spread feedback control system using nondestructive energy-spread monitors with multi--strip-line electrodes and their performance in KEKB operation.

High-resolution bunch-length monitor capable of measuring an rms value of a few mm

A bunch-length monitor based on detecting the beam spectrum is presented. The monitor comprises a stripline electrode and a heterodyne detector with a switch. The detailed performance of the monitor was examined on a bench as well as with a beam of the TRISTAN main ring. Calibration was carried out at a low beam current. The measured bunch lengths agree well with the calculated values. It has been demonstrated that the monitor can measure an rms bunch length of 3 mm. The repeatability of the measurement was within ±0.2 mm when the bunch length was 5.7 mm.

Tune measurement in the NSLS booster synchrotron

The NSLS booster is a 7 to 750 MeV synchrotron with a 0.7 Hz repetition rate. The betatron tunes can change during acceleration by as much as 0.1 units, causing beam loss as they cross resonance lines. Precise measurements with a conventional swept spectrum analyzer have always been difficult because of the rapid variation of tune as the magnets are ramped. We are now using a system based on a Tektronix 3052 Digital Signal Processing System that can obtain an effectively continuous measurement of both the horizontal and vertical tunes during a single acceleration cycle. Betatron oscillations are stimulated for the measurements by applying broadband noise to the beam through stripline electrodes. We will describe the instrumentation, our measurements of tune as a function of time during the acceleration cycle, and the resulting improvements to the booster operation.

A real time bunch-length monitor using the beam spectrum and measurements of bunch lengthening

A bunch length monitor used for detecting two frequency components of a beam spectrum has been developed for the TRISTAN accumulation ring (AR). The principle, design and performance of the monitor are described. The monitor comprises a stripline electrode, a coaxial cable and two identical synchronous detectors. Calibration of the monitor was carried out using the natural bunch length at a low beam current. The bunch length was measured at an injection energy of 2.5 GeV by the monitor and a streak camera. The imaginary part of the longitudinal coupling impedance was estimated by the potential well bunch lengthening and synchrotron tune shift.

Residual chirp in integrated-optic modulators

The authors have analyzed and measured the dispersion effects of residual chirp arising from asymmetry in field overlap in Mach-Zehnder structures. A clear influence of chirp was seen at 7 Gb/s and a propagation length of 75-km nondispersion shifted fiber at lambda =1.55 mu m. It is shown that a MZ-modulator with field overlap in one arm only and operated in the blue-shift mode is the best choice for single coplanar stripline (CPS) electrode MZ-modulators in this case. Calculations have shown good agreement with measured results. This indicates that a simple model for fiber mode propagation have shown good agreement with measured results. This can be used together with a FFT-algorithm for calculating the effect of residual chirp from external modulators in multigigabit dispersive fiber-optic systems. >

Full-wave analysis of traveling-wave electrodes with finite thickness for electro-optic modulators by the method of lines

In order to optimize broadband electrooptic modulators with traveling-wave electrodes, detailed information about the propagation constant, the field distribution, and the wave impedance of the modulating field is needed. To get accurate results for these characteristic values, the numerically efficient method of lines (MoL) is used. The MoL takes advantage of the planar structure by discretizing the wave equation in the directions parallel to the metallization plane, whereas an analytical formulation is retained for the transverse direction. Thus, not only the hybrid character of the modulating field but also the finite conductor thickness and anisotropy of the substrate are taken into account. Results for asymmetric coplanar stripline electrodes with typical dimensions on SiO/sub 2/ buffered LiNbO/sub 3/ are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-speed low-voltage modulation with a nonsymmetric Mach-Zehnder interferometer

The authors demonstrate broadband optical modulation with a Ti:LiNbO/sub 3/ nonsymmetric interferometer at microwave frequencies up to 16 GHz. The 3-dB bandwidth of 8.7 GHz is only slightly less than the theoretical limit of 9.6 GHz for a 1-cm-long device. The device uses a 2- mu m-thick gold-plated asymmetric stripline electrode, with a characteristic impedance of 40 Omega and ohmic loss of 3 dB/cm at 10 GHz. The DC switching voltage is 6.5 V, and the on/off ratio is -16 dB. Fabrication tolerances in the nonsymmetric interferometer are much less strict than for directional coupler modulators with comparable performance, making this device a better candidate for use in communications systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-Efficiency Ozonizer Using Traveling Wave Pulse Voltage

The energy yield of ozone generation can be raised substantially by using a fast-rising narrow pulse voltage in combination with a transmission-line type ozonizer. The pulse voltage proceeds in the form of a traveling wave to produce very active coronas. Both wire-to-cylinder type ozonizers and parallel-strip-line-with-insulator type ozonizers are tested. The former produces streamer coronas along the wire and indicates a high ozonizer-based energy yield Yo but its volume yield Yu is very low. The latter produces pulse-induced intense-glow coronas, and indicates very high Yo and Yu. However, the energy yield based on the stored energy of the pulse-forming condenser Yc still remains low, because of poor coupling of the pulse energy with the ozonizers. The plate-type ozonizer, comprising zigzag-shaped strip-line electrodes on the insulator plates, represents one of the practical embodiments of the stripline ozonizer. The pulse-peaking method provides a possibility of enhancing the level of Yo. An improvement of the coupling method is likely to improve the level of Yc.

Traveling-wave electrooptic modulator

An integrated-optics Mach-Zehnder interferometric modulator in LiNbO3 has been designed and fabricated. The electrodes are 3-μm thick asymmetric coplanar striplines formed by ion-beam etching techniques. The push–pull design and the r33 electrooptic coefficient of LiNbO3 are utilized for efficient modulation. Complete modulation is achieved with 6.5 V for the 6-mm long device at 0.83-μm wavelength and with 18 V at 1.3-μm wavelength. The 3-dB bandwidth of the modulator is 3.5 GHz, being limited by the excessive resistive loss of the stripline electrodes. Since this particular modulator retains a dc electrical bias, it performs either as an intensity modulator by applying a π/2 dc phase bias to achieve maximum linearity or as a frequency shifter by changing the dc bias point to π. In addition, we analyzed the principle of operation of the Y junction by observing both the in-phase and the out-of-phase modes of a multimode waveguide modulator.