Kicker Magnet Research Articles

Electric field contributions of fast beam injection and ejection systems for particle accelerators

The effect of an electric field has been treated as smaller than that of a magnetic field in the control of a high-energy beam orbit, and it has been ignored in the magnets of almost all high-energy particle accelerators. There is currently a strong demand for high-energy accuracy field performance of the order of 1% in pulsed magnets to suppress beam loss at injection/ejection in high-intensity particle accelerators. The effect of the electric field increases as particle energy decreases. The electric field induced in a gap of pulsed magnets is complex as its characteristics vary with time and space. Here, electric field contributions to various kicker magnet systems are summarized.

Generating coherent THz radiation in electron storage rings using an ac sextupole magnet and a vertical kicker magnet

This paper proposes a new method for generating coherent radiation in the THz region from an electron storage ring. When the vertical chromaticity is modulated by an ac sextupole magnet, a vertical beam deflection caused by a kicker magnet produces a wavy spatial structure in the electron bunch after a number of revolutions. The vertically polarized synchrotron radiation from the wavy bunch becomes coherent at the wavelength of the spatial structure. This narrow bandwidth radiation is extremely strong, can be tuned by controlling ring parameters, and is easy to generate. By appropriate choice of ring parameters it is possible to generate radiation at 1 THz.

Design and Circuit Simulation of a Magnetic Switching System for Kicker Magnet Power Supply of 3 GeV RCS in J-PARC

A magnetic switching system replacing thyratron of the kicker magnet power supply in the J-PARC 3 GeV rapid cycling synchrotron (RCS) was studied for stable operation. The core of the magnetic switch is required to have a square B-H loop as an ideal switch. Nano-crystalline alloy (Finemet; FT-1H) was selected for the magnetic core. B-H curves at high magnetization rate (dB/dt) were measured. Magnetization rate dependence of magnetic field and permeability were evaluated based on magnetic domain models. We speculate that the magnetization progress is dominated by the bar-domain mode in the range of magnetization rate we measured. Low leakage current of the magnetic core before saturation flows to the kicker magnets. Closed orbit distortion, , in the RCS caused by the leakage current was evaluated. Calculated results show that the can be suppressed sufficiently. A circuit of the magnetic switching system was designed. A Spice model of the magnetic switching system is described and the simulation results are shown.

Design and Prototype Test of CSNS/RCS Injection and Extraction Magnets

The China Spallation Neutron Source (CSNS) accelerator consists of a linear accelerator (Linac), a rapid cycle synchrotron (RCS) and two beam transport lines. The injection and extraction systems of the RCS play an important role in connecting these four parts of accelerator. The injection system consists of three sets of bump magnets and two septum magnets, and the extraction system is composed of ten fast kicker magnets and a Lambertson magnet. The design of all these magnets is carefully considered. To prove the design concepts, a prototype bump magnet and a prototype kicker magnet have been successfully developed and tested.

Fast-rise high-field multi-turn coil kicker magnet operating in saturation region

A high magnetic field with a fast-rise time can be achieved even for magnets with multi-turn coils by using the excitation method over the saturation point. Through several experiments, it is shown that the proposed two- or three-turn coil magnets can be useful for ejection from particle accelerators. This method is expected to be further improved to enable the application of a high-impedance pulse generator with faster-rise outputs, and to save energy for pulse forming devices.

Fast-rise high-field kicker magnet operating in saturation

A new fast-rise and high-field kicker magnet system, based on the excitation over the saturation point of magnetic materials, is proposed. Several experiments have been carried out, and three times larger magnetic field density in a half rise time than a conventional kicker system has been achieved using a highly compact conventional magnet, with a low remanent field, less than 1 G. The new system is useful for particle ejection, especially in compact accelerators used in medical and industrial applications. The outline of this new system and experimental results are described here.

Performance of extraction kicker magnet in a rapid cycling synchrotron

Installation of the kicker magnets in the extraction section of the rapid cycling synchrotron in the J-PARC facility has been completed. They succeeded in extracting the proton beam accelerated up to 3 GeV in the first commissioning with beam. The operation parameters of the kicker system agreed well with the parameters, which were estimated from the magnetic field measurement and the current test of each power supply. The distribution of the integrated magnetic field is flat enough to meet the beam requirements. The beam based measurement of the flattop of the magnetic field was performed with the beam position monitors. Although a ringing structure was observed, which exceeded the specified limit, the degree of the flattop distortion could be corrected by the timing adjustment of the output current. The stability of the power supply is on the order of � 0:2%, which is sufficient to achieve stable beam extraction. The rise time of the output current largely depends on the gas pressure in the thyratrons. Dependence of the rise time on the gas pressure was strictly measured and the number of unwanted prefires could be reduced.

Simulations of full impact of the Large Hadron Collider beam with a solid graphite target

AbstractThe Large Hadron Collider (LHC) will operate with 7 TeV/c protons with a luminosity of 1034 cm−2 s−1. This requires two beams, each with 2808 bunches. The nominal intensity per bunch is 1.15 × 1011protons and the total energy stored in each beam is 362 MJ. In previous papers, the mechanisms causing equipment damage in case of a failure of the machine protection system was discussed, assuming that the entire beam is deflected onto a copper target. Another failure scenario is the deflection of beam, or part of it, into carbon material. Carbon collimators and beam absorbers are installed in many locations around the LHC close to the beam, since carbon is the material that is most suitable to absorb the beam energy without being damaged. In case of a failure, it is very likely that such absorbers are hit first, for example, when the beam is accidentally deflected. Some type of failures needs to be anticipated, such as accidental firing of injection and extraction kicker magnets leading to a wrong deflection of a few bunches. Protection of LHC equipment relies on the capture of wrongly deflected bunches with beam absorbers that are positioned close to the beam. For maximum robustness, the absorbers jaws are made out of carbon materials. It has been demonstrated experimentally and theoretically that carbon survives the impact of a few bunches expected for such failures. However, beam absorbers are not designed for major failures in the protection system, such as the beam dump kicker deflecting the entire beam by a wrong angle. Since beam absorbers are closest to the beam, it is likely that they are hit first in any case of accidental beam loss. In the present paper we present numerical simulations using carbon as target material in order to estimate the damage caused to carbon absorbers in case of major beam impact.

Preliminary study of residual orbit oscillation in BEPCII

BEPCII has two rings each with an injection system. The injection system of each ring consists of two kicker magnets and a septum magnet. The injection layout of two rings is the same. Both two kickers would kick the beam in horizontal plane. The betatron phase advance in the horizontal plane between two kickers is designed exactly 180° in order to reduce the perturbation to the circulating beams during injection. In fact, the residual orbit oscillation will originate because of the existence of a variety of errors. The Librea Electron BPM processor is used to acquire the beam position data in turn-by-turn mode and to analyze the residual orbit oscillation. According to the measurement results, minimization of the residual orbit oscillation can be done by adjusting the peak field strength and trigger timing delay of two kickers. With very small residual orbit oscillation the two beams can keep collision condition during the injection.

Magnetic Field Mapping and Excitation Test in Vacuum for the Kicker Magnet in J-PARC RCS

Installation of the kicker magnets in the extraction section of the RCS in J-PARC facility was completed. They extract a proton beam accelerated up to 3GeV. Since high voltage of 30 kV, which corresponds to 60 kV for charging the pulse forming line, is applied to the magnet every 40 msec, they are installed in vacuum chambers to prevent the electrical breakdown. However, magnetic field mapping is difficult in vacuum. Therefore, we performed the mapping in the air with applying one third of the operational voltage after checking linear dependence of magnetic field to exciting current. A short search coil on the 3-axis stages was used in the magnetic field mapping. The results showed that the good uniformity was achieved in the whole aperture. The magnetic field distribution of the same type of kicker magnet was in good agreement with each other. The excitation test with the operational charging voltage of 60 kV was also performed in vacuum. At the first stage, we were bothered by the electric breakdown. It was noticed that the reduction of outgassing rate by baking was very effective to suppress the discharge. And the continuous excitation was found to have a conditioning effect for the stable operation.

Overview of the 13,000 Magnets in the International Linear Collider

The international linear collider has about 80 km of beamlines which require over 13,000 magnets for focusing and steering the beams. Approximately 18% are superconducting magnets and the rest conventional warm iron-dominated magnets with copper coils, totaling about 135 styles. Superconducting technology is primarily used for the magnets located in the linacs' RF cryomodules, but it is also required for the spin rotation solenoids, damping ring wigglers, positron source undulator and beam delivery octupoles, sextupoles and final doublet quadrupoles. A major criterion for ILC magnet design is to achieve very high in spite of the very large number of magnets. The availability goal of the ILC is 85% (or better) and the magnets have been budgeted to cause no more than 0.75% down time. Alignment and mechanical stability requirements in many areas are very challenging. In the Beam delivery system, beam positions must be maintained at sub-micron levels to collide the beams at the interaction point. The ILC has 11 styles of kicker, pulsed or septum magnets. Some kickers need rise and fall times of a few ns and will require very powerful pulsers. Strategies for dealing with the major challenges confronting the ILC magnets will be described.

Field Measurement of DC Magnets at 3-GeV RCS in J-PARC

The J-PARC RCS (rapid cycling synchrotron) is designed to inject the beam from the LINAC, to change their charge from to , to accelerate the beam from 400 MeV to 3 GeV, with protons per pulse at 25 Hz repetition rate, and to extract the beam after the acceleration to the MLF (material and life science experimental facility) and the MR (main ring). Thus the RCS has the beam circulating ring and three beam transport lines. The RCS ring consists of several magnets, and the DC magnets are installed for beam injection and extraction. The four steering magnets and two septum magnets are installed at injection line in order to adjust the beam injection point. One quadratic magnet, two steering magnet and two septum magnets are installed at dump line for the part of the beam with their charge not changed from to at the charge stripping foil. Two deflecting magnets to kick out the beam without exciting the pulse kicker magnets and three septum magnets are installed at the extraction line. Up to now, the DC magnets are developed and manufactured, the field measurements are carried out, and magnets installation into the RCS tunnel are finished. The field distributions of DC magnets are measured by using the new field mapping system with three one-dimensional hall-probes on a 3-axis movable stage. In the case of the quadrupole magnet, the field measurements are not only field mapping but also analyze its magnetic higher order components by the harmonic rotating coil. As a result, the measured field quality meets the design performance requirements of the DC magnets.

Formation and fast extraction of a very short-bunched proton beam for the investigation of free radicals

For the investigation of free radicals with regards to cancer radiotherapy by ions, short-bunch formation followed by fast extraction was applied to a 7 MeV proton beam at S-LSR after electron-beam cooling. Using phase rotation with an applied RF voltage of 800 V, a short-bunch with a duration of 3.1 ns at 2 σ was created for a beam intensity of 1.4×10 8, and fast extracted by a kicker magnet. Short-bunch formation by bunched cooling with a minimum bunch length of 15.7 ns at 2 σ was also carried out with an extraction efficiency of almost 100%.

Multi-gap Pseudospark Switches for High Voltage Applications

The long-term goal of the described experiments is to construct multi-gap pseudospark switches, which can handle reliably the specifications of the pulse forming network (PFN) for the injection/extraction kicker magnet system of the future heavy ion synchrotron accelerator complex SIS100/300 at the Gesellschaft fuer Schwerionenforschung (GSI). The PFN requires an high-voltage switch, that can handle an hold-off voltage up to 70 kV, peak currents up to 6 kA and pulse durations up to 7 mus. In this paper most of the reported experimental data have been obtained by using a two-gap prototype pseudospark switch with total hold-off voltage up to 30 kV. There are two major problems correlated with the development of such multi-gap systems. The first one concerns efficient and reliable triggering of switch for the overall switch lifetime. Two trigger systems have been studied, the so-called high-dielectric trigger (HDT), which already has proven its long term capability, and second, a novel system, based upon the electron emission from carbon nanotubes (CNT). The CNT- trigger still suffers from an insufficient small lifetime of 104 discharges. The second critical part concerns the instant breakdown initiation in the individual gaps, separated by a drift space. In the experiments with this prototype an active pre-ionization of the drift space was nor foreseen. For both trigger systems the measured delay and jitter in the first gap vary from 50 to 60 ns and 15 to 30 ns, respectively; corresponding the second gap has a delay and a jitter of up to 200 and 45 ns, respectively.

Reduction of Outgassing for Suppressing Electrical Breakdown in the Kicker Magnet of J-PARC RCS

Extraction kicker magnets in the RCS of the J-PARC project are now under construction. They are pulse magnets with high charging voltage of 60 kV, which are installed in vacuum chambers. They mainly consist of aluminum alloy for the electrode plates and ferrites for the magnetic cores. Some structures of the magnet were improved to suppress discharge, and we thoroughly reduced the rate of outgassing from the components. The surface of the aluminum alloy was finished by pit-free electropolishing. Aluminum alloy and ferrites cores were baked under vacuum before construction of the magnet. They were each baked until water, which is the main outgassing component, was reduced. As a result, their outgassing rates were reduced by two or three orders of magnitude. The effect of the excitation of the magnet was examined. Outgassing of certain components increased with application of the high voltage. These components were reduced by repeated periods of continuous excitation.

Magnetic Field Measurement of the Extraction Kicker Magnet in J-PARC RCS

Kicker magnets in the J-PARC (Japan Proton Accelerator Research Complex) RCS (Rapid Cycling Synchrotron) are being constructed at JAERI (Japan Atomic Energy Research Institute) as the extraction pulse magnet. They kick the accelerated 3 GeV proton beam to the following extraction line at a repetition rate of 25 Hz. The kicker magnet is a distributed-parameter line type in order to obtain a fast rise time of the magnetic field. It is also designed with a large aperture in order to accept a maximum beam power of 1 MW. Therefore, impedance mismatch and fringe fields have a large distorting effect on the flatness of the kicker magnetic field. We examined these effects by simulation and measurement, and contrived to improve the field flatness. In this paper, we present the characteristic features of the RCS kicker systems, describe our magnetic field measurement and improvement, and briefly introduce the field mapping which we are performing now

Electromagnetic Modeling of the AGS A10 Injection Kicker Magnet

The present Alternating Gradient Synchrotron (AGS) injection kicker magnets at the A5 location were designed for 1.5 GeV proton injection. Recent high intensity runs have pushed the transfer kinetic energy to 1.94 GeV, but with an imperfect matching in transverse phase space. Space charge forces result in both fast and slow beam size growth and beam loss. A proposed increase in the AGS injection energy to 2 GeV with adequate kick strength would greatly reduce the beam losses making it possible to increase the intensity from 70 TP (70*1012 protons/s) to 100 TP. RD the design goal is to achieve a field uniformity, for protons, of plusmn3% over 90% of the cross-sectional area of the aperture. TRIUMF has proposed a design for a 12.5 Omega transmission line kicker magnet powered by a matched 12.5 Omega pulse forming line. This paper presents the results of detailed 2D and 3D electromagnetic modeling of the kicker magnet, and a novel mathematical model of the kicker

Kicker Magnet System of the RCS in J-PARC

Kicker magnets are installed in the extraction section of the RCS (Rapid Cycling Synchrotron) in J-PARC (Japan Proton Accelerator Research Complex) facility. They extract a 3 GeV proton beam and inject it into a downstream beam transport line at a repetition rate of 25 Hz. The power supply is mainly composed of the charging unit, the pulse forming network, and thyratrons as switching device. The maximum charging voltage is 80 kV. The kicker magnet is a distributed (transmission line) twin-C type. The circuit parameters are designed to have the 10 Omega characteristic impedance. The magnets are installed in vacuum chambers to prevent voltage breakdown. In order to accept 1 MW beam power, strict conditions are imposed on the kicker system. In the first part of this paper, we give an outline of the RCS extraction kicker system. Next, we report the specifications and performance of the power source and magnet. In addition, we report the measurements of the vacuum performance and magnetic field

Development of the kicker magnet for muses

In the MUSES project, kicker magnets are used for the fast extraction of ion-beams. The extraction kicker field is required to rise from approximately 10% to 99% of the full strength of 0.084 T during the time interval between bunches. The high performance of the kicker magnet is important for the efficiency of beam extraction. Based on the traveling-wave-type kicker magnet, we have succeeded in shortening field rise-time and improving the field uniformity. We have measured the magnetic field variation and distribution with a long and short search coils. To measure the field variation accurately, we have used newly devised coaxial-type attenuators instead of a conventional high-voltage probe. In order to improve the signal-to-noise ratio, two signals measured by switching the polarity of the search coil are averaged upon changing the sign. The rise-time of the waveform is approximately 83 ns, and the flat-top time is 888 ns. The uniformity of the magnetic field along the horizontal axis is better than ±0.2% in the range of 85 mm. We have developed a kicker magnet mostly satisfying our requirements for the MUSES project.

A fast kicker magnet for the PSI 600 MeV proton beam to the PSI ultra-cold neutron source

The new type of ultra-cold neutron source presently under construction at PSI requires the possibility of transporting the full high-intensity proton beam, currently 2 mA, for about 8 s every 800 s onto a spallation target located at the centre of the source. For this purpose, a fast kicker magnet with a rise time (5–95%) of 0.5 ms has been built. The required magnet and power supply have been manufactured at PSI and were installed during a shutdown. A first test of the fast beam switching process, however, for safety reasons with a reduced beam intensity of 20 μ A , was performed successfully.