High power fast kicker system for SNS beam extraction

The ion source for the Spallation Neutron Source (SNS) is a radio-frequency, multicusp source designed to deliver H− beam pulses of 45 mA to the SNS accelerator, with a pulse length of 1 ms and a repetition rate of 60 Hz. In order to achieve this performance the source must operate with both high peak rf power, ∼45 kW, and high average rf power, ∼3 kW, over an operational run period of 3 weeks. The most critical source component in this respect is the plasma-immersed, porcelain coated rf antenna which can be susceptible to damage during high power operation. The DESY group has developed an external antenna configuration utilizing an Al2O3 plasma chamber which has demonstrated a very long operational period exceeding 25 000 h. Their source operates with peak rf powers comparable to the SNS source but with greatly reduced average rf powers, ∼50 W. In order to explore the applicability of this external antenna concept to high average power ion sources like the SNS source, we have performed thermal, mechanical, and electromagnetic analyses of the Al2O3 plasma chamber. This article discusses the final design which has resulted from these studies as well as estimates of the power limitations of such devices.

Induction machines have the unique capability of delivering very high current and peak power in a pulsed mode. It was the need for high power for fusion that led Nicholas Christofilus in the 1950’s to invent and build Astron, the first induction accelerator [1]. Since then, various high power applications have led to the construction of the Electron Ring Accelerator (ERA) [2], Experimental Test Accelerator (ETA) [3], Advanced Test Accelerator (ATA) [4], the flash radiography machine FXR and the high repetition rate machine, ETA II [5], which was designed to deliver high average power as well as high peak power. The largest of these machines is ATA with design goals of 50 MeV and 10 kA. All of the high current electron machines since ERA are “short-pulse” devices ( 50 ns). Meanwhile, the invention of heavy ion fusion in the 70’s led to the development of induction machines for ion acceleration [6]. For this application, the devices tend to have long pulses (>1 μs). The induction machines for ions and electrons operate on the same principle. The pulse length difference between electron and ion machines is historical and incidental, although long-pulse devices lead to different approaches to magnetic material and pulse power technology than short-pulse machines. While some of the past applications, particularly those related to the Strategic Defense Initiative, have come and gone, the need for high power continues to exist in energy, environment, national defense, and basic sciences. In this paper, we will review three ongoing applications, one in fusion energy, one in defense, and one in high energy physics. Induction machines for heavy ion fusion [7], for radiography in hydrodynamic tests [8], and for relativistic-klystron twobeam-accelerators [9] are three areas of active research. Induction machines have also been considered for other applications such as treatment of nuclear wastes [10], neutron spallation sources [11], and μμ collider components [12]. These applications will not be reviewed here because of space limitations. In addition, the inductive voltage adder (IVA) technologies are described in a separate paper in these proceedings [13]. The three applications we will review were chosen to demonstrate that with vastly different goals, different machine parameters, and very different architectures, a similar set of performance objectives has led to technological advances along closely parallel paths. In any large machine, the economic issues of cost and efficiency, and the technological issues of machine and beam performance are equally important considerations. We hope to show how these factors have affected the development paths in these three areas. We will first summarize recent activities in each one of these fields, and then proceed to describe issues and advances in the control of beam energy flatness, emittance preservation, and beam instability suppression. While these issues are common to all accelerators, the fact that we are working with very intense beams and long pulses makes the challenges of induction machines unique. For the purpose of this review, we will broadly include the induction accelerators proper, as well as their injectors.

In a paper presented at the 1977 Particle Accelerator Conference, R. Faulkner and R. Cooper outlined the design of the LAMPF Line D Fast Kicker System. At that time the prototype had been constructed and initial tests were complete. After the Kicker was reassembled in final operating configuration, some components were extensively modified, and considerable operational experience has since been obtained. The system has now operated in production for over 500 hours. The modifications made to the original design were few but important in terms of reaching the system design objectives. Much of the continuing component development program has centered on upgrading reliability at sustained high average power levels. The Kicker is presently capable of delivering 7-μs-long pulses at a 120-Hz repetition rate with a peak current of 5800 A. It has operated for complete LAMPF prodtuction cycles without maintenance. Continued development work has concentrated on the high power load resistor, the pulse forming network (PFN) capacitor bank, the charging inductor, and the elimination of component failure caused by high voltage/current discharges. This paper discusses Kicker problem areas and solutions.

DOE proposes to construct and operate a state-of-the-art, short-pulsed spallation neutron source comprised of an ion source, a linear accelerator, a proton accumulator ring, and an experiment building containing a liquid mercury target and a suite of neutron scattering instrumentation. The proposed Spallation Neutron Source would be designed to operate at a proton beam power of 1 megawatt. The design would accommodate future upgrades to a peak operating power of 4 megawatts. These upgrades may include construction of a second proton accumulator ring and a second target. The U.S. needs a high-flux, short-pulsed neutron source to provide the scientific and industrial research communities with a much more intense source of pulsed neutrons for neutron scattering research than is currently available, and to assure the availability of a state-of-the-art facility in the decades ahead. This next-generation neutron source would create new scientific and engineering opportunities. In addition, it would help replace the neutron science capacity that will be lost by the eventual shutdown of existing sources as they reach the end of their useful operating lives in the first half of the next century. This document analyzes the potential environmental impacts from the proposed action and the alternatives. The analysis assumes a facility operating at a power of 1MW and 4 MW over the life of the facility. The two primary alternatives analyzed in this EIS are: the proposed action (to proceed with building the Spallation Neutron Source) and the No-Action Alternative. The No-Action Alternative describes the expected condition of the environment if no action were taken. Four siting alternatives for the Spallation Neutron Source are evaluated: Oak Ridge National Laboratory, Oak Ridge, TN, (preferred alternative); Argonne National Laboratory, Argonne, IL; Brookhaven National Laboratory, Upton, NY; and Los Alamos National Laboratory, Los Alamos, NM.

The Department of Energy (DOE) has given the Spallation Neutron Source (SNS) project approval to begin Title I design of the proposed facility to be built at Oak Ridge National Laboratory (ORNL). During the conceptual design phase of the SNS project, the target station bulk-biological shield was characterized and the activation of the major target station components was calculated. Shielding requirements were assessed with respect to weight, space, and dose-rate constraints for operating, shutdown, and accident conditions utilizing the SNS shield design criteria, DOE Order 5480.25, and requirements specified in 10 CFR 835. Since completion of the conceptual design phase, there have been major design changes to the target station as a result of the initial shielding and activation analyses, modifications brought about due to engineering concerns, and feedback from numerous external review committees. These design changes have impacted the results of the conceptual design analyses, and consequently, have required a re-investigation of the new design. Furthermore, the conceptual design shielding analysis did not address many of the details associated with the engineering design of the target station. In this paper, some of the proposed SNS target station preliminary Title I shielding design analyses will be presented. The SNS facility (with emphasis on the target station), shielding design requirements, calculational strategy, and source terms used in the analyses will be described. Preliminary results and conclusions, along with recommendations for additional analyses, will also be presented.

The expansion of the Brookhaven accelerator facilities, and the on-going efforts to raise the AGS beam intensity, have been a driving force for the addition of new kickers and the upgrading of older ones to meet this challenge. All kicker power supply systems are running above their design specifications to provide wider operating ranges. The newly upgraded Booster fast extraction kicker power supply was commissioned in September 1997. Its compact high voltage modulator structure offers a pulse length almost three times longer than the preceding package within the confines of the same physical space. The AGS A5 injection kicker and the AGS G10 extraction kickers are also discussed. In order to expedite design, assembly, and commissioning, and to facilitate interchangeability, standardized modules have been adopted where possible. This paper gives an overview of the AGS and Booster fast injection and extraction kicker systems including their parameters, structure and status.

The fast muon kicker for the muon g−2 experiment at Fermilab is being developed by Cornell group. The kicker is a pulsed magnet that provides the transverse kick to the muon particles required to direct them onto the stable orbit of the storage ring. To minimize the coherent betatron oscillation and maximize the storage efficiency of muons, it is desired that the magnetic pulse generated from the kicker have, approximately, 230 Gauss peak value and 120 ns full width. Based on the experiences from the earlier g−2 experiment at Brookhaven National Laboratory, we have redesigned the system using a triaxial blumlein pulse forming network and the prototype model has been built and tested. The details of the design and the test of the kicker are described in this paper.

Recently, all solid-state pulsed power modulators, which are operated with high repetition rate, long lifetime and high reliability, have been developed to be used for industrial applications of plasmas, such as high repetition rate pulsed gas lasers, high energy density plasma (EUV sources) and pulse ozonizer. We have studied and developed high repetition rate compact pulsed power modulator for discharge plasma in water. This modulator is consisted of thyristor switch and magnetic pulse compression (MPC) circuits. This modulator is able to generate an output voltage of about 25 kV with voltage rise time of less than 200 ns. A repetition rate is 500 pulses per second (pps). We conducted the operation test and generated the streamer kind discharges in the water. We observed that plasma behavior is changed at high repetition rate of 500 pps.

This document introduces the planned new search for the neutron Electric Dipole Moment at the Spallation Neutron Source at the Oak Ridge National Laboratory. A spin precession measurement is to be carried out using Ultracold neutrons diluted in a superfluid Helium bath at T = 0.5 K, where spin polarized 3He atoms act as detector of the neutron spin polarization. This manuscript describes some of the key aspects of the planned experiment with the contributions from Caltech to the development of the project. Techniques used in the design of magnet coils for Nuclear Magnetic Resonance were adapted to the geometry of the experiment. Described is an initial design approach using a pair of coils tuned to shield outer conductive elements from resistive heat loads, while inducing an oscillating field in the measurement volume. A small prototype was constructed to test the model of the field at room temperature. A large scale test of the high voltage system was carried out in a collaborative effort at the Los Alamos National Laboratory. The application and amplification of high voltage to polished steel electrodes immersed in a superfluid Helium bath was studied, as well as the electrical breakdown properties of the electrodes at low temperatures. A suite of Monte Carlo simulation software tools to model the interaction of neutrons, 3He atoms, and their spins with the experimental magnetic and electric fields was developed and implemented to further the study of expected systematic effects of the measurement, with particular focus on the false Electric Dipole Moment induced by a Geometric Phase akin to Berry’s phase. An analysis framework was developed and implemented using unbinned likelihood to fit the time modulated signal expected from the measurement data. A collaborative Monte Carlo data set was used to test the analysis methods.

The SNS accumulator ring extraction fast-kicker system was design, developed, and prototype tested at the Brookhaven National Laboratory. Its construction has just begun. The system is for one-turn fast extraction ejecting proton beam from the ring into the extraction septum gap and further deflecting into the ring-to-target beam transport line. The system consists of fourteen high-voltage modulators, their local control and auxiliary systems, and fourteen window frame magnet sections. High-voltage transmission cables will be used for pulse transmission from modulators to their corresponding magnet sections. The high-voltage and high-current pulse has a rise time about 200 ns, a pulse duration about 700 ns, and a current amplitude above 2500 Amp per modulator. The modulator design features a Blumlein Pulse-Forming-Network with ultra-low inductance high energy storage pulsed capacitors, an ultra-fast high-power hollow anode thyratron, a parallel resistor stack for low beam-impedance termination, and a saturable inductor stack for beam current isolation and pulse rise time sharpening. This design is driven by the considerations of low beam loss, high maintainability and reliability. All high voltage modulators will be placed outside the ring tunnel and the system is immune to one-kicker failure. In addition, the enlarged magnet aperture can accept all four working points. The design concept has been successfully proven by the prototype test. The techniques, considerations, and other related issues of the system design, development and construction are discussed in this paper.

Beam coupling phenomena have been observed in most fast kicker systems through out Brookhaven Collider-Accelerator complex. With ever-higher beam intensity, the signature of the beam becomes increasingly recognizable. The beam coupling at high intensity produced additional heat dissipation in high voltage modulator, thyratron grids and thyratron driver circuit sufficient to damage some components, and causes trigger instability. In this paper, we will present our observations, basic coupling mode analysis, relevance to the magnet structures, issues related to the existing high voltage modulators, and considerations of the future design of the fast kicker systems.

Quasi continuous wave (QCW) fiber lasers operating in the near IR at 1070 nm have unique properties such high pulse energy with high peak power and very good beam quality. Consequently extreme high power densities are possible allowing for adequate coupling and high quality machining of materials that are typically transparent at these wavelengths. QCW lasers can operate with variable pulse length in pulsed mode at high repetition rate as well as in CW mode at high average power which translates into high throughput machining. Single mode and multimode fiber lasers can be used to match processing needs.In this paper we will present results covering laser processing with QCW fiber lasers of materials that are typically difficult to machine at near IR wavelengths, namely ‘white ceramics’ and sapphire.Results are shown for alumina, aluminum nitride and zirconia toughened alumina (ZTA). These are ceramics used in industries such as LED packaging as well as RF and microwave packaging. High speed drilling up to 3000 holes/sec is shown with hole diameters ranging from 100 to 15 microns, in material thicknesses ranging from 635 to 100 microns. Examples of high speed cutting and scribing are also presented.Results are shown for high quality cutting of sapphire up to 3 mm thick. Sapphire has received increased attention in the consumer electronics industry due to its increased use in applications ranging from mobile phone and tablet displays, to their lens cover, in addition to more common applications such as windows for the semiconductor and defense industry.Quasi continuous wave (QCW) fiber lasers operating in the near IR at 1070 nm have unique properties such high pulse energy with high peak power and very good beam quality. Consequently extreme high power densities are possible allowing for adequate coupling and high quality machining of materials that are typically transparent at these wavelengths. QCW lasers can operate with variable pulse length in pulsed mode at high repetition rate as well as in CW mode at high average power which translates into high throughput machining. Single mode and multimode fiber lasers can be used to match processing needs.In this paper we will present results covering laser processing with QCW fiber lasers of materials that are typically difficult to machine at near IR wavelengths, namely ‘white ceramics’ and sapphire.Results are shown for alumina, aluminum nitride and zirconia toughened alumina (ZTA). These are ceramics used in industries such as LED packaging as well as RF and microwave packaging. High speed drilling up to...

Several important applications in optical communications require high power fiber coupled laser sources operating at 1.3 /spl mu/m, 1.48 /spl mu/m and 1.55 /spl mu/m. Semiconductor diode lasers for these wavelengths can be fabricated using the InP/lnGaAsP material system. High power operation requires careful selection of the active region, p and n doping and the lateral waveguide structure. Additionally, distributed feedback (DFB) lasers require appropriate choice of grating feedback. High power, narrow linewidth and low noise single mode diode laser sources operating at 1.3 /spl mu/m and 1.55 /spl mu/m wavelengths have applications in cable television transmission systems, microwave photonics, interferometric sensors and as an alternative to diode-pumped solid state lasers. High output power is desirable to overcome losses in external modulators and for large scale distribution systems. It is particularly important for 1.3 /spl mu/m applications as reliable and efficient fiber amplifiers are not commercially available at this wavelength. 1.3 /spl mu/m DFB lasers with 440 mW chip power, over 150 mW fiber coupled power and 100 kHz linewidth have been demonstrated.

The control of high voltage at high power, particularly opening switches, has been difficult in the past. Using gate turnoff thyristors (GTOs) arranged in series enables large currents to be switched at high voltage. A high voltage opening switch has been successfully demonstrated in our Laboratory. This switch uses GTOs in series and successfully operates at voltages higher than the rated voltage of the individual devices. It is believed that this is the first time this has been successfully demonstrated, in that GTDs have been operated in series before, but always in a manner as to not exceed the voltage capability of the individual devices. In short, the devices have not worked together, sharing the voltage, but one device has been operated using several backup devices. Of particular interest is how well the individual devices share the voltage applied to them. Equal voltage sharing between devices is absolutely essential, in order to not exceed the voltage rating of any of the devices in the series chain. This is accomplished at high (microsecond) switching speeds. Thus, the system is useful for high frequency applications as well as high power, making for a flexible circuit system element. This demonstration system is rated at 5 KV and uses 1 KV devices. A larger 24 KV system is under design and will use 4.5 KV devices. In order to design the 24 KY switch, the safe operating area of the large devices must be known thoroughly.

The high-voltage DC power supply for electron beam furnace belongs to Special Power Supplies. It has the characteristics of high voltage and high power. At present, the high voltage DC power supplies for electron beam furnace are mostly controlled by the silicon controlled rectifier operated by power frequency, which not only has the disadvantages of large volume but also doesn't has the characteristics of anti-short circuit capacity、 rapid protection and restart. This characteristic affects the service life of the electron gun and the quality of the smelting. To solve the above problems, a high frequency resonant converter has been used in high voltage power supply, reduced the volume of power supply and the switching loss, and achieved rapid protection and restart. Simulation and experimental research show that the power supply can meet the requirement of smelting.