Pulse Stretcher Research Articles

Amsterdam Pulse Stretcher on its Way

Amsterdam Pulse Stretcher on its Way

Ultrasonic pulse Doppler apparatus

An ultrasonic pulse Doppler apparatus has: range gate (20) for separately performing range-gating of the respective received ultrasonic echo signals of the oscillation elements of an ultrasonic probe (1) each time the signals are respectively adjusted in correspondence with the direction of a received ultrasonic beam; pulse stretcher filter (21) for extending the duration of the respective plurality of range-gated received signals while storing the energy of the signals; phasing/adding stage (7a) for matching the phases of a plurality of output signals from the pulse stretcher filter and performing addition thereof; detection portion (12) for effecting coherent detection of an output signal from said phasing/adding stage; and Doppler signal generating components (15, 16) for respectively generating Doppler signals on the basis of an output signal from the detection portion. The received echo signal of each of the oscillation elements is range-gated, and the duration of the respective range-gated signals is extended by the pulse stretcher filter. Subsequently, the signals are matched in phase and added. Accordingly, the level of the received signal hardly reaches the limit of the dynamic range of a signal processing circuit employed.

A high speed electrostatic kicker for the pulse stretcher ring at Saskatchewan accelerator laboratory

Abstract The linear accelerator laboratory (SAL) at Saskatoon recently installed and commissioned a pulse stretcher ring for upgrading the performance of the existing SLAC style pulsed linac. Two fast electrostatic kickers were developed to deflect the ring's closed orbit for multiturn injections. The first kicker has been used successfully to inject 200 MeV 300 ns to 1 μs pulses. The second kicker is being assembled and upon completion, it is planned to use the pair to inject 300 MeV 1 μs pulses. The unique features of this style of deflector are its relatively small size, simple operation, and wide range of capabilities.

SSTR — the 150 MeV pulse stretcher of Tohoku University

This paper describes the Tohoku University 150 MeV pulse stretcher and its operation and use. The ring accepts a pulsed beam from the electron linac and produces a continuous current. An extracted beam of 1 μA has been obtained with a duty factor of 80%. The energy spread of the extracted beam was measured to be 0.2%. The stretcher supplies this continuous beam for use in coincidence experiments. Presently (e, e′p) and tagged photon experiments are being successfully performed.

Pulse Stretcher and Coincidence Experiments

Pulse Stretcher and Coincidence Experiments

Block Replicate Gates for Ion-Implanted Bubble Devices

A two-layer conductor is used for replicating bubbles in ion-implanted bubble devices. The first layer is a parallel conductor used to cut the bubbles which have been stretched by the hairpin conductor in the second layer. There was sufficient operation margin even with a low drive field and a bias field margin of 22.5 Oe was obtained at a drive field of 60 Oe. Error brought on by the stretch pulse will be improved by lengthening the corner pattern. In addition, replicate-in/transfer-out operation was verified.

Ion Pulse Compressor and Stretcher Ring for Linear Meson Factory

The time structure of the accelerated H- beam of Moscow meson factory is defined by technical features of linear acceleration and inadequate to the demands of a considerable part of the physics program envisaged. A new type of a magnetic ring for ion pulse time structure transformation is proposed. The most essential operating modes are as follows: 1) the compression of every stored pulse up to the hundreds times; 2) slow ejection of every pulse over 10 ms. Multiturn chargechanging H-? H+ injection will be used for the effective storage. The magnetic ring is an isochronous one (r=-rtr) for the pulse compression mode. Bunch beam structure is maintained without RF bunching system. The beam will be slowly ejected by the modified Piccioni method. The 99% ejection efficiency can be achieved, but the special azimutal distribution of a dispersion function is needed. The main beam dynamics features are shown together with the magnet ring configuration.

RF System for a 1 GeV Pulse Stretcher Ring

A design study has been completed for the RF system of a pulse stretcher ring to be operated in conjunction with the Bates Linear Accelerator (BLA). The 390m circumference ring is to operate from 300 MeV to 1 GeV, with 80 mA injected current and 1 msec extraction time. The stretcher ring is for nuclear physics research and has radiation damping time and quantum lifetime long compared to the extraction time. The special requirements of the RF system have been considered. Dynamic behavior at the fundamental frequency has been investigated by computer simulation. Higher-order mode impedance limitation has been specified by an investigation of transverse multi-bunch multi-turn instabilities.

High Duty Factor, Monochromatic Extraction from EROS

Simulations of the monochromatic extraction process in the pulse stretcher ring (PSR) of the Saskatchewan Accelerator Laboratory have been done using several different RF techniques. The effects of the extraction sextupoles on circulating particles cancel over several turns unless the PSR tune approaches a 1/3 integer resonance condition. This is accomplished by having a large chromaticity (-15) and allowing the energy of the particles to decrease either through synchrotron radiation losses or by changing the RF frequency of the PSR cavity. In the synchrotron loss mode the particles can be delayed by trapping them in the RF bucket and spilling them at a later time by abruptly lowering the RF voltage. Results indicate that it should be possible to extract a beam with a duty factor greater than 70%, an energy spread of ±10-4 and horizontal emittance less than 0.8 mm-mrad for all operating energies.

The Amsterdam Pulse Stretcher

In order to increase the duty factor (d.f.) of the present 500 MeV electron linac from 2.5 % to > 90 %, it is proposed to add a pulse stretcher to the facility. By replacing 4 of the 12 existing 4 MW klystrons by 25 MW types, the injection energy will be increased to E = 700 MeV. A peak current of 40 mA will be injected during three turns with 365 pps. to yield an extracted beam current of 40 ?A. The machine operates near a third order resonance. The chromaticity is non-zero. Extraction proceeds by changing the cavity frequency (2856 MHz); this will push the beam into the unstable region of the phase space. An energy compressor will reduce the momentum spread of the injected beam to ?dp/p? = 0.1 %.

CEBAF — a high energy, high duty factor electron accelerator for nuclear physics

The Nuclear Science Advisory Committee has recommended the construction of the Continuous Electron Beam Accelerator Facility (CEBAF) as proposed by the Southeastern Universities Research Association (SURA), a consortium of more than thirty institutions in the southeastern United States. The accelerator will be capable of delivering intense ( I ave > 100 μA), quasi-continuous (duty Factor > 90%) beams of electrons with energies up to 4.8 GeV. Short (1.2 μs), intense ( I pk = 200 mA) pulses of electrons will be accelerated by passing twice through a conventional pulsed linac. The pulses then will be injected into and stored in a pulse stretcher ring, the circumference of which is close to the length of the electron pulse. During the period between pulses (1ms) the stored electrons will be extracted to yield a high duty factor beam. Delivery of arbitrarily polarized beams will be possible. Experimental facilities will include three end stations. Two will be used for experiments utilizing the primary electron beam; the third will serve as a tagged photon facility.

Simulations of Half and Third Integer Resonant Extraction from a One-GeV Pulse Stretcher Ring

In the past few years, the pulse stretcher ring (PSR) concept has emerged as a viable method for extending the duty factor of pulsed linacs. The viability is a result of considerations such as cost and expected extracted beam quality. A few of the projects emphasize high average extracted beam intensity. This is accomplished through a high injection frequency (1 kHz) and relatively high injected peak currents (greater than or equal to80mA). To enhance the injection efficiency, the number of turns of injection are minimized so the ring is long and there are fewer turns for extraction. There is considerable experience with beam extraction over large numbers of turns from synchrotrons, but time uniform extraction over fewer turns has not been treated as thoroughly. In this paper, some of the extraction calculations made for the proposed MIT-Bates One-GeV Pulse Stretcher Ring are discussed. The theory used for the simulation procedure will be reviewed, the results summarized, and some points of operational interest mentioned.

Applications of the Second-Order Achromat Concept [1,2,3] to the Design of Particle Accelerators

A property of the second-order achromat, whereby dipole and sextupole families may be inserted into a lattice for chromatic corrections without introducing second-order geometrical (on momentum) optical distortions, has been incorporated in several new particle accelerator designs. These include the SLC at SLAC, LEP at CERN, the EROS pulse stretcher ring at Saskatoon, the CEBAF ring at SURA, and the MIT ring.

Sore - A Pulse Stretcher for the Saskatchewan 300-MeV Linac

A design study has been made of a pulse stretcher to increase the duty factor of the 300 MeV electron accelerator of the Saskatchewan Accelerator Laboratory. The design was constrained by the desire to house the pulse stretcher within the existing accelerator building and to make maximal use of existing beam transport lines. The pulse stretcher ring consists of two 180/sup 0/ bend regions connected by achromatic straight sections. The overall length is 50.49 m and the width is 6.64m. The modes of injection and extraction will be available. In the first mode a shortened linac pulse of 300 ns duration will be injected during a single turn directly into the closed orbit of the pulse stretcher. A second mode of injection/extraction involves use of a longer linac pulse. The basic geometry of the PSR is dictated by the dimensions of the accelerator vault and access room.

Overview of CW Electron Accelerator Proposals

Electron beams in the MeV to GeV energy range have been used for nuclear studies for the last thirty years. The precision of measurements made using electrons is sufficiently high that they are also now used as starting points for the analysis of data obtained using strongly interacting probes such as pions and protons. Virtually all measurements made to data have been of the inclusive variety. Enhancing the precision of such measurements, through such means as more accurate particle differentiation and improved time resolution, has meant making the duty factor of the beam as high as possible. The global interest in high duty factor electron accelerators has consequently risen. This paper groups both existing and proposed high duty factor accelerators into three categories. The first group covers those involving a pulsed accelerator and a pulse stretcher ring. The second category consists of machines based on the microtron concept. The third group includes the recirculated linac. The current proposals for high duty factor accelerators are divided into two groups: those involving the upgrade of an existing pulsed accelerator and those involving the construction of a new accelerator. The proposals for new accelerators are further categorized into those based on linac pulsemore » stretcher combinations and those based on microtrons. This paper assesses the existing and proposed activities of these facilities as they currently stand at laboratories around the world.« less

Multi-GeV Electron Linac-Pulse Stretcher Design Options

The Linac-Pulse Stretcher Ring system is evaluated as a design for a high duty factor (> 90%), intense (240 ?A), electron accelerator for operation in the 0.5 to multi-GeV (> 4 GeV) region. Options within this system are discussed in light of their predicted initial and operational cost, flexibility, and reliability. The ramifications of the choice of a particular cavity type, accelerating gradient, repetition rate, beam pulse length, and number of beam recirculations for the linac design are discussed both with respect to the linac itself and to the Pulse Stretcher Ring. The Pulse Stretcher Ring concept is analysed in terms of injection schemes (single or multi-turn), extraction methods (half or third integer, chromatic or achromatic), and operation parameters (machine tune and chromaticity).

An Energy Independent Electron Spin Precessor

The delivery on target of a polarized electron beam from a linear accelerator is straightforward. With circular accelerators this delivery becomes understandably more difficult. In order to maintain the polarization of an electron beam in a circular machine such as a synchrotron or pulse stretcher ring the electron spins must be oriented vertically so as to be parallel to the dominant guide fields. Extraction from these machines occurs in the horizontal plane so the extracted beam retains the vertical polarization. It is generally desirable to have not vertical but longitudinal polarization of the beam at the target; this requires a reorientation of the spins. The straightforward solution to this problem is to put a solenoid in the beam line to precess the spin into the horizontal plane followed by a horizontally deflecting dipole to precess the spin into the momentum direction. The angle of spin precession is energy dependent. What is needed is a method of varying the effective bend angle. One method used with polarized protons from the ZGS at Argonne involved a movable beam line. An alternative method is to utilize the noncommutativity of rotations in three dimensions. To do this requires two or more solenoids and twomore » or more dipoles. This paper discusses the theory and implementation of this method and describes a solenoid-dipole-solenoid-dipole configuration beam line suitable for the 4 GeV electron accelerator proposed by the Southeastern Universities Research Association.« less

Accelerator Development at Bates

The past year has seen the completion of a major expansion of the Bates Accelerator Laboratory. A second experimental hall, South Hall, and several magnetic spectrometers have been constructed. The accelerator's maximum energy has been raised from 400 to 750 MeV by means of beam recirculation. A current two-year project for the fabrication of an additional RF transmitter plus a 30% increase in RF peak power capability will increase energy further to ca. 1 GeV. During the same period pulse-to-pulse beam sharing between the high-resolution spectrometer area and South Hall will become available. In January 1981 the Laboratory submitted their ''Proposal for a Long-Range Expansion Program'' to DOE-NSF. The proposed development consists of three stages. Stage I calls for the addition of a pulse stretcher ring to furnish a CW beam to the South Hall beam lines. Additional experimental space for internal target experiments and photon tagging research are also included. Stage II increases the accelerator energy to 2.1 GeV (at 140 microamps) by means of a five-pass head-to-tail recirculator. Stage III is, at this time, a plan rather than a proposal. It increases accelerator energy to 4 GeV by extending the accelerator length and power and adds another pulsemore » stretcher ring and three new experimental areas for the higher energy work. This paper discusses each of these stages in detail and recommends their funding and scheduling.« less

150-MeV Pulse Stretcher of Tohoku University

The present paper describes the Tohoku University 150 MeV pulse stretcher and the results of the test operation. The ring stores a pulsed electron beam from the electron linac and converts it into a continuous one. The test operation has proved that it works successfully. Broadening of the extracted beam in the vertical direction due to a coupling resonance was observed in the early operation. This problem was resolved by readjustment of the tune. And an extracted beam of 1 ?A has been obtained with a duty factor of 80 %. The energy spread of the extracted beam was measured to be 0.2 %.

Design Philosophy for High-Resolution Rate and Throughput Spectroscopy Systems

The paper describes the philosophy behind the design of a pulse processing system used in a semiconductor detector x-ray spectrometer to be used for plasma diagnostics at the Princeton TFTR facility. This application presents the unusual problems of very high counting rates and a high-energy neutron background while still requiring excellent resolution. To meet these requirements three specific new advances are included in the design: (i) A symmetrical triangular pulse shape is employed in the main pulse-processing channel. A new simple method of generating a close approximation to the symmetrical triangle has been developed. (ii) To cope with the very wide dynamic range of signals while maintaining a constant fast resolving time, approximately symmetrical triangular pulse shaping is also used in the fast pulse pile-up inspection channel. (iii) The demand for high throughput has resulted in a re-examination of the operation of pile-up rejectors and pulse stretchers. As a result a technique has been developed that, for a given total pulse shaping time, permits approximately a 40% increase in throughput in the system. Performance results obtained using the new techniques are presented.