Beam Extraction Efficiency Research Articles

MO‐D‐BRD‐05: The Proton Beam Therapy Facility at PSI

The centre for proton therapy at the Paul Scherrer Institute was expanded recently following the commissioning of a new superconducting‐magnet cyclotron (COMET) dedicated to patient treatment. The accelerator was built by ACCEL Instruments GmbH (Varian), based on a design from the National Superconducting Cyclotron Laboratory (Michigan State University). The cyclotron is specified to provide a 500 nano‐Ampere beam of protons at a fixed energy of 250 MeV. The large magnetic field (∼ 3T) required at extraction is provided by the superconducting coils. A high power radio‐frequency system, operating at 72.8 MHz (second harmonic of the cyclotron frequency) provides the required acceleration of protons following their emission from a cold‐cathode ion source. The facility has also been up‐graded with the addition of new gantry (Gantry‐2) for patient treatment and a new beam line dedicated to eye treatments (OPTIS2). A novel feature of COMET is the high beam extraction efficiency (> 80%). This limits component irradiation and facilitates the regular maintenance periods which are an important consideration for any patient treatment center where high reliability and availability are required. We will describe the modes of operation of PROSCAN and, in particular, the spot‐scanning technique used to irradiate tumours. Magnetic elements permit rapid transverse deflection of a pencil beam for two dimensional scanning. An energy “degrader” allows rapid scanning in energy over the range of 70 – 238 MeV. This results in a variable depth of penetration of the beam, thus permitting a complete three dimensional scan. The beamlines which transport protons from COMET towards the two patient gantries and to OPTIS2 will also be discussed. They require sophisticated diagnostics for safe and reliable use of the facility. The various diagnostics include ionization chambers, secondary emission monitors and multi‐leaf Faraday cups. They are used to measure beam current, profile, position, halo and loss. The role of the diagnostics as interlocks for safe operation of the beamlines will also be described.Learning Objectives:1. Understanding the principle of the spot scanning technique.2. Understanding the issues concerning diagnostics for safe beam‐line operation.

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.

Beam extraction studies at 900 GeV using a channeling crystal

Luminosity-driven channeling extraction has been observed for the first time in a 900 GeV study at the Fermilab Tevatron. This experiment, Fermilab E853, demonstrated that useful TeV level beams can be extracted from a superconducting accelerator during high luminosity collider operations without unduly affecting the background at the collider detectors. Multi-turn extraction was found to increase significantly the efficiency of the process. The beam extraction efficiency was about 25%. Studies of time dependent effects found that the turn-to-turn structure was governed mainly by accelerator beam dynamics. An investigation of a pre-scatterer using the accelerator flying wire system showed that a fiber could produce a significant extracted flux, consistent with expectations. Based on these results, it is feasible to construct a parasitic 5-10 MHz proton beam from the Tevatron collider.

Methods for Increasing the Efficiency of Electron Beam Extraction Through a Gas-Dynamic Window

The possibilities and methods of increasing the efficiency of the extraction of a steady-state electron beam through a gas-dynamic window using gas-dynamic and electric phenomena accompanying this processes are considered.

Design of an electron cyclotron resonance ion source for the isotope separator and accelerator at TRIUMF

A 2.45 GHz electron cyclotron resonance ion source has been designed and built to ionize radioactive atoms and produce single charged ion beams for the isotope separator and accelerator at TRIUMF. The source is characterized by its short axial length (8 cm) and the small pair of magnetic coils (diam=φ26 cm) placed adjacent to the source cavity. A small diameter quartz tube is inserted in the cavity to confine the plasma to a small volume and to shorten total ion transient time for the exotic gaseous elements with short and intermediate half life. The computer code POISSON is used to design the magnetic coils. A three-electrode extraction system simulated with the code IGUNE is used to study the beam extraction efficiency. In this article the design of the source, extraction system, and the preliminary results on beam emittance and energy spread are presented; the results on ion transient time, ionization efficiency, and beam extraction efficiency are presented in a separate article.

Highly efficient extraction of a proton beam by using bent single crystals

A substantially increased beam extraction efficiency can be achieved in the case of a multiple beam’s passage through a crystal. This suggestion was verified in experiments with short (5–7 mm long) curved single crystal with bending angles of 1.5–1.7 mrad performed at the Institute of High Energy Physics. The peak effiency values obtained were 47±3%, and the maximum average efficiency was 42±2% for a 23% intensity taken from an accelerated beam. The maximum extracted beam intensity was 6×1011 protons per cycle.

High-efficiency multipass extraction of 70-GeV protons from an accelerator with a short bent crystal

Using channeling in a 5-mm crystal with a bending angle of 1.5 mrad, a radical increase in the efficiency of beam extraction from accelerator was achieved due to an increased number of particle encounters with crystal. The measured world-highest efficiency of crystal extraction, over 40%, is in good agreement with theory predictions. The extracted beam intensity of 6×10 11 ppp was obtained, five orders of magnitude higher than previous results.

First results of experiments on high-efficiency single-crystal extraction of protons from the U-70 accelerator

A radical increase in the efficiency of beam extraction from an accelerator is achieved with a short (7 mm long) crystal bent by a small angle (1.7 mrad) by increasing the number of times particles pass through the crystal. A particle extraction efficiency of ~20%, in agreement with the prediction of the theory, was achieved experimentally. A record high intensity of the extracted beam 1.9×1011 protons per cycle, which is four orders of magnitude higher than previous results, is obtained.

Electrical characteristics of a low pressure wire discharge and an application to high current density electron gun

The electrical characteristics of a wire discharge plasma were investigated, in particular, taking notice of the effect of electron trapping by axial magnetic fields. It was found that the plasma property changed remarkably, when the magnetic fields were applied. This property may be used to control the wire discharge plasma. The wire discharge plasma plays an important part as an ion source of an ion-induced secondary emission electron gun. This type of electron gun was demonstrated. The maximum electron beam current obtained was 90mA/cm 2 at beam energy of 100keV. In our calculation model, the secondary emission coefficient γ is 12.0 for 100keV helium ion and the electron beam extraction efficiency β obtained is 0.35.

Design of an advanced minimum B for electron cyclotron resonance multicharged ion sources

An advanced configuration of minimum-B field is designed for the electron cyclotron resonance (ECR) multicharged ion sources. The aim is to dramatically increase the efficiency of ion beam extraction by correcting the deformed magnetic flux tube containing hot plasma. The correction is performed by reversing the polarity of successive multipoles in the longitudinal direction. This method enables us to adopt the quadrupole that causes the greatest deformation. In addition, the most intense electron acceleration can be achieved with the quadrupole, since the radial field gradient is the largest of all multipoles.

On the theory of proton beam multiturn extraction with bent single crystals

The efficiency of high energy proton beam extraction with a crystal deflector under particle multiple passage conditions is considered. It is shown that multiple passage increases significantly the extraction efficiency; partly, the deflector angular acceptance is wider than channeling critical angle. Examples for 20 and 3 TeV beams are calculated.

A simple technique for generating single-mode nanosecond pulses of 10.6 μm radiation

A technique for generating short pulses of 10.6 μm radiation is presented. This technique produces pulses of 10 −9−10 −8 s duration of single-mode radiation with diffraction-limited divergence of the beam and good extraction efficiency of the energy stored in the cavity.

A Support System for Beam Adjustment of Cyclotron Based on Fuzzy Grading Model and Texture Display

For inexperienced operators of cyclotron, an operational support system using computer systems is acquiring a greater importance as cyclotrons have recently become popular in industrial applications. In start-up operation, many components should be tuned up in order to maximize beam extraction efficiency. Experienced operators somehow manage this process through trial and error using their experience and intuition. This paper proposes the following methods:(1)Adjustment sequence is divided into six blocks. The independent adjustment operation for those blocks can make the operation simple and reduce the operators' burden.(2)A model which represents the relation between the beam distribution patterns and the experienced operators' grade is easily formulat ed by using fuzzy integral. This grading model is very useful for inexperienced operators who judge these patterns.(3)A multi-dimensional data display using polka-dot texture is proposed as an intuitive display . It is a mapping of features of the beam pattern onto properties of texture. Inexperienced operators can easily analyze the beam pattern through this texture display.

A long-pulse millimeter-wave free electron maser

An experimental free electron maser (FEM) facility is described which operates in the millimeter-wave regime. The experiment demonstrates that high gain and beam extraction efficiency can be obtained with low-current but high-quality electron beams. In the oscillator configuration, microwave powers of 110 kW were achieved with a 300-kV, 4-A beam, corresponding to a beam extraction efficiency of 9.2%. At low beam currents, with the system operating in the linear regime, the FEM gain curve was measured. The experiment uses a Pierce-type gun with a calculated beam emittance of 10.7-mm mrad at 300 kV and 4 A. The wiggler is of the iron permanent magnet hybrid design. The experiment is intended as a first step towards the development of continuous-wave (CW) devices that use beam energy recovery to make use of low-current, high-voltage power supplies. >

カウフマン型低エネルギイオン源

The Kaufman type ion source with a broad beam has been redesigned for high-current and low-energy ion beam sputtering. The three-grid ion extraction system was employed for low-energy operations. The computer simulations of ion beam trajectories were carried out to obtain the suitable geometrical conditions for the aperture diameters, the grid thickness and the grid separations. A significant improvement in low-energy ion beam extraction efficiency was successful achieved.

The JINR Phasotron: Status and Progress

The synchrocyclotron of the Laboratory of Nuclear Problems for 680 MeV protons with a beam intensity of 2.3 mA and beam extraction efficiency of 5-7%, operational now for 30 years, has been under conversion since 1979. The conversion is aimed at making a phasotron with spatial variation of the magnetic field using the building and the magnetic core of the former accelerator. This spatial variation ensures vertical focusing of accelerated particles in the magnetic field growing along the radius and thus enables a reduction in the frequency range of the accelerating voltage which, in turn, results in a circa three-fold increase in the accelerating voltage and the cycle repetition. The conversion includes replacement of the electromagnetic windings, pole tips, accelerator chamber, dee with the resonance line, rotating capacitor, R.F. generator, ion source, beam extraction system, and auxiliary equipment. A computerized control system, based on microprocessors, will also be implemented. This paper reports the status of the conversion to date.

Invited Paper-Extraction Studies in an AVF Cyclotron

For the extraction of the beam in an AVF cyclotron a regenerative system or an electrostatic channel can be used. Some factors of importance for the beam will be discussed. Extraction with an electrostatic channel can give very high external beam quality and extraction efficiency. For such a system it is of importance whether the beam is extracted before or after the νR= <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> resonance. The beam can even pass the νR=2νZ resonance without blowing up vertically if attention is being paid to the radial oscillation amplitude and some machine parameters. The general orbit theory can be used for an analytical study of a regenerative system in an A.V.F. cyclotron.

Invited Paper-The Separated-Orbit Cyclotron

The separated-orbit cyclotron (SOC) is a cyclic accelerator which combines the advantages of the isochronous cyclotron, the synchrocyclotron, and the linear accelerator. In an SOC, injected ions are accelerated by radio frequency cavities interspersed with the sectors of a magnet structure that guides and focuses the beam along a fixed spiral path. The magnet structure, intersected radially at equal azimuthal intervals by the rf cavities, is designed so that the time per revolution of the particles is independent of their energy, as in an isochronous cyclotron, and it may incorporate any of the well-known methods for focusing ions, such as are used in various types of synchrocyclotrons. The particles accelerated in the SOC are phase focused with respect to a synchronous phase angle corresponding to a chosen rate of energy gain and a peak accelerating voltage. This is made possible by the independent magnetic focusing for the separated orbits since the transverse dimensions of the beam are much smaller than the separation between adjacent turns, 100% beam extraction efficiency should be easily achieved. Variable energy can be obtained by moving the extraction magnet to intercept all of the beam at the right turn for the energy desired. The original concept of the SOC featured a spiral-helix ion path, sometimes called beehive, Fig. 1, in which the orbit separation necessary to accommodate the independent magnet structure for successive turns was gained mainly by axial displacement.