Magnet Beamline Research Articles

A beamline zero-degree spectrometer for measurements of projectile fragment distributions

A technique for using a section of a beamline as a zero-degree spectrometer is described. The beamline magnets of the K1200 cyclotron at NSCL were operated as a zero-degree medium acceptance spectrometer to measure projectile fragment distributions. Projectile fragments were produced in a fragmentation target at the exit of the cyclotron and detected at the end of the beamline with a detector array consisting of two position-sensitive detectors and a ΔE−E telescope. Energy loss, position and angle at the focal plane and time of flight were measured for the isotopes produced. A procedure was developed to calculate the reaction angle and the momentum of the isotopes from the measured quantities. Typical examples of momentum and angular distributions of projectile fragments from a 14N beam at 75 MeV/u with Al and Ta targets at and near 0° are shown.

Development of the Chalk River program for 36Cl

The AMS program at the Chalk River TASCC (Tandem Accelerator Superconducting Cyclotron) facility is directed toward 36Cl measurements in hydrological and other samples. The automatic data acquisition/accelerator control system has been commissioned and progress is reported on particle identification with a Bragg-type detector and 36S background control with a gas-filled beamline magnet. Evidence for large Cl memory effects in a Hiconex 860 sputter source is also presented.

Construction and testing of A ± 16° superconducting beamline magnet

A prototype of the beamline switching magnets needed for operation of the National Superconducting Cyclotron Lab's 1.6 GeV/c heavy ion beam transport system has been constructed and is undergoing tests. The device features a compact design, as well as good cryogenic and magnetic efficiency. In the operational range of 1.0 to 1.75 T the required field uniformity of ± 0.1% has been obtained. The design current density in the potted coils is 17 kA/cm2at 1.75 T, and the magnet has operated at a current density of 20 kA/cm2at 1.8 T without a quench.

Major Facility Overhauls at LAMPF

The Clinton P. Anderson Meson Physics Facility (LAMPF) is a linear proton accelerator designed to operate at 800 MeV and 1.0 mA. It has been operating at power levels above 200 microamperes since February of 1976 and now routinely operates near the design level. This paper outlines the problems encountered with the original target cell components, the repairs required since 1976, and specifically details the steps involved in the complete replacement of the vital target cell components. These components include target boxes, collimators, main beam line magnets, and the front-end magnets of the secondary beam lines. The A-2 target cell was replaced in the spring of 1983 and the A-1 target cell was replaced in the spring of 1984. Both have operated satisfactorily since their completion, with only minor difficulties. The overhaul and total component replacement in the beam stop area (A-6) was completed in early May 1985 and has just been placed in operation. The upgrade, in addition to the replacement of the beam stop and the vacuum-to-air window with state-of-the-art designs, provides a greatly increased capability of both proton and neutron irradiation of materials.

Status and trends of S.C. magnet development in Europe

Many applications of s.c. magnets have been proposed and considered during the last decade. They may be classified into three catagories: S.c. magnets as research tools in particle and solid state physics, in energy technology, and for various industrial applications. All these are still pursued in Europe but a considerable shift in effort to specific projects has occurred during the last decade. Some main projects are discussed: beam line magnets for new particle accelerators, high field magnets including hybrid magnets, s.c. magnets for fusion devices such as the Large Coil Project or Tore-Supra, and s.c. magnets for NMR devices or magnetic separation of weak magnetic materials. The main trend is towards very high fields and magnets with large field volume. Both are extremely challenging for improving the conductor and magnet performance with respect to stable and non-degrading operation under mechanical load conditions. Developments in the focus of present interest are improvement of the stress-strain behaviour of Nb 3 Sn conductors and operation of magnets with subcooled helium. In addition, engineering and computations to predict mechanical performance are getting more and more important.

Control System of Beam Line Magnets in KEK

A computer control and monitor system was constructed to handle power supplies of the beam line magnets. The interface modules are installed in CAMAC crates linked by a CAMAC serial highway. The structure and performance of the system are presented.

A Fast Energy Dump for Beam Line Magnets

Tests of the 200A and 500A versions show excellent agreement with calculations and have operated without incident for some time. A 5000A version of a slightly different configuration has functioned well for over six months. The introduction of the fast ramp down circuits has substantially increased the flexibility of the Neutrino beam line by permitting the effective use of the accelerator flat top.

Control of Beam Line Magnets by the CAMAC Serial Highway

A computor control system of magnets in the low energy separated beams in KEK is reported. The system consists of five CAMAC crates and a central minicomputor. The CAMAC crates are connected by a CAMAC Serial Highway. The transmission is 128 k bytes/sec byte serial mode. Compared to the manual remote control arrangement, improvements in beam line operation can be identified.

Mechanical and Thermal Stresses in Superconducting Accelerator and Beam-Line Magnets

A solution to a similar problem has been given previously in which the magnetic field was generated by two sheet currents varying as cosine theta. One sheet current was located at the boundary between the innermost cylinder and the middle cylinder of structural material. The other sheet was located at the boundary between the middle cylinder and the outermost cylinder of structural material. The problem of improving the representation of the magnet excitation by replacing the two current sheets with a thick cosine theta current distribution in the middle structural region is discussed.

Characteristics of Inversion Operation on Fermilab Phase Controlled Pulsed Power Supplies

A well known property of phase controlled rectifiers with pulsed inductive loads is the ability to advance firing angles from full rectification (positive voltage) to full inversion (negative voltage). Though these properties have been effectively used in the Main Ring power supplies, they have not been extensively utilized for beam line magnet power supplies. Modifications to permit advancing phase angle sufficiently to permit inversion were made on TransRex 500 KW power supplies and Ling 55 KW power supplies. The objective of these modifications was to rapidly reduce the current in magnet loads to zero upon command. The modifications required and the performance of the power supplies are discussed.

Superconducting Coil Manufacturing Method for Low Current DC Beam Line Magnets

A method of manufacturing superconducting multipole coils for 40 to 50 kG DC beam line magnets with low current is described. We built small coils and tested them successfully to short sample characteristics. The coils did not train after the first cooldown. The coils are porous and well cooled to cope with mechanical instability and energy deposited in the coil from the beam particles. The coils are wound with insulated strand cable. The cable is shaped rectangularly for winding simplicity and good tolerances. After the coil is wound, the insulated strands are electrically connected in series. This reduces the operating current and, most important, improves the coil quench propagation due to heat conduction of one strand adjacent to the other. A well distributed quench allows the magnet energy to distribute more uniformly to the copper in the superconductor wire, giving self-protected coils. We are now fabricating a one-meter long, 43 kG. 6-inch bore tube superconducting dipole. The porous coil design and coil winding methods are discussed.

Operating Experience with the HEUB Superconducting Dipoles

Four large aperture superconducting dipole magnets have been installed in the High Energy Unseparated Beam at the Brookhaven AGS. This beam services the Multiparticle Spectrometer (MPS) facility. The upstream two magnets are mounted on a sliding base so that they can also be used as part of beam A3. These two magnets have been in use since the fall of 1976 and all four magnets were in operation by the end of that year. The magnet power supplies are computer controlled by the same system that operates the conventional beam line magnets. In this paper the operating experience with these magnets, their refrigeration system and the associated instrumentation is summarized.

The effect of beam line magnet misalignments

The misalignment of a magnet in a beam line will cause an alteration of the beam envelope at any later point in that beam line. The position of a misaligned magnet may be described in terms of six coordinates, three translational and three rotational. The effect of a misalignment on a single particle trajectory is derived to first order, including bilinear terms. A bilinear effect is one which affects the beam line focusing characteristics, but not the central ray, such as the effect of rotating a quadrupole about its axis. The effect on the beam envelope is calculated, both for a known magnet displacement and for an uncertain magnet position. The formalism has been included in the computer program TRANSPORT 1).

Research work on superconducting magnet systems in Germany

Various applications of sc magnets are pursued in our country. Development in nuclear physics, especially new developments for dc and pulsed superconducting beam line magnets are reported. Research work on magnets for plasma and fusion physics concentrates on systems studies, toroidal systems, and energy storage devices and will become one of the most challenging fields for magnet builders in the future. Industrial applications of sc magnets are investigated for high speed transportation systems, sc machinery and magnetic separation devices. Programs and results are discussed.

Positioning Tolerances of Beam Line Magnets

The positioning tolerances of magnets are an important consideration in the design and installation of a beam line. A misaligned magnet can both shift the beam centroid and affect the beam line transmission characteristics. To first order and without misalignments, the coordinates at any point of a beam particle are given as a transfer matrix times the initial coordinates. To this we add a term linear in the misalignment parameters giving the beam centroid shift, and a term bilinear in the initial particle coordinates and the misalignment parameters giving the effect on the beam focal properties. This formalism has been incorporated into the computer program TRANSPORT. The effect of either a known misalignment or an uncertainty in position may be exhibited. In a single run, up to ten magnets may be separately misaligned, and their separate effects on the beam coordinates printed in a table.

Superconducting Magnets and Cryogenics

Several significant superconducting beam line magnet systems are being constructed in the U.S. These will demonstrate the practicability of superconductors in beam lines. It is now time to consider some of the more subtle engineering problems associated with these magnets in order to assure a next generation of highly usable magnets. This paper presents some engineering approachs to better magnets for the future.