R. K. Bhandari

A new method of finding the pole profile in quadrupole magnets for obtaining high field quality

The field quality in quadrupole magnets depends mainly on the pole profile. One often uses a circular pole of optimized radius to reduce the field errors. Hyperbolic profiles which are modified at the pole edges are also used. In the design of these magnets one first chooses a profile and then calculates the error harmonics. Here we have described a new method in which we choose the error harmonics first and then find the profile thus ensuring that the field quality is good. The method can also be applied to other multipole magnets.

Modification of cosθ coil shape in superconducting dipole magnets for reducing the coil size

In coil-dominated superconducting dipole magnets the coil size and hence the cost of the magnet can be reduced by optimizing the shape of the coil. We have used the variational calculus and a random search technique to show that the coil shape markedly deviates from the conventional cosθ design when one reduces the coil size while holding the field and field quality to specified values. A block-coil dipole giving a field of 7.0T has been designed on the basis of the optimization. With iron yoke this can give a field of 8.4T.

New method of designing pole profile in combined function magnets of high field quality

Combined function magnets are often used in synchrotrons and beam lines. The field quality of such magnets depends mainly on the pole profile. A new method is described for determining the finite pole shapes of such magnets for obtaining field qualities of 1×10−4 or better. Profiles of the typical quadrupole-sextupole and dipole-quadrupole magnets are presented.

A simple design of sextupole magnets with optimized circular pole faces

A circular pole face for a sextupole magnet makes the mechanical design simple to fabricate. We have optimized the radius of the circular face to minimize the field error. We have obtained a thumb rule that the optimized radius for a sextupole should be 0.56 times the half-aperture of the magnet.

Sufficient cusp magnetic field for designing a novel electron cyclotron resonance ion source

Some have used a cusp modified minimum-B field configuration for designing an electron cyclotron resonance ion source (ECRIS) for 2.45 GHz μ-wave (microwave) frequency. A few ECRIS of this type were tested for >2.45 GHz also but later on converted into the conventional ones because of their poor performance. In this note is an attempt to understand the problems of the old cusp field ECRIS. They are mitigated using a highly permeable midiron disk and negatively biased metal ring and disk in the midplane and at the injection end to design and construct a compact and cost-effective ECRIS of the future.

Triple drift ion beam bunching systems for enhanced bunching efficiency

To obtain high efficiency in bunching ions one generally uses a multiharmonic buncher or a double drift buncher. Here we have explored the possiblity of using a triple drift bunching system to obtain still higher bunching efficiency. It consists of three bunchers separated in space. The first buncher is excited with the fundamental rf wave whereas the other two bunchers are driven by the second harmonic. We have optimized the parameters of such a system and have shown that by using only two rf frequencies one can obtain bunching efficiency higher than what can be obtained with a multiharmonic buncher consisting of nine harmonics.

Abrupt variation in ion current with biased disk voltage in the electron cyclotron resonance ion source

The performance of the biased disk in the 6.4GHz electron cyclotron resonance ion source at VECC, Kolkata was studied at a pressure of ∼1×10−7Torr. We observed an abrupt variation of beam current with bias voltage. For low negative bias voltages (from 0 to −5V) the beam current gradually decreases and then shows a sudden change in magnitude at a voltage of about −6V. The higher the charge state, the higher is the magnitude of this change. For H+ also the current changes abruptly, but the jump is from a higher to a lower current. This indicates a sudden change in the charge-state distribution of the beam, likely corresponding to a suddenly improved confinement.

On line multitarget selection device with multiple facilities

We have developed a multitarget holding device as a subsystem for atomic or nuclear physics experiments. A permanent magnet stepper motor rotates the device for target selection without breaking the vacuum. The target holder is potentially isolated from the rest of the system with the help of a Teflon block. The device and its controlled circuits are described below.

A method of designing magnetic channels of improved field quality for superconducting cyclotrons

Magnetic channels are used in the extraction system of superconducting cyclotrons for focusing and extracting the high energy beam. In order to preserve the beam quality, the field gradient produced by the channels should be constant. We have evolved a procedure based on the linear programming technique for optimizing the geometry of magnetic channels. With this, we have reduced the deviation in the field gradient not only in the median plane but through the beam aperture.