G. Mishra

Bi-harmonic free electron laser gain with variably polarizing undulator

A variably polarizing undulator free electron laser at higher harmonics is proposed. Analytical theory of the spectral feature of the radiation and the free electron laser gain for the higher harmonics are presented. The analytical results are supported by a numerical procedure.

Inclusion of electron betatron motion on longitudinal Wiggler-undulator radiation

Abstract In this paper we discuss the modification induced in the brightness by the inclusion of off-axis field contributions in a longitudinally polarised wiggler field. Some features of the off-axis field contribution to longitudinal undulator are presented for an analytical comparison with the results relevant to the brightness of a conventional undulator.

Inclusion of Finite Permeability on Design and Optimization of an Electromagnetic Undulator

We derive an alternate analytical expression for the optimum dimensions of an electromagnetic undulator with a finite permeability lamination core. The analytical expressions are compared with earlier results under an infinite permeability approximation of the lamination core of the electromagnetic undulator design.

Magnetic Measurements of a Third Harmonic Table-Top Undulator for Free Electron Lasers

We describe the measurement studies of a third harmonic undulator. The harmonic undulator is fabricated by placing shims at suitable locations along the length of a table-top six-period planar undulator. The undulator field is measured with a Hall probe and pulsed wire bench. The pulsed wire data show good agreement with the Hall probe data.

Effect of an axial magnetic field on electron betatron oscillations in undulator magnets

In this paper we examine the effects of an axial magnetic field on electron betatron oscillations in an undulator magnet. The electron betatron oscillations give rise to several betatron harmonics and reduce the spectral intensity at odd harmonics. An axial magnetic field suppresses these parasitic harmonics thereby improving the intensity.

Betatron contributions to the angular gain spectrum of a free-electron laser with an imperfect beam trajectory

The effect of betatron oscillations on the angular gain spectrum of a free-electron laser is examined in the case of an imperfect beam trajectory. The use of an axial magnetic field is suggested to improve the beam–mode coupling and gain of the laser.

Analysis of undulator radiation with an electromagnet undulator

In this paper we discuss the theory of undulator radiation in an electromagnet undulator. We discuss the spectral properties of undulator radiation when electrons are injected off the undulator axis. This paper highlights the distinctive features of the radiation spectrum from electromagnet undulators, as compared to PPM undulators.

Magnetic performance of DEVU25.20h undulator at IDDL, DAVV,India

In this paper, we describe the design development and magnetic performance of a prototype DEVU25.20h, variable gap hybrid undulator at IDD laboratory, DAVV, Indore, India. The undulator is NdFeB based hybrid undulator with twenty five period and 20 mm each period length. Low cost M35 grade cobalt steel is used as the pole material of the undulator. The abc coefficients of the new pole material is prescribed and the measured performance and characteristics of the undulator is evaluated using RADIA. The detailed design parameters and performance indicators are summarized in Table 1 and Table 2 respectively.

Development of Stretched wire measurement bench at IDDL, DAVV Indore

A stretched wire magnetic measurement bench is under development at IDDL, DAVV, Indore. In this method a multistrend wire consisting of N turns is stretched inside the undulator to measure the field integrals of the undulators. The wire moved with constant velocity of translation measures the first integral of the undulator field. The cross motion of the wire at the undulator ends measures the second field integral. The measurement accuracy depends on the wire conditions and material properties. In this paper we follow an analytical approach to find the voltage fluctuations due to wire vibrations during the field measurement. It is shown that the voltage fluctuations depend on undulator gap, magnitude of the impulse on the wire. The mass density and the length of the wire also cause sizeable voltage fluctuations. The analytical derived expression is analysed to optimize system parameters for minimum errors during the measurement.

Design and fabrication of PPM and hybrid undulator for free electron laser applications

Two undulators for free electron laser applications are under fabrication at Insertion Device Development & Measurement Laboratory, DAVV, Indore. The first one is of PPM type with twenty periods, 50 mm each period. The second one is a hybrid undulator with twenty five periods, 20 mm each period. NdFeB magnets of rectangular cross section 12.5mm, 12.5mm & 6.25 mm, 6.25 mm will be used for the undulators respectively. Each magnet length is of 50 mm. Each magnet is scanned by a laser micrometer to ensure gap uniformity along the length of the undulator. In this paper we describe the technical design details of both the undulators.