Geetanjali Sharma

Wakefield Acceleration in a Dual-Grating Waveguide

The wakefield acceleration in a dual grating waveguide slow wave structure (DGWSWS) is proposed. Analytical expression of the wakefield amplitude and frequency is calculated. The wakefield amplitude is analyzed in terms of the grating waveguide parameters, i.e., grating width and grating slot height. The results indicate that the grating wakefield accelerators with shallower slots can operate at terahertz with competitive accelerating gradients when compared with a dielectric wakefield accelerator.

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.

Effects of Sextupolar Undulator Magnetic Field Contributions on Inverse Free Electron Laser Accelerator

In this paper, we include the important effects of sextupolar field contributions on saturation gain and length of a linear polarized undulator driven inverse free electron laser (IFEL) that arise when the electrons are injected off axis. The modified IFEL equations are derived and analyzed. Both the accelerating gradient and the saturation length of the IFEL are influenced by the imperfect beam trajectory. For a fixed laser wavelength, the effects are more pronounced in the case of short period undulator in comparison with a larger period undulator IFEL. A useful empirical fit is prescribed to estimate the tolerance of the IFEL for imperfect beam trajectory.

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.

Application of polygon based laser micrometer for magnet size measurement studies

In this paper, we describe development of a polygon mirror based laser micrometer for magnet size measurement for undulator fabrication. In the laser micrometer, a laser light source is focused on to the facets of a rotating polygon mirror at an angle of 350 that reflects the laser beam. The parallel light emerging from the polygon mirror surface falls on the object through an F-theta lens. The F-theta lens is used for collimating the output of a scanning mirror system and to provide a flat field at the image plane of the scan. The object obstructs the light. A collimating lens at the other side of the object focuses the light onto a detector. The shadow caused by the obstruction results in an output voltage for a period of time that is proportional to the size of the object. We have used the laser micrometer for 12.5mm and 6.25mm magnets measurement. This is an efficient noncontact method of magnet sorting for use in undulator fabrication, synchrotron radiation and FEL application.

Pulsed wire measurements of harmonic undulators for free electron laser

Bi-harmonic undulators are designed and field integrals are measured in a pulsed wire bench. An analytical formula is given for the shim counting and positioning along the length of the undulator. It is observed that the wire rigidity and stiffness of the thick wire do not affect the bi-harmonic undulator field measurement and gives comparable results with hall probe data.

An overview of the undulator field measurement studies at insertion device lab, DAVV

This paper describes undulator field measurement procedures by hall probe and the pulsed wire method. The Hall probe method gives the direct field mapping and calculates the field integrals through double numerical integration. A pulsed wire magnetic measurement method is an optical method which has been independently developed by DAVV. It gives directly the field integrals and calculates the field mapping via a double numerical differentiation. The measurement methods are illustrated with field measurement of a six period PPM undulator and a third harmonic undulator.