| Paper | Title | Page |
|---|---|---|
| TUPEC004 | Tuning and RF Characterization of Plane Wave Transformer (PWT) Linac Structures | 1713 |
|
||
|
Four and eight cell Plane Wave Transformer (PWT) linac structures have been developed as part of the injector development for the Compact Ultrafast Terahertz Free Electron Laser (CUTE-FEL) at RRCAT. In this paper, we discuss the tuning of resonant frequency and waveguide-cavity coupling coefficient for these structures, and compare results obtained from cold tests with those predicted by RF simulations. We also compare energy gain and RF properties of these structures, determined from transient and steady state behavior of the structure during recent high power tests, with those predicted by cold tests. |
||
| TUPEC005 | Development and Commissioning of the CUTE-FEL Injector | 1716 |
|
||
|
The injector system for the Compact Ultrafast Terahertz Free Electron Laser (CUTE-FEL) consists of a 1 ns, 90 kV pulsed thermionic electron gun, a 476 MHz sub-harmonic prebuncher, and a standing wave, S-band Plane Wave Transformer (PWT) linac capable of accelerating beam to 10 MeV. Beam from this injector will be transported to the entrance of the undulator through a beam transport line, with the required diagnostic elements, that has been designed, developed and commissioned. The control system and the low and high power microwave lines have also been commissioned. In this paper, we discuss salient features of the injector system and results from recent commissioning trials of the injector. |
||
| TUPE012 | Stability analysis of Free-Electron Laser Resonators | 2170 |
|
||
|
The stability of free-electron laser (FEL) resonators differs from that of resonators of conventional lasers, because of the nature of the FEL interaction. Therefore the stability diagram is modified, and near-concentric configurations are preferred to near-confocal. We study the stability of FEL resonators (especially for g1 =/ g2) using simulations, as well as using a simple thin-lens model, and show that the near-concentric configuration is indeed preferable, while the confocal configuration becomes unstable. Also, since FELs can be widely tuned in wavelength, we investigate the stability of the resonator as a function of the wavelength. |
||
| THPEA003 | An Analytical Formulation for Prediction of Geometrical Dimensions of a Photocathode Gun for Desired RF Properties | 3679 |
|
||
|
Tuning of a photocathode gun for desired RF properties of the pi mode, such as FB ~1, fpi = 2856 MHz, and beta ~1, requires precise tuning of the resonant frequency and beta of its independent cells. In this paper, we present a parametric and analytical formulation to predict geometrical dimensions of independent cells and the coupling slot on the full cell to obtain the desired pi mode RF parameters during operation, taking into account the effect of brazing and vacuum. We also compare results obtained from low power RF measurements on a photocathode gun with those predicted by the above formulation. |
||
| THPEC001 | Optimization of Nonlinear Wakefield Amplitude in Laser Plasma Interaction | 4056 |
|
||
|
Nonlinear, high-amplitude plasma waves are excited in the wake of an intense laser pulse propagating in a cold plasma, providing acceleration gradients up to GeV/m. Linear analytic analyses have shown that the wakefield amplitude is optimal for a certain ratio of the pulse length and plasma wavelength*,**. Here we present results of simulation studies to optimize the nonlinear wakefield amplitudes. Variation in the laser pulse length is considered for maximizing amplitudes of wakefields generated by half-sine and Gaussian pulse profiles. Further, the advantages of using a transversely inhomogeneous plasma for the generation of the nonlinear wakefields are studied and compared with the homogeneous case. * E. Esarey, P. Sprengle, J. Krall and A. Ting, IEEE Trans. Palsma Sci. 24, 252 (1996) |
||
| THPEC002 | Simulation of Electron Acceleration by Two Laser Pulses Propagating in a Homogenous Plasma | 4059 |
|
||
|
We study electron acceleration by two laser pulses co-propagating one behind the other in a homogeneous plasma. We show, using one-dimensional simulations, that the wake amplitude can be amplified or diminished depending on the time delay between the two lasers, in agreement with linear analytic theory. We extend the study to the bubble regime using two-dimensional simulations. We find that the one-dimensional optimization holds in two dimensions also. Trapping and acceleration of quasi-monoenergetic electrons (up to around 300 MeV) is found in the bucket behind the second laser, even for low intensities, where there is no trapping with a single laser. Thus, this scheme could be very useful for achieving a desired accelerated energy with less intense lasers, or, equivalently, increasing the accelerated energy for a given laser intensity. * G. Raj, A. K. Upadhyay, R. K. Mishra and P. Jha, Phys. Rev. ST Accel. and Beams 11, 071301 (2008). |