doyuran@physics.ucla

1. F-Cup IP Angle of the trajectory Inside the Magnet Outside the Magnet X`[rad] Study of X-ray Harmonics of the Inverse Compton Scattering Experiment at UCLA Adnan Doyurana, Joel Englanda , Chan Joshib , Pietro Musumecia , James Rosenzweiga, Sergei Tochitskyb , Gil Travisha, Oliver Williamsa a UCLA/Particle Beam Physics Laboratory, b UCLA/Laser Plasma Group, Los Angeles, CA 90034, USA doyuran@physics.ucla.edu Abstract Design Electron, Laser and Scattered Photon Beam Parameters We propose an Inverse Compton Scattering experiment, which will investigate nonlinear properties of the scattering utilizing the terawatt CO2 laser system in Neptune Laboratory at UCLA. When the normalized amplitude of the vector potential a0 is larger than unity the scattering occurs in the nonlinear region; therefore, higher harmonics are also produced. We discuss the experimental setup and procedure to measure the angular and spectral distribution of the higher harmonics scattered from 14 MeV electron beam. We also present a calculation tool for the Double Differential Spectrum (DDS) distribution and total number of photons produced for both head-on and 90o scattering. We decided to do the experiment at 90o to avoid complications due to strong diffraction of the incoming laser. We discuss the electron and laser beam parameters for the experiment. Electron and Laser Beam Parameters Scattered Photon Beam Parameters Introduction Inverse Compton Scattering UCLA/NEPTUNE Laboratory Accelerator consists of a photo-injector RF Gun (BNL/SLAC/UCLA), a solenoid, PTW Linac, a chicane compressor, Three triplets for final focusing, 10 steering magnets, two integrating current transformers (ICT) for charge measurements and a number of pop in monitors for beam measurements. The accelerator can deliver up to 15 MeV Electron beams with ~5 mm-mrad emittance and 300 pC charge. We plan to do the experiment with 14 MeV electrons. Nonlinear Harmonics The photo-injector gun is driven by 10 ps long UV laser at 266 nm. A 1024 nm mode locked Nd:YAG laser is amplified by Nd:Glass regenerative amplifier and then quadrupled which yields up to 200 J pulse energy. Frequency of harmonics Achieved beam parameters for NEPTUNE. Wavelength of harmonics High intensity CO2 laser can be focused to achieve the normalized laser strength parameter . Therefore it is possible to investigate the nonlinear properties of the Inverse Compton Scattering. In order to avoid the additional nonlinearities due to diffraction we choose a transverse scattering geometry (I=90o). UCLA/NEPTUNE Laboratory houses a Terawatt CO2 laser system which delivers 10.6 m CO2 pulses with 200 ps pulse length and up to 100 J energy pulses (500 GW) Radiation Spectrum for circularly polarized laser beam* *Ride, Esarey, Baine, Phys. Rev. E, Vol 52, p 5425 (1995) Inverse Compton Calculations Note: All the variables are defined in the paper a0 is the normalized amplitude of the vector potential of the incident laser field (just like K, undulator parameter) 75 mm waist radius using an F3 and 50 mm waist radius using F2 focusing geometries are achieved experimentally in Neptune. The M factor is estimated to be 1.93. For F2 geometry the Rayleigh range is 0.75 mm. 500 GW laser yields an intensity of 1.25x1016 W/cm2 and . Since a0 is proportional to 0 wavelength it is advantageous to use CO2 laser compared to YAG lasers. For F3 geometry the Rayleigh range is 1.7 mm. 500 GW laser yields an intensity of 5.5x1015 W/cm2 and . Radiation Spectrum for linearly polarized laser beam* Bandwidth where N0 is the number of periods that electrons interact. 10% bandwidth is estimated for the fundamental I0 is the intensity and 0 is the wavelength of the incident laser Frequency of the scattered photons where 0 is the frequency of the incident laser,  is the relativistic factor of electron beam, z0 is component of the electron initial velocity in the direction of laser pulse. (z0=1 for head on scattering and z0=0 for 90o scattering. Half opening angle of the harmonics 15 mrad half angle is estimated Nonlinear Harmonics Spectrum Experimental Setup Normalized intensity distribution of the scattered photons of the first three harmonics The detector is centered at zo along z (=0) axis. The distances in x and y are measured in units of (x/zo)~  Permanent Magnet Quadrupole (PMQ) System for Final Focus For circularly polarized laser at 90o geometry Four permanent magnet cubes (NdFeB) are positioned to produce Quadrupole field at the axis. Radia Program is used to design the magnet to produce 110 T/m gradient. Octagonal iron yoke provide proper field flow and hyperbolic iron tips produce perfect quadrupole field inside the magnet. The prototype was build and it is good agreement with the simulation. 1% field error in the magnetization of the cubes in worst orientation causes 10 mm axis offset which is quite reasonable. The cubes are measured and sorted to reduce possible errors. n=1 n=2 n=3 Permanent Magnet Dipole (PMD) for Energy Spectrometer Beam Transport for Inverse Compton Scattering A Permanent magnet Dipole is designed to serve as energy spectrometer and dump for the electron beam. It bends the beam by 90o. The geometry is chosen so that beam always exits the dipole at 90o for various energies only with some offset. Iron Yoke is designed for proper field flow Magnets are made out of NdFeB high grade magnets which can yield 1.2-1.4 T magnetization. The Magnetic field inside the gap is ~0.85 T. For 14 MeV energy design electrons the bend radius is about 55mm For linearly polarized laser at 90o geometry where electron’s velocity is parallel to plane of polarization PMD Beam size plot along the Neptune beamline for Inverse Compton experiment simulated by MAD program. Trajectory of the electron beam in PMD For linearly polarized laser at 90o geometry where electron’s velocity is perpendicular to plane of polarization Inside the Magnet X[mm] Outside the magnet Angle of the 14 MeV electron trajectory in the PMD gap. Angle linearly changes from p/4 to -p/4 inside the magnet. Trajectory of the 14 MeV electron beam in the PMD gap. Beam enters the magnet by 45 o angle and exits by 45 o angle. Y axis is the length of the magnet and x axis is width. Field distribution inside the PMD gap simulated by Radia