Compton X-ray Source Research Articles

Lattice and beam dynamics for the pulse mode of the laser-electron storage ring for a Compton x-ray source

We present the lattice design for the pulse mode of the compact laser-electron storage ring for a Compton x-ray source. The lattice is optimized to suppress the intrabeam scattering (IBS), which is the dominant factor that leads to emittance growth. To better simulate the beam dynamics in the pulse mode, we developed a macroparticle 3D Monte Carlo algorithm. The IBS module can perform an element-to-element calculation to evaluate the emittance change due to IBS, while the Compton scattering module can provide the spatial and temporal information of the x-ray photon yield. Parameters of the storage ring, electron beam, and scattered photon yield of the pulse mode of this Compton x-ray source are presented.

Characterization results of the BNL ATF Compton X-ray source using K-edge absorbing foils

Spectral and angular information of inverse Compton sources is shown to be obtainable using only an X-ray imaging device and various foils with K-edges in keV energy range. Beam parameters can be chosen such that on-axis photons are above the K-edge for a given material, where absorption is very strong and there is relatively zero transmission. Photons observed off-axis are red-shifted and fall below the K-edge, therefore being transmitted and creating a “ring” pattern in the ideal case. Starting with photon energies below the K-edge and aperturing for small angles on-axis allows one to scan the electron beam to higher energy until all scattered photons are above the K-edge and absorbed, thus presenting a method of bandwidth measurement. Using these methods, we present experimental results of the bandwidth and double differential spectrum (DDS) for angle and energy of Compton photons generated at the Brookhaven National Laboratory Accelerator Test Facility (BNL ATF).

Optics for the lattice of the compact storage ring for a Compton X-ray source

We present two types of optics for the lattice of a compact storage ring for a Compton X-ray source. The optics design for different operation modes of the storage ring are discussed in detail. For the pulse mode optics, an IBS-suppression scheme is applied to optimize the optics for lower IBS emittance growth rate; as for the steady mode, the method to control momentum compact factor is adopted [Gladkikh P, Phys. Rev. ST Accel. Beams 8, 050702] to obtain stability of the electron beam.

Status of the inverse Compton backscattering source at Daresbury Laboratory

Inverse Compton scattering is a promising method to implement a high-brightness, ultra-short, energy tuneable X-ray source at accelerator facilities and at laser facilities using laser wake-field acceleration. We have developed an inverse Compton X-ray source driven by the multi-10-TW laser installed at Daresbury Laboratory. Polarized X-ray pulses will be generated through the interaction of laser pulses with electron bunches delivered by the energy recovery linac commissioned at the ALICE facility with spectral peaks ranging from 0.4 to 12 Å, depending on the electron bunch energy and the scattering geometry. X-ray pulses containing up to 10 7 photons per pulse will be created from head-on collisions, with a pulse duration comparable to the incoming electron bunch length. For transverse collisions the laser pulse transit time defines the X-ray pulse duration. The peak spectral brightness is predicted to be up to 10 21 photon/(s mm 2 mrad 2 0.1% Δ λ/ λ). Called COBALD, this source will be initially used as a short-pulse diagnostic for the ALICE electron beam and will explore the extreme challenges of photon/electron beam synchronization, which is a fundamental requirement for all conventional accelerator and laser wake-field-acceleration-based sources.

Design study of the KAERI Compton X-ray source depending on the laser intensity in the linear or non-linear regime

Quasi-monochromatic X-rays can be generated via Compton backscattering at the KAERI superconducting (SC) radio-frequency (RF) Linac system. The KAERI SC RF Linac with one 352 MHz cryomodule is now operating at 10 MeV. For a few keV Compton X-rays, an electron beamline is designed at the straight section, just after the SC linac, while an optical beamline is designed and fabricated based on the fiber laser delivery. Both will be installed in fall, 2006. In this paper, we estimate the parameters of Compton X-rays at a given system using three different commercial lasers and suggest the scheme to generate higher harmonics using an intense ultra-short laser.

A Compton X-ray source based on a SC linac at KAERI

A quasi-monochromatic X-ray source based on a KAERI SC linac system has been designed and is being manufactured now. 10 MeV 10 mA electron beam together with 20 W 1.06 μm laser beam will be used for 1.8 keV Compton X-ray generation with a few percentage of energy spread and 10 7 photons /s flux. A simple straight beamline was designed to deliver the electron beam with no degradation of its emittance and energy spread and to focus it to a proper size to produce the desired X-rays. We expect the first demonstration of 1.8 keV Compton X-ray generation in autumn 2006.

Electron optics of a future SC ERL at KAERI

A project of a high-power FEL at Korea Atomic Energy Research Institute is described. The FEL is driven by a superconducting energy recovery linac. The future ERL will be connected to the existing machine without any modification. It consists of two 180° bents and two straight sections: one is for the FEL, another for a Compton X-ray source. One can choose the regime controlling the lenses. The total ERL is isochronous to avoid any problem with longitudinal beam instability. The total relative emittance degradation through the whole machine is ≈1.5. The FEL will be based on a 2 m helical in-vacuum undulator made of permanent magnets. One mirror of the optical cavity is blind and made of copper, the other one, the outcoupler, is semi-transparent and made of CVD diamond. The expected average power is a few kW, the tuning range 35–70 μm.

Coherent compton x-ray sources

Coherent x rays can be produced by scattering of laser light by a beam of relativistic electrons, provided that the electron beam is density modulated or the scattering is done at, or near, 90°. Since the coherent scattering is proportional to N2, where N is the number of electrons, and the incoherent scattering is proportional to N, also a modest degree of coherence can substantially increase the x-ray yield. The theory of laser-electron-beam scattering is reviewed and compared with the emission of radiation by an electron beam in an undulator. Examples of the practical implementation of an intense source of coherent x rays are discussed.

X-ray spectrum and variability of 3C 120

The X-ray luminosity of 3C 120 is variable by a factor of 2.5 on time scales of days to months. The spectral slope of the 2-10 keV X-rays changes systematically in the sense that the higher intensity states are steeper. Simple power laws fitted to the data are consistent with an energy index alpha of 0.51 + or - 0.13 at minimum intensity and 0.83 + or - 0.03 at maximum, with a continuous variation in between. A more complicated spectral shape cannot be ruled out, but changes in absorbing column density alone cannot explain the data. The results are interpreted in terms of beamed synchrotron emission from a relativistic jet, a model which has been invoked previously for the spectra of BL Lac objects. The spectral variability is in marked contrast to the behavior of 3C 273, another superluminal source in which the X-ray spectral index is constant to a high degree of accuracy despite variability in time scales and amplitudes which are quite similar to those of 3C 120. The difference may be due to the degree of beaming of the respective core components. Another model which is consistent with the data involves thermal emission from isothermal shocks in a hot (approximately 10 to the 8th K) medium. Thermal Compton and spherical accretion X-ray source models do not reproduce the correct behavior of alpha versus flux.