Moohyun Yoon

Electron dynamics and acceleration study in a magnetized plasma-filled cylindrical waveguide

In this article, EH01 field components are evaluated in a cylindrical waveguide filled with plasma in the presence of external static magnetic field applied along the direction of the mode propagation. The electron acceleration inside the plasma-filled cylindrical waveguide is investigated numerically for a single-electron model. It is found that the electron acceleration is very sensitive to the initial phase of mode-field components, external static magnetic field, plasma density, point of injection of the electron, and microwave power density. The maximum amplitude of the EH01 mode’s field components is approximately 100 times greater than the vacuum-waveguide case for operating microwave frequency f=7.64GHz, plasma density n0=1.08×1017m−3, initial phase angle ϕ0=60°, and microwave power ∼14MW in a cylindrical waveguide with a radius of 2.1cm. An electron with 100keV gets 27MeV energy gain in 2.5cm along the waveguide length in the presence of external power ∼14MW with a microwave frequency of 7.64GHz....

Electron acceleration by a chirped circularly polarized laser pulse in vacuum in the presence of a planar magnetic wiggler

Ultrahigh-gradient acceleration, by a chirped circularly polarized (CP) laser pulse in the presence of a planar magnetic wiggler, is investigated numerically. A simple linear chirped profile of laser frequency has been introduced in our model. The combined effect of frequency chirping and the tapered wiggler magnetic field on the electron acceleration is discussed in detail. It is found that the chirping parameter, the wiggler field tapering parameter, the initial phase of the laser, the laser spot size and laser intensity all have a strong influence on the electron acceleration. If an optimal tapered wiggler magnetic field in the same direction as the magnetic field of the laser pulse is externally applied during the trailing part of the pulse, the electron can gain and retain significant energy in the form of cyclotron oscillations even after the passing of the laser pulse.

Generation of Attosecond X-ray and gamma-ray via Compton backscattering

The generation of an isolated attosecond gamma-ray pulse utilizing Compton backscattering of a relativistic electron bunch has been investigated. The energy of the electron bunch is modulated while the electron bunch interacts with a co-propagating few-cycle CEP (carrier envelope phase)-locked laser in a single-period wiggler. The energy-modulated electron bunch interacts with a counter-propagating driver laser, producing Compton back-scattered radiation. The energy modulation of the electron bunch is duplicated to the temporal modulation of the photon energy of Compton back-scattered radiation. The spectral filtering using a crystal spectrometer allows one to obtain an isolated attosecond gamma-ray.

Measurement of storage-ring lattice functions: Application to the Pohang Light Source

Measurement of the lattice functions was carried out in the storage ring for the light source. The measurement includes β, dispersion functions, phase advances, tunes, momentum compaction, chromaticities, and linear coupling. Two methods were used for the β measurement; a quadrupole-tweaking method and a method using a sensitivity matrix. Using the sensitivity-matrix method gives additional information on the phase between monitors and correctors, as well as the fractional part of the tunes. The linear-coupling constant was obtained by driving the tunes across the coupling resonance and measuring the minimum tune separation. It is also shown that by using four skew-quadrupole circuits, the coupling constant can be varied arbitrarily. In this article, a detailed method for the lattice-function measurement is presented, and the result applied to the storage ring of the Pohang Light Source is given. The measured results are compared with the design values and shown to be in good agreement.

Electron acceleration in a warm magnetized plasma-filled cylindrical waveguide

The effect of plasma-electron collision and their thermal motion is investigated on the externally injected electron in a warm magnetized plasma-filled cylindrical waveguide of cross section of 13.68 cm2. The numerical results are presented for the external electron-energy gain and its trajectory in a nonrelativistic γe=1 and stationary v0=0 warm magnetized plasma-filled waveguide. Results shows that for an electron-cyclotron frequency ωc greater than the electron-plasma frequency ωp, a 100 keV electron acquires a 1.74 MeV energy in a 2.5 cm distance for plasma density n0=1.08×1017/m3, magnetic field B0=0.193 T, microwave frequency f=7.64 GHz, plasma-electron thermal velocity vth=0.2c, and plasma-electron collision frequency ν=4 GHz, which is lower than the 7 MeV electron energy in a cold magnetized plasma-waveguide case. Space-charge effects and other nonlinear effects are assumed to be negligible in this model.

Electron acceleration by a short laser beam in the presence of a long-wavelength electromagnetic wave

A scheme for laser-induced acceleration of an electron injected initially at an angle to the direction of a short-wavelength laser is investigated, where an additional long-wavelength electromagnetic wave is introduced to achieve high energy gain. Due to the beating effect of the electromagnetic waves, the electron can gain additional energy. Some computational results are presented to estimate the electron energy gain by the proposed scheme, where the gain increases by increasing the difference of the wavelengths.

Synchrotron Radiation Facilities in Korea: Pohang Light Source and Future XFEL Project

The Pohang Light Source (PLS) at the Pohang Accelerator Laboratory (PAL) is a third-generation light source, the only synchrotron radiation facility in Korea, and the fifth machine of its kind in the world (see Figure 1). In 1988, PAL was organized for the construction of the PLS. Ground-breaking was celebrated in 1991, and PLS construction was completed in 1994. In 1995, the PLS opened two beamlines to public users. The PLS was initially operated at 2.0 GeV in 1995. Since 2002, the energy of the electron beam has been upgraded to 2.5 GeV (see Table 1 for the principal parameters of PLS). Remarkable increases in the number of beamlines, users, and scientific results have been achieved since the opening of the PLS in 1995. Two or three beamlines have been added each year for the past 15 years, and as of February 2009 we have in total 27 beamlines in operation and 3 beamlines under construction, which will be completed by the end of 2009 (Figures 2 and 3).

Beam Dynamics in a 10-GeV Linear Accelerator for the X-Ray Free Electron Laser at PAL

We investigated beam dynamics in a 10-GeV linear accelerator for SASE (Self-Amplified Spontaneous Emission) Free-Electron Laser (FEL) at PAL. The linac is designed to provide the optimal beams to generate radiation of the wavelength of 1-¿ in the undulator. An optimum choice of beam parameters is performed to reduce the correlated energy spread after final beam compression and to make accelerator system insensitive to rf jitters. The two-stage bunch compressors are designed to reduce the effects of coherent synchrotron radiation and thus the transverse emittance is not significantly increased. The bunch compressors are also designed such that the effects of nonlinearities due to wakefields, rf curvature and second order momentum compaction become as small as possible in the linear accelerator. With a careful choice of beam and accelerator parameters, the bunch compression process can be made more linear, which minimizes bunch length that can be achieved and helps to reduce high peak current spikes in the beam distributions, which may deteriorate the SASE performance. The tracking simulations in the linear accelerator include longitudinal and transverse wakefields, and the effects of errors such as rf gun timing, rf phase and rf voltage. The simulations also include the X-band rf section and its wakefield. In result, through these design studies, we could get beam parameters and accelerator parameters to be able to provide the radiation power of 6 GW in the wavelength of 1-¿ in a 94-m-long undulator. Results on low-charge case of 0.2 nC and the microbunching instability are also shown. It is shown that the designed linac with a tuneable lattice shows satisfactory performances for a 10-GeV X-ray FEL facility.

Rotating coil method for the measurement of deflecting magnetic fields in cathode ray tube

A fast and reliable method for measuring and analyzing the magnetic fields of the deflecting yoke (DY) in a cathode ray tube (CRT) is presented. The measurement is based on the rotating coil method and uses a set of coils to measure the axial distribution of DY magnetic fields. The output voltage of each coil is integrated and then Fourier transformed to obtain the multipole error components. The magnetic vector and scalar potentials are calculated from the measured data using a theory of complex magnetic potential. The results of the rotating coil measurement are compared with those of the conventional Hall probe mapping method. Both results agree reasonably well, indicating that the rotating coil method can be applied for efficient measurement of a complicated DY magnetic field; the required time for measurement is very short and on-line analysis of multipole error fields is possible.

Design study of a superconducting gantry for carbon beam therapy

This paper describes beam-optics design of a gantry for carbon ions in cancer therapy accelerators. A compact design is important for such a gantry. The designed gantry is compact such that its size is comparable to the size of the existing proton gantries. This is made possible by introducing superconducting double helical coils for dipole magnets. The gantry optics is designed in such a way that it provides rotation-invariant optics, a variable beam size, and point-to-parallel scanning of a beam. For large-aperture magnet, a three-dimensional magnetic field distribution is obtained by invoking a computer code, and a number of particles are tracked by integrating equations of motion numerically together with a three-dimensional interpolation. The beam-shape distortion due to the fringe field is reduced to an acceptable level by optimizing the coil windings with the help of a genetic algorithm. Higher-order transfer coefficients are calculated and shown to be reduced greatly with appropriate optimization of the coil windings.