J. S. Oh

PROTOTYPE PULSE MODULATOR FOR HIGH-POWER KLYSTRON IN PLS LINAC

2.8 Pohang Accelerator Laboratory (PAL) is constructing a 2 GeV electron linac. To achieve the final electron energy, it employs total eleven units of high power klystron (65 or 80 MW) and pulse modulator (>150 MW) as RF power source. PAL is now constructing 200 MW modulators (400 kV, 4.4 ps flat top, 800 0 load). A prototype 150 MW modulator (350 kV, 3.5 p s flat top, 840 fl load) is already constructed and under operation with a dummy load. Required parameters of modulators and construction of the prototype are presented.

Design Considerations for the Stability Improvement of Klystron-Modulator for PAL XFEL

The PAL (Pohang Accelerator Laboratory) 2.5-GeV linac is planed to be converted to a SASE-XFEL facility (PAL XFEL) that supplies coherent X-rays down to 0.3-nm wavelength. The PAL XEL requires a new 1.2-GeV linac that will be combined to the existing linac to increase a beam energy upto 3.7-GeV. This XFEL linac should supply highly bright beams with emittance of 1.2 mm-mrad, a peak current of 3.5 kA, and a low energy spread of 0.03%. The RF stability of 0.02% is required for both RF phase and amplitude to get stable SASE output. This stability is mainly determined by a low level RF drive system and klystron-modulators. The stability level of the modulator has to be improved 10 times better to meet the pulse stability of 0.02%. The regulation methods such as traditional de-Qing and precision inverter charging technology are reviewed to find out suitable upgrade shceme of the modulators. Design considerations for the stability improvement of klystron-modulators for PAL XFEL are presented.

Cold test on C-band standing-wave accelerator

For a compact X-ray source, we designed a C-band standing-wave electron accelerator. It is capable of producing 4-MeV electron beams with 50-mA peak beam current. As an RF source, we use 5-GHz magnetron with duty factor of 0.08%. The accelerating structure is bi- periodic and on-axis coupled structure, operated with pi/2- mode standing waves. Each cavity in the bunching and normal cell is designed by the MWS code and measured with aluminium prototype cavity. As per the dispersion relation derived from the measurement results, calibration factor obtained for the actual copper cavity.

Pulsed plasma process for the flue gas removal from the industrial incinerator using peak 200-kV, 10-kA pulse modulator

The electrical discharge process, especially the pulsed plasma discharge process can be applied to the removal of pollutant gases from industrial plants such as power generation plants and incinerators. Up to now, most of the study has been performed in a laboratory scale with short-term tests due to the lack of a reliable pulse modulator with a high average power. The pulsed corona discharge method shows encouraging results for the removal of NOx and SO2 gases based on smallscale experiments. A 120-kW high average power modulator for industrial applications of the pulsed corona process to remove flue gas has been designed and manufactured. It is one of the largest scale modulator systems in the world for treating NOx and SO2 simultaneously. Its design specifications are as follows: an average power of 120 kW, a peak voltage of 200 kV with a full width at half maximum (FWHM) of 500 nsec, a peak current of 10 kA, and a pulse repetition rate of 300 Hz. It is required to have long lifetime and high reliability for commercial plant application because the downtime for maintenance affects plant availability. A high-power, fast semiconductor switch, a magnetic-pulse-compression (MPC) switch, and a fast-pulse transformer are essential components to meet these requirements. The 120-kW high average power modulator has been installed and tested at an industrial incinerator plant with a gas flow of 50,000 Nm/Hr. This modulator was operated with pulses of up to 150 kV with 500-nsec (FWHM) pulse widths at a 240-Hz repetition rate in a plasma reactor. This paper presents the design details and operational test results. Especially, the dynamic operating characteristics of the MPC modulator combined with the non-thermal plasma reactor were measured, and the SO2 and NOx removal characteristics were analyzed.

Cold test of compact C-band standing-wave accelerating structures

We designed and fabricated a C-band standing-wave accelerating structure for a compact industrial electron accelerator. It is capable of producing 4-MeV electron beams with 50-mA pulsed beam current. As an RF source, we use a 5-GHz magnetron with 1.5-MW peak power and 0.08% duty factor. This structure is bi-periodic and operated with the pi/2-mode standing-waves. It is on-axis coupled with magnetic coupling slots on the side wall. Each cavity in the bunching and the normal cells is designed by using the MWS code. The coupler cell is designed by using the Omega3p code for determining the resonant frequency and the external Q2. With the measurement of the aluminum prototype cavities, we determined the final dimensions for actual OFHC-copper cavity. In this paper, we present the low-power measurement results for the actual column: the pi/2-mode resonant frequency, the coupling coefficient, and distribution of the field strength.

Commissioning of L-band intense electron linac for industrial applications

An intense L-band electron linear accelerator is under construction at CESC (Cheorwon Electron-beam Service Center) for industrial applications. It is capable of producing 10-MeV electron beams with 30-kW average beam power. For high-power capability, we adopted 1.3 GHz, and the RF source is a 25-MW pulsed klystron with 60-kW average RF output power. The PFN-type modulator and the matched transformer provide 264-kV beam voltage with 230-A beam current to the klystron. The RF pulse length is 7 mus, and the repetition rate is 350 Hz. The thermionic E-gun generates 80-kV electron beams with pulsed 1.6 A. The pre-buncher, a single standing-wave cavity, is used before the bunching section, which is built-in with the regular accelerating section. The accelerating structure is a disk-loaded waveguide with a constant-impedance operated in the 2pi/3-mode. It is to be operated under the fully beam-loaded condition, where the beam power is maximum. The electron beams are accelerated within 6 mus since the traveling-wave filling time of the accelerating structure is almost 0.8 mus. In this paper, we present details of the accelerator system and commissioning results.

Current status of L-band electron accelerator for irradiation source

An intense L-band electron accelerator is designed and under development for CESC (Cheorwon Electron-beam Service Center) irradiation applications. It is capable of producing 10-MeV electron beams with average 30 kW. For an RF source, a Thales klystron is used with 1.3 GHz, pulsed 25 MW, and average 60 kW. The accelerator column, fabricated by IHEP in China, is operated with 2pi/3 mode traveling-wave under the fully-beam-loaded condition. The modulator was fabricated with inverter power supplies. The klystron was assembled to the klystron tank with pulse transformer. The high-voltage pulse test was conducted for the klystron tube. In this paper, we present design details of the accelerator and current status.

Physics Requirements of PAL‐XFEL Undulator

Pohang Accelerator Laboratory(PAL) is planning a 0.3 nm SASE (Self Amplification of Spontaneous Emission) XFEL based on 3.7 GeV linear accelerator. For short saturation length, application of SPring8 type in vacuum undulator is needed. This reflects the experiences from SPring8 SCSS project. The end structures were designed to be asymmetric along the beam direction to ensure systematic zero 1st field integral. The thickness of the last magnets were adjusted to minimize the transition distance to the fully developed periodic field. This approach is more convenient to control than adjusting the strength of the end magnets. The final design features 4 mm minimum pole gap, 15 mm period, peak effective field of 1.09 Tesla. In this article, the physical design of the undulator, the design of the end structure, and the physics requirements of the undulator system will be presented.

Wake Field Effect on the Sase Performance of PAL XFEL

The PAL XFEL will supply coherent radiations from VUV to X-rays. X-ray FEL for 0.3 nm lasing requires a minimum 3-GeV driver linac and a 60-m long in-vacuum undulator with a narrow variable gap. The linac should supply highly bright beams with emittance of 1.2 mm-mrad, a peak current of 3.5 kA, and a lower energy spread less than 0.03%. The beam quality is degraded along the undulator trajectory due to the energy loss, the wake field, and the magnetic field errors, etc. Especially the wake field effect is most sensitive parameter due to the narrow gap of the undulator. The preliminary design details of undulators for PAL-XFEL are presented with parametric analysis. The SASE performance is analyzed using simulation tool SIMPLEX [1].

Average 120-kW MPC modulator for plasma de-NO/sub x//de-SO/sub x/ system

The pulsed corona discharge process shows the encouraging results for the removal of NO/sub x/ and SO/sub x/ gases based on small-scale experiments. The lifetime and the reliability of the system are major difficulties to realize this newly developed technology because the downtime for maintenance affects the plant availability. The combination of a high power solid-state switch with a magnetic pulse compressor (MPC) is a suitable scheme to meet these requirements. An average 120-kW MPC modulator has been constructed and tested with a plasma reactor for an industrial incinerator plant. The plasma reactor has wire-plate electrodes and can treat the gas of 50000 Nm/sup 3//Hr. This modulator can generate 150 kV pulses with 500 nsec (FWHM) pulse width, and 300 Hz repetition rate. This paper presents design details and the operational characteristics of the MPC modulator.