S.H. Nam

Commissioning of the PLS-II

After 14 years of successful operation, the Pohang Light Source (PLS) has completed PLS-II upgrade to meet the increasing demand from the growing user community. The PLS-II upgrade has increased the beam energy from 2.5 GeV to 3 GeV; the number of insertion devices has been increased by a factor of two (20 IDs); and the beam current has been increased to 400 mA from 200 mA. The beam emittance has been reduced to below 10 nm while retaining the existing PLS tunnel as well as the existing injection system. During the six months of commissioning in the latter half of 2011, we have successfully achieved 14 insertion device operations and top-up operations with 100 mA beam current and 5.8 nm beam emittance. In this paper, we report the experimental results obtained from the PLS-II commissioning.

A new modulator controller of the PLS linac

The 2-GeV electron linac at Pohang accelerator laboratory (PAL) has been operated continuously as a full energy injector for the Pohang Light Source (PLS) since Dec. 1994. There have been continuous efforts to improve the klystron-modulator (K&M) system to make it more stable and reliable. To improve self-diagnostic, operation, monitoring, and remote communication, we developed a new modulator controller based on an industrial PC platform. The modulator controller mainly consisted of an interlock signal conditioning module, a fast pulse signal-conditioning module, and the main PC platform. Operating system of the PC is Windows NT 4.0, and application software is developed with C++. The interlock signal-conditioning module generally carries digital and slowly varying clean analog signals. The fast pulse signal-conditioning module is used for preconditioning fast pulse and DC signals that inherently have high noise levels, such signals as a beam voltage, a beam current, an EOLC current, a HVDC voltage, and a HVDC current. All operation data of the K&M system can be acquired and saved in real time. We are upgrading the main PLS, control system with EPICS. The industrial PC platform will function as an input/output controller (IOC) in the future EPICS PLS control system.

The low level RF system for 100 MeV proton linac of KOMAC

At the 100 MeV proton linac of the KOMAC (Korea Multi-Purpose Accelerator Complex), the low level RF system provides field control for the entire KOMAC proton linac, including an RFQ and a DTL1 at 350 MHz as well as 7 DTL cavities at 700 MHz. In addition to field control, it provides cavity resonance control, and incorporates the personnel and machine protection functions. An accelerator electric field stability of /spl plusmn/ 1% in amplitude and /spl plusmn/ 1/spl deg/ in phase is required for the RF system. In order to accomplish these requirements, a digital feedback control technique is adopted for flexibility of the feedback and feed forward algorithm implementation. In this paper, the detailed description of the low level RF system is given.

Field analysis of TWT HVPS transformer and HV module

The role of a high power density DC power supply is very important in designing a compact and high efficiency TWT microwave amplifier. In order to fabricate a compact power supply, it is necessary to reduce transformer volume by increasing switching frequency of the power supply. However, a step-up ratio of the transformer in the high voltage DC power supply could not be indefinitely increased due mainly to self-resonance by stray capacitance and leakage inductance. Therefore, the pulse transformer should be carefully designed to fulfill its function in the power supply. A high frequency and high voltage pulse transformer is designed, fabricated, and tested. Switching frequency of the transformer is 100 kHz. Input and output voltages of the transformer are 250 V and 4 kV, respectively. Normal operation power of the transformer is 3 kW. Maximum allowed volume of the transformer is 400 cm/sup 3/. The transformer is installed in a metal box that has nominal operation temperature of 85 degree centigrade. The transformer and other high voltage components in the box are molded with silicon RTV that has a very low thermal conductivity. Calculated and measured results of various parameters such as transformer loss, temperature rise, leakage inductance, distributed capacitance, and hysterisis characteristics are presented. In addition, field analysis results obtained with ANSYS code for the transformer and the HV module are also presented.

Spectroscopic measurement of high current vacuum arc plasma in triggered vacuum switch

The purpose of this experiment is to improve understanding of the high current vacuum arc phenomena in a triggered vacuum switch (TVS). The TVS used in the experiment has a rod array electrode. The cross section of each rod has trapezoidal shape. A spectroscopic measurement was performed up to 150 kA peak current at the center of electrodes. The tested electrode material was Fe. Measured Fe spectrum range was from 200 nm to 900 nm. Measurement result showed that over 90 percent of the charge states were Fe II, and the others were Fe I and Fe III. By assuming a local thermal equilibrium (LTE), electron temperatures of the TVS arc were determined from the relative line intensity ratio of Fe II. The electron temperatures at the center of electrodes were measured as 1.5 eV and 2.5 eV with 26 kA and 64 kA peak currents, respectively. The electron temperature increased with its peak current.

Performance of the Pohang Light Source

Abstract The Pohang Light Source has actively supported users since the commissioning in 1994. In 1999, we had two decisive breakthroughs for the machine performance; installation of feedback systems to actively damp the coupled-bunch instabilities, and 2.5 GeV operation through energy ramping of the 2.0 GeV electron beam from the linac. Now we can provide two stable operation modes, 2.0 and 2.5 GeV modes. This paper describes the upgraded machine performance and the beamline status of the Pohang light source. Having started with two beamlines in 1995, the facility now has 12 beamlines operational, 1 beamline under commissioning, and 7 beamlines under construction.

Commissioning and performance of the Pohang Light Source

Abstract Commissioning results and the operational performance of the Pohang Light Source, the first synchrotron radiation facility in Korea, are described.

Status of timing system and its upgrade for the PLS storage ring

The timing system for the Pohang Light Source (PLS) storage ring consists of a trigger synchronize module, a fine delay module, a repetition rate pulse generator module, and so on. All the timing modules are installed in the VXI crate and controlled by the 32 bit microprocessors with the host computer. Although the timing system has been operated without any serious problems since commissioning in 1994, there were some minor troubles, and the performances were not so excellent. Therefore, upgrade of the timing system is progressing with a synchronous universal counter and other commercial modules of NIM type for increasing of a reliability, easy maintenance, low timing jitters, and all types of beam filling pattern.

A new PLS-II in-vacuum undulator and characterization of undulator radiation

This paper describes the result of overall studies from development to characterization of undulator radiation. After three years of upgrading, PLS-II has been operating successfully since 21st March 2012. During the upgrade, we developed and installed an in-vacuum undulator (IVU) that generates brilliant X-ray beam. The IVU with a 3 GeV electron beam generates undulator radiation up to ~ 21 keV by using 11th higher harmonic. The characterizations of the undulator radiation at an X-ray beam line in PLS-II agreed well with the simulation. Based on this performance demonstration, the in-vacuum undulator is successfully operating at PLS-II.

High Coulomb transfer pseudo-spark switch

In realizing electro-magnetic launchers, one of key components is a switch that can transfer high energy to a load and also has a precise triggering capability. The pseudo-spark switch is a good candidate to such applications. Various designs of the pseudo-spark switch had been tested at different institutes for high-energy transfer, but not high enough to fulfill specifications of the launcher experiment. To adopt required specifications of the launcher that are 20 kV nominal hold-off voltage, 150 kA peak current, /spl sim/1 ms pulse-width, and /spl sim/ 1,000 shot lifetime, a pseudo-spark switch is designed and fabricated. A high dielectric surface discharge trigger unit is employed in the switch. Two different pseudo-spark switch geometries are fabricated and tested. One has hollow anode and hollow cathode with axially symmetric ring slit bore hole channels. Another has radial hollow anode and cathode with multi-channel bore holes. All electrodes are made of stainless steel. A maximum 100 kJ capacitor bank is used to test coulomb transfer capability of the switch. The 100 kJ capacitor bank is consisted of two parallel-connected 50 /spl mu/F, 45 kV capacitors. Helium and argon are used in the switch test at different pressure ranges.