Young-Do Joo - Academia.edu (original) (raw)

Papers by Young-Do Joo

The RF system for PLS-II upgrade, of which beam current and emittance are 400 mA and 5.6 nmrad at... more The RF system for PLS-II upgrade, of which beam current and emittance are 400 mA and 5.6 nmrad at 3 GeV, becomes much more important compared to PLS. To reduce the HOM intensity in RF cavities for stable beam, a superconducting RF cavity is selected for the PLS-II. The RF system has to compensate beam loss power of 663 kW from 24 bending magnets, 20 insertion devices and other losses by RF HOM and broadband losses along vacuum chambers. For sufficient energy acceptance and lifetime the design RF voltage is 4.5 MV. Three 500 MHz superconducting cavities will be operated from October 2012, following successful commissioning with PLS NC cavities from July 2011. For the 3 SRF cryomodules, a 700 W class He cryogenic system will be prepared in 2011. The design of PLS-II SRF system including cryogenic system will be reported in the paper.

Three superconducting RF cavities were commissioned with electron beam in way of one by one durin... more Three superconducting RF cavities were commissioned with electron beam in way of one by one during the last 3 years, and now PLS-II is in user service on the way of beam current to 400mA, the target of PLS-II. The cavities and cryomodules were prepared with SRF standard technology and procedures, then vertical test, windows conditioning, cryogenic test in each cryomodule, horizontal power test, conditioning, and commissioning without and with beam at PLS-II tunnel by collaboration with industries. All the cavities showed stable performances as good as not-observing any RF instability from cavities, couplers and windows up to 400 mA beam store, but observing several cavity quenches and minor vacuum bursts by abrupt power with control and human errors. The initial beam current for user run were recorded as 150 mA with one cavity, 280 mA with two cavities and 320 mA with three cavities. The 400 mA beam was also achieved with two cavities by decay mode and also with three cavities by top-up mode. The stabilities of RF amplitude and phase are good enough not to induce beam instabilities.

The Stanford Linear Accelerator Energy Doubler (SLED) system for the PAL (Pohang Accelerator Labo... more The Stanford Linear Accelerator Energy Doubler (SLED) system for the PAL (Pohang Accelerator Laboratory) XFEL (X-ray Free Electron Laser) is requested to operate with an RF input power of 80 MW and a pulse width of 4 μs. We designed a new SLED system with a biplanar 3 dB power divider and dual side- wall coupling irises by using the finite-difference time- domain (FDTD) simulation. The new SLED system proved to be a good solution that reduces the probability of RF breakdown in high powered operations. We fabricated the prototype of the new SLED system and carried out the high power RF test.

During the beam store test up to 400 mA in the storage ring, it was observed that the vacuum pres... more During the beam store test up to 400 mA in the storage ring, it was observed that the vacuum pressure around the RF window of the superconducting cavity rapidly increases over the interlock level limiting the availability of the maximum beam current storing. We investigated the cause of the window vacuum pressure increment by studying the changes in the electric field distribution at the superconducting cavity and waveguide according to the beam current. An equivalent physical modeling was developed using a finite -difference time domain (FDTD) simulation and it revealed that the electric field amplitude at the RF window is exponentially increased as the beam current increases, thus this high electric field amplitude causes a RF breakdown at the RF window.

Proceedings of The 21st International Workshop on Vertex Detectors — PoS(Vertex 2012), 2013

Pohang light source (PLS) had been operated for 14 years successfully. The number of beamlines of... more Pohang light source (PLS) had been operated for 14 years successfully. The number of beamlines of PLS was two at the beginning stage. The number of beam-lines has been increased two or three every year. And the total beam-lines in operation became 28 in 2010 and 3199 users had visited PAL for their experiments [1]. The user community gradually extended and they became to require brighter beam to see small signal from a sample. To meet this requirement of the user community, the PLS machine was upgraded as PLS-II. The main goals of the PLS-II machine are to increase the beam energy from 2.5 to 3 GeV, and to increase the number of insertion device (ID) by the factor of two (20 IDs). This PLS-II upgrade project had been completed in 2011 and user service has been started in 2012. We will report the current status of PLS-II machine in this paper. .

Journal of the Korean Physical Society, 2013

The Stanford Linear Accelerator Energy Doubler (SLED) system for the PAL (Pohang Accelerator Labo... more The Stanford Linear Accelerator Energy Doubler (SLED) system for the PAL (Pohang Accelerator Laboratory) XFEL (X-ray Free Electron Laser) is requested to operate with an RF input power of 80 MW and a pulse width of 4 μs. We designed a new SLED system with a biplanar 3 dB power divider and dual sidewall coupling irises by using the finite-difference timedomain (FDTD) simulation. The new SLED system proved to be a good solution that reduces the probability of RF breakdown in high powered operations. We fabricated the prototype of the new SLED system and carried out the high power RF test.

A prototype rf window was developed in collaboration with Pohang Accelerator Laboratory (PAL) and... more A prototype rf window was developed in collaboration with Pohang Accelerator Laboratory (PAL) and domestic companies. The PAL designed the S-band TE012 rf window and conducted the high power performance tests of single rf window to verify the operation characteristics for the application to the PLS-II Linac. The test was performed in the in-situ facility consisting of a modulator, klystron, waveguide network, vacuum system, cooling system, and rf analyzing equipment. As the test results with SLED, no breakdown appeared up to 75 MW peak power with 4.5 μs rf pulse width at a repetition rate of 10 Hz. The test results with the current operation level of PLS-II Linac confirms that the rf window well satisfies the criteria of PLS Linac operation. INTRODUCTION The PLS with 2.5 GeV linear accelerator (Linac) in the Pohang Accelerator Laboratory (PAL) upgraded PLSII machine with 3.0 GeV injector Linac in 2011. Currently, the PLS-II Linac have 17 RF Modules, which is consists of klystron dri...

IEEE Transactions on Plasma Science, 2002

A novel slow-wave structure (SWS), the coaxial inverted helical groove structure, is presented an... more A novel slow-wave structure (SWS), the coaxial inverted helical groove structure, is presented and those of its properties used for wide-band traveling-wave tube (TWT) are investigated. The first part of the paper concerns the wave properties of this structure in the case of a vacuum. The influence of the geometrical dimensions on dispersion characteristics and interaction impedance are investigated. The theoretical results reveal a very weak dispersion for the fundamental wave in the structure. The negative dispersion can be realized by a suitable selection of the structural parameters. The interaction impedance of the fundamental wave is about 10. The interaction impedance of the 1 space harmonic wave is much lower than that of the fundamental wave. Thus, the risk of backward wave oscillation is reduced. The software high frequency structure simulator (HFSS) is also used to calculate the dispersion property of the SWS. The simulation results from HFSS and the theoretical results agree well, which supports the theory. In the second part, a self-consistent linear theory of a coaxial inverted helical groove TWT is presented. The typical small signal gain per period is about 0.5 dB and the 3-dB small-signal gain bandwidth can exceed 25% with a 33-dB gain of tube.

Journal of the Korean Physical Society

We prove that the noise in the vertical readback from some of beam position monitors (BPMs) in th... more We prove that the noise in the vertical readback from some of beam position monitors (BPMs) in the vacuum chamber of Pohang Light Source (PLS) are caused by the transverse electric (TE) longitudinal harmonic resonances. In the numerical simulation on the PLS vacuum chamber, one of the longitudinal harmonics of TE mode is found at the operation frequency of BPM and the frequency of this mode is matched with the peak frequency in the experimental measurement of RF power transmission through the BPM pickup electrodes.

Journal of the Korean Vacuum Society, 2011

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

It is known that the position reading obtained from the beam position monitor (BPM) mounted at th... more It is known that the position reading obtained from the beam position monitor (BPM) mounted at the storage ring can be corrupted by the resonance mode. We carried out a three dimensional finitedifference time-domain (FDTD) simulation of vacuum chambers of the storage ring of the Pohang Light Source (PLS) without simplified modeling to measure the frequencies of resonance modes excited in the vacuum chamber. The frequencies of resonance modes obtained by the eigenmode simulation are well matched with the peak frequencies of RF transmission scattering matrix (S 21) graph of sector vacuum chamber measured using a network analyzer. It is found that a transverse electric (TE) resonance mode exists in the operation frequency band of BPM and the vertically oriented electric field of TE resonance mode is linked to the BPM position reading noise. Based on this study, we can easily design a vacuum chamber free from the BPM position reading noise caused by the TE resonance mode.

Journal of the Korean Physical Society, 2015

Journal of the Korean Physical Society, 2015

ABSTRACT The beam stability is one of the most important issues for the user service of the synch... more ABSTRACT The beam stability is one of the most important issues for the user service of the synchrotron radiation facility. After the upgrade of the Pohang Light Source (PLS-II), the electron-beam orbit is maintained within a root-mean-squred (rms) 1-μm range by using an orbit feedback system. However, that does not guarantee the radiation stability at the end of the beamline because unknown factors, such as focusing mirrors and double-crystal monocrometers, are present in the beamline. As a first step to solve this problem, photon-beam-position monitors (PBPMs) are installed in the front ends of the beamline to monitor the radiation stability. If the radiation is stable at the starting point of the beamline, we can move to the other components downstream that make the radiation unstable. In this paper, a correlation study will be presented between the beam-position monitor (BPM) and the PBPM. In addition, the effect of the orbit feedback system on the correlation will be described.

Third IEEE International Vacuum Electronics Conference (IEEE Cat. No.02EX524), 2002

ABSTRACT The negative dispersion in a wideband helix TWT is operative for ensuring a successful o... more ABSTRACT The negative dispersion in a wideband helix TWT is operative for ensuring a successful operation with lower second harmonic at the lowest frequency and higher power at the highest frequency. In the previous work, we studied a wideband TWT experimentally with a relatively simple SWS which uses rectangular BeO rods without the metal vanes. The angular thickness of the rectangular supports is made larger than their radial thickness, which makes this structure somewhat 'heavily loaded'. In this study, unequal rectangular ceramic rods were employed to enhance the second harmonic level at the lower frequencies and efficiency at the higher frequencies. The dispersion and the interaction impedance of the structure were predicted by a 3-D HFSS code. The hot simulations carried out using a 1-D nonlinear code.

It is known that the position reading obtained from the beam position monitor (BPM) mounted at th... more It is known that the position reading obtained from the beam position monitor (BPM) mounted at the storage ring can be corrupted by the resonance mode. We carried out a three dimensional finitedifference time-domain (FDTD) simulation of vacuum chambers of the storage ring of the Pohang Light Source (PLS) without simplified modeling to measure the frequencies of resonance modes excited in the vacuum chamber. The frequencies of resonance modes obtained by the eigenmode simulation are well matched with the peak frequencies of RF transmission scattering matrix (S 21) graph of sector vacuum chamber measured using a network analyzer. It is found that a transverse electric (TE) resonance mode exists in the operation frequency band of BPM and the vertically oriented electric field of TE resonance mode is linked to the BPM position reading noise. Based on this study, we can easily design a vacuum chamber free from the BPM position reading noise caused by the TE resonance mode.

Journal of the Korean Physical Society, 2015

ABSTRACT One hundred seventy-two accelerating structures are required for the Pohang Accelerator ... more ABSTRACT One hundred seventy-two accelerating structures are required for the Pohang Accelerator Laboratory X-ray free-electron laser’s (PAL-XFEL’s) 10-GeV main linear accelerator. So far, we have purchased 80 structures from Mitsubishi Heavy Industry (MHI), which have quasi-symmetric couplers in the accelerating structure to reduce the quadruple and the sextuple components of the electric field in the coupling cavity. High-power tests have been conducted for the first structure of the MHI structure, and Research Instruments (RI) has developed a 3-m long accelerating structure that has an operating frequency of 2856 MHz and in/out couplers of quasi-symmetric racetrack shape for the PAL-XFEL linear accelerator. This structure also has been tested by PAL and RI in the Pohang accelerator laboratory (PAL) to check the maximum available electric field gradient. We will describe the test results of these structures and the current status for the fabrication of the other accelerating structures in this paper.

2008 IEEE International Vacuum Electronics Conference, 2008

Abstract CW Terahertz imaging system is being constructed to investigate the response of cell to ... more Abstract CW Terahertz imaging system is being constructed to investigate the response of cell to the terahertz wave. This system consists of a 0.2 THz radiation source and some off-axis-parabolic mirrors (OAPs) with 2 dimensional (2D) translation stage. Detection is ...

Microwave and Optical Technology Letters, 2002

An n-dielectric tube prototype structure consisting of a helix surrounded by adjoining dielectric... more An n-dielectric tube prototype structure consisting of a helix surrounded by adjoining dielectric tubes in an o¨erall en¨elope was studied by HFSS for flat-to-negati¨e dispersion characteristics needed for wideband tra¨eling-wa¨e tubes. The prototype structure obtained was then '' synthesized'' to obtain a wedge-shaped n-step staircase dielectric support structure for a helix.

Japanese Journal of Applied Physics, 2003

ABSTRACT A stationary 1-D nonlinear code based on Lagrangian disk model is developed on the basis... more ABSTRACT A stationary 1-D nonlinear code based on Lagrangian disk model is developed on the basis of a simple set of analytical expressions to study nonlinear dynamics in the helix slow-wave structure used in a traveling wave tube. The loss profiles such as triangular and Gaussian types are modeled as stairsteps and a simple formula is developed to found the loss at a plane for such loss profile. In contrast to the earlier works in nonlinear theory, at present, no numerical method is used at any stage. The method, introduced in this work, is general in nature because it can handle (a) multi-section structure with sever, (b) different loss profiles, namely, center (Gaussian) and tip (triangular: increasing or decreasing), (c) space charge effect on the electrons, (d) backward waves arising due to reflections, etc. Accuracy of the theory and code is verified with comparison of the computed present results with the results from simulation code MAGIC and published elsewhere and found to be in good agreement. The generation and suppression of the harmonic power are studied for a typical structure. It is found that the introduction of resynchronization section of the reduced pitch enhances the fundamental power with the reduction of the second harmonic power. In addition, the method can be used for any helix slow-wave-structure consisting of homogeneous/inhomogeneous dielectric support rods in isotropic/anisotropic overall metallic enclosure, because the axial propagation constant and interaction impedance obtained for any structure and model such as sheath and tape helix approximations or from any simulation codes can be used as the input in the program to make the code more general.

The RF system for PLS-II upgrade, of which beam current and emittance are 400 mA and 5.6 nmrad at... more The RF system for PLS-II upgrade, of which beam current and emittance are 400 mA and 5.6 nmrad at 3 GeV, becomes much more important compared to PLS. To reduce the HOM intensity in RF cavities for stable beam, a superconducting RF cavity is selected for the PLS-II. The RF system has to compensate beam loss power of 663 kW from 24 bending magnets, 20 insertion devices and other losses by RF HOM and broadband losses along vacuum chambers. For sufficient energy acceptance and lifetime the design RF voltage is 4.5 MV. Three 500 MHz superconducting cavities will be operated from October 2012, following successful commissioning with PLS NC cavities from July 2011. For the 3 SRF cryomodules, a 700 W class He cryogenic system will be prepared in 2011. The design of PLS-II SRF system including cryogenic system will be reported in the paper.

Three superconducting RF cavities were commissioned with electron beam in way of one by one durin... more Three superconducting RF cavities were commissioned with electron beam in way of one by one during the last 3 years, and now PLS-II is in user service on the way of beam current to 400mA, the target of PLS-II. The cavities and cryomodules were prepared with SRF standard technology and procedures, then vertical test, windows conditioning, cryogenic test in each cryomodule, horizontal power test, conditioning, and commissioning without and with beam at PLS-II tunnel by collaboration with industries. All the cavities showed stable performances as good as not-observing any RF instability from cavities, couplers and windows up to 400 mA beam store, but observing several cavity quenches and minor vacuum bursts by abrupt power with control and human errors. The initial beam current for user run were recorded as 150 mA with one cavity, 280 mA with two cavities and 320 mA with three cavities. The 400 mA beam was also achieved with two cavities by decay mode and also with three cavities by top-up mode. The stabilities of RF amplitude and phase are good enough not to induce beam instabilities.

The Stanford Linear Accelerator Energy Doubler (SLED) system for the PAL (Pohang Accelerator Labo... more The Stanford Linear Accelerator Energy Doubler (SLED) system for the PAL (Pohang Accelerator Laboratory) XFEL (X-ray Free Electron Laser) is requested to operate with an RF input power of 80 MW and a pulse width of 4 μs. We designed a new SLED system with a biplanar 3 dB power divider and dual side- wall coupling irises by using the finite-difference time- domain (FDTD) simulation. The new SLED system proved to be a good solution that reduces the probability of RF breakdown in high powered operations. We fabricated the prototype of the new SLED system and carried out the high power RF test.

During the beam store test up to 400 mA in the storage ring, it was observed that the vacuum pres... more During the beam store test up to 400 mA in the storage ring, it was observed that the vacuum pressure around the RF window of the superconducting cavity rapidly increases over the interlock level limiting the availability of the maximum beam current storing. We investigated the cause of the window vacuum pressure increment by studying the changes in the electric field distribution at the superconducting cavity and waveguide according to the beam current. An equivalent physical modeling was developed using a finite -difference time domain (FDTD) simulation and it revealed that the electric field amplitude at the RF window is exponentially increased as the beam current increases, thus this high electric field amplitude causes a RF breakdown at the RF window.

Proceedings of The 21st International Workshop on Vertex Detectors — PoS(Vertex 2012), 2013

Pohang light source (PLS) had been operated for 14 years successfully. The number of beamlines of... more Pohang light source (PLS) had been operated for 14 years successfully. The number of beamlines of PLS was two at the beginning stage. The number of beam-lines has been increased two or three every year. And the total beam-lines in operation became 28 in 2010 and 3199 users had visited PAL for their experiments [1]. The user community gradually extended and they became to require brighter beam to see small signal from a sample. To meet this requirement of the user community, the PLS machine was upgraded as PLS-II. The main goals of the PLS-II machine are to increase the beam energy from 2.5 to 3 GeV, and to increase the number of insertion device (ID) by the factor of two (20 IDs). This PLS-II upgrade project had been completed in 2011 and user service has been started in 2012. We will report the current status of PLS-II machine in this paper. .

Journal of the Korean Physical Society, 2013

The Stanford Linear Accelerator Energy Doubler (SLED) system for the PAL (Pohang Accelerator Labo... more The Stanford Linear Accelerator Energy Doubler (SLED) system for the PAL (Pohang Accelerator Laboratory) XFEL (X-ray Free Electron Laser) is requested to operate with an RF input power of 80 MW and a pulse width of 4 μs. We designed a new SLED system with a biplanar 3 dB power divider and dual sidewall coupling irises by using the finite-difference timedomain (FDTD) simulation. The new SLED system proved to be a good solution that reduces the probability of RF breakdown in high powered operations. We fabricated the prototype of the new SLED system and carried out the high power RF test.

A prototype rf window was developed in collaboration with Pohang Accelerator Laboratory (PAL) and... more A prototype rf window was developed in collaboration with Pohang Accelerator Laboratory (PAL) and domestic companies. The PAL designed the S-band TE012 rf window and conducted the high power performance tests of single rf window to verify the operation characteristics for the application to the PLS-II Linac. The test was performed in the in-situ facility consisting of a modulator, klystron, waveguide network, vacuum system, cooling system, and rf analyzing equipment. As the test results with SLED, no breakdown appeared up to 75 MW peak power with 4.5 μs rf pulse width at a repetition rate of 10 Hz. The test results with the current operation level of PLS-II Linac confirms that the rf window well satisfies the criteria of PLS Linac operation. INTRODUCTION The PLS with 2.5 GeV linear accelerator (Linac) in the Pohang Accelerator Laboratory (PAL) upgraded PLSII machine with 3.0 GeV injector Linac in 2011. Currently, the PLS-II Linac have 17 RF Modules, which is consists of klystron dri...

IEEE Transactions on Plasma Science, 2002

A novel slow-wave structure (SWS), the coaxial inverted helical groove structure, is presented an... more A novel slow-wave structure (SWS), the coaxial inverted helical groove structure, is presented and those of its properties used for wide-band traveling-wave tube (TWT) are investigated. The first part of the paper concerns the wave properties of this structure in the case of a vacuum. The influence of the geometrical dimensions on dispersion characteristics and interaction impedance are investigated. The theoretical results reveal a very weak dispersion for the fundamental wave in the structure. The negative dispersion can be realized by a suitable selection of the structural parameters. The interaction impedance of the fundamental wave is about 10. The interaction impedance of the 1 space harmonic wave is much lower than that of the fundamental wave. Thus, the risk of backward wave oscillation is reduced. The software high frequency structure simulator (HFSS) is also used to calculate the dispersion property of the SWS. The simulation results from HFSS and the theoretical results agree well, which supports the theory. In the second part, a self-consistent linear theory of a coaxial inverted helical groove TWT is presented. The typical small signal gain per period is about 0.5 dB and the 3-dB small-signal gain bandwidth can exceed 25% with a 33-dB gain of tube.

Journal of the Korean Physical Society

We prove that the noise in the vertical readback from some of beam position monitors (BPMs) in th... more We prove that the noise in the vertical readback from some of beam position monitors (BPMs) in the vacuum chamber of Pohang Light Source (PLS) are caused by the transverse electric (TE) longitudinal harmonic resonances. In the numerical simulation on the PLS vacuum chamber, one of the longitudinal harmonics of TE mode is found at the operation frequency of BPM and the frequency of this mode is matched with the peak frequency in the experimental measurement of RF power transmission through the BPM pickup electrodes.

Journal of the Korean Vacuum Society, 2011

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

It is known that the position reading obtained from the beam position monitor (BPM) mounted at th... more It is known that the position reading obtained from the beam position monitor (BPM) mounted at the storage ring can be corrupted by the resonance mode. We carried out a three dimensional finitedifference time-domain (FDTD) simulation of vacuum chambers of the storage ring of the Pohang Light Source (PLS) without simplified modeling to measure the frequencies of resonance modes excited in the vacuum chamber. The frequencies of resonance modes obtained by the eigenmode simulation are well matched with the peak frequencies of RF transmission scattering matrix (S 21) graph of sector vacuum chamber measured using a network analyzer. It is found that a transverse electric (TE) resonance mode exists in the operation frequency band of BPM and the vertically oriented electric field of TE resonance mode is linked to the BPM position reading noise. Based on this study, we can easily design a vacuum chamber free from the BPM position reading noise caused by the TE resonance mode.

Journal of the Korean Physical Society, 2015

Journal of the Korean Physical Society, 2015

ABSTRACT The beam stability is one of the most important issues for the user service of the synch... more ABSTRACT The beam stability is one of the most important issues for the user service of the synchrotron radiation facility. After the upgrade of the Pohang Light Source (PLS-II), the electron-beam orbit is maintained within a root-mean-squred (rms) 1-μm range by using an orbit feedback system. However, that does not guarantee the radiation stability at the end of the beamline because unknown factors, such as focusing mirrors and double-crystal monocrometers, are present in the beamline. As a first step to solve this problem, photon-beam-position monitors (PBPMs) are installed in the front ends of the beamline to monitor the radiation stability. If the radiation is stable at the starting point of the beamline, we can move to the other components downstream that make the radiation unstable. In this paper, a correlation study will be presented between the beam-position monitor (BPM) and the PBPM. In addition, the effect of the orbit feedback system on the correlation will be described.

Third IEEE International Vacuum Electronics Conference (IEEE Cat. No.02EX524), 2002

ABSTRACT The negative dispersion in a wideband helix TWT is operative for ensuring a successful o... more ABSTRACT The negative dispersion in a wideband helix TWT is operative for ensuring a successful operation with lower second harmonic at the lowest frequency and higher power at the highest frequency. In the previous work, we studied a wideband TWT experimentally with a relatively simple SWS which uses rectangular BeO rods without the metal vanes. The angular thickness of the rectangular supports is made larger than their radial thickness, which makes this structure somewhat 'heavily loaded'. In this study, unequal rectangular ceramic rods were employed to enhance the second harmonic level at the lower frequencies and efficiency at the higher frequencies. The dispersion and the interaction impedance of the structure were predicted by a 3-D HFSS code. The hot simulations carried out using a 1-D nonlinear code.

It is known that the position reading obtained from the beam position monitor (BPM) mounted at th... more It is known that the position reading obtained from the beam position monitor (BPM) mounted at the storage ring can be corrupted by the resonance mode. We carried out a three dimensional finitedifference time-domain (FDTD) simulation of vacuum chambers of the storage ring of the Pohang Light Source (PLS) without simplified modeling to measure the frequencies of resonance modes excited in the vacuum chamber. The frequencies of resonance modes obtained by the eigenmode simulation are well matched with the peak frequencies of RF transmission scattering matrix (S 21) graph of sector vacuum chamber measured using a network analyzer. It is found that a transverse electric (TE) resonance mode exists in the operation frequency band of BPM and the vertically oriented electric field of TE resonance mode is linked to the BPM position reading noise. Based on this study, we can easily design a vacuum chamber free from the BPM position reading noise caused by the TE resonance mode.

Journal of the Korean Physical Society, 2015

ABSTRACT One hundred seventy-two accelerating structures are required for the Pohang Accelerator ... more ABSTRACT One hundred seventy-two accelerating structures are required for the Pohang Accelerator Laboratory X-ray free-electron laser’s (PAL-XFEL’s) 10-GeV main linear accelerator. So far, we have purchased 80 structures from Mitsubishi Heavy Industry (MHI), which have quasi-symmetric couplers in the accelerating structure to reduce the quadruple and the sextuple components of the electric field in the coupling cavity. High-power tests have been conducted for the first structure of the MHI structure, and Research Instruments (RI) has developed a 3-m long accelerating structure that has an operating frequency of 2856 MHz and in/out couplers of quasi-symmetric racetrack shape for the PAL-XFEL linear accelerator. This structure also has been tested by PAL and RI in the Pohang accelerator laboratory (PAL) to check the maximum available electric field gradient. We will describe the test results of these structures and the current status for the fabrication of the other accelerating structures in this paper.

2008 IEEE International Vacuum Electronics Conference, 2008

Abstract CW Terahertz imaging system is being constructed to investigate the response of cell to ... more Abstract CW Terahertz imaging system is being constructed to investigate the response of cell to the terahertz wave. This system consists of a 0.2 THz radiation source and some off-axis-parabolic mirrors (OAPs) with 2 dimensional (2D) translation stage. Detection is ...

Microwave and Optical Technology Letters, 2002

An n-dielectric tube prototype structure consisting of a helix surrounded by adjoining dielectric... more An n-dielectric tube prototype structure consisting of a helix surrounded by adjoining dielectric tubes in an o¨erall en¨elope was studied by HFSS for flat-to-negati¨e dispersion characteristics needed for wideband tra¨eling-wa¨e tubes. The prototype structure obtained was then '' synthesized'' to obtain a wedge-shaped n-step staircase dielectric support structure for a helix.

Japanese Journal of Applied Physics, 2003

ABSTRACT A stationary 1-D nonlinear code based on Lagrangian disk model is developed on the basis... more ABSTRACT A stationary 1-D nonlinear code based on Lagrangian disk model is developed on the basis of a simple set of analytical expressions to study nonlinear dynamics in the helix slow-wave structure used in a traveling wave tube. The loss profiles such as triangular and Gaussian types are modeled as stairsteps and a simple formula is developed to found the loss at a plane for such loss profile. In contrast to the earlier works in nonlinear theory, at present, no numerical method is used at any stage. The method, introduced in this work, is general in nature because it can handle (a) multi-section structure with sever, (b) different loss profiles, namely, center (Gaussian) and tip (triangular: increasing or decreasing), (c) space charge effect on the electrons, (d) backward waves arising due to reflections, etc. Accuracy of the theory and code is verified with comparison of the computed present results with the results from simulation code MAGIC and published elsewhere and found to be in good agreement. The generation and suppression of the harmonic power are studied for a typical structure. It is found that the introduction of resynchronization section of the reduced pitch enhances the fundamental power with the reduction of the second harmonic power. In addition, the method can be used for any helix slow-wave-structure consisting of homogeneous/inhomogeneous dielectric support rods in isotropic/anisotropic overall metallic enclosure, because the axial propagation constant and interaction impedance obtained for any structure and model such as sheath and tape helix approximations or from any simulation codes can be used as the input in the program to make the code more general.