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Wu, Y. K.

Paper Title Page
MOPAS036 A Physics Based Approach for Ramping Magnet Control in a Compact Booster 515
 
  • S. M. Hartman, S. F. Mikhailov, V. Popov, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
 
  Funding: Supported by US DoE grant #DE-FG02-01ER41175.

At Duke University, a booster synchrotron was recently commissioned as part of the HIGS upgrade. For the ramping magnet power supply controls, a scheme was developed to present the high level operator interface in terms of the physics quantities of the accelerator, i.e. the effective focusing strength of the magnets. This scheme allows for the nonlinearities of the magnets – a result of the extremely compact footprint of this booster – to be incorporated into the low level software. This facilitates machine studies and simplifies use of physics modeling. In addition, it simplifies operation, allowing the booster to ramp to any energy from the 0.27 GeV of the injector linac to the 1.2 GeV maximum of the Duke Storage Ring. The high level of flexibility of this system if further advanced by incorporating the level of tunability typically found in a storage ring control system. Tuning changes made during steady-state operation are automatically propagated to the waveforms which make up the booster ramp. This approach provides a good match to the wide operation modes of the Duke Storage Ring and its associated free electron laser, and may useful for other compact booster synchrotrons.

 
MOPAS037 New Generation Digital Longitudinal Feedback System for Duke FEL and HIGS Facilities 518
 
  • Y. Kim, M. D. Busch, P. Wang, W. Wu, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
  • J. Choi, I. S. Ko, I. S. Park
    PAL, Pohang, Kyungbuk
  • D. Teytelman
    Dimtel, Redwood City, California
 
  To increase intensity of the High Intensity Gamma-ray Source (HIGS) which is driven by the Duke storage ring FEL via Compton scattering, stored beam current should be increased. However, high-current multi-bunch operation in the Duke storage ring is limited by strong longitudinal coupled-bunch beam instabilities. To control those instabilities, we have been developing an active longitudinal feedback system which is based on the Integrated Gigasample Processor (iGP) through collaboration with Dimtel, Inc. and Pohang Accelerator Laboratory. In this paper, we report the present status of our longitudinal feedback system.  
MOPAS038 Power Supply System for a Compact 1.2 GeV Booster Synchrotron 521
 
  • V. Popov, M. D. Busch, S. M. Hartman, S. F. Mikhailov, O. Oakeley, P. W. Wallace, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
 
  Funding: Supported by US DoE grant #DE-FG02-01ER41175.

A booster synchrotron has been recently commissioned at Duke University as part of the High Intensity Gamma-ray Source (HIGS) upgrade. All dipole and quadrupole magnets are fed by the same power supply in order to facilitate synchronization. A 500kW retired thyristor controlled power supply has been completely rebuilt to provide high accuracy ramping of current in the range between 150A and 700A in a 1.3 sec repetition cycle. Reproducibility of current at extraction energy is better than 0.1% for entire operational range of energy. Conflict of a fast ramping operation and a magnet protection in the case of emergency shutdown was resolved using additional thyristor switches. All trim power supplies involved in ramp have been matched with the main power supply for the time response and voltage range. The injection and extraction schemes require rapidly ramping Y-correctors. The required peak power about 4 kW in these correctors is provided by a combining a low voltage DC power supply and a pulse boosting circuit. We present the challenges of designing and developing booster power supply system. And also we report measured performance and operational experience in this paper.

 
TUPMS015 Challenges for the Energy Ramping in a Compact Booster Synchrotron 1212
 
  • S. F. Mikhailov, S. M. Hartman, J. Li, V. Popov, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
 
  Funding: This work is supported by the US DoE grant #DE-FG02-01ER41175

A booster synchrotron has been recently commissioned at Duke University FEL Laboratory as a part of the High Intensity Gamma-ray Source (HIGS) facility. The booster will provide top-off injection into the storage ring in the energy range of 0.27 - 1.2 GeV. In order to minimize the cost of the project, the booster is designed with a very compact footprint. As a result, unconventionally high field bending magnets at 1.76 T are required. A main ramping power supply drives all dipoles and quadrupoles. Quadrupole trims are used to compensate for tune changes caused by the change of relative focusing strength during ramping. Sextupoles compensate for chromatic effects caused by dipole magnet pole saturation. All these compensations have to be performed as a function of beam energy. Above 1.1 GeV, where the magnets are heavily saturated, the reduction of dynamic aperture is compensated by redistribution of strength among the sextupole families. With these compensations, effects of the magnet saturation do not cause any considerable beam loss during energy ramping.

 
TUPMS017 Accelerator Physics Research and Light Source Development Programs at Duke University 1215
 
  • Y. K. Wu
    FEL/Duke University, Durham, North Carolina
 
  Funding: This work is supported by the US AFOSR MFEL grant #FA9550-04-01-0086 and by U. S. DoE grant DE-FG05-91ER40665.

The Duke Free-Electron Laser Laboratory (DFELL) has recently completed two major accelerator/light source development projects - we successfully commissioned the world's first distributed optical klystron FEL (DOK-1 FEL) and a new 0.27-1.2 GeV booster synchrotron. The DOK-1 FEL has a much improved FEL gain compared with traditional optical klystrons. This allows the DOK-1 FEL to become a versatile light source for UV-VUV operation and as a driver for a high-intensity Compton gamma-source. The top-off booster injector for the Duke storage ring is part of the upgrade project of High Intensity Gamma-ray Source (HIGS), a facility jointly developed by the DFELL and Triangle Universities Nuclear Laboratory (TUNL). The accelerator and light source development has created new opportunities for the accelerator physics research. In this paper, we will report our recent progress in accelerator and light source development as well as the ongoing accelerator physics research programs to meet the new challenges in the areas of beam dynamics and beam instability.

 
TUPMS014 Commissioning of the Booster Injector Synchrotron for the HIGS Facility at Duke University 1209
 
  • S. F. Mikhailov, M. D. Busch, M. Emamian, S. M. Hartman, Y. Kim, J. Li, V. Popov, G. Swift, P. W. Wallace, P. Wang, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
  • O. Anchugov, N. Gavrilov, G. Y. Kurkin, Yu. Matveev, D. Shvedov, N. Vinokurov
    BINP SB RAS, Novosibirsk
  • C. R. Howell
    TUNL, Durham, North Carolina
 
  Funding: This work is supported by the US DoE grant #DE-FG02-01ER41175

A booster synchrotron has been built and recently commissioned at Duke University Free Electron Laser Laboratory (DFELL) as part of the High Intensity Gamma-ray Source (HIGS) facility upgrade. HIGS is developed collaboratively by the DFELL and Triangular Universities Nuclear Laboratory (TUNL). The booster will provide top-off injection into the Duke FEL storage ring in the energy range of 0.27 - 1.2 GeV. When operating the Duke storage ring to produce high energy Compton gamma ray beams above 20 MeV, continuous electron beam loss occurs. The lost electrons will be replenished by the booster injector operating in the top-off mode. The compactness of the booster posed a challenge for its development and commissioning. The booster has been successfully commissioned in 2006. This paper reports experience of commissioning and initial operation of the booster.

 
THPAS038 Compensation of the Beam Dynamics Effects Caused by the Extraction Lambertson Septum of the HIGS Booster 3582
 
  • J. Li, S. Huang, S. F. Mikhailov, V. Popov, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
 
  Funding: Supported by US DoE grant #DE-FG02-01ER41175

As part of the High Intensity Gamma-Ray Source (HIGS) upgrade, the booster synchrotron has been recently commissioned. The booster ramps the electron beam between 0.27 and 1.2 GeV for top-off injection into the Duke storage ring. It has symmetrical injection/extraction schemes with a bumped orbit. The injection/extraction kickers and corresponding septa are located in the opposite straight sections of the booster ring separated by about 1/4 of the vertical betatron wave. Due to the nonideal properties of the magnetic material, the magnetic field leaks out into the stored beam chamber, which directly results in orbit distortion, tune and chromaticity shifts and change of coupling. These effects caused by the extraction septum have been measured as a function of extraction energy. Based upon the measurements, we have developed a scheme to compensate the dynamics effects mentioned above.

 
FRPMS039 Growth Time of Longitudinal Coupled Bunch Mode Instability in the Duke FEL Facility 4036
 
  • Y. Kim, J. Li, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
 
  To determine the required power of an RF amplifier for the longitudinal feedback system (LFS), the growth time of the longitudinal coupled bunch mode instability (CBMI) in the Duke storage ring should be known in advance. In 2005, we measured the longitudinal beam instability with four and eight symmetrically filled buckets in the Duke storage ring. By analyzing measured data, the growth time of the longitudinal CBMI can be estimated. At a beam energy of 274 MeV, the projected growth time is about 0.37 ms for a total stored current of 160 mA. To damp harmful longitudinal CBMI with a relative energy deviation of 0.1% (rms) within the growth time, a sufficient RF power of 135 W (rms) should be delivered to an LFS kicker at a central frequency of 758.8375 MHz. In this paper, we describe measurements of the growth time and the estimation of the RF power requirement for the LFS.  
FRPMS040 BPM signal conditioning for a wide range of single bunch current operation in Duke storage ring 4042
 
  • J. Li, P. Wang, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
 
  Funding: Supported by US DoE grant #DE-FG02-01ER41175.

The beam position monitor system of the Duke storage ring has been in operation since 1998. Recently, by injecting at higher energy with a booster synchrotron, the single bunch current threshold is much more increased. This makes the BPM system do not work properly and rises the risk to damaged the BPM signal processing modules. To get reliable orbit data and protect the BPM modules, we carefully studied the BPM signal, and then found a way to overcome this problem. This paper will report the study results and the solution method.

 
FRPMS041 A Direct Electron Beam Energy Spread Measurement System for Beam Instability and FEL Research 4045
 
  • S. Huang, S. Huang
    PKU/IHIP, Beijing
  • J. Li, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
 
  Funding: Supported by US AFOSR MFEL grant #FA9550-04-01-0086.

One of critical beam parameters for the storage ring based light sources is the energy spread of the electron beam. An accurate measurement of the energy spread remains a challenge. It is well known that the electrons with different energies can degrade the spontaneous emission spectrum of a two-wiggler system in an optical-klystron configuration. The reduced modulation in the spectrum can be used to determine the energy spread of the beam. This paper describes our newly developed energy spread measurement system employing a scanning spectrometer and a fast CCD. A fast CCD with a burst mode of operation is used so that dynamical changes of the energy spread from tens of microseconds to tens of milliseconds can be measured. This system will be used in the beam instability research and free-electron laser research. Together with compact wigglers, such a system can be developed as a dedicated beam diagnostic for storage rings and linacs.

 
FRPMS042 Electron Beam Diagnostics for Compact 1.2 GeV Booster Synchrotron 4051
 
  • V. Popov, M. D. Busch, S. M. Hartman, J. Li, S. F. Mikhailov, P. W. Wallace, P. Wang, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
  • G. Y. Kurkin
    BINP SB RAS, Novosibirsk
 
  Funding: Supported by US DoE grant #DE-FG02-01ER41175.

First operational experience has been gained with the linac and booster diagnostic system during the commissioning of the booster synchrotron at Duke University. Beam charge measurements are provided by Faraday cups, Integrated Current Transformers (ICT) and Modular Parametric Current Transformer (MPCT). Beam position monitoring is based on BPM system delivered from Bergoz company. Betatron tune measurements use synchrotron radiation (SR) and are different for two modes of operation: stored beam and energy ramping. Transverse profile and temporal beam structure monitoring employ insertable screens, CCD cameras, striplines and dissector. The diagnostics provided good understanding of electron beam behavior and allowed to adjust important beam parameters within design specifications. An overview of the diagnostic instrumentation of the Duke linac and booster synchrotron is given along with measurement examples and discussion of operational experience.

 
FRPMS043 The Feasibility Study of Measuring the Polarization of a Relativistic Electron Beam using a Compton Scattering Gamma-Ray Source 4057
 
  • C. Sun, Y. K. Wu
    FEL/Duke University, Durham, North Carolina
 
  The Compton scattering of a circularly polarized photon beam and a polarized electron beam leads to an asymmetric distribution of the gamma rays. This asymmetry has been calculated for the High Intensity Gamma-ray Source (HIGS) beam at Duke University. Owing to the high intensity of the HIGS beam, this asymmetry is determined to be measurable with a small statistic error using a simple gamma-ray beam imaging system. We propose to set up this system to measure the polarization of the electron beam in the Duke storage ring.  
FRPMS044 A Tune Measurement System for Low Current and Energy Ramping Operation of a Booster Synchrotron 4063
 
  • Y. K. Wu, J. Li, S. F. Mikhailov, V. Popov, P. Wang
    FEL/Duke University, Durham, North Carolina
 
  Funding: This work is supported by the US AFOSR MFEL grant #FA9550-04-01-0086 and by U. S. DOE grant DE-FG05-91ER40665.

The betatron tune measurement system is one of the most important diagnostics for any circular accelerator. During the commissioning of a booster synchrotron newly developed for top-off injection into the Duke storage ring, a versatile tune measurement system employing a photomultiplier tube (PMT) and a space filter has been developed to provide reliable measurements for low current operation at a few micro-amperes of beam-current. Using the turn-by-turn technique, this tune measurement system is being used as a live tune monitor during the booster energy ramping. This system has also be used to measure chromaticity and other important beam parameters. In this paper, we describe the tune measurement system in detail and report our most recent experimental results using this system.