P. Wallace

Commissioning of the booster injector synchrotron for the HIGS facility at duke university

A booster synchrotron (Duke booster) 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 collaboration between the DFELL and Triangle Universities Nuclear Laboratory (TUNL). The booster provides top-off injection into the Duke FEL storage ring in the energy range of 0.24 -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 are replenished by the booster injector operating in the top-off mode. The present operational injection and extraction rate of the machine allows us to routinely replenish up to 5-108 electrons per second. 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.

Status of the booster synchrotron for Duke FEL storage ring

In this paper we present current status of the Booster Synchrotron for the Duke FEL storage ring. The Booster which is recently under design, fabrication and construction, will provide full energy injection into the storage ring at energy from 0.3 to 1.2 GeV. The Duke storage ring FEL (SR FEL) operates in lasing mode with 193-700 nm wavelength range. The geometry of the Duke SR FEL provides for interacting head-on collision of e-beam and FEL photons. This mode of operation is used to generate intense beams of /spl gamma/-rays from 2 MeV to about 200 MeV (currently from 2 MeV to 58 MeV). Generation of /spl gamma/-rays with energy exceeding 20 MeV causes the loss of electrons, which will be replaced by injection from the Booster operating in a top-off mode. The paper presents design and status for elements of magnetic system and vacuum system, as well as design and parameters of fast extraction kicker with 11 nS pulse duration. All these element are designed and will be fabricated by Budker Institute of Nuclear Physics, Novosibirsk, Russia.

Improving power supply performance for the Duke storage ring

As part of the recent Duke storage ring hardware upgrade (2001-2002), a power supply improvement program was put in place to bring all major DC supplies to their specifications. In carrying out this program, power supplies have been modified, tuned, and thoroughly tested. In its actual operation configuration, each power supply was subject to extensive testing to determine its DC stability, reproducibility and linearity, AC ripple and noise, and ramping performance. As a result, all major DC supplies have been improved to meet most important performance specifications for 1 GeV operation.

Power supply system for a compact 1.2 GEV booster synchrotron

Low cost power supply system for compact full energy booster synchrotron was designed, developed and successfully commissioned at Duke University. 500 kW second hand thyristor controlled power supply has been completely rebuilt to provide high accuracy ramping of current in the range between 150 A and 700 A in a 1.3 sec repetition cycle. Reproducibility of current at injection and extraction energy of better than 0.2 % was achieved. Conflict of requirements of a fast ramp operation and a magnet protection in the case of emergency shutdown was resolved by means of additional thyristor switches. All trim power supplies involved in ramp have been matched with main power supply for the time response and voltage range. Vertical injection to and extraction from the booster requires a strong Y-bump. Combination of low voltage DC power supply and pulse boosting circuit has eliminated the need of expensive power supply for peak power about 4 kW. Challenges of design, main parameters of the booster power supply system and discussion of operation experience are presented in this paper.

Status of the Booster Injector for the Duke FEL Storage Ring

This paper presents the current status of the booster synchrotron for the Duke Free Electron Laser Laboratory (DFELL) storage ring. The booster will provide full energy injection into the storage ring in a wide energy range from 0.27 to 1.2 GeV. When operating the DFELL storage ring as the High Intensity Gamma Source (HIGS) to produce gamma photons above 20 MeV with Compton scattering, continuous electron loss occurs. The top-off mode operation of the booster injector will enable the continuous operation of the HIGS facility by replenishing the lost electrons. The design requirement for a compact booster with the single bunch extraction capability remains a challenge for the machine development. Presently, the booster project is in the installation phase. The magnetic elements, vacuum chambers, injection and extraction kickers have been developed in collaboration with and fabricated at the Budker Institute of Nuclear Physics (BINP), Russia. The diagnostic and control system is being developed at DFELL. The commissioning of the booster synchrotron will start at the end of 2005.

3 kA Power Supplies for the Duke OK-5 FEL Wigglers

The next generation electromagnetic OK-5/Duke storage ring FEL wigglers [1], [2] require three 3kA/70V power supplies with current stability about 20 ppm and current ripples less than 20 ppm in their full operating range. Duke FEL Laboratory acquired three out-of-service SCR controlled power supplies (Trans-Rex, 5kA/100V), which were built almost 30 years ago. The existing archaic firing circuit, lack of any output voltage filtering and with an outdated DCCT, would not be able to meet the above requirements. To deliver the desirable high performance with very limited funds, all three Trans-Rex power supplies have been completely rebuilt in-house at DFELL. Modern high stability electronic components and a high precision Danfysik DCCT have been used. A new symmetrical firing circuit, efficient passive filter and reliable transformer-coupled active filter are used to reduce output current ripples to an appropriate level. At the present time, all three refurbished power supplies are in operation. One of these power supplies was used since August, 2004 to feed OK-4 wigglers with good overall performance. Others two have been tested and used as power supplies for magnetic measurements.

Commissioning of the New RF System with the HOM Damped RF Cavity

A new 178 MHz RF system has been commissioned at Duke Storage Ring. It consists of a 140 kW tetrode transmitter; higher order modes (HOM) damped RF cavity and the necessary frequency and voltage control electronics. The cavity walls are made of copper-on-stainless steel bimetal (8 mm Cu, 7 mm SS). The cavity has a larger beam pipe opening (700 mm in diameter) in the down-stream side, which allows the HOM propagating out of the cavity and being absorbed by the ceramic loads. The design details and the commissioning results are presented in this paper.

Electron beam diagnostics for compact 1.2 GeV booster synchrotron

First operational experience has been gained with the linac and booster diagnostic system during the commissioning of the booster synchrotron at Duke University. The booster was designed and developed as an injector for the storage ring as a part of the High Intensity Gamma-ray Source (HIGS) upgrade of Duke FEL storage ring. Booster beam instrumentation includes: beam charge measurements (Faraday cups, Integrated Current Transformers (ICT), Modular Parametric Current Transformer (MPCT)), beam position monitoring (BPM), betatron tune measurements using synchrotron radiation (SR), transverse profile and temporal beam structure monitoring (insertable screens, striplines, dissector). The diagnostics provided good understanding of electron beam behavior and allowed us to adjust important beam parameters within design specifications. An overview of the diagnostic instrumentation of the Duke Booster synchrotron is given along with measurement examples and discussion of operational experience.

Trim Power Supplies for the Duke Booster and Storage Ring

The on-going Duke storage ring upgrades and the development of a new booster synchrotron injector require more than 100 units of high performance unipolar and bipolar trim power supplies in the current range of - 15 A to + 15 A. However, most of the trim power supplies on the market do not deliver two critical performance features simultaneously: a high current stability and a low current noise. An in-house trim power supply development program has been put in force to design, fabricate, and test low cost linear power supplies with current stability about 100 ppm and current ripples less than 100 ppm in a broad band. A set of unipolar power supplies (0-12 A) have been designed, fabricated and successfully tested. Since August, 2004 they have been used in storage ring operation with excellent performance. The prototype of bipolar power supplies (±15 A) has been designed and tested as well. The main design principles and the performance results of both unipolar and bipolar supplies have been presented in this paper.