S. Hartman

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.

A physics based control system for the Duke storage ring

At the Duke FEL Lab, we have developed a new storage ring control system in terms of the physics quantities of the accelerator. Instead of controlling power supply currents in Amperes, this system controls the effective focusing of magnets. By directly controlling the physics quantities, this control system allows tighter integration of the physics model based high level controls with the EPICS based low-level controls. EPICS events have been extensively used to provide time synchronization during the energy and lattice ramping. This new control system also facilitates the implementation of multiple functions on shared control channels. As a result, the physics based control system simplifies many complex control tasks, improves the beam stability during ramping, and facilitates machine studies. With better understanding of the accelerator, it is possible to fine tune this control system to present users with a virtual accelerator whose operation is independent of the ring energy.

A physics based approach for ramping magnet control in a compact booster

At Duke University, a booster synchrotron was recently commissioned as part of the high intensity gamma-ray source (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 the use of physics modeling. In addition, it simplifies operation, allowing the booster to ramp to any energy from the 0.24 GeV of the injector linac to the 1.2 GeV maximum of the Duke storage ring. The high level of flexibility of this system is 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 (FEL), and may be useful for other compact booster synchrotrons.

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.

Challenges for energy ramping in a compact booster synchrotron

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 provides top-off injection into the storage ring in the energy range of 0.24-1.2 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 injection, energy ramping, and extraction.

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.

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.

A Control System for the Duke Booster Synchrotron

The Duke Free Electron Laser Laboratory is developing a booster synchrotron to provide full energy injection into the Duke electron storage ring. In this paper, we describe the development of the control system for the booster. Requirements include the competing needs of simple and reliable turn-key operation for the machine as a booster; and the sophistication and flexibility of operation of the machine as a storage ring for commissioning, machine studies and as a light source. To simplify operations and machine studies, the high level controls will present the system in terms of the physics quantities of the accelerator, allowing a tight integration between the physics model and the low level hardware control, as we have previously implemented for the Duke storage ring.

A New Timing System for the Duke Booster and Storage Ring

A dedicated booster synchrotron is being constructed at the Duke FEL Laboratory to provide fullenergy injection into the main electron storage ring. A new timing system has been developed to coordinate the injection of electron bunches from the linac to the booster, the ramping of energy in the booster, and extraction of bunches into the main ring. The timing system will allow the extraction of any bunch in the booster into any selected bucket in the main ring to provide top-off injection for any of the various operational bunch patterns of the main ring. A new master oscillator has also been developed for the RF system of the booster. The oscillator may be tuned independently or phase-locked to the master oscillator of the main ring. The issues of the soft phase locking process of the new master oscillator are discussed. The timing system and new oscillator have been fabricated and tested and are ready for operation.