The Complete HIGS Facility
What are the upgrades ?
The ongoing "upgrades" at HIGS are of three major sections of the facility. The most significant is the installation of the DOE-sponsered Booster-Injector. In addition, a new RF cavity , and a new optical klystron (OK-5) is also being installed. Following sections outline justification and a brief introduction of these upgrades. Please visit the Gamma-Ray beam section for understanding of the facility and beam for a better understanding of the following sections. For any further information, please contact Prof. Calvin Howell (HIGS Upgrade Manager, howell@tunl.duke.edu), or Prof. Ying Wu (wu@fel.duke.edu).
Booster Injector
Gamma-Rays at HIGS are produce via inter-cavity Compton backscattering. If the recoil imparted to the electrons in this process leaves them beyond the energy acceptance of the Duke Storage Ring, DSR, ( - of the RF cavity), the electrons are lost. Presently, the electron losses start at 20 MeV gamma-ray production and become siginificant at 40 MeV gamma-ray energy. The proposed energy spectrum for gamma-ray energies tops at ~225 MeV. Therefore, it is essential to replace the lost electrons at these high energies in order to have a continuous operation. A solution to this problem is to inject electrons at full energy of the electron storage ring, and hence the need for a Booster-Injector (B-I).
In principle, the Booster-Injection is a simple process. The B-I at HIGS will take the electrons from the LINAC at 270 MeV, ramp the energy to meet the injection energy of the DSR, and the electrons will be extracted at desired intervals to fill any RF buckets in the DSR.
The Booster-Injector is being constructed at the BINP (Russia) and will be delivered to Duke. Construction of the extension to the building which will house the Booster has already begun.
RF Cavity
Electron currents upto 100 mA can be stored in the DSR in 64 RF buckets. However, if high current is required in smaller number of bunches (2,4,8,16), the original RF cavity suffers from excitation of higher-order-modes (HOM). The HOMs couple the transverse and longitutinal motions of the beam, and hence causes instabilities and eventual loss of the current. In order to achieve conditions for high photon flux (large current), a new RF cavity was conceived and is being currently installed. This RF cavity is designed with a special attention to damping the HOM. This RF cavity was also manufactured at BINP, Russia.
OK-5
A significant portion of the HIGS physics program calls for the availability of both linear and circular polarization of the gamma-ray beam. Currently, the OK-4 system only provided with linear polarization. The new optical klystron (OK-5) has arrived at HIGS and is being introduced into the DSR in a phase-wise program. The OK-5 will be able to deliver gamma-rays in different polarization vectors, linear (horizontal, vertical), and circular (forward, backward), with respect to the direction of the photons.