SLAC, Menlo Park, California, USA
Duke ECE, Durham, North Carolina, USA
Plasma wakefield studies are normally conducted as single-shot experiments. Here, single-shot means that the plasma returns to its original state before the next bunch passes through the plasma. The time scale for the plasma to return to equilibrium is 10-100 ns, which is comparable to the bunch separation in proposed linear colliders. The SLAC linac typically delivers beam at a rate of 10 Hz to FACET but can be operated in a manner that delivers two electron bunches per RF pulse. We explore operation modes with beam separations as small 5.6 ns so that high repetition rate plasma wakefield acceleration can be studied at FACET.
TUYB1
SLAC, Menlo Park, California, USA
WEOAA1
LBNL, Berkeley, California, USA
SLAC, Menlo Park, California, USA
JLAB, Newport News, Virginia, USA
Fermilab, Batavia, USA
We present an overview of design studies and R&D toward NGLS a Next Generation Light Source initiative at LBNL. The design concept is based on a multi-beamline soft x-ray FEL array powered by a CW superconducting linear accelerator, and operating with a high bunch repetition rate of approximately 1 MHz. The linac design uses TESLA and ILC technology, supplied by an injector based on a CW normal-conducting VHF photocathode electron gun. Electron bunches from the linac are distributed by RF deflecting cavities to the array of independently configurable FEL beamlines with nominal bunch rates of ~100 kHz in each FEL, with uniform pulse spacing, and some FELs capable of operating at the full linac bunch rate. Individual FELs may be configured for different modes of operation, including self-seeded and external-laser-seeded, and each may produce high peak and average brightness x-rays with a flexible pulse format.
SLAC, Menlo Park, California, USA
A beam “dechirper” based on a corrugated, metallic vacuum chamber has been proposed recently to cancel residual energy chirp in a beam before it enters the undulator in a linac-based X-ray FEL*. Rather than the round geometry that was originally proposed, we consider a pipe composed of two parallel plates with corrugations. The advantage is that the strength of the wake effect can be tuned by adjusting the separation of the plates. The separation of the plates is a few millimeters, and the corrugations are fractions of a millimeter in size. The dechirpers need to be meters long in order to provide sufficient longitudinal wakefield to cancel the beam chirp. Considerable computation resources are required to determine accurately the wakefield for such a long structure with small corrugation gaps. Combining the moving window technique and parallel computing using multiple processors, the parallel finite-element electromagnetic suite ACE3P allows efficient determination of the wakefield through convergence studies. In this paper, we will calculate the longitudinal, dipole and quadrupole wakefields for the dechirper and compare the results with those of analytical approaches.
* K.L.F. Bane, G. Stupakov, Nucl. Instrum. Meth. A690 (2012) 106-110.
SLAC, Menlo Park, California, USA
In LCLS-II, a fast kicker and Lambertson-type septum magnet will be installed just upstream of the undulator region, in order to allow electron bunches to be directed to either of two undulators. In the envisioned scenario both undulators receive bunches with the same current profile and the same energy which will be between 7–13.5 GeV. The kicker is used to separate the two trajectories vertically in the septum by 7 mm and thus the high current beams travel close to septum metallic walls and the short-range resistive wall wakefields can become a limitation. This paper will analyze the impact of the longitudinal and transverse wakefields on the LCLS-II performance.