Engineering topics

Akre, Ron

Publications and source records attributed to Akre, Ron.

4 records

DOE OSTI2012

LLRF System Upgrade for the SLAC Linac

The Linac Coherent Light Source (LCLS) at SLAC is in full user operation and has met the stability goals for stable lasing. The 250pC bunch can be compressed to below 100fS before passing through an undulator. In a new mode of operation a 20pC bunch is compressed to about 10fS. Experimenters are regularly using this shorter X-ray pulse and getting pristine data. The 10fS bunch has timing jitter on the order of 100fS. Physicists are requesting that the RF system achieve better stability to reduce timing jitter. Drifts in the RF system require longitudinal feedbacks to work over large ranges and errors result in reduced performance of the LCLS. A new RF system is being designed to help diagnose and reduce jitter and drift in the SLAC linac.

43 PARTICLE ACCELERATORS↗

DOE OSTI2012

Identifying Longitudinal Jitter Sources in the LCLS Linac

The Linac Coherent Light Source (LCLS) at SLAC is an x-ray Free Electron Laser (FEL) with wavelengths of 0.15 nm to 1.5 nm. The electron beam stability is important for good lasing. While the transverse jitter of the beam is about 10-20% of the rms beam sizes, the jitter in the longitudinal phase space is a multiple of the energy spread and bunch length. At the lower energy of 4.3 GeV (corresponding to the longest wavelength of 1.5 nm) the relative energy jitter can be 0.125%, while the rms energy spread is with 0.025% five times smaller. An even bigger ratio exists for the arrival time jitter of 50 fs and the bunch duration of about 5 fs (rms) in the low charge (20 pC) operating mode. Although the impact to the experiments is reduced by providing pulse-by-pulse data of the measured energy and arrival time, it would be nice to understand and mitigate the root causes of this jitter. The thyratron of the high power supply of the RF klystrons is one of the main contributors. Another suspect is the multi-pacting in the RF loads. Phase measurements down to 0.01 degree (equals 10 fs) along the RF pulse were achieved, giving hints to the impact of the different sources.

43 PARTICLE ACCELERATORS↗

DOE OSTI2011

SLC Interferometer System and Phase Distribution Upgrades

Many of the components used in the Stanford Linear Collider (SLC) phasing system date back 30 years to the construction of SLAC. At the start of SLC the phase reference system was upgraded with many of the original components remaining. The R.F. drive system phase stability requirements became tighter with operation and optimization of the SLC. This paper describes analysis done on the R.F. drive system and interferometer system during the 1996 run and down time, modifications to the systems during the 1996-97 down time, and the improvements in stability from the modifications.

43 PARTICLE ACCELERATORS↗

DOE OSTI2011

Calibration System for SLC 476MHz to 2856MHz Multipliers

The two mile long Main Drive Line (MDL) distributes 476MHz at each of the 31 sectors along its length. Each of the 31 sectors has a six times multiplier which drives the 2856MHz phase reference system for that sector. This system is used to set and maintain phase of the accelerator structures over time. During previous runs significant down time resulted from sector phasing which was required after multiplier replacement. A system was designed to calibrate the phase of the 476MHz input to the phase of the 2856MHz output of the multiplier units. This enabled multipliers to be replaced without rephasing sectors.

43 PARTICLE ACCELERATORS↗