Accelerator Small Projects
Radiabeam/SLAC Dechirper – Transition to Operations
Team:
Iverson, Rick; Maxwell, Tim; Krejcik, Patrick; Lutman, Alberto; Guetg, Marc; Zemella,
Johann; Zhang, Zhen; Bane, Karl; Stupakov, Gennady; Novokhatski, Alexander;
Marinelli, Agostino; Gassner, Georg; Reese, Edward; Babbitt, Alisha; Oven, Ziga;
Cedillos, Antonio; Carrasco, Manny A.; Stanek, Michael W.; Huang, Zhirong;
Scope:
The Radiabeam/SLAC Dechirper can be used to either increase or decrease the energy chirp along the
electron bunch to provide flexible control of the time-correlated LCLS FEL bandwidth. It can be used for
all electron energies and bunch lengths. New capabilities of using the Dechirper to measure the
electron bunch length with attosecond resolution and to deliver 2-pulse-2-color beams are under
development but will not be addressed in this initial phase of transfer to operations.
TTO Project goal:
The goal is to streamline and automate the method for aligning the Dechirper and controlling FEL
bandwidth such that any accelerator operator can independently follow the procedure and set the
Dechirper in a few minutes.
Description:
The Dechirper consists of two modules containing opposing rails that are two meters in length. The rails
are flat plates with small corrugations. Both modules are installed just after dogleg-2 on the linac to
undulator beam line. The jaws of the upstream module move in the vertical plane and the jaws of the
downstream module move in the horizontal plane. The gap of the Dechirper rails can be controlled by
both the Dechirper Matlab GUI or directly by EPICs control panels. The XTCAV screen is used to assess
and tune the energy spread of the electron bunches. The SXR spectrometer or the FEE spectrometer
can be used to assess and tune the FEL bandwidth for soft or hard x-rays, respectively.
Schedule:
The ability to use the Dechirper to control the LCLS FEL bandwidth should be transferred to operations
by April 2016 or earlier.
Method:
The following tasks have been identified in working towards this TTO project goal
1. Machine Protection System –The physics team in conjunction with the controls and engineering
groups will verify that sufficient engineering safeguards are in place to prevent the following:
a. The Dechirper being hit by sustained, direct beam
b. Collision of opposing Dechirper rails
2.
3.
4.
5.
6.
7.
c. Irradiation of the downstream LCLS undulators
i. This is generally covered generally by the existing LCLS MPS
ii. Dechirper control software can and should provide additional precautions to
protect the undulator hall (TDUND) during potentially invasive procedures
Develop a new slow feedback to control the beam position and pointing both entering and
exiting the Dechirper (R. Iverson, L. Piccoli).
Procedure documentation – The team will review and enhance written procedures for all of the
following and maintain such documentation in the MCC Wiki:
a. Introductory explanation of the Dechirper and its use in chirp control
b. Dechirper operation procedures and documentation for each of the following:
i. EPICS motion control panels (T. Maxwell, Z. Oven, A. Babbitt)
ii. Feedback system control (R. Iverson, L. Piccoli, A. Lutman, P. Krejcik)
iii. Alignment (M. Guetg, T. Maxwell)
iv. Chirp and bandwidth control (T. Maxwell, M. Guetg)
v. FAQ & any Known Issues that arise (All)
c. The physics team and/or controls group will maintain documentation on Machine
Protection System control and status when the Dechirper is in use.
GUI development for Dechirper setup
a. Enhance TREX GUI to provide quantitative electron chirp and bandwidth analysis.
b. Develop a global GUI that scripts the setup procedure and combines the views from
other GUIs such as the TREX, feedbacks etc. (M. Guetg, T. Maxwell)
c. Work with ACR Operations to tailor the Dechirper GUI to streamline operation (physics
team).
Training
a. The physics team will train LCLS operators by referring to the above documentation and
GUIs.
b. Throughout the training phase, the physics team will revise the written procedures
based on operator feedback.
Develop a new fast feedback to control the beam position after the Dechirper (R. Iverson, A,
Lutman, P. Krejcik, L. Piccoli).
The physics team will take into consideration potential future applications of the Dechirper
(passive streaker, slice orbit spoiler) and ensure future documentation links to the setup and
troubleshooting documentation created by this TTO.