Short-Pulse X-ray at the Advanced Photon Source Overview

Transcription

1 Short-Pulse X-ray at the Advanced Photon Source Overview Vadim Sajaev and Louis Emery Accelerator Operations and Physics Group Accelerator Systems Division Mini-workshop on Methods of Data Analysis in Beam Measurements March 13, 2013

2 Outline Advanced Photon Source operation overview Deflecting cavity method description Short-Pulse X-rays (SPX) project description 2

3 Accelerator Operations Overview 7 GeV light source operating at 100 ma 1104 m circumference 40 sectors, 35 ID straights Effective emittance of 3.1 nm Vertical emittance of 40 pm Various undulators produce photons of kev Two fill modes support timing studies 100 ma, 24 bunch mode (150 ns separation) Bunch length 33 ps rms 65% of time (~9 h lifetime) 100 ma, hybrid mode Bunch length 50 ps rms 15% of time (~6 h lifetime) Both require top-up 100 ma, 324 bunch mode does not require top-up (~60h lifetime) Hybrid mode pattern 3

4 Short pulses in storage rings Keeping short (<10ps rms) electron bunches in storage rings is extremely difficult due to quantum nature of the synchrotron radiation Laser slicing A laser is used to change energy of a very short slice of the electron bunch, radiation pulse can then be separated 100-fs-long pulses can be achieved A very powerful laser is required that limits repetition rate Low-alpha Lattice is adjusted to produce short pulses, a few ps rms Suffers from large emittance and very low average current Deflecting cavities An electron beam is streaked in vertical direction such that the photon beam can then be sliced Compatible with high repetition rate 2-ps FWHM pulse can be achieved 4

5 Deflecting cavities concept 1 Deflecting cavity at harmonic h of ring rf frequency. Radiation from tail electrons vertical position Ideally, second cavity exactly cancels effect of first if phase advance is n*180 degrees. time Radiation from head electrons 1 A. Zholents et al., NIM A 425, 385 (1999). 5

6 X-ray pulse duration From betatron motion equations, for a slice of the beam we can get: Cavity Undulator SR optics Distance L y ' 1 s = V E sin s c y ' 1 s V E c s y 2 s =y ' 1 s RF ID sin y ' 2 s= y ' 1 s RF ID cos ID sin y 3 s= y 2 s y ' 2 s L y ' 3 s =y ' 2 s where V and w are the deflecting voltage and frequency, E is beam energy, s is slice coordinate inside the bunch, b and y are beta functions and phase 6

7 X-ray pulse duration The pulse duration after the slits is: py s = p y tan p y The slice photon size at the location of the slits is: s 2 p y = 2 e y L 2 2 e y ' L 2 2 p y ' Photon beam Slits The photon beam tilt is: = V E c RF ID sin L RF ID cos ID sin In case of =nand large L 1 : s = E c ID V 2 2 ey ' p y ' RF 1 M. Borland, PRSTAB 8, (2005). 7

8 Main SPX parameters Two cryomodules will be installed, each cryomodule containing 4 deflecting cavities One cavity provides 0.5 MV deflecting voltage for a total of 2 MV per cryomodule Operating frequency is 2.8 GHz - 8th harmonic of the main RF frequency The cryomodules will be installed in downstream end of ID straight sections in sectors 5 and 7 Straight section length will be increased from 5 m to ~8 m Cryomodule length is approximately 3 m leaving ~5 m for ID installation Long SS 5ID Short SS 6ID Long SS 7ID 8

9 Long Straight Section (LSS) Scheme LSS can be implemented at APS with a simple scheme Remove the Q2 magnets on either side of SS Remove the adjacent correctors Remove the adjacent BPMs Slide other components away from the ID Q2 Q2 Increases space available for ID from 4.8 to ~7.7m Most cost-effective option for LSS Can use existing spare magnets for installation 9

10 Deflecting Cavity models cavity Rf input HOM Power through HOM Port: 239 W Ports for LOM/HOMs (shown flipped vertically) Beam pipe HOM power through FPC port: 145 W LOM Power through LOM Port: 1.38 kw 10