Singleshot longitudinal phasespace measurement of electron beams work

Single-shot longitudinal phase-space measurement of electron beams (work in progress) Yine Sun, Mike Church, Philippe Piot and Chris Prokop July 14, 2011 APC seminar, Fermilab

Introduction • NML is foreseen to produce low-emittance highpeak-current electron bunches; • The beam could eventually be used to support beam physics and advanced accelerator concepts experiment; • We need to characterize the beam in all the dimensions including the longitudinal phase space (LPS); single-shot LPS diagnostics is the “dream diagnostics” for the light source community. 7/14/2011 APC seminar, Yine Sun 2

Principle of LPS measurement (1) • Single-shot LPS diagnostics → (z, δ)in mapped into (x, y)out; • Diagnostic line configuration: horizontal bend (z, δ)in screen (x, y) out Vertically-deflecting cavity (TM 110) • Deflecting cavity is operated at zero-crossing, so head and tail are deflected in opposite direction. 7/14/2011 APC seminar, Yine Sun 3

Principle of LPS measurement (2) • Horizontal position at the screen: horizontal emittance contribution initial fractional momentum horizontal dispersion • Vertical position after the deflecting cavity: initial longitudinal position vertical emittance contribution 7/14/2011 cavity strength APC seminar, Yine Sun 4

Transverse beam profile (x, y) Input longitudinal phasespace grid (z, δ) ? x z Output transverse configuration-space grid (x, y)? y δ cavity on; magnet off y x cavity on; magnet off 7/14/2011 cavity off; magnet on APC seminar, Yine Sun cavity on; magnet on 5

Limitation of the measurement method • Dilution to the final (x, y) density profile from finite initial transverse beam size (x 0, y 0) ; • Finite length deflecting mode cavity itself introduces unwanted additional energy spread as well as a chirp in (z, δ): 7/14/2011 APC seminar, Yine Sun 6

Improved deflecting cavity (A. Zholents, ANL/APS/LS-327) • By adding an half-cell accelerating-cavity on each side of the deflecting cavity, the induced chirp (quadratic with κ) can be compensated. require a small vertical spot throughout TDC 7/14/2011 APC seminar, Yine Sun 7

Possible NML LPS line layout (1) NML high energy beamline (M. Church) (0, 113. 5) (0. 355 116. 03) 8 (0. 5, 117. 06) 1. 524 3. 6 (1. 524, 129. 36) quad 7/14/2011 kicker cavity APC seminar, Yine Sun dipole dump 8

Possible NML LPS line layout (2) No kicker, single bunch operation required for longitudinal phase space measurement (0, 117) (0, 118. 5) 8 1. 524 (1. 524, 129. 36) quad 7/14/2011 cavity APC seminar, Yine Sun dipole dump 9

Simulations using the layout (2) • Explore how the initial LPS maps onto the (x, y) space using ELEGANT simulation • Initial beam parameter – γ=1500, variable εn, initial CS: (0, 40 m) in transverse planes • Initial LPS marcoparticles arranged on a grid (to explore resolution + distortions) – Δγ/γ= 1/1500 – Δt=1 ps 7/14/2011 APC seminar, Yine Sun 10

Simulations using the layout (2) • Three quads upstream cavity → focus beam on viewer in both directions • Dispersion at screen ~ 1 m 7/14/2011 APC seminar, Yine Sun 11

Beam distribution on screen • εn =0. 15 μm, no aperture cavity OFF cavity ON 7/14/2011 APC seminar, Yine Sun 12

Beam distribution on screen • εn =1. 5 μm, no aperture cavity OFF cavity ON 7/14/2011 APC seminar, Yine Sun 13

Beam distribution on screen • εn =1. 5 μm, 0. 1 mm vertical slits cavity OFF cavity ON 7/14/2011 APC seminar, Yine Sun 14

beam distribution on viewer • εn =15 μm, no vertical slits cavity OFF cavity ON 7/14/2011 APC seminar, Yine Sun 15

beam distribution on viewer • εn =15 μm, 0. 1 mm vertical slits cavity OFF cavity ON 7/14/2011 APC seminar, Yine Sun 16

Summary • Preliminary simulation shows that the LPS diagnostics at high energy ( ~750 Me. V) with deflecting voltage of 7. 5 MV from a 3. 9 GHz cavity is promising; • LPS can be well resolved for normalized emittance below 1. 5 um; • The use of a slit upstream of the TDC improves measurement for larger emittances; • Further studies are needed (effect of slit, resolution limit from timing jitter of the cavity, screen resolution etc. , and the other possible LPS line layout) … 7/14/2011 APC seminar, Yine Sun 17