Beam Size Measurements

Beam Size Measurements

J. Turner, W. Colocho, Y. Feng, J. Krzywinski, H. Loos,

D. Ratner, J. Welch

2LCLS Physics/Beam Size Measurements

Red Slate, 3/13/13

Table of measurements

• 380eV 1/30/13: x-ray beam size with slits and profile monitors + gain length measurement of saturation point.

• 380eV 2/27/13: Electron beam size and match on Beam Finder Wires plus same as 1/30/13.

• 1200eV 2/18/13: Beam size vs. undulator length by orbit kick.

• 1200eV 3/5/13: e- size and match, x-ray size, gain length, x-ray size vs. blocks of undulators.


Red Slate, 3/13/13

Measurements 1/30/13

• 380eV 1/30/13: • Fundamental below k-edge for N2, so

harmonics and fundamental both get cut roughly equally in the gas attenuator.– slit knife edge (FEE Slits 74.7m past end of

undulator, – x-ray profile monitors:

• YAGXRAY (45m past end of undulator) – Beam size and Gain Length measure of saturation point

• NFOV (Direct Imager 87m past end of undulator)


Red Slate, 3/13/13

Initial 380eV Measurements 1/30/13

• Collimator Scan FEE Slit scans done with the other plane cut to a 1mm ribbon

• Rms x-ray size is C/sqrt(2)= ~700um


Red Slate, 3/13/13

380eV Beam Size 1/30/13

• 380eV, CSR 0.5um C filter in. YAGXRAY, , there was no background subtraction of spontaneous, but zoom makes that baseline.


Red Slate, 3/13/13


• 380eV, CSR 0.5um C filter in. NFOV, there was no background subtraction of spontaneous. N2 attenuator set at 2.7torr (0.15% transmission)


Red Slate, 3/13/13


• 0.5um carbon filter. YAGXRAY Using kick method. Can't get a good gain length below saturation, but looks like saturation is reached around und #10


Red Slate, 3/13/13


• 0.5um carbon filter. YAGXRAY Using kick method. Power increase is linear beyond undulator 11.


Red Slate, 3/13/13


• 380eV 2/27/13:– Gain length measure of saturation point– Electron beam size and match on BFWs (beam

finder wires)– slit knife edge (FEE Slits 74.7m past end of

undulator, – x-ray profile monitors:

• YAGXRAY (45m past end of undulator) – Beam size and Gain Length measure of saturation point

• NFOV (Direct Imager 87m past end of undulator)


Red Slate, 3/13/13


• 0.5um C filter inserted (looking at mix of fundamental and third harmonic)Saturation around undulator 10.


Red Slate, 3/13/13

2.7GeV (380eV) Beam Size 2/27/13

• 2.7GeV e- size (goes with 380eV x-ray data)


Red Slate, 3/13/13


• 2.7GeV e- size in undulator (goes with 380eV x-ray data)


Red Slate, 3/13/13


• 2.7GeV e- horizontal emittance and match in undulator (goes with 380eV)


Red Slate, 3/13/13


• 2.7GeV e- vertical emittance and match in undulator (goes with 380eV)


Red Slate, 3/13/13


• 380eV, Direct Imager intensity vs. Gas Attenuator transmission ratio with 1mj x-rays. Data at 0.2 transmission ratio. (~1.9torr)


Red Slate, 3/13/13


• 380eV, CSR 0.5um C filter in. NFOV. Poor Y fit, but X ok.


Red Slate, 3/13/13


• 380eV, CSR 0.5um C filter in. NFOV, move beam across screen. Same gas pressure as previous.


Red Slate, 3/13/13


• 1200eV 2/18/13: NFOV beam size vs. shortened undulator using corrector kick.


Red Slate, 3/13/13


• 1200eV, 0.05% transmission at 4torr N2. NFOV. CSR filter was OUT during this scan. Mistake.


Red Slate, 3/13/13


• 1200eV 3/05/13: full gain length, electron beam size and (mis) match, beam size before and after mirrors. Cut off is 2200eV for SOMS, this eliminates all harmonics with the fundamental at 1200eV. X-ray beam size vs. blocks of undulators.


Red Slate, 3/13/13


• 1200eV,


Red Slate, 3/13/13

1200eV Electron Beam Size 3/5/13

• 1200eV, ~5.2GeV


Red Slate, 3/13/13


• 1200eV, ~5.2GeV


Red Slate, 3/13/13


• 1200eV, ~5.2GeV

• Horrible mismatch


Red Slate, 3/13/13


• 1200eV, ~5.2GeV


Red Slate, 3/13/13


• 1200eV, CSR 0.5um C filter in. P3S1, 13% transmission N2 1.9torr


Red Slate, 3/13/13


• 1200eV, CSR 0.5um C filter in. NFOV, 13% transmission N2 1.9torr. (X axis error of exactly factor of 2.)

674.2


Red Slate, 3/13/13


• We took very rough beam size image data with u1:13 in followed by a strong xcor kick at u13. We also took data with u21:u33 in, all other segments out, and orbit corrected upstream of u21.Preliminary analysis of two such shots

• u1:13 yrms = 548 um, 12:48:52• u21:33 yrms = 738 um, 13:07:37• Note the strange relative size with the downstream section giving a

larger beam size than the upstream section. Evidently this technique did not work. The two sections were supposed to give the same divergence angle and only differ in the effective source location. We used a strict linear taper and had about 0.5 -0.7 mJ on the gas detector. Henrik worked on matching the beta function going into the undulator using correctors and BFW before we started the beam size measurements. There was a considerable mis-match that he did not have time to take out.


Red Slate, 3/13/13

Summary

• About measurements: Important factors in obtaining a reasonable measurement are: elimination of CSR from first dump bend; background subtraction of the spontaneous x-rays; coping with cutoff in gas apertures; and capability of measuring and preventing saturation in either YAG profile monitors or cameras.

• 380eV data, though measurements were problematic due to cutoff in gas apertures, was was with a relatively matched electron beam and measurements are consistent with simulation. Simulation and measurement are just under 1mm rms which represents an upper bound on the measurements taken.

• x-ray beam size data with very large electron betatron mismatch (>2) differs by a factor of 2 from a matched simulation. Data taken on a day where the match was not measured showed a smaller beam.

• Future 1200eV study will be planned with a matched electron beam to verify the size.

Documents

Beam Size Measurements