Improvement of Fresnel zone plate beam-profile monitor and application to ultralow emittance beam profile measurements

We describe the improvements of a Fresnel zone plate (FZP) beam-profile monitor, which is being developed at the KEK-ATF damping ring to measure ultralow emittance electron-beam profiles. This monitor, which is designed to have a submicrometer spatial resolution, is based on x-ray imaging optics composed of two FZPs. Various improvements were performed to the old setup. First, a new crystal monochromator was introduced to suppress the beam image drift. Second, the two FZP folders were improved in order to realize a precise beam-based alignment during x-ray imaging. Third, a fast mechanical shutter was installed to achieve a shorter time resolution, and an x-ray mask system was also installed to obstruct direct synchrotron radiation through the FZPs. These improvements could make beam-profile measurements more precise and reliable. The beam profiles with less than $50\mu \mathrm{m}$ horizontal beam size and less than $6\mu \mathrm{m}$ vertical beam size could be measured within a 1 ms time duration. Furthermore, measurements of the damping time and the coupling dependence of the ATF damping ring were successfully carried out with this upgraded FZP monitor.

Figure 1

X-ray imaging optics with two FZPs (CZP and MZP).

Figure 2

Setup of the FZP monitor.

Figure 3

Picture of the new Si monochromator.

Figure 4

Measurements of the long-term drift of the Si monochromator. The horizontal axis shows the elapsed time (minutes) and the vertical axis shows the measured vertical center of the beam image. The open triangles (solid squares) show the measured vertical center of the beam image before (after) the Si crystal monochromator was upgraded.

Figure 5

(left) Image of the raw x-ray SR detected on the x-ray CCD. (right) Image of the CZP on the x-ray CCD after inserting the CZP.

Figure 6

Block diagram of the FZP monitor with a new fast mechanical shutter.

Figure 7

Setup of a performance test of the fast mechanical shutter on a test bench.

Figure 8

Measurement results of the shutter opening time in the NORMAL mode. The horizontal axis shows the input TTL pulse width into the shutter controller. The vertical axis shows the full-width half maximum of the measured pulse width detected by the photodiode.

Figure 9

CCD images of the beam profile and background (A) before and (B) after insertion of the x-ray mask with a pinhole diameter of $300\mu \mathrm{m}$.

Figure 10

Typical beam image obtained by the FZP monitor after the background was subtracted. Beam current was a 4.4 mA in a single-bunch mode. The shutter opening time was fixed to 1 ms. The horizontal and vertical bars of $50\mu \mathrm{m}$ show the scales at the source point.

Figure 11

Sample of (a) horizontal and (b) vertical beam profiles with their fitted Gaussian curves. The shutter opening time was fixed to 1 ms. Data are from $2005/6/1$.

Figure 12

Solid squares showing the measurement of the (a) horizontal and (b) vertical beam sizes as a function of the shutter opening time. The beam current was fixed at 4 mA in a single-bunch mode. Data are from $2005/4/8$.

Figure 13

Dependences of the measured (a) horizontal beam image center and (b) vertical beam image center corresponding to the shutter trigger time from beam injection when the shutter opening time was fixed to 1 ms. Data are from $2005/4/8$.

Figure 14

Cumulative vertical displacements of (a) CZP and (b) MZP.

Figure 15

Solid squares (open circles) showing the measurement of the vertical beam sizes as a function of the shutter opening time when the power supply of the Si crystal monochromator was turned off (on).

Figure 16

Measured beam size taken on $2005/4/8$ by the FZP monitor vs beam current in the single-bunch mode. The lines are from a calculation with intrabeam scattering, assuming coupling ratios of $0.4\%$, $0.5\%$, and $0.6\%$.

Figure 17

Measured beam size taken on $2005/6/1$ by the FZP monitor vs beam current in the single-bunch mode. The lines are from a calculation with intrabeam scattering, assuming coupling ratios of $0.4\%$, $0.5\%$, and $0.6\%$.

Figure 18

Measured energy spread at the extraction line vs beam current in the single-bunch mode. The lines are from a calculation with intrabeam scattering, assuming coupling ratios of $0.4\%$, $0.5\%$, and $0.6\%$.

Figure 19

Measured vertical damping time with/without the damping wigglers. The horizontal axis shows the elapsed time from beam injection into the damping ring. The vertical axis shows the measured beam size by the FZP monitor. The open circles (black boxes) show the vertical beam sizes without (with) damping wigglers.

Figure 20

Measured beam profiles when the skew correction was carefully carried out (A) and all of the skew magnets were turned off (B). The data were taken on $2005/6/1$ with a 4.4 mA current.

Figure 21

Measured horizontal beam sizes (a) and vertical beam sizes (b) and tilt angles (c) vs stored current in the ATF damping ring. The solid boxes (open circles) show the data for the skew on (skew off) condition. The solid (dotted) lines of graph (a) and graph (b) are from calculations, assuming coupling ratios of $0.5\%$ ($3.0\%$).