Feasibility of diffraction radiation for noninvasive beam diagnostics as characterized in a storage ring

In recent years, there has been an increasing demand for noninvasive beam size monitoring on particle accelerators. Ideally, these monitors should be cost effective and require little or no maintenance. These monitors should also be suitable for both linear and circular machines. Here, the experimental setup is described in detail, and the results from a diffraction radiation beam size monitor are presented. This monitor has been tested on the Cornell Electron Storage Ring using a 1 mA ($1.6\times {10}^{10}$ particles per bunch) single bunch electron beam at 2.1 GeV energy. Images of the target surface and the angular distribution of the emitted diffraction radiation were acquired at wavelengths of 400 and 600 nm. These measurements are compared to two analytical models.

Figure 1

Schematic models of the (a) ODR target geometry and (b) ODRI mask and target geometry.

Figure 2

A summary of the steps performed in the PVPC technique for beam size measurement: (a) three-dimensional angular distribution of DR, (b) the vertical projection obtained by integrating over the horizontal angle, and (c) the simulated visibility curves for different wavelengths. At a specified wavelength, the visibility measurement obtained from the data is compared to the corresponding simulated visibility curve to obtain the vertical beam size measurement. The parameters are as follows: $a=0.5\mathrm{mm}$, $\overline{a_x}=0\mathrm{mm}$, $\gamma =4110$, ${\theta }_0=70°$, in (a) and (b) $\lambda =600\mathrm{nm}$ and ${\sigma }_y=0\mu \mathrm{m}$.

Figure 3

A schematic of the layout of CesrTA [23].

Figure 4

A technical drawing of the vacuum chamber as viewed from the upstream beam port (top) and from above (bottom) showing the replacement chamber (left) and target mechanism (right) by N. Chritin.

Figure 5

A technical drawing of the optical system. From left to right is the folding mirror in the motorized holder, the lenses on flip stages for target imaging and angular distribution observation, the fixed bandpass filter, the Glan-laser polarizer in a rotation stage, and the camera mounted on a translation stage for the two observation positions.

Figure 6

Silicon etched target (top) and molecular adhesion target (bottom).

Figure 7

Measured (a) flatness and (b) aperture size of a chemically etched and sandblasted target from batch 2.

Figure 8

Images of the target surface taken during the insertion of the target around the stored electron beam. Because of the orientation of the optical system, the images are rotated by 90°; i.e. the horizontal plane along which the target is inserted is parallel with the target tines, and the width of the target aperture is in the vertical direction. The local disks of DR are clearly visible at the slit edges. The fairly uniform illumination due to the SR background passing through the mask aperture is also seen.

Figure 9

Target holder with mask and target mounted (by N. Chritin).

Figure 10

Comparison of the relative photon yield from the polished and sandblasted regions of the target surface.

Figure 11

Asymmetric light emission due to a $-52\mu \mathrm{m}$ beam offset with respect to the center of the target aperture: (a) the intensity distribution across the target surface and (b) the corresponding line profile with a fitted exponential curve, characteristic of DR emission, of the form $f(y)=A\exp (By)+C$, where $A=8.92$, $B=0.008$, and $C=0.026$. The target aperture is $500\mu \mathrm{m}$.

Figure 12

Relation between the asymmetry of the DR intensity from the target tines and the beam position controlled by a vertical bump and measured by a nearby BPM.

Figure 13

An example of the DR angular distribution: $\lambda =600\mathrm{nm}$, 0.5 mm target, and 2 mm mask.

Figure 14

A comparison of projected vertical polarization components for different beam sizes at 600 nm.

Figure 15

Simulated (blue line) and expected (green dashed line) visibility curves for a 0.5 mm target and 600 nm wavelength.

Figure 16

Resultant visibility curve (dashed line) at 600 nm wavelength and 0.5 mm target aperture from a least squares fit of the average visibility at two beam sizes (green crosses).

Figure 17

DR angular distribution at 400 nm wavelength and 0.5 mm target aperture.

Figure 18

Comparison of the 400 nm line profile from Fig. 17 and expected ODR distribution.

Figure 19

Contour plots of the angular distributions at 600 nm for (a) ODR and (b) ODRI.

Figure 20

ODRI line profile at 600 nm wavelength for ${\sigma }_y=17.6\mu \mathrm{m}$, ${\sigma }_y^{\prime }=4.08\mu \mathrm{rad}$.

Figure 21

ODRI line profile at 600 nm wavelength for ${\sigma }_y=36.6\mu \mathrm{m}$, ${\sigma }_y^{\prime }=8.46\mu \mathrm{rad}$.

Figure 22

A beam offset of $120\mu \mathrm{m}$ obtained using a least squares fit for ODRI data with the beam offset in the target as the only fit variable.