Recent Developments of Beam Diagnostics

The paper introduces some of the recent developments in beam diagnostics,which include the beam position measurement techniques with sub-micrometer resolution,the beam size measurement techniques with sub-micrometer resolution,and the bunch length measurement techniques with sub-picosecond resolution.The cavity beam position monitor and the digital BPM signal processing technique are introduced for the beam position measurement techniques. The laser wire beam profile monitor,and the optical transition radiation/optical diffraction radiation beam size monitor are introduced for the beam size measurement techniques.The spectral techniques of coherent radiation,the transverse deflecting cavity,the rf zero-phasing technique,and the electro-optic techniques are introduced for the bunch length measurement techniques.

Spot-scanning beam delivery with laterally- and longitudinally-mixed spot size pencil beams in heavy ion radiotherapy

The three-dimensional （3D） spot-scanning method is one of the most commonly used irradiation methods in charged particle beam radiotherapy. Generally, spot-scanning beam delivery utilizes the same size pencil beam to irradiate the tumor targets. Here we propose a spot-scanning beam delivery method with laterally- and longitudinally- mixed size pencil beams for heavy ion radiotherapy. This uses pencil beams with a bigger spot size in the lateral direction and wider mini spread-out Bragg peak （mini-SOBP） to irradiate the inner part of a target volume, and pencil beams with a smaller spot size in the lateral direction and narrower mini-SOBP to irradiate the peripheral part of the target volume. Instead of being controlled by the accelerator, the lateral size of the pencil beam was adjusted by inserting Ta scatterers in the beam delivery line. The longitudinal size Of the pencil beam （i.e. the width of the mini-SOBP） was adjusted by tilting mini ridge filters along the beam direction. The new spot-scanning beam delivery using carbon ions was investigated theoretically and compared with traditional spot-scanning beam delivery. Our results show that the new spot-scanning beam delivery has smaller lateral penumbra, steeper distal dose fall-off and the dose homogeneity （1-standard deviati^n/mean） in the target volume is better than 95%.

Simulation of beam size multiknobs correction at the Accelerator Test Facility 2 at KEK

The ATF2 project is the final focus system prototype for the ILC and CLIC linear collider projects, with a purpose of reaching a 37 nm vertical beam size at the interaction point （IP）. During the initial commissioning, we started with larger-than-nominal β-functions at the IP in order to reduce the effects from higher-order optical aberrations and thereby simplifying the optical corrections needed. We report on the simulation studies at two different IP locations developed based on waist scan, dispersion, coupling and β function multiknobs correction in the large β optics of ATF2, in the presence of two kinds of magnet inaccuracies （quadrupole gradient and roll errors） to generate all possible linear optic distortions at the IP. A vertical beam size which is very close to the nominal beam size is obtained based on the simulation study.

The beam-based calibration of an X-ray pinhole camera at SSRF

A pinhole camera for imaging X-ray synchrotron radiation from a dipole magnet is now in operation at the Shanghai Synchrotron Radiation Facility （SSRF） storage ring.The electron beam size is derived by unfolding the radiation image and the point spread function （PSF） with deconvolution techniques.The performance of the pinhole is determined by the accuracy of the PSF measurement.This article will focus on a beam-based calibration scheme to measure the PSF system by varying the beam images with different quadrupole settings and fitting them with the corresponding theoretical beam sizes.Applying this method at SSRF,the PSF value of the pinhole is revised from 37 to 44μm.The deviation in beam size between the theoretical value and the measured value isminimized to 4% after calibration.This optimization allows us to observe the horizontal disturbance due to injection down to as small as 0.5μm.

Mitigating the effects of higher order multipole fields in the magnets of the Accelerator Test Facility 2 at KEK

The ATF2 project is the final focus system prototype for the ILC and CLIC linear collider projects, with the purpose of reaching a 37nm vertical beam size at the interaction point. In the nanometer beam size regime, higher order multipoles in magnets become a crucial point for consideration. The strength and rotation angle of the ATF2 QEA magnets were reconstructed from the IHEP measurements and compared with the KEK ones to be identical. Based on the study of the skew multipoles sensitivity, we report on the analysis of the possible mitigation of the measured multipoles. A suggestion is given which will benefit the ATF2 present commissioning to reach the goal beam size, and also the reduced β optics in future.