一种应用于HIRFL-CSR上的非拦截式剩余气体电离束流剖面探测器(英文)

The precise determination of the transverse beam profile is an important issue for the operation and the development of any accelerator facility. At hadron LINACs the application of traditional intersecting methods, like wire scanners and SEM‐grids, are restricted by the high current and the related risk of material melting. At synchrotrons non‐destructive methods are favored to monitor the properties of the circulating beam. Recent developments and technical challenges for the non‐destructive devices Beam Induced Fluorescence (BIF) Monitors and Ionization Profile Monitors (IPM) are described.

Nonuniformities of the extraction fields, the velocity distribution of electrons from ionization processes and strong bunch fields are just a few of the effects affecting Ionization Profile Monitor measurements and operation. Careful analysis of these phenomena require specialized simulation programs. A handful of such codes have been written independently by various researchers over the recent years, showing an important demand for this type of study. In this paper we describe the available codes and discuss various approaches to Ionization Profile Monitor simulations. We propose benchmark conditions to compare these codes among each other and we collect data from various devices to benchmark codes against the measurements. Finally we present a community effort with a goal to discuss the codes, exchange simulation results and to develop and maintain a new, common codebase.

The Ionization Profile Monitor (IPM) has been used extensively to study the horizontal and vertical beam size vs energy in the AGS. Typical results from early in the present running cycle are reported here.

Primarily to study emittance blowup during injection and ramping, an ionization profile monitor has been developed for the Tevatron. It is based on a prototype installed in the Main Injector, although with extensive modifications. In particular, the electromagnetic shielding has been improved, the signal path has been cleaned up, and provisions have been made for an internal electron source. Due to the good Tevatron vacuum, a local pressure bump is introduced to increase the primary signal, which is then amplified by a microchannel plate and detected on anode strips. For the DAQ, a custom ASIC developed for the CMS experiment is used. It is a combined charge integrator and digitizer, with a sensitivity of a few fC, and a time-resolution that allows single bunch measurement. Digitization is done in the tunnel to reduce noise. Preparations for detector installation were made during the long 2004 shutdown, with the installation of magnets, vacuum chambers, vacuum pumps and cabling. The actual detector will be installated during the fall 2005 shutdown. This paper describes the design of the detector and associated electronics, and presents various bench test results.

New technology has permitted significant performance improvements of establihsed instrumentation techniques including beam position and profile monitoring. Fundamentally new profile monitor strategies are required for the next generation of accelerators, especially linear colliders (LC). Beams in these machines may be be three orders of magnitude smaller than typical beams in present colliders. In this paper we review both the present performance levels achieved by conventional systems and present some new ideas for future colliders.

High performance TeV energy electron / positron colliders (LC) are the first machines to require online, non-invasive beam size monitors for micron and sub-micron for beam phase space optimization. Typical beam densities in the LC are well beyond the threshold density for single pulse melting and vaporization of any material, making conventional wire scanners ineffective. Using a finely focused, diffraction limited high power laser, it is possible to devise a sampling profile monitor that, in operation, resembles a wire scanner. Very high resolution laser-based profile monitors have been developed and tested, first at FFTB (SLAC) and later at SLC and ATF. The monitor has broad applicability and we review here the technology, application and status of ongoing research programs.

Simulation of wire scanner for high repetition free electron laser facilities

Mycosis fungoides is a rare T-cell lymphoma, but it accounts for about half of all cases of cutaneous 7-cell lymphoma. Radiation has long been used to treat patients with this radiosensitive disease. However, a significant proportion of patients present with generalized plaques or recurrence of lesions outside or even within the previously irradiated area, it challenged radiotherapists for decades how to irradiate skin (the superficial layer of a somewhat ”cylinder-like” human body) with not only larger field and higher dose but also tolerable toxicity. Radiation with low energy electrons generated by modern linear accelerators, depositing their energy within limited depth could spare deeper tissues. The six-dual-field technique, which provide more satisfying dose distribution for these requirements was developed at Stanford University three decades ago. Since then, the patients treated with total skin electron beam radiation would have better clinical response and minor toxicity. We adopted the six-dual-field technique to treat a 49-year-old male with generalized plaques. The source-to-surface distance was extended to be 323 cm, and an acrylic beam spoiler was installed to scatter the beam and attenuate the electron energy. The resulting electron energy was 2.62 MeV, generated by a 6 MeV Linac, the output of which was degraded to deliver 0.0648 cGy/MU (at the depth of maximum dose, d(subscript max). The collimator was fully opened to 40×40 cm^2 without a cone. The hinge angle of the dual-field was determined to be 20 degrees. The measured multiplication factor was 2.68. We prescribed a tumor dose at 5 mm depth beneath the skin surface (90% isodose profile). Overall, 1212 MU were required for each field. Beam flatness was within ±5% and ±10% in the vertical and horizontal dimensions, respectively. Thermoluminescent dosimeters (TLD) were used to evaluate dose homogeneity at 45 sites. Individualized boost or shielding was used at appropriate sites. Radiation therapy was administered for 4 consecutive days per week, with 2 days constituting a treatment cycle. On the first day of a cycle, half of the 6 dual-fields were irradiated, with the other half treated the other day A total dose of 36 Gy over 18 cycles was given with a fraction dose of 2 Gy. A 10-day midway break was given. The skin lesions responded well to this regimen, and itching was completely relieved prior to completion of the first half of the treatment course. Side effects (marked dermatitis of palms and soles and total hair loss) were acceptable. The patient refused subsequent adjuvant therapy. Despite total skin radiation can achieve good initial clinical outcome, the management of patients with mycosis fungoides is still challenging. This disease has a predisposition to relapse, and the chance is dismal to cure patients with the disease beyond limited plaque stage for the time being. In additicn to radiation therapy, a variety of modalities have been in clinical use or in investigation. We suppose combination treatment should be administered in these patients to improve long-term control.

A bunch by bunch profile monitor system using optical transition radiation (OTR) is developed for an Accelerator Test Facility (ATF) linac. The ATF consists of a 1.5 GeV linac and a damping ring is now under constructing in KEK. The linac accelerates a multi-bunch beam (20 bunches/pulse, 2 × 10 electrons/bunch, 2.8 ns spacing between bunches). The energy spread of the multi-bunch caused by the transient beam loading is a significant problem for the injection of the damping ring. The linac has energy compensation system to compensate the energy spread of the multi-bunch. In order to measure the energy and energy spread of each bunch, we developed the monitor system. The system and the measurement result are reported. I n t r o d u c t i o n The Accelerator Test Facility (ATF) consists of a 1.5 GeV linac and a damping ring(DR) is now under constructing in KEK. The DR is designed to realize a small vertical emittance, eny = ~30 nm, for future Linear Collider. The commissioning of the ATF linac had been started from November 1995 and the commissioning of the DR will be started in the end of this year. The linac accelerates multi-bunch beam. The beam has 20 bunches of 2 × 10 electrons with 2.8 ns spacing. In order to reduce the energy spread of the multi-bunch beam, due to the transient beam loading, Energy Compensation System (ECS) were installed and the preliminary experiment was carried out [1]. The measurement system of the energy and the energy spread of each bunch is needed for tuning the ECS. The optical transition radiation (OTR) monitor was already developed for the 80 MeV injector section [2]. The OTR is emitted when the charged particles go through the interface which have different dielectric constants. The polished stain less steal was employed as the emitter for the OTR monitor. A fast gate camera (Hamamatsu C2925) is used for observed the bunch by bunch profile in the multi-bunch beam when apply the gate signal to each beam timing. This monitor could measure the beam emittance, energy and energy spread of each bunch at the 80 MeV injector section. The OTR monitor at 1.5 GeV section is designed and tested for the above purpose. The spot size limit of the OTR monitor according to ~γλ /2π [3]. At 1.5 GeV section, the spot size limit is 0.24 mm for 500nm wavelength. This value is assumed that is not so affected the beam size measurement. Recently, the spot size limit was discussed and tested [4, 5]. OTR monitor system The monitor setup is shown in Fig. 1. The OTR monitor is located at the downstream of the first bending magnet and the first quadrupole magnet of the beam transport line. The position deviation at the place is calculated by ∆x=η ∆E E , where h is the dispersion function. Fig. 1. Location of the OTR monitor for ATF linac. The actuator system has two screens and can be stopped each screen position at the beam line. One is fluorescent screen, the other is the OTR emitter made by polished stain less steal which has 1 mm thickness and 1/2λ flatness. The emitted light (fluorescent light/OTR) is reflected by a mirror to avoid the x-ray and fed to a gate camera and a CCD camera by a half mirror. The fluorescent light is observed by the CCD camera and the OTR is observed by the gate camera. Both profile by these monitors can compare each other. Trigger control and video analyze system The control system of the gate camera is shown in Fig. 2. The gate camera can observed the bunch by bunch beam profile when apply the appropriate gate width and timing. The timing signal is created from the beam trigger. The signal is delayed in 2.8 ns step and met to each beam timing by the delay module. The delay module makes delay by count the reference clock from start signal. The reference clock is synchronized to the accelerating frequency. The trigger jitter of the delay module is less than 10 ps. The fine delay C1097 (Hamamatsu) adjusts the gate timing to the center of the beam timing. The LINAC 96

This paper deals with the Electromagnetic (EM) field characterization of an S-band Linear Accelerator (LA) Cavity, which is extensively used in cancer treatment. The analysis of the proposed cavity is carried out using an Eigen-mode full-wave EM solver. Mathematical formulation of cavity parameters using the Finite Element Method up to the system of equations is presented. The EM formulization uses a simple 2D square box as segmentation element and also node-based basis functions are used inside the cavity than the edge-based functions. The proposed numerical analysis of a single cavity of LA system is also applicable for a system with multiple numbers of cavities. The cavity has a resonance of 3.0474 GHz and a Q-factor of 17181.6 with finite conducting boundaries at the ends of the drift tube. The nose cone structure in the cavity is essential to have a stronger E-field at the center where the beam passes. Further, the particle acceleration is not constant along the axis of the cavity, which may have severe consequences for beam dynamics. Proper beam dynamics in LA plays a key role in reducing the mortality rate in cancer therapy applications.

FLASH radiotherapy requires real-time, non-invasive beam monitoring systems capable of operating under ultra-high dose rate (UHDR) conditions without perturbing the therapeutic beam. In this work, we characterized the extraction system of Supersonic Gas Curtain-based Ionization Profile Monitor (SGC-IPM) for its capabilities as a transverse beam profile and position monitor for FLASH protons. The monitor utilizes a tilted gas curtain intersected by the incident beam, leading to the generation of ions that are extracted through a tailored electrostatic field, and detected using a two stage microchannel plate (MCP) coupled to a phosphor screen and CMOS camera. CST Studio Suite was employed to conduct electrostatic and particle tracking simulations evaluating the ability of the extraction system to measure both beam profile and position. The ion interface, at the interaction region of proton beam and gas curtain, was modeled with realistic proton beam parameters and uniform gas curtain density distributions. The ion trajectory was tracked to evaluate the performance across multiple beam sizes. The simulations suggest that the extraction system can reconstruct transverse beam profiles for different proton beam sizes. Simulations also supported the system’s capability as a beam position monitor within the boundary defined by the beam size, the dimensions of the extraction system, and the height of the gas curtain. Some simulation results were benchmarked against experimental data of 28 MeV proton beam with 70 nA average beam current. This study will further help to optimize the design of the extraction system to facilitate the integration of SGC-IPM in medical accelerators.

The MIT-Bates Linear Accelerator Center is an electron scattering facility for basic research in medium energy nuclear physics. It consists of a 1 GeV 2.856 GHz linear accelerator and recirculator, two main experimental halls, and the 190 m circumference South Hall Ring (SHR). Both polarized and unpolarized electron sources are available. The SHR can be operated in storage mode, providing high current beam for use with internal targets, or in pulse-stretcher mode, using resonant extraction to deliver high duty factor beam to fixed target experiments. Spin control is installed for both stored and extracted beams. Extensive beam diagnostics are available on all beamlines. These include beam position monitors with multiple data acquisition modes, beam current monitors covering several orders of magnitude in current and frequency response, wire scanners, polarimeters, and so on. Details and applications of the Bates instrumentation are presented.

We have constructed and tested a 2 um resolution beam profile monitor based on optical transition radiation (OTR). Theoretical studies of OTR [1] show that extremely high resolution, of the order of the wavelength of the light detected, is possible. Such high‐resolution single pulse profile monitors will be very useful for future free electron laser and linear collider projects. Using the very low emittance 1.3 GeV electron beam at the KEK Accelerator Test Facility (ATF) [2] (1.4nm ex × 15pm ey), we have imaged transition radiation from 5 micron σ beam spots. Our test device consisted of a finely polished target, a thin fused silica window, a 35 mm working distance microscope objective (5x and 10x) and a triggered CCD camera. A wire scanner located near the target is used to verify the profile monitor performance. In this paper we report results of beam tests.

The delivery on target of a polarized electron beam from a linear accelerator is straightforward. With circular accelerators this delivery becomes understandably more difficult. In order to maintain the polarization of an electron beam in a circular machine such as a synchrotron or pulse stretcher ring the electron spins must be oriented vertically so as to be parallel to the dominant guide fields. Extraction from these machines occurs in the horizontal plane so the extracted beam retains the vertical polarization. It is generally desirable to have not vertical but longitudinal polarization of the beam at the target; this requires a reorientation of the spins. The straightforward solution to this problem is to put a solenoid in the beam line to precess the spin into the horizontal plane followed by a horizontally deflecting dipole to precess the spin into the momentum direction. The angle of spin precession is energy dependent. What is needed is a method of varying the effective bend angle. One method used with polarized protons from the ZGS at Argonne involved a movable beam line. An alternative method is to utilize the noncommutativity of rotations in three dimensions. To do this requires two or more solenoids and twomore » or more dipoles. This paper discusses the theory and implementation of this method and describes a solenoid-dipole-solenoid-dipole configuration beam line suitable for the 4 GeV electron accelerator proposed by the Southeastern Universities Research Association.« less

In the CTF3 (CLIC test facility 3) run of November 2007, a vertical beam instability has been found in the combiner ring during operation. After a careful analysis, the source of the instability has been identified in the vertical deflecting modes trapped in the rf deflectors and excited by the beam passage. A dedicated tracking code that includes the induced transverse wakefield and the multibunch multipassage effects has been written and the results of the beam dynamics analysis are presented in the paper. The mechanism of the instability was similar to the beam breakup in a linear accelerator or in an energy recovery linac. The results of the code allowed identifying the main key parameters driving such instability and allowed finding the main knobs to mitigate it. To completely suppress such beam instability, two new rf deflectors have been designed, constructed, and installed in the ring. In the new structures the frequency separation between the vertical and horizontal deflecting modes has been increased, changing the position of the rods inside the cells, and special antennas have been inserted to absorb the power released by the beam to the modes. The deflectors have been made in aluminum to reduce the costs and delivery time and have been successfully tested and installed in the ring. The design, the realization procedures, and the rf test results are illustrated.