Stochastic cooling experiments for CSRe at IMP Zhu, G.Y.; Wu, J.X.; Caspers, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2019, Letnik:
932
Journal Article
Recenzirano
A novel type of perforated travelling wave pick-up/kicker structure was developed for CSRe stochastic cooling which was originally proposed by F. Caspers at CERN. The simulated and measured results ...of shunt impedance of the slotted travelling wave pickup electrode are in reasonable agreement. In December 2015 stochastic cooling of heavy ions was successfully applied for the first time at the CSRe storage ring of IMP in Lanzhou, China. During four days of commissioning, transverse and longitudinal cooling could be observed. Both the time-of-flight and the notch filter methods were used for longitudinal cooling. The measured cooling rates are presented.
A perpendicular biased ferrite loaded accelerating cavity is studied for a possible upgrade of the CERN accelerator complex which could help to overcome the intensity limitations occurring at the SPS ...injection. The required accelerating cavity should cover a frequency range of 18 to 40 MHz with high cavity Q, which poses high demands on the ferrite material properties. A test setup is presented to measure the relative permeability and magnetic losses of full scale ferrite garnets (350 mm outer and 200 mm inner diameter) in a magnetic bias field within the frequency range of interest. An one-port reflection measurement provides adequate input to model the relative permeability of the ferrite in numerical simulations for different magnetic bias fields. A resonant measurement setup was used to cross-check simulation results with measurement data and to investigate the magnetic losses of the ferrite material. A numerical model of a simplified accelerating cavity is used to study the capability of the garnet G-510 as a perpendicular biased tuning ferrite.
Fast kicker magnets are used to inject beam into and extract beam out of the CERN accelerator rings. These kickers are often ferrite loaded transmission line type magnets with a rectangular shaped ...aperture through which the beam passes. The interaction of the beam with the resistive part of the longitudinal beam coupling impedance leads to power dissipation and heating of different elements in the accelerator ring. In particular, power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. In addition, the imaginary portion of the beam coupling impedance contributes to beam instabilities. A good knowledge of electromagnetic properties of materials up to GHz frequency range is essential for a correct impedance evaluation. This paper presents the results of transmission line measurements of complex initial permeability and permittivity for different ferrite types. We present an approach for deriving electromagnetic properties as a function of both frequency and temperature; this information is required for simulating ferrite behaviour under realistic operating conditions.
Performance of the resonant Schottky pickup at CSRe Wu, J.X.; Zang, Y.D.; Nolden, F. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
12/2013, Letnik:
317
Journal Article
Recenzirano
Odprti dostop
•The single particle sensitivity of the new resonant pickup installed on CSRe was successfully confirmed.•This device will be used for nuclear mass and lifetime measurement, as well as other ...uses.•For the R/Q measurement, the perturbation measurement and the beam measurement have good agreements.
For a bunched beam, the signals on pickups are coherent, providing a signal power proportional to the square of the number of particles. For a coasting beam the individual particle signals have a random phase; therefore, the overall signal is proportional to the particle number N. As a consequence, Schottky signals are often relatively weak and have to compete with many noise sources. For a small number of particles, the S/N is always a problem. To achieve a high signal-to-noise ratio and better temporal resolution, which could yield important physical information about fast processes, a resonant pickup was developed at GSI (Nolden et al., 2011 1), and a similar device is now installed in the CSRe 2 at IMP. This device will be used for nuclear mass and lifetime measurement, as well as other uses. The final goal of the pickup is to detect single particles. In Dec 2012, we performed an experiment with a 112Sn50+ beam with an energy of 253MeV/u, and the single particle sensitivity of the pickup was successfully confirmed. This paper presents hardware measurements of the pickup as well as beam measurements.
Cavities that are partially filled with ferrite material provide a tunable resonance frequency by making use of the changing μ-characteristics of ferrites when exposed to an external magnetic bias ...field. The concept of using either parallel or perpendicular magnetic biasing to reach a certain resonance frequency of a cavity has been known for many years. However, a cavity based on superposition of perpendicular and parallel magnetic fields to obtain improved ferrite characteristics was suggested in W. R. Smythe "Reducing ferrite tuner power loss by bias field rotation," IEEE Trans. Nucl. Sci., vol. 30, no. 4, pp. 273-275, 1983, but to our knowledge was neither tested nor built. Such a 2-directional biasing is expected to provide a reduction in RF losses for an identical tuning range as compared with the classical 1-directional magnetic bias. We have successfully tested this theory with a measurement set-up consisting of a ferrite-filled cavity, exposed to external biases that allow the clear separation of the two orientations of superposed magnetic bias fields. The outcome is an enlargement of tuning range with high cavity Q and the possibility of fast tuning. In this paper, we describe the measurement set-up and present the tuning ranges that we attained by applying different bias schemes.
The transverse broadband impedances of major components in the BRing (booster ring) of HIAF (High Intensity Heavy-ion Accelerator Facility) are estimated using the analytical formulas or the ...wakefield solver in the CST Studio Suite. At low frequency, the transverse broadband impedance model of BRing isZ1H(ω)=−417.14ikΩ/m(horizontal)andZ1V(ω)=−530.19ikΩ/m(vertical), which are larger than the threshold impedance for the transverse mode-coupling instability. The ceramic rings in the vacuum chamber are the primary source of impedance. With a goal of mitigating the instability by reducing the impedance of ceramic rings, a high conductivity coating is discussed in detail. In addition, a prototype of ceramic rings-loaded thin-wall vacuum chamber is manufactured and the impedance measurements are performed. When ceramic rings are coated by2μm-copper, the CST simulation and experiment results show that the transverse broadband impedance of ceramic rings-loaded thin-wall vacuum chamber can be reduced fromZ1H(ω)=−291.69ikΩ/mandZ1V(ω)=−352.37ikΩ/mtoZ1H(ω)=−46.16ikΩ/mandZ1V(ω)=−64.56ikΩ/m. Furthermore, in this case the transverse broadband impedance model of BRing is reduced by more than 50% toZ1H(ω)=−171.61ikΩ/mandZ1V(ω)=−242.38ikΩ/m.
Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation at high currents. Furthermore, it is difficult ...to probe their density over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave transmitted over a section of the accelerator and used it to measure the average electron cloud density over a 50 m section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center.
The electron cloud effect can pose severe performance limitations in high-energy particle accelerators as the CERN Super Proton Synchrotron (SPS). Mitigation techniques such as vacuum chamber thin ...film coatings with low secondary electron yields (SEY<1.3) aim to reduce or even suppress this effect. The microwave transmission method, developed and first applied in 2003 at the SPS, measures the integrated electron cloud density over a long section of an accelerator. This paper summarizes the theory and measurement principle and describes the new SPS microwave transmission setup used to study the electron cloud mitigation of amorphous carbon coated SPS dipole vacuum chambers. Comparative results of carbon coated and bare stainless steel dipole vacuum chambers are given for the beam with nominal LHC 25 ns bunch-to-bunch spacing in the SPS and the electron cloud density is derived.
PDF
