The CERN SPS Experiment on Microwave Transmission through the Beam Pipe

Kroyer, T.; Caspers, F.; Mahner, E.; Wien, T.

doi:10.1109/pac.2005.1591060

Cited by 14 publications

(17 citation statements)

References 2 publications

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“…A technique to measure the average electron cloud density in a section of a storage ring non-destructively, parasitically, and in real time, has been devised by Caspers and Kroyer, and tested at the SPS [13][14][15]. The technique consists in injecting microwaves into the vacuum chamber and detecting their phase shift and attenuation a distance ∆L away.…”

Section: Microwave Propagation Through the Electron Cloudmentioning

confidence: 99%

HINS R&D Collaboration on Electron Cloud Effects: MidyearReport

Furman¹,

Sonnad²,

Vay³

2006

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We present a report on ongoing activities on electron-cloud R&D for the MI upgrade. These results update and extend those presented in Refs. 1, 2. In this report we have significantly expanded the parameter range explored in bunch intensity N b , RMS bunch length σz and peak secondary emission yield (SEY) δmax, but we have constrained our simulations to a field-free region. We describe the threshold behaviors in all of the above three parameters. For δmax ≥ 1.5 we find that, even for N b = 1 × 10 11 , the electron cloud density, when averaged over the entire chamber, exceeds the beam neutralization level, but remains significantly below the local neutralization level (ie., when the electron density is computed in the neighborhood of the beam). This "excess" of electrons is accounted for by narrow regions of high concentration of electrons very close to the chamber surface, especially at the top and bottom of the chamber, akin to virtual cathodes. These virtual cathodes are kept in equilibrium, on average, by a competition between space-charge forces (including their images) and secondary emission, a mechanism that shares some features with the space-charge saturation of the current in a diode at high fields. For N b = 3 × 10 11 the electron cloud build-up growth rate and saturation density have a strong dependence on σz as σz decreases below ∼ 0.4 m, when the average electron-wall impact energy roughly reaches the energy Emax where δ peaks. We also present improved results on emittance growth simulations of the beam obtained with the code WARP/POSINST in quasi-static mode, in which the beam-(electron cloud) interaction is lumped into Ns "stations" around the ring, where Ns = 1, 2, . . . , 9. The emittance shows a rapid growth of ∼ 20% during the first ∼ 100 turns, followed by a much slower growth rate of ∼ 0.03%/turn. Concerning the electron cloud detection technique using microwave transmission, we present an improved dispersion relation for the TE mode of the microwaves, and a corresponding analytic estimate of the phase shift. I. ELECTRON CLOUD BUILD-UP.A. Remarks on the simulations.We have replaced the Poisson solver of the code POSINST [3][4][5][6], used in the computation of the electron cloud space-charge forces, by a multigrid-type solver that is much faster and more accurate than the old one. We have carefully tested the new solver in stand-alone mode, and we are confident that it gives correct (indeed, quite accurate) results. Owing to its inefficiency, the old solver could realistically be used only for very coarse grids, leading to intermittent problems at high N b and/or high δ max that sometimes crashed the code. For MI simulations, the improved code yields results only a few percent different from the old ones [1] for those cases in which the above-mentioned problem did not materialize. For other cases, notably the simulation of an LHC * Work supported by the FNAL HINS R&D Effort and by the US DOE under contract DE-AC02-05CH11231.† Electronic address: mafurman@lbl.gov; URL: http://mafurman. lbl.go...

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Section: Microwave Propagation Through the Electron Cloudmentioning

confidence: 99%

HINS R&D Collaboration on Electron Cloud Effects: MidyearReport

Furman¹,

Sonnad²,

Vay³

2006

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“…The power losses also exceed 6 kW. Previous studies made by F. Caspers and T. Kroyer show that around 100 W of heat power can be dissipated for an operation temperature 100 K above the cooling temperature [1]. …”

Section: +2"57("+%#-/!$%-#""mentioning

confidence: 89%

“…It requires pulse voltages up to 2.5k kV, rising in less than 6 ns at a repetition rate up to 8.8 MHz. These figures are at the border of what can be provided by the travelling wave fast choppers and the capacitive-type chopping technologies [1,2,3,4]. We have reviewed the current fast and slow chopping structures and their associated pulse generator [5].…”

mentioning

confidence: 99%

A single bunch selector for the next low � continuous wave heavy ion beam

Dem

Giacomo

2007

2007 IEEE Particle Accelerator Conference (PAC)

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The MEBT line of EURISOL heavy ion postaccelerator and the SPIRAL2 deuton/ion accelerator should transport a continuous wave (cw) beam from a 88.05 MHz RFQ (! respectively 0.035 and 0.04) to a drift-tube linac. A high frequency chopper is being studied to select only 1 bunch over N, respectively 10 < N and 100 < N as asked by the physicists. It requires pulse voltages up to 2.5k kV, rising in less than 6 ns at a repetition rate up to 8.8 MHz. These figures are at the border of what can be provided by the travelling wave fast choppers and the capacitive-type chopping technologies [1,2,3,4]. We have reviewed the current fast and slow chopping structures and their associated pulse generator [5]. Some preliminary RF simulations to adapt the present chopping devices to our requirements are presented. The main limitations of these technologies when applied to select one bunch in cw ion accelerators are also shown. Our first studies and results to solve the arising problems are discussed. $%-/.7*+-$.%"The MEBT line of the EURISOL post-accelerator and the SPIRAL2 accelerator should transport continuous wave (cw) beams from a RFQ operating at the 88.05 MHz frequency ("%!= 11.36 ns) to a drift tube linac (DTL). Both superconducting linacs are designed to have effective acceleration respectively for radioactive heavyions with a ratio A/q from 4 to 8, and either for deuton or heavy ions with a A/q of 3 and 6. The maximum beam current is respectively 1 !"!and 5 mA. The space charge effects are negligible in the EURISOL case. Many EURISOL experiments will require to chop the beam for periods from 10 ns to 1 ms, which will be made by means of a high frequency chopper located in the MEBT line. Due to the physicist requirements the EURISOL and SPIRAL2 choppers should operate like a single bunch selector: one bunch over N should pass through the chopper output with the repetition rate resumed in table 1.After having adapted existing 50-# travelling-wave (TW) electrodes to our cases, power constraints will be observed due to the cw mode of the beam and the physicist requirements. Two alternative ways might answer the requirements. We also decided to investigate another way to decrease power consumption: a 100-# meander microstrip line. The length of the strip line can lead to attenuation and dispersion of the pulse signal along its propagation. +2"5.7("+.%#-/!$%-#""Fast rising times can be achieved either by travelling wave structures [2,3,4] or by capacitive-type (C-type) chopper [6]. This scheme is used when rise time lower than 10 ns are searched. Chopper structure working at voltage level similar to those required for EURISOL are being studied for proton injectors foreseen to operate in the 300 to 400 MHz frequency range and within rise/fall time of the deflecting pulse shorter than 2 ns. In preliminary studies the 50-# SPL electrode was adapted to EURISOL and SPIRAL2 cases. For EURISOL and SPIRAL2, N-1 bunches over N should be suppressed where N exceeds respectively 10 and 100. These values imply a duty cycle of the high vo...

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“…This technique suggested in Ref. [1] has been employed in the experiments at PEP-II [4] and secondary peaks have been observed at the expected frequency.…”

Section: A Brief Note On Experimental Measurement Of Phase Shiftmentioning

confidence: 99%

“…Experimental results conducted at the SPS have been reported [1], and some preliminary experimental investigation has also been conducted at the PEP II low energy ring [4] will be reported. While it is clear that more progress is required in the experimental and simulation efforts, we can already state that results obtained so far are encouraging.…”

Section: Introductionmentioning

confidence: 99%

Simulation and analysis of microwave transmission through an electron cloud, a comparison of results

Sonnad

Furman

Veitzer

et al. 2007

2007 IEEE Particle Accelerator Conference (PAC)

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Simulation studies for transmission of microwaves through electron cloudes show good agreement with analytic results. The elctron cloud produces a shift in phase of the microwave. Experimental observation of this phenomena would lead to a useful diagnostic tool for acessing the local density of electron clouds in an accelerator. These experiments are being carried out at the CERN SPS and the PEP-II LER at SLAC and is proposed to be done at the Fermilab maininjector. In this study, a brief analysis of the phase shift is provided and the results are compared with that obtained from simulations.

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The CERN SPS Experiment on Microwave Transmission through the Beam Pipe

Cited by 14 publications

References 2 publications

HINS R&D Collaboration on Electron Cloud Effects: MidyearReport

HINS R&D Collaboration on Electron Cloud Effects: MidyearReport

A single bunch selector for the next low � continuous wave heavy ion beam

Simulation and analysis of microwave transmission through an electron cloud, a comparison of results

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