Stability limits with Landau damping in the FCC-hh

Abstract

The resistive wall impedance is one of the expected main drivers of transverse beam instabilities in the proposed Future Circular Collider hadron-hadron option (FCC-hh). We obtain the resistive wall impedance for the FCC-hh beam screen from a two-dimensional finite element solver. The impedances and resulting growth rates are compared to the LHC, using similar models for the resistivity of the copper layer. Similar to the LHC and in addition to active feedback, dedicated octupole magnets together with a finite chromaticity should be employed for Landau damping, as a cure against transverse beam instabilities. The stability boundary provided by an LHC-like octupoles configuration in combination with an electron lens is obtained from a dispersion relation including the two-dimensional tune spreads. The prediction from the simple dispersion relation are compared to the corresponding beam transfer function and to the stability boundaries reconstructed using particle tracking with an effective impedance. The electron cloud induced tune spreads and their scaling with higher energy and smaller beam pipe radius are estimated. Besides the important estimation of growth rates and stability threshold for FCC-hh we also try to improve the understanding of the scaling of coherent instabilities and their thresholds with energy towards a possible highest-collider limit, using the example of two high-energy colliders, the existing LHC and the proposed FCC-hh. K: Accelerator modelling and simulations (multi-particle dynamics; single-particle dynamics); Coherent instabilities

Potential impedance reduction by REBCO-coated conductors as beam screen coating for the Future Circular Hadron Collider

“…The medium frequency range is specified as the frequency range of the beam at which the skin depth is still small enough to penetrate only the first conducting layer. For the FCC-hh, the lowest frequency important for the beam impedance is close to the revolution frequency f min ≈ 2.1 kHz at injection, while the highest frequency depends on the bunch length f max ≈ 3 GHz [9,18]. In the FCC-hh baseline, the Cu is thick enough that eqs.…”

“…An applied magnetic field on Cu induces a magnetoresistive effect, dominant at very high purity and low temperatures, generally taken into account over Kohler's law [21]. It is important to note that in the pertinent frequency and temperature range of interest in the FCC-hh, this effect can be disregarded [18], and hence, is not taken into consideration in our investigation. Differently, an applied magnetic field of 1 T on REBCO induces vortices in the materials with normal conducting cores, which interact with each other forming a vortex lattice impacting the surface impedance.…”

Landau damping of transverse head-tail instabilities with a pulsed electron lens in hadron synchrotrons

“…The resistive wall impedance Z ⊥ y ∝ 1/ Q p , relevant for many hadron accelerators (e.g. [11,33]), is used in this section.…”

“…Instability mitigation methods (linear chromaticity adjustments, Landau damping, transverse feedback system, linear coupling, and others) play a crucial role in the operation of synchrotrons for high beam intensities [4]. This contribution focuses on Landau damping, an effect caused by energy exchange between coherent and incoherent motion, in bunched beams in ring accelerators [3][4][5][6][7][8][9][10][11][12][13][14][15]. This effect requires an incoherent betatron tune spread in the bunch.…”

“…LO are a standard source of the transverse detuning to mitigate transverse instabilities in several accelerators, e.g. the LHC [10], SIS100 [5] and the proposed Future Circular Collider (hh) (FCC-hh) [11]. In recent years, several alternative to LO methods of Landau damping were proposed, mainly for high energy hadron colliders.…”