Experimental simulation of beam propagation over long path lengths using radio-frequency and magnetic traps

Phys. Rev. Accel. Beams

Tokashiki

2019

Self Cite

This paper addresses the generalization of the single-particle betatron resonance condition derived by Courant and Snyder more than a half century ago. A two-dimensional resonance condition including the effect of space-charge interaction was recently conjectured from one-dimensional Vlasov predictions made by Sacherer, Okamoto, and Yokoya [K. Ito et al., Phys. Rev. Accel. Beams 20, 064201 (2017)]. The condition is remarkably simple which only contains a few measurable quantities and indicates the possibility that twice as many resonance stop bands as expected from the conventional incoherent picture may exist at high beam density. Self-consistent multiparticle simulations are performed systematically to locate low-order stop bands in the tune diagram. The proposed betatron resonance formula is shown to explain the basic feature of numerical observations, which suggests that no serious incoherent resonance is activated inside the phase-space core of a dense beam matched to the external linear focusing potential. It is confirmed that the coherent tune-shift factor of any collective mode is less than unity and practically considered as a constant over the whole tune space in a typical high-intensity storage ring. The procedure for finding the optimum operating point of the ring is discussed on the basis of the coherent picture instead of the commonly used picture relying on the concept of incoherent tune spread. Despite years of theoretical efforts by many researchers, the coherent resonance concept is still not being employed for the construction of a stability tune diagram. We here provide a simple prescription to draw the diagram quickly. The present study also indicates the possibility of complete suppression of emittance exchange on particular difference resonances by choosing a proper emittance ratio.

Section: A Noncoupling Resonancesmentioning

confidence: 87%

Section: Empirical 2d Coherent Resonance Conditionmentioning

confidence: 99%

Empirical condition of betatron resonances with space charge

Kojima

Phys. Rev. Accel. Beams

Tokashiki

2019

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“…Previous experiments on the resonant instability of space-charge-dominated beams have actually relied on a particular machine with a particular lattice configuration [5][6][7][8][9][10][11]. To overcome this practical limitation, we here employ the novel tabletop apparatus called "S-POD" (Simulator of Particle Orbit Dynamics) [12][13][14][15][16][17][18][19]. This experiment is based on an isomorphism between the equations of non-neutral plasma motion in a linear Paul trap (LPT) and the equations of intense beam motion in a strong focusing channel [20].…”

Section: Introductionmentioning

confidence: 99%

“…III how S-POD works, we proceed to experimental observations. In our past experiments with S-POD [14][15][16][17][18][19], the sinusoidal focusing model was often adopted to approximate the AG focusing effect from the FODO lattice. This simplification is experimentally validated in Sec.…”

Section: Introductionmentioning

confidence: 99%

Coherent resonance stop bands in alternating gradient beam transport

Ito

Phys. Rev. Accel. Beams

Tokashiki

et al. 2017

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An extensive experimental study is performed to confirm fundamental resonance bands of an intense hadron beam propagating through an alternating gradient linear transport channel. The present work focuses on the most common lattice geometry called "FODO" or "doublet" that consists of two quadrupoles of opposite polarities. The tabletop ion-trap system "S-POD" (Simulator of Particle Orbit Dynamics) developed at Hiroshima University is employed to clarify the parameter-dependence of coherent beam instability. S-POD can provide a non-neutral plasma physically equivalent to a chargedparticle beam in a periodic focusing potential. In contrast with conventional experimental approaches relying on large-scale machines, it is straightforward in S-POD to control the doublet geometry characterized by the quadrupole filling factor and drift-space ratio. We verify that the resonance feature does not essentially change depending on these geometric factors. A few clear stop bands of low-order resonances always appear in the same pattern as previously found with the sinusoidal focusing model. All stop bands become widened and shift to the higher-tune side as the beam density is increased. In the spacecharge-dominated regime, the most dangerous stop band is located at the bare betatron phase advance slightly above 90 degrees. Experimental data from S-POD suggest that this severe resonance is driven mainly by the linear self-field potential rather than by nonlinear external imperfections and, therefore, unavoidable at high beam density. The instability of the third-order coherent mode generates relatively weak but noticeable stop bands near the phase advances of 60 and 120 degrees. The latter sextupole stop band is considerably enhanced by lattice imperfections. In a strongly asymmetric focusing channel, extra attention may have to be paid to some coupling resonance lines induced by the Coulomb potential. Our interpretations of experimental data are supported by theoretical predictions and systematic multiparticle simulations.

“…At Hiroshima University, a unique tabletop tool called "S-POD" (Simulator of Particle Orbit Dynamics) has been developed which allows acceleratorfree experiments on diverse beam-dynamics issues [4][5][6][7][8][9][10]. The S-POD system is based on a compact linear Paul trap in which we can confine a large number of ions 1 .…”

Section: Introductionmentioning

confidence: 99%

Design Study of a Multipole Ion Trap for Beam Physics Applications

Fukushima

Plasma and Fusion Research

2015

A unique linear Paul trap is designed for a systematic experimental study of nonlinear beam dynamics with the tabletop apparatus "S-POD" at Hiroshima University. S-POD is the abbreviation of "Simulator of Particle Orbit Dynamics" where we can produce a non-neutral plasma physically equivalent to a charged-particle beam in an alternating-gradient focusing channel. Unlike a regular Paul trap with four quadrupole rods, the present trap configuration includes extra electrodes that enable us to control the strengths and time structures of low-order nonlinear fields independently of the linear focusing potential. We here consider the insertion of thin metallic plates in between the quadrupole rods. The size and arrangement of those extra electrodes are optimized by using a Poisson solver. Simple scaling laws are derived to make a quick estimate of the sextupole and octupole field strengths as a function of the plate dimension. Particle tracking simulations are performed to demonstrate the controlled excitation of nonlinear resonances in the modified Paul trap.