Overcoming a fast transverse instability by means of octupole-induced tune spread in the Relativistic Heavy Ion Collider

During the Relativistic Heavy Ion Collider commissioning in 2001 a fast transverse instability was observed on the ramp. In general this could be counteracted with increased chromaticity, resulting in Landau damping. However this method could not be applied around transition energy where chromaticities have to change sign. So octupoles were used near transition energy to create transverse Landau damping and avoid the transverse instability, emittance blowup, and beam loss. This paper describes the considerations that led to the present scheme, as well as experimental results

RHIC Optics for Transition Jump

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EMITTANCE COMPENSATION FOR MAGNETIZED BEAMS

Emittance compensation is a well established technique for minimizing the emittance of an electron beam from a RF photo-cathode gun. Longitudinal slices of a bunch have a small emittance, but due to the longitudinal charge distribution of the bunch and time dependent RF fields they are not focused in the same way, so that the direction of their phase ellipses diverges in phase space and the projected emittance is much larger. Emittance compensation reverses the divergence. At the location where the slopes of the phase ellipses coincide the beam is accelerated, so that the space charge forces are reduced. A recipe for emittance compensation is given in. For magnetized beams (where the angular momentum is non-zero) such emittance compensation is not sufficient because variations in the slice radius lead to variations in the angular speed and therefore to an increase of emittance in the rotating game. We describe a method and tools for a compensation that includes the beam magnetization

LOW EMITTANCE ELECTRON BEAMS FOR THE RHIC ELECTRON COOLER

An electron cooler, based on an Energy Recovery Linac (ERL) is under development for the Relativistic Heavy Ion Collider (RMIC) at Brookhaven National Laboratory. This will be the first electron cooler operating at high energy with bunched beams. In order to achieve sufficient cooling of the ion beams the electron have to have a charge of 5 nC and a normalized emittance less than 4 {mu}. This paper presents the progress in optimizing the injector and the emittance improvements from shaping the charge distribution in the bunch

RHIC longitudinal parameter revision

Recent experience showed that bunch rotations are needed in the AGS for gold as well as proton operations before the beams are injected into RHIC. The longitudinal bunch area is increased for gold operation from 0.3 up to 0.5 eV{center_dot}s/u at design intensity. This paper reviews the revised longitudinal parameters in RHIC during injection, acceleration, transition crossing, rebucketing, and storage for gold and proton beams, accommodating for the change in injection conditions at the AGS

PARMELA simulation for BNL 704MHz SRF gun in low emittance operation

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Design of an Interaction Region for the Linac-Ring Version of the Electron-Ion Collider ERHIC

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Orbit correction techniques for a multipass linac

The CEBAF accelerator includes a linac section which accelerates multiple beams with different energies. Problems arise when performing orbit correction, due to the fact that correction of higher energy passes disturb lower energy trajectories. Therefore, a perfect orbit correction cannot be obtained for all energy beams at the same time. We present methods and performance (using simulation results) for performing orbit corrections in such a system. Limitations to the correction method are also addressed. 2 refs., 5 figs

A fast optics and orbit correction program

CEBAF is a large recirculating linear accelerator with approximately 1600 magnet power supplies in the beam transport system. The average beam power can be as great as 800 kW, concentrated into a spot of area less than 0.01 mm{sup 2}. Control of the transport is therefore quite critical, to avoid missteering the beam. To prevent dangerous beam losses and to prepare optics changes, the control programs must read the magnet power supplies and calculate the optics in a virtually real-time manner. A program named OLE (On-Line Envelope) has been developed at CEBAF to give a graphical display of the calculated machine {beta} function or, equivalently, the beam envelope. The time interval necessary to execute the program is somewhat less than one second, short enough that the operator can use it for setting up his lattice. Emphasis in the design was placed on speed of program execution at the expense of generality of application. As a result, the accelerator operator will be able to alter the magnetic field in any element in the machine, calculate the {beta} functions in both planes at the entrance and exit of each magnet, and display graphs of the functions, all within one second. The time that is required is short enough that the process approximates fairly well real-time operation