R. C. York

The Maryland electron ring for investigating space-charge dominated beams in a circular fodo system

The University of Maryland Electron Ring (UMER), currently under construction, has been designed to study the physics of space-charge dominated beams at extremely large values of the betatron tune shift which exceed those of existing strong-focusing synchrotrons and rings by more than an order of magnitude. In this paper, the unique design features of this research facility, the new beam physics to be investigated, and recent experimental results in the injector prototype as well as simulation studies are reviewed.

Niobium cavity development for the high-energy linac of the Rare Isotope Accelerator

This paper will cover the design of a 6-cell /spl beta//sub g/ = 0.47 cavity for the Rare Isotope Accelerator, as well as the fabrication and RF testing of single-cell prototypes. Single-cell prototypes were chosen as a first step, as they provide a quick and inexpensive way to find out whether the desired field level and Q can be reached, and to check for problems with multipacting. An accelerating gradient of 8 MV/m was chosen as a goal for the /spl beta//sub g/ = 0.47 cavity.

Magnetic elements for the A1900 fragment separator at the NSCL

A high rigidity, large acceptance fragment separator, the A1900, is being built at the NSCL. The device consists of twenty-four quadrupoles, four dipoles, sixteen sextupoles and sixteen octupoles. There are five sizes of the quadrupoles, three of which will contain sets of nested multipoles. The quadrupoles and the dipoles are superferric, with maximum pole tip fields of 2.5 T and 2 T, respectively. The quadrupole coils and the multipoles are random wound, potted using conductor from 0.85 to 1.35 mm in diameter. The dipole is layer wound with insulated conductor with a cross section of one by two mm. All coils are self protecting in case of a quench.

Nearly copropagating sheared laser pulse FEL undulator for soft x-rays

A conceptual design for a soft x-ray free-electron laser (FEL) using a short-pulsed, high energy near infrared laser undulator and a low-emittance modest-energy (?170?MeV) electron beam is described. This low-cost design uses the laser undulator beam in a nearly copropagating fashion with respect to the electron beam, instead of the traditional ?head-on? fashion. The nearly copropagating geometry reduces the Doppler shift of scattered radiation to yield soft, rather than hard x-rays. To increase the FEL gain a sheared laser pulse from a Ti?:?sapphire or other broadband laser is used to extend the otherwise short interaction time of the nearly copropagating laser undulator beam with a relativistic electron beam.

New directions in superconducting radio frequency cavities for accelerators

Superconducting radio frequency (SRF) cavities used in present-day accelerators for the acceleration of charged particles near the speed of light are based on the axially symmetric TM010 mode of a pillbox cavity. Future accelerators such as the Linear Collider require high accelerating gradients to limit the length of the linac. Two techniques to improve the gradient are being explored: a cavity that is half reentrant to improve the electromagnetic characteristics, and improved heat transfer via cooling channels and surface modification at the helium interface. These changes could potentially increase the gradients and reduce the cryogenic losses. For other applications more important criteria are simplicity, acceleration of high beam current, or the ability to use advanced materials such as Nb/sub 3/Sn or high-T/sub c/ superconductors. A new type of cavity based on the TM01p pillbox mode with p>0 offers such improvements.

Cryomodule design for the Rare Isotope Accelerator

The Rare Isotope Accelerator (RIA) driver linac will produce >400 MeV/u proton through uranium beams using many types of superconducting accelerating cavities such as quarter wave, spoke, and elliptical cavities. A cryomodule design that can accommodate all of the superconducting cavity and magnet types is presented. Alignment of the cold mass uses a titanium rail system, which minimizes cryomodule size, and decreases both the tunnel cross-section and length. The titanium rail is supported from the top vacuum plate by an adjustable tri-link, which is similar to existing Michigan State University magnet technology. A prototype cryomodule is under construction for testing 805 MHz, v/c=0.47, six-cell niobium cavities in realistic operating conditions. Details of the design and progress to date are presented.

Advanced Beam-Dynamics Simulation Tools for RIA

We are developing multi-particle beam-dynamics simulation codes for RIA driver-linac simulations extending from the low-energy beam transport (LEBT) line to the end of the linac. These codes run on the NERSC parallel supercomputing platforms at LBNL, which allow us to run simulations with large numbers of macroparticles. The codes have the physics capabilities needed for RIA, including transport and acceleration of multiple-charge-state beams, beam-line elements such as high-voltage platforms within the linac, interdigital accelerating structures, charge-stripper foils, and capabilities for handling the effects of machine errors and other off-normal conditions. This year will mark the end of our project. In this paper we present the status of the work, describe some recent additions to the codes, and show some preliminary simulation results.

Status report on multi-cell superconducting cavity development for medium-velocity beams

The Rare Isotope Accelerator (RIA) is being designed to supply an intense beam of exotic isotopes for nuclear physics research. Superconducting cavities are to be used to accelerate the CW beam of heavy ions to 400 MeV per nucleon, with a beam power of up to 400 kW. Because of the varying beam velocity, several types of superconducting structures are needed. This paper covers the fabrication of three prototype RIA 6-cell /spl beta//sub g/ = 0.47 cavities and the RF tests on the first and second of these cavities.

Design studies of the reaccelerator RFQ at NSCL

The reaccelerator system under development at the National Superconducting Cyclotron Laboratory (NSCL) will consist of a helium gas Radioactive Ion Beam (RIB) stopper, an electron beam ion trap, a cw radio frequency quadrupole (RFQ), and a superconducting linac to accelerate RIBs up to 3 MeV/u with charge-to-mass ratios (Q/A) of 0.2 - 0.4. The RFQ will operate in cw mode at a frequency of 80.5MHz to accelerate RIBs from 12 keV/u to 600 keV/u. An external multi-harmonic buncher will be used to achieve a small longitudinal emittance beam out of the RFQ. In this paper, we describe the design of the RFQ and the result of beam dynamics simulation.

Experimental study of a 322 MHz v/c=0.28 niobium spoke cavity

The Rare Isotope Accelerator (RIA) will accelerate heavy ions to >400 MeV/u using an array of superconducting cavities. A proposed linac design based on harmonics of 80.5 MHz will require six cavity types to cover the entire velocity range: three quarter wave resonators, one spoke cavity (half wave resonator), and two 6-cell elliptical cavities. A prototype 322 MHz niobium spoke with optimum velocity of 0.28 c has been fabricated. Each spoke would generate over 1 MV at 4 K for acceleration from v/c=0.20 to 0.40. Details of the design and experimental study are presented.