• E.S. Lessner, V.S. Assev, P.N. Ostroumov
  ANL, Argonne, Illinois

The driver linac of the projected RIA facility is a versatile accelerator, a 1.4-GV, CW superconducting linac designed to simultaneously accelerate several heavy-ion charge states, providing beams from protons at about 1 GeV to uranium at 400 MeV/u at power levels at a minimum of 100 kW and up to 400 kW for most beams. Acceleration of multiple-charge-state uranium beams places stringent requirements on the linac design. A steering algorithm was derived that fulfilled the driver’s real estate requirements, such as placement of steering dipole coils on SC solenoids and of beam position monitors outside cryostats, and beam-dynamics requirements, such as coupling effects induced by the focusing solenoids.* The algorithm has been fully integrated in the tracking code TRACK** and is used to study and optimize the number and position of steering elements that minimize the multiple-beam centroid oscillations and preserve the beam emittance under misalignments of accelerating and transverse focusing elements in the driver linac.

*E.S. Lessner and P.N. Ostroumov, Proceedings of the 9-th European Particle Accelerator Conference, July 2005, pp.1476-1478. **V.N. Aseev, P.N. Ostroumov, E.S. Lessner, and B. Mustapha, these proceedings.

• N. Vinogradov, V.N. Aseev, M.R.L. Kern, P.N. Ostroumov, R.C. Pardo, R.H. Scott
  ANL, Argonne, Illinois

The Rare Isotope Accelerator (RIA) facility utilizes the concept of simultaneous acceleration of two charge states from the ion source. We are building a prototype two charge-state (2Q) injector of the RIA Driver Linac, which includes an ECR ion source originally built by Berkeley Ion Equipment Corporation, a LEBT and one-segment of the prototype RFQ. The reassembly and commissioning of the ECR source has been completed. During the commissioning process we modified and replaced several major components of the BIE-100 to increase the source performance. A new diagnostic station has been designed and built for accurate measurements of the output beam emittance. The paper will discuss detailed beam dynamics studies together with extensive emittance measurements of various ion beams. The status of the design and fabrication of 100 kV high voltage platform, achromatic bending system, multi-harmonic buncher, and a full power 57.5 MHz RFQ segment will be presented.

• B. Mustapha, V.N. Aseev, E.S. Lessner, P.N. Ostroumov
  ANL, Argonne, Illinois

The new ray-tracing code TRACK was developed* to fulfill the special requirements of the RIA accelerator systems. The RIA lattice includes an ECR ion source, a LEBT containing a MHB and a RFQ followed by three SC linac sections separated by two stripping stations with appropriate magnetic transport systems. No available beam dynamics code meet all the necessary requirements for an end-to-end simulation of the RIA driver linac. The latest version of TRACK was used for end-to-end simulations of the RIA driver including errors and beam loss analysis.** In addition to the standard capabilities, the code includes the following new features: i) multiple charge states ii) realistic stripper model; ii) static and dynamic errors iii) automatic steering to correct for misalignments iv) detailed beam-loss analysis; v) parallel computing to perform large scale simulations. Although primarily developed for simulations of the RIA machine, TRACK is a general beam dynamics code. Currently it is being used for the design and simulation of future proton and heavy-ion linacs at TRIUMF, Fermilab, JLAB and LBL.

*P.N. Ostroumov and K.W. Shepard. Phys. Rev. ST. Accel. Beams 11, 030101 (2001). **P.N. Ostroumov, V. N. Aseev, B. Mustapha. Phys. Rev. ST. Accel. Beams, Volume 7, 090101 (2004).

• B. Mustapha, V.N. Aseev, P.N. Ostroumov
  ANL, Argonne, Illinois
• J. Qiang, R.D. Ryne
  LBNL, Berkeley, California

In order to benchmark the newly developed beam dynamics code TRACK we have performed comparisons with well established existing codes. During code development, codes like TRANSPORT, COSY, GIOS and RAYTRACE were used to check TRACK's implementation of the different beam line elements. To benchmark the end-to-end simulation of the RIA driver linac, the simulation of the low-energy part (from the ion source to the entrance of the SC linac) was compared with PARMTEQ and found to agree well. For the simulation of the SC linac the code IMPACT is used. Prior to these simulations, the code IMPACT had to be updated to meet the special requirements of the RIA driver linac. Features such as multiple charge state acceleration, stripper simulation and beam collimation were added to the code. IMPACT was also modified to support new types of rf cavities and to include fringe fields for all the elements. This paper will present a comparison of the beam dynamics simulation in the RIA driver linac between the codes TRACK and IMPACT. A very good agreement was obtained which represents another validation of both codes.

• J.W.  Staples, R. Keller, A. Sessler
  LBNL, Berkeley, California
• W. Chou
  Fermilab, Batavia, Illinois
• P.N. Ostroumov
  ANL, Argonne, Illinois

Accelerator-driven High-Energy Density Physics experiments require typically 1 nanosecond, 1 microcoulomb pulses of mass 20 ions accelerated to several MeV to produce eV-level excitations in thin targets, the "warm dense matter" regime. Traditionally the province of induction linacs, RF-based acceleration may be a viable alternative with recent breakthroughs in accelerating structures and high-field superconducting solenoids. A reference design for an RF-based accelerator for HEDP research is presented using 15 T solenoids and multiple-gap RF structures configured with either multiple parallel beams (combined at the target) or a single beam and a small stacking ring that accumulates 1 microcoulomb of charge. In either case, the beam is ballistically compressed with an induction linac core providing the necessary energy sweep and injected into a plasma-neutralized drift compression channel resulting in a 1 mm radius beam spot 1 nanosecond long at a thin foil or low-density target.

• E.S. Lessner, P.N. Ostroumov
  ANL, Argonne, Illinois

The RIA facility will include various complex systems and must provide radioactive beams to many users simultaneously. The availability of radioactive beams for most experiments at the fully-commissioned facility should be as high as possible within design cost limitations. To make a realistic estimate of the achievable reliability a detailed analysis is required. The RIA driver linac is a complex machine containing a large number of SC resonators and capable of accelerating multiple-charge-state beams. At the pre-CDR stage of the design it is essential to identify critical facility subsystem failures that can prevent the driver linac from operating. The reliability and availability of the driver linac are studied using expert information and data from operating machines such as ATLAS, APS, JLab, and LANL. Availability studies are performed with a Monte-Carlo simulation code previously applied to availability assessments of the NLC facility [http://www.slac.stanford.edu/xorg/accelops/Full/LCoptsfull] and the results used to identify subsystem failures that affect most the availability and reliability of the RIA driver, and guide design iterations and component specifications to address identified problems.

*J.A. Nolen, Nucl. Phys. A. 734 (2004) 661.

• P.N. Ostroumov, K.W. Shepard
  ANL, Argonne, Illinois
• G.W. Foster, I.G. Gonin, G. Romanov
  Fermilab, Batavia, Illinois

The proposed 8-GeV driver at FNAL is based on ~480 independently phased SC resonators. Significant cost saving is expected by using an rf power fan out from high-power klystrons to multiple cavities. Successful development of superconducting (SC) multi-spoke resonators operating at ~345-350 MHz provides a strong basis for their application in the front end of multi-GeV linear accelerators. Such a front-end operating at 325 MHz would enable direct transition to high-gradient 1300 MHz SC TESLA-style cavities at ~400 MeV. The proposed front end consists of 5 sections: a conventional RFQ, room-temperature (RT) cross-bar H-type (CH) cavities, single-, double^- and triple-spoke superconducting resonators. For several reasons which are discussed in this paper there is a large advantage in using independently phased RT CH-cavities between the RFQ and SC sections in the energy range 3-15 MeV.

• P.N. Ostroumov, V.N. Aseev
  ANL, Argonne, Illinois
• A. Kolomiets
  ITEP, Moscow

The RIB linac includes two strippers for the heaviest ions and three main sections: a room temperature injector up to an energy of ~100 keV/u, a superconducting (SC) linac for ions with charge-to-mass ratio 1/66 or more up to an energy of ~1 MeV and a higher energy SC linac to produce 10 MeV/u beams up to the mass of uranium. The RIA post-accelerator is a complex system designed for acceleration singly-charged ions before the stripper and includes many different accelerating and focusing structures operating both at room and cryogenic temperatures. Extensive accelerator design studies and end-to-end beam dynamics simulations have been performed to minimize the cost of the linac while providing high-quality and high-intensity radioactive beams. Specifically, we have found that cost-effective acceleration can be provided by several hybrid RFQs in the front end. The hybrid RFQs have been proposed and developed for acceleration of low-velocity heavy ions.* For the beam focusing in the second section it is appropriate to use electrostatic lenses and SC quadrupoles inside common cryostats with the resonators. The electrostatic lenses are most effective in the first cryostat of the SC linac.

*P.N. Ostroumov and A.A. Kolomiets. Proc. of the PAC-2001, Chicago, IL, June 18-22, 2001, p. 4077.

• P.N. Ostroumov, K.W. Shepard
  ANL, Argonne, Illinois
• J.R. Delayen
  Jefferson Lab, Newport News, Virginia

A design option for the 1.4 GV, multiple-charge-state driver linac required for the U.S. Rare Isotope Accelerator Project based on 345 MHz, 3-cell spoke-loaded cavities has been previously discussed.* This paper updates consideration of design options for the RIA driver, including recent results from numerically-modeling the multi-charge-state beam dynamics and also cold test results for prototype superconducting niobium 3-cell spoke-loaded cavities.

*"High-energy ion linacs based on superconducting spoke cavities," K.W. Shepard, P.N. Ostroumov, and J.R. Delayen, Phys. Rev. ST Accel. Beams 6, 080101 (2003).

• A.V. Novikov-Borodin, V.A. Kutuzov
  RAS/INR, Moscow
• P.N. Ostroumov
  ANL, Argonne, Illinois

There are several heavy-ion linac projects being developed worldwide. For example, the Rare Isotope Accelerator Facility [J.A. Nolen, Nucl. Phys. A. 734 (2004) 661] currently being designed in the U.S. will use both heavy-ion and light ion beams to produce radionuclides via the fragmentation and spallation reactions, respectively. With simultaneous beam delivery to more than one target independent adjustment of relative beam intensities is essential. A fast traveling wave chopper can be used to modulate cw beam intensity at low energy ~200 keV/u. Such a device should have high frequency characteristics at high power level. By increasing the wave impedance of the traveling wave structure up to 200 Ohm one can reduce power requirements to the fast voltage pulser. Several design options of the high-impedance structure are discussed.

• R.W. Garnett, J.A. Billen, T.P. Wangler
  LANL, Los Alamos, New Mexico
• K.R. Crandall
  TechSource, Santa Fe, New Mexico
• P.N. Ostroumov
  ANL, Argonne, Illinois
• J. Qiang, R.D. Ryne
  LBNL, Berkeley, California
• R.C. York, Q. Zhao
  NSCL, East Lansing, Michigan

We are developing multuparticle beam-dynamics simulation codes for RIA driver linac simulations extending from the low-energy beam transport 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 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. In this paper we present the status of the work, describe some recent additions to the codes, and show preliminary end-to-end simulation results for a representative driver-linac design.