INFN/LNL, Legnaro, Padova
Consorzio RFX, Associazione Euratom-ENEA sulla Fusione, Padova
The SPES project* at Laboratori Nazionali di Legnaro foresees the contruction of a RIB facility based on a fission target driven by a 40 MeV proton beam. After the 238U carbide target the 1+ charged ions will be selected by a high resolution mass spectometer, charge enhanced by a charge breeder and accelerated up to 10 MeV/A for 132Sn. The Legnaro superconducting accelerator complex, PIAVE injector and ALPI main accelerator, in its present configuration fits the requirements for SPES post acceleration. Nevertheless an upgrade of its performaces both in overall transmission and final energy is needed and a solution which minimizes the impact on the present structures will be presented.
*http://www.lnl.infn.it/~spes/
RIKEN Nishina Center, Wako, Saitama
Present status of the RIKEN heavy-ion linac (RILAC) will be reported, which has been used for the injector to the RIKEN RI-beam factory since 2006 as well as for the nuclear physics experiments on superheavy elements since 2002. An alternative injector to the RI-beam factory, consisting of a superconducting ECR ion source, an RFQ, and three DTLs, will be also discussed. The construction of the ion source will be completed in this year and the extraction test of the beams will be started from 2009. An RFQ linac, originally developed for the ion implantation*, was given to RIKEN through the courtesy of Kyoto University. Reconditioning of this RFQ is underway, which will be modified for the new injector in the near future.
*H. Fujisawa: Nucl. Instrum. Methods A345, 23 (1994).
CERN, Geneva
UMAN, Manchester
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
The High Intensity and Energy ISOLDE (HIE-ISOLDE) proposal is a major upgrade of the existing ISOLDE and REX-ISOLDE facilities with the objective of increasing the energy and the intensity of the delivered radioactive ion beam. For the energy increase a staged construction of a superconducting linac based on sputtered quarter wave cavities is foreseen downstream of the present normal conducting linac. A funded R&D program has been launched at the end of 2007 in order to prepare a full Technical Design Report covering all the issues of such a linac, including cavity prototyping and testing, cryomodule design, beam dynamics and beam diagnostics. We report here on the status and planning of the R&D activities for the SCREX-ISOLDE linac.
RLNR, Tokyo
In order to obtain high intensity ion beams from a linear accelerator (linac) stably, it is necessary to suppress the defocusing force due to the space charge effect. The defocusing force is extremely strong in low energy and high intensity beams. Therefore, high intensity ion beam acceleration in the low energy region is one of the most difficult conditions to achieve. One of the solutions is the relaxation of the defocusing force by dividing the high intensity beam into several beams. Thus, a multibeam IH type Radio Frequency Quadrupole (IH-RFQ) linac has been proposed for a high intensity injector system. In particular, we have been developing a two-beam type IH-RFQ cavity as a prototype of the multibeam type IH-RFQ by using computer code. This prototype has the capability of accelerating charged particles to mass ratio (q/A) greater than 1/6 from 5 keV/u up to 60 keV/u. The expected total output current is 87.2 mA for the total input beam current of 120 mA.
NSC/KIPT, Kharkov
Experiments with heavy ion beams accelerated to an energy of 8.5 MeV/u as well as the work at developing new methods of acceleration and upgrading of accelerating structures are carried on at the Kharkov heavy-ion linear accelerator MILAC. The accelerating H-type structure with drift tubes of interdigital type (IH-structure) has been introduced in the main section and two pre-stripping sections of the MILAC accelerator. New original methods of tuning developed at MILAC have enabled the formation of uniform distribution of the accelerating field along the whole length of the accelerating structure. The introduction of IH accelerating structures of various modifications at the MILAC accelerator substantially extends the scientific and applied ranges of research. It involves experimental studies with heavy ions beams for production of track-etched membranes, generation of unique radionuclides, developments of proton and ion therapy, studies of radiation characteristics of constructional materials for nuclear engineering, investigations into the processes of fusion-fission of superheavy nuclei, and many other problems of nuclear physics.
LANL, Los Alamos, New Mexico
Laser interactions with thin solid targets can produce sheath fields of tens of TV/m, which have been used to accelerate ions to several MeV with ps pulse lengths, high currents, and low transverse emittance. While previous results have had 100% energy spread, recent experiments using foils coated with a few monolayers have produced quasi-monoenergetic beams with 17% energy spread near 3 MeV. Such beams may be of interest as injectors or sources. Simulations show the potential for acceleration to hundreds of MeV or GeV energies using very thin foils.
CERN, Geneva
The Compact Linear Collider (CLIC) is studied by a growing international collaboration. Main feasibility issues should be demonstrated until 2010 with the CLIC Test Facility (CTF3) constructed at CERN. The CLIC design parameters have recently been changed significantly. The rf frequency has been reduced from 30 GHz to 12 GHz and the loaded accelerating gradient from 150 MV/m to 100 MV/m. The consequences and logic of these changes will be reviewed and coherent parameter sets for a 3 TeV and a 500 GeV machine will be presented. The status and perspectives of the CLIC feasibility study will be presented with a special emphasis on experimental results obtained with CTF3 towards drive beam generation as well as progress on the high gradient accelerating structure development. The frequency change allows using high power X band test facilities at SLAC and KEK for accelerating structure testing at 11.4 GHz. The design gradient of 100 MV/m has been achieved in a recent test at SLAC with a very low breakdown-rate.
KEK, Ibaraki
The KEKB linac continuously injects 8 GeV electron and 3.5 GeV positron beams into the KEKB rings: HER(high energy ring) and LER(low energy ring). The energy spread of the 8-GeV electron beam, which is accelerated to an 1.7 GeV 180-degree arc section and reaccelerated after this arc to a final energy of 8 GeV, is optimized by adjusting rf acceleration phases so as to assure efficient injections. When rf phases are slightly changed or drifted for some reasons, the beam not only shows larger energy spreads but also indicates two clusters on a beam profile monitor located at large energy dispersions. In this connection, a longitudinal beam profile was measured after the arc section with a streak-camera system utilizing an OTR(Optical Transition Radiation) bunch monitor. The observed bunch shape clearly shows a two-microbunch structure, suggesting that it could be generated in the arc section. Various experimental data as well as some CSR-related speculations are presented.
JINR, Dubna, Moscow Region
JINR/LHE, Moscow
800 MeV electron linac (LINAC-800) is under construction at JINR. It will be used as a driver for Volume FEL and as a test bench for commissioning of elements of the ILC. Presently the electron injector is commissioned and the electron beam of 50 keV of the energy at current of about 15 mA was obtained. The results of the injector operation at nominal parameters (400 keV, 300 mA) and commissioning of the first accelerating section at 20 MeV are discussed.
SLAC, Menlo Park, California
UW-Madison/SRC, Madison, Wisconsin
Funding: The work of PE and JW was supported by the US Department of Energy under contract DE-AC02-76SF00515. The work of RAB and KJK was supported by National Science Foundation Award No. DMR-0537588.
For electron bunches driving a hard X-ray free electron laser, the electron bunch high qualities should be preserved as well as possible in the acceleration and compression. For typical configuration, the electron bunch is accelerated in rf cavity and compressed in magnetic chicane. Besides the rf curvature and high-order optics terms in a chicane, the collective effects during the bunch acceleration, transportation, and compression can further distort the phase space and even lead to instability. Among these collective effects, the coherent edge radiation dominates and governs the overall bunch property; while the longitudinal space charge is the main cause for microbunching instability. Random jitter couples to the wakefields and affect the final bunch properties. We study these effects and discuss their implication to general linac design and optimization.
UMAN, Manchester
The Hashemite University, Zarka
Based on Lienard-Weichert method of retarded potentials and the potential due to the image of charges on the cathode, a rigorous relativistic description of the beam transport inside the rf-photoinjector is presented. The velocity dependent effects are explicitly taken into account in a complete analytical description. Simulations are presented for parameters of the ELSA photo-cathode.
ANL, Argonne
Northern Illinois University, DeKalb, Illinois
Funding: This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC-02-06CH11357.
A prototype injector capable to produce multiple-charge-state heavy-ion beams is being developed at ANL. The injector consists of an ECR ion source, a 100 kV platform and a Low Energy Beam Transport (LEBT). The latter comprises two 60-degree bending magnets, electrostatic triplets and beam diagnostics stations. Several charge states of bismuth ions from the ECR have been extracted, accelerated to an energy of 1.8 MeV, separated and then recombined into a high quality beam ready for further acceleration. This technique allows us to double heavy-ion beam intensity in high-power driver linac for future radioactive beam facility. The other application is the post-accelerators of radioactive ions based on charge breeders. The intensity of rare isotope beams can be doubled or even tripled by the extraction and acceleration of multiple charge state beams. We will report the results of emittance measurements of multiple-charge state beams after recombination.
IUAC, New Delhi
The first module of the booster superconducting linear accelerator, consisting of a total of three modules, each having 8 quarter wave coaxial line bulk Nb resonators, has been commissioned at IUAC. During initial operation of the first linac module, the energy gain was found to be much lower due to various problems which are now identified and solved. After acceleration through the linac module and subsequent re-bunching using a superconducting Rebuncher, a 158 MeV silicon beam having pulse width of 400 ps was delivered to conduct nuclear physics experiments. The other two linac cryostats and the required 16 resonators to be installed in those two cryostats are in the final stage of fabrication. Work has progressed on a high current injector that would act as an alternate source of heavy ions for the superconducting linac. The first element of the high current injector is a high Tc superconducting magnet ECR source (PKDELIS) which would be followed by a room temperature radio frequency quadrupole accelerator and drift tube linac cavities. Prototypes of the RFQ working at 48.5 MHz, and that of the DTL working at 97 MHz, have been fabricated and are undergoing tests.
TRIUMF, Vancouver
PAVAC, Richmond, B.C.
The medium beta section of the ISAC-II superconducting linac (β=5.7% and 7.1%) has been operational since April 2006 providing 20 MV of accelerating potential at 106 MHz. The ‘high beta' extension to the linac, in progress, will see the addition of twenty 141 MHz quarter wave cavities at β=11%. The design specification calls for cw operation at a voltage gain of at least 1.1 MV/cavity for no more than 7 W of power dissipated in the cavity. This operation point corresponds to challenging peak surface fields of 30 MV/m and 60 mT. The cavity design is similar in concept to the medium beta cavities except for the addition of a drift tube to render symmetric the accelerating fields. A prototyping and qualification program was initiated with PAVAC Industries Inc. of Richmond, B.C. Two full size models in copper and two in niobium have been completed. The niobium cavities have been warm and cold-tested and characterized for frequency, rf performance and mechanical stability. The cold performance of both cavities exceeds the specification and the final frequency is within tuning range. The design, fabrication details and test results will be presented.
LANL, Los Alamos, New Mexico
NRL, Washington, DC
LLNL, Livermore, California
Stanford University, Stanford, Califormia
Beam-Wave Research, Inc., Union City
Funding: Supported by the High-Energy Laser Joint Technology Office
We are investigating spoke resonators that originally were proposed for moderate energy proton acceleration for application in high-average-current free-electron lasers (FEL). This structure holds the promise of alleviating the BBU limitations of conventional rf structures. Spoke resonator have several advantages: 1) strong coupling simplifies the access to higher order modes (HOM), 2) at the same frequency a spoke resonator is about half the size of an elliptical resonator, 3) the spokes provide additional mechanical stability and stiffening , 4) the power and HOM couplers can be attached to the cavity body and do not take up additional space along the length of the accelerator, 5) the presence of the spokes limits the polarizations of the HOMs to two orientations which facilitates the selection of HOM coupler positions. The rf performance of a spoke resonator specifically designed for high-current electron applications (beta=1.0) will be presented and compared with the expected performance of elliptical resonators designed for such applications. Besides the structure's effectiveness for acceleration also HOM properties will be presented.
JASRI/SPring-8, Hyogo-ken
The acceleration gradient is limited by breakdown in an accelerating rf structure, including its surface condition of the inner wall. The surface treatment is an important technique to achieve the maximal acceleration gradient of an accelerating structure. We chose chemical etching as a method of surface treatment for accelerating rf structures made of copper. To study rf breakdown and effect of surface treatments, we used a pillbox-type single cell rf gun cavity. The highest cathode surface field (190 MV/m) of rf gun cavity was accomplished with this surface treatment under rf-conditioning elapsed time (21 days) in 2004. SPring-8 rf gun has been operating with the highest gradient in the world. This indicates that our treatment is considerably effective to improve the inner cavity surface made of copper. Further, we developed the high-pressure chemical etching for more complicated inner structures in 2006. Using a cartridge-type photocathode rf gun, high-field experiments were performed with cathode plugs chemical etching treated under deferent pressure condition. We report these results on highest gradient, using test copper samples treated with high-pressure chemical etching.
KEK, Ibaraki
High-gradient experiments have been performed using a narrow waveguide that has a field of approximately 200 MV/m at an rf power of 100 MW. The study investigates the characteristics of different materials at high-gradient rf breakdown. This paper reports the results of high-gradient experiments and observations of the surface of stainless-steel waveguides.
SLAC, Menlo Park, California
Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.
We report on the L-band rf power distribution system (PDS) developed at SLAC for Fermilab's NML superconducting test accelerator facility. The makeup of the system, which allows tailoring of the power distribution to cavities by pairs, is briefly described. Cold test measurements of the system and the results of high power processing are presented. We also investigate the feasibility of eliminating the expensive, lossy circulators from the PDS in the ILC linacs by taking advantage of our scheme of pair-feeding through 3-dB hybrids. A computational model is used to simulate the impact on field stability of inter-cavity coupling due to reduced isolation. Measurements of typically achievable hybrid port isolations provide the likely magnitude for such coupling.
JLAB, Newport News, Virginia
Muons, Inc, Batavia
Funding: Supported in part by DOE STTR grant DE-FG02-05ER86253
Neutrino Factories and Muon Colliders require rapid acceleration of short-lived muons to multi-GeV and TeV energies. A Recirculated Linear Accelerator (RLA) that uses a single Linac and teardrop return arcs (the so called 'Dogbone' RLA) can provide exceptionally fast and economical acceleration to the extent that the focusing range of the RLA quadrupoles allows each muon to pass several times through each high-gradient cavity. Since muons are generated as a tertiary beam they occupy large phase-space volume and the accelerator must provide very large transverse and longitudinal acceptances. The above requirements drive the design to low rf frequency. A new concept of rapidly changing the strength of the RLA focusing quadrupoles as the muons gain energy is being developed to increase the number of passes that each muon will make in the rf cavities, leading to greater cost effectiveness. We are developing the optics and technical requirements for RLA designs, using superconducting rf cavities capable of simultaneous acceleration of both μ+ and μ- species, with pulsed Linac quadrupoles to allow the maximum number of passes.