TRIUMF, Vancouver
The replacement of the 30-year-old Philips cryogenerator with a modern LINDE-1630 helium refrigerator is an important component of TRIUMF’s ongoing 500 MeV cyclotron refurbishing program. Two 10.7 m long cryopanels are cooled with liquid helium rather than with 17 K helium gas, as was the case with the cryogenerator. This has increased the pumping speed and, respectively, improved the vacuum in the approximately 100 m3 cyclotron tank. Additionally, the thermal shield, previously cooled with helium gas, is now cooled with liquid nitrogen. These changes have resulted in increased reliability of the cyclotron vacuum system and, consequently, longer operation periods without maintenance. The new refrigeration unit was commissioned in September 2007. The results from over one year of operational experience are discussed. Also, data on hydrogen cryopumping is presented.
CIAE, Beijing
TRIUMF, Vancouver
The design and cryo-test system of a plug-in cryopump used in CYCIAE-100 is introduced. The plug-in cryopump consists of two cryopanels, a baffle, a half-opened shield, and two GM refrigerators (CGR411, CVI) which power is 83W/80K at the first stage and 7.5W/20K at the second stage, its designed pumping speed is 15000L/s. Cryo-test system of plug-in cryopump employs the flux method to test pumping speed, cool-down time, ultimate pressure, temperature distribution on cryopanel and capacity at the pressure of 10-6Pa to 1Pa. The heat load calculation of cryopanel and shield including baffle is conducted in succession. In the end a comparison between design parameters and test results is drawn.
TRIUMF, Vancouver
DAE/VECC, Calcutta
TRIUMF (Canada) and VECC (India) are planning to each build a 1.3GHz 50MeV/500kW superconducting electron linac as a driver for producing radioactive ion beams through photo-fission. The two institutes have launched a collaboration with the initial goal to design, build and test a 5-10MeV superconducting injector cryomodule capable of accelerating up to 10mA. A testing area is being set-up at TRIUMF to house the electron gun, rf buncher, injector cryomodule, diagnostic station and beam-dump for beam studies. The project will test all critical elements of the final linac; beam halo generation, HOM excitation, LLRF and rf beam loading and cavity and cryomodule design/performance. The scope and status of the project will be described.
TRIUMF, Vancouver
PAVAC, Richmond, B.C.
The ISAC-II heavy ion linear accelerator has been in operation at TRIUMF since 2006. The high beta section of the accelerator, consisting of twenty cavities with optimum beta=0.11, is currently under production and is scheduled for completion in 2009. The cavities are superconducting bulk Niobium two-gap quarter-wave resonators with a frequency of 141 MHz, providing, as a design goal, a voltage gain of Veff=1.08 MV at 7 W power dissipation. Production of the cavities is with a Canadian company, PAVAC Industries of Richmond, B.C. after two prototype cavities were developed, produced and successfully tested. Cavity production details and test results will be presented and discussed.
TRIUMF, Vancouver
LPSC, Grenoble
Most ion sources at ISOL (isotope separation on-line) facilities can produce only singly charged ions but efficient post acceleration requires high charge states. For light ions this can be achieved by stripping after a first moderate acceleration but with heavy ions this is no longer possible and charge state breeding is necessary. The breeder should be able to work at a high efficiency for the required charge state and especially for short-lived radioactive isotopes the process should be fast. For the ISAC facility at TRIUMF an ECRIS charge breeder (14 GHz PHOENIX from Pantechnik) has been chosen as it is well adapted to the continuous mode operation of the accelerator and for radioactive ions there is practically no limit for the beam intensity. After off-line optimization on a test bench the source has been moved on-line to the ISAC facility. Mass separated beams of radioactive ions from the on-line ion sources can be directed into the source. During a first test in fall 2008 a beam of 80Rb14+ was successfully created from 80Rb1+ and accelerated by the ISAC post accelerator. A summary of the results from the test bench and from the on-line commissioning will be presented.
TRIUMF, Vancouver
DAE/VECC, Calcutta
A 0.5 megawatt electron linear accelerator is being designed at TRIUMF in support of its expanding rare isotope program, which targets nuclear structure and astrophysics studies as well as material science. The first stage of the project, a 25 MeV, 5 mA, cw linac matching the isotope production target power-handling capability in the next five-year plan, is planned to be completed in 2013. The injector cryomodule development, which is being fast tracked, is the subject of a scientific collaboration between TRIUMF and the VECC laboratory in Kolkata, India. The paper gives an overview of the accelerator design progress.
TRIUMF, Vancouver
In the TRIUMF cyclotron when a spark occurs it is necessary to shut off the RF drive and to initiate a RF restart procedure. It is also desirable to restore the full operational dee voltage as soon as possible in order to prevent thermal detuning of the resonant cavity. However, when the RF drive is shut off, the disappearance of Lorentz force on the resonator hot-arms causes the hot-arms to vibrate at their mechanical resonant frequency. When the RF field is being restored, the electromagnetic resonance is coupled to the mechanical resonance through the Lorentz force, and the amplitudes of both the mechanical vibration and the RF field depend on the timing when RF drive is re-applied. Computer simulations and experimental results will be presented to demonstrate that an optimum exists as to when to initiate the RF restart. With this optimal timing, the Lorentz force is used to damp the mechanical vibrations of the hot-arms. The reduction in hot-arm vibrations increases the probability of successful restarts as well as reduces the stress on the RF components.
TRIUMF, Vancouver
An energy upgrade in the Radioactive Ion Beam (RIB) facility at ISAC-II will see the installation of 20MV of superconducting heavy ion linac. The addition includes twenty beta=11% bulk niobium quarter wave cavities housed in three cryomodules with six cavities in the first two and eight cavities in the last. Each cavity is specified to add 1MV in accelerating potential corresponding to peak surface fields of ~30MV/m. Transverse focusing is achieved with a 9T superconducting solenoid inside each cryomodule. The first module in the expansion has now been assembled and tested. Developments include a new ball screw tuner, locally produced cavities, modified coupler design and LN2 cryogenic circuits. The new developments are described and the results of the first cold tests are presented.
University of Pennsylvania, Philadelphia, Pennsylvania
TRIUMF, Vancouver
The quality factor of superconducting radio-frequency cavities typically degrades with increasing field at moderate gradients before the on-set of field emission. The origin of the so called medium field Q-slope is not fully described and understanding it would be important in order to develop a cavity design or treatment which minimizes this effect, allowing us to produce cavities with reduced cryogenic losses. This paper will present an analysis of the medium field Q-slope data measured on cavities at different frequencies treated with buffered chemical polishing (BCP) at TRIUMF. The data is compared with existing models and agreements-discrepancies will be highlighted.
TRIUMF, Vancouver
The rf control system for the 1.3 GHz TRIUMF e-linac elliptical superconducting cavities is a hybrid analogue/digital design. It is based in part on an earlier design developed for the 1/4 wave superconducting cavities of the ISACII linac. This design has undergone several iterations in the course of its development. In the current design, down-conversion to an intermediate frequency of 138MHz is employed. The cavity operates in a self-excited feedback loop, while phase locked loops are used to achieve frequency and phase stability. Digital signal processors are used to provide amplitude and phase regulation, as well as mechanical cavity tuning control. This version also allows for the rapid implementation of operating firmware and software changes, which can be done remotely, if the need arises. This paper describes the RF control system and the experience gained in operating this system with a single-cavity test facility.
TRIUMF, Vancouver
DAE/VECC, Calcutta
TRIUMF proposes a 1/2 MW electron linac (e-linac) for radioactive ion beam production via photofission. The e-linac is to operate CW using 1.3 GHz superconducting (SC) technology. The accelerator layout consists of a 100 keV thermionic gun, a normal conducting buncher, an injector module, and main linac modules accelerating to a final energy of 50 MeV. The design beam current is 10 mA. The beam dynamics of the injector, where electrons make the transition to the fully relativistic state, has been identified as the most critical part of the design and is the subject of simulations (starting at the gun cathode) using realistic EM fields in PARMELA and TRACK. CW operation demands the novel choice of adopting an SC capture section. A preliminary design of the injector foresees a capture section composed either of two independent or two coupled single-cell cavities, beta <1, that increase the energy to about 500 keV, followed by one nine-cell cavity that boosts the energy up to 10 MeV. The design parameters are subjected to a global optimization program. In this paper we present results from the beam dynamics study as well as details and final outcome of the optimization process.
TRIUMF, Vancouver
Funding: TRIUMF receives funding via a contribution agreement through the National Research Council of Canada.
The TRIUMF cyclotron is 6-fold symmetric, but has a 3rd harmonic magnetic field gradient error. As well, there is a 3rd harmonic component generated from the beating of the primary harmonics with the 9th harmonic. Both can contribute and drive the nur=3/2 resonance. As a consequence, the radial phase space ellipses become stretched and mismatched; this introduces a radial modulation of beam density and thereby causes a sensitivity of the extracted current to, for example, small changes in rf voltage. The cyclotron has "harmonic" correction coils, but these were designed to generate a first harmonic, not a third harmonic. Their 6-fold symmetric layout can only generate a 3rd harmonic at one particular phase and so can only partially compensate for this resonance. For a complete compensation, the 6 pairs of this harmonic coil would have to shift in azimuth by ~30degr. This paper describes the simulations performed with COMA to study the effect of this resonance. Initial measurement results are also presented.
TRIUMF, Vancouver
SFU, Burnaby, BC
UBC, Vancouver, B.C.
Funding: TRIUMF receives funding via a contribution agreement through the National Research Council of Canada.
For ISAC at TRIUMF, radioactive isotopes are generated with a 500MeV proton beam. The beam power is up to 40kW and can easily melt the delicate target if too tightly focused. We protect this target by closely monitoring the distribution of the incident proton beam. There is a 3-wire scanner monitor installed near the target; these give the vertical profile and the +45 and -45 degree profiles. Our objective is to use these 3 measured projections to find the 2-D density distribution. By implementing the maximum entropy (MENT) algorithm, we have developed a computer program to realize tomographic reconstruction of the beam density distribution. Of particular concern is to make the calculation sufficiently efficient that an operator can obtain the distribution within a few seconds of the scan. As well, we have developed the technique to perform phase space reconstruction, using many wire scans and the calculated transfer matrices between them. In this paper we present details of the computer code and the techniques used to improve noise tolerance and compute efficiency.
TRIUMF, Vancouver
Injection from an external ion source into a cyclotron results in unavoidable emittance growth when the cyclotron's pole gap is not small compared with the first turn radius. In such a congested geometry, the injected beam first has the two transverse directions coupled on entering the axial magnetic field of the cyclotron, then transverse and longitudinal phase spaces are coupled by the inflector. Generally, to avoid loss, the beam is focused tightly through the inflector. It thus arrives at the first turn strongly mismatched because the vertical focusing in such a cyclotron is rather weak (vertical tune < 0.3). Space charge exacerbates the mismatch because it depresses the vertical tune further. Emittance growth from all these effects can be calculated using the full Sacherer 6D envelope formalism. We develop the technique to include cyclotrons and in particular the transverse optics of the rf gaps, and apply it in particular to the re-design of the TRIUMF 300 keV vertical injection line.
TRIUMF, Vancouver
Fixed-Field Alternating-Gradient (FFAG) accelerators span a large range of momenta and have markedly different reference orbits for each momemtum. In the non-scaling (NS) versions proposed for rapid acceleration, the orbits are geometrically dissimilar. In particular, none of the orbits within bending magnets are arcs of circles and this complicates tune calculation. One approach to NS-FFAG design is to employ alternating combined-function magnets. Second generation NS-FFAGs designs attempt to mitigate the variation of betatron tunes; and careful calculation of orbits and tunes is essential. Starting from an analytic magnetic potential for the combined-function magnet, we elucidate expressions for orbit calculation which are second order in the cyclotron motion and arbitrary order in the momentum (no expansion is used).
UBC & TRIUMF, Vancouver, British Columbia
It is sometimes asserted that Thomas's proposal to provide additional axial focusing in cyclotrons (to enable them to operate isochronously at relativistic energies) by introducing an azimuthal variation in the magnetic field was an early example of alternating-gradient focusing. While Thomas cyclotrons certainly exhibit alternating field gradients, it is shown that the alternating focusing produced is very much weaker than the edge focusing (everywhere positive) arising from orbit scalloping.
UBC & TRIUMF, Vancouver, British Columbia
TRIUMF, Vancouver
This paper describes tracking studies of FFAGs and radial-sector cyclotrons with reverse bends using the cyclotron equilibrium orbit code CYCLOPS. The results for FFAGs confirm those obtained with lumped-element codes, and suggest that cyclotron codes will prove to be important tools for evaluating the measured fields of FFAG magnets. The results for radial-sector cyclotrons show that the use of negative valley fields would allow axial focusing to be maintained, and hence allow intense cw beams to be accelerated, to energies of the order of 10 GeV.
TRIUMF, Vancouver
The ISAC facility, located at TRIUMF, first began delivering radioactive ion beams (RIBs) in 1998, added post-accelerated beam capability in 2001, and is regarded as one of the premiere RIB facilities in the world. The existing constraints on RIBs of Z<83 and accelerated beams of A/q<30 with energies limited to 5MeV/u are being addressed. A charge-state booster for RIBs has been commissioned to alleviate the A/q<30 restriction and has successfully delivered multi-charge beams through the ISAC accelerators. The 5MeV/u license limit will be removed once an on-line beam monitor is commissioned, allowing beams of up to 11MeV/u to be delivered presently, and increased to over 20MeV/u when the next accelerator phase is installed. In 2008, an actinide target was used to produce RIBs of Z>82; this successful test was performed on a uranium target with yields measured and radiation safety monitored. A new Beam Delivery group has been formed to integrate all aspects of RIB production, which has led to improved efficiency and greater experimental results. These new capabilities will be presented, showing how 2009 promises to be both an exciting and productive year at ISAC.