Tech-X, Boulder, Colorado
KEK, Ibaraki
BNL, Upton, Long Island, New York
Funding: Supported in part by the DOE Office of Science, Office of Nuclear Physics under grant No. DE-FG02-06ER84508.
Non-scaling FFAGs are sensitive to a slew of resonances during the acceleration ramp. An important consideration - because it affects the amount of rf power required - will be the speed at which resonances must be crossed. We present simulations of possible non-scaling FFAGs, focusing especially on the effects of space charge, using newly developed capabilities in the code PTC*.
* E. Forest, Y. Nogiwa, F. Schmidt, "The FPP and PTC Libraries", ICAP'2006.
Tech-X, Boulder, Colorado
Funding: Supported by the US DOE Office of Science, Office of Nuclear Physics under grant DE-FG02-06ER84508.
The design of an accelerator with a large energy acceptance requires careful consideration of fringe-field effects*. This applies particularly to the design of fixed-field alternating gradient (FFAG) accelerators. We consider magnets in straight and curved geometries, and with multipole or mid-plane symmetries. The longitudinal magnet profiles we consider include a simple hyperbolic tangent and a more realistic six-parameter Enge function. We show that when the fields are modeled using power series expansions in a transverse parameter, the domain of convergence is determined by the fringe-field decay length. We also demonstrate the use of these models in the tracking code PTC**.
*M. Berz, B. Erdelyi, and K. Makino, "Fringe field effects in small rings of large acceptance", PRSTAB 3, 124001, 2000
**E. Forest, Y. Nogiwa, F. Schmidt, "The FPP and PTC Libraries",ICAP'2006
Tech-X, Boulder, Colorado
KEK, Ibaraki
BNL, Upton, Long Island, New York
Funding: Supported in part by the DOE Office of Science, Office of Nuclear Physics under grant No. DE-FG02-06ER84508.
Recent simulations of non-scaling FFAGs suggest that the effects of magnet fringe fields are of signal importance. We present PTC* simulations that include realistic models for the fringes. In particular, we study how fringe extent and other parameters affect important measures of machine performance.
*E. Forest, Y. Nogiwa, F. Schmidt, "The FPP and PTC Libraries", ICAP'2006.
Tech-X, Boulder, Colorado
BNL, Upton, Long Island, New York
Funding: Supported by the US DOE Office of Nuclear Physics under grants DE-FC02-07ER41499 and DE-FG02-04ER84094; used NERSC resources under grant DE-AC02-05CH11231.
Magnetic field errors can limit the dynamical friction force on co-propagating ions and, hence, increase the cooling time. We present theoretical and numerical results for reduction of the friction force due to bounded transverse magnetic field errors, as a function of wavelength. VORPAL * simulations using a binary collision algorithm ** show that small-wavelength field errors affect the friction logarithmically, via the Coulomb log, while long-wavelength errors reduce the friction by effectively increasing the transverse electron temperature. A complete understanding of finite-time effects and the role of small impact parameter collisions is required to correctly interpret the simulation results. We show that the distribution of electron-ion impact parameters is similar to a Pareto distribution, for which the central limit theorem does not apply. A new code has been developed to calculate the cumulative distribution function of electron-ion impact parameters and thus correctly estimate the expectation value and uncertainty of the friction force.
* C. Nieter and J. Cary, J. Comp. Phys. 196 (2004), p. 448.
** G. Bell et al., J. Comp. Phys. 227 (2008), p. 8714.