Quiet start and autotasking for PARMELA

The simulation code PARMELA has been widely used in the accelerator community for many years. Because of its simplicity, it is still used in many laboratories. When used to simulate the space charge in high current density electron bunches however, the results for the emittance and the other beam parameters can differ considerably from those obtained with PIC codes. This discrepancy comes in part from the noise introduced by the point to point space charge calculation used in PARMELA, when the particle distribution is not uniform. Here we present a new loading scheme which makes the initial distribution in the phase spaces more uniform and reduces greatly the noise introduced by artificial local bunching. At the same time, the code has been slightly modified in order to permit autotasking and vectorization on CRAY computers; the speed up factor obtained for the calculation time is proportional to 4 times the number of CPU available on the computer. Preliminary-simulations of a 17 GHz RF Gun with the PIC code MAGIC and PARMELA show relatively good agreement considering that PARMELA does not handle Wakefields and radiations.<
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