Effect of Numerical Noise on Beam Emittance Growth in Pic Code*

In particle-in-cell (PIC) simulation, errors in space charge forces are of random character. It results in an unphysical increase of effective beam emittance, even while symplectic integrator is used. To establish quantitative measure of this effect on beam dynamics, an analytical model of equilibrium beam affected by random errors in space charge field calculations is considered. An explicit expression connecting beam emittance growth with beam brightness, integration step and the value of random error in space charge field is discussed.