beam-command.asciidoc



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Table of Contents


1. Beam Command

1.1. Particle Definition
1.2. Beam Energy
1.3. Other Attributes
1.4. References


1. Beam Command


All OPAL commands working on a beam require the setting of various
quantities related to this beam. These are entered by a BEAM command:


label:BEAM, PARTICLE=name, MASS=real, CHARGE=real,
      ENERGY=real, PC=real, GAMMA=real, BCURRENT=real,
      NPART=real, BFREQ=real;


The label is optional, it defaults to UNNAMED_BEAM.


1.1. Particle Definition

The beam particle is defined by PARTICLE attribute, which includes a
direct assignment of the particle mass and charge, as indicated below. The
mass values are taken from Atomic Mass Data Center [1] and Kinetic
Database [2]. In the case of heavy ion beams, it is
important to note that a specific type of fully ionized isotope are considered.
The mass of the ions is calculated by subtracting the mass of the electrons and
the binding energy [3] from the atomic mass. For other type
of particle beams, this attribute must not be used. Instead, the particle beam
is defined by means of MASS and CHARGE attributes specified by the user.


PARTICLE

The name of particles in the machine.

OPAL knows the mass (see Predefined Symbolic Constants)
and the charge for the following particles:


ELECTRON

The particles are electrons
(MASS = m_e, CHARGE = -1).

POSITRON

The particles are positrons
(MASS = m_e, CHARGE = +1).

MUON

The particles are of type muon
(MASS = m_\mu, CHARGE = -1).

PROTON

The particles are protons
(MASS = m_p, CHARGE = +1).

ANTIPROTON

The particles are anti-protons
(MASS = m_p, CHARGE = -1).

DEUTERON

The particles are of type deuteron
(MASS = m_d, CHARGE = +1).

HMINUS

The particles are negative hydrogen ions (H^-)
(MASS = m_{hm}, CHARGE = -1).

H2P

The particles are molecular hydrogen ions (H_2^+)
(MASS = m_{h2p}, CHARGE = +1).

ALPHA

The particles are of alpha particles
(MASS = m_{\alpha}, CHARGE = +2).

CARBON

The particles are fully-stripped carbon-12 ions
(MASS = m_c, CHARGE = +6).

XENON

The particles are fully-stripped xenon-129 ions
(MASS = m_{xe}, CHARGE = +54).

URANIUM

The particles are fully-stripped uranium-238 ions
(MASS = m_u, CHARGE = +92).


For other particle types one may enter:


MASS

The particle mass in GeV.

CHARGE

The particle charge expressed in elementary charges.


1.2. Beam Energy

To specify the energy there are three attributes (in order of priority):


GAMMA

The particle energy divided by its mass.

ENERGY

The particle energy in GeV.

PC

The particle momentum in GeV/c.


1.3. Other Attributes

The other attributes are:


BFREQ

The bunch frequency in MHz.

BCURRENT

The bunch current in A.
\mathrm{BCURRENT} = Q \times \mathrm{BFREQ}
with Q the total charge.

NPART

The number of macro particles for the simulations

NSLICE

The number of slices per bunch

MOMENTUM_TOLERANCE

Fractional tolerance to deviations in the distribution compared to the reference momentum at initialisation. If ⇐ 0, no tolerance checking is done (default=1e-2).


1.4. References


[1] M. Wang et al., The AME 2020 atomic mass evaluation (II). Tables, graphs and references, Chinese Phys. C, 45, 030003 (2021). Atomic Mass Data Center, Atomic Mass Evaluation - AME2020.


[2] Kinetic Database for Astrochemistry.


[3] NIST Atomic Spectra Database Ionization Energies Form, Atomic Spectra Database, NIST Standard Reference Database 78 (Version 5.9).