source: PSPA/madxPSPA/doc/usrguide/Introduction/cavity.html @ 430

Last change on this file since 430 was 430, checked in by touze, 11 years ago

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1<head>
2<title>RFCAVITY</title>
3<!-- Changed by: Chris ISELIN, 27-Jan-1997 -->
4<!-- Changed by: Hans Grote, 30-Sep-2002 -->
5</head>
6
7<body bgcolor="#ffffff">
8
9<center>
10EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH
11<IMG SRC="http://cern.ch/madx/icons/mx7_25.gif" align=right>
12<h2>RF Cavity</h2>
13</center>
14
15<pre>
16label: RFCAVITY, L=real,VOLT=real,LAG=real,HARMON=integer,FREQ=real;
17                  <!-- HARMON=integer, BETRF=real,PG=real,
18                 FREQ=real,SHUNT=real,TFILL=real; -->
19</pre>
20An RFCAVITY has eight real attributes and one integer attribute:
21<ul>
22<li>L:
23The length of the cavity (DEFAULT: 0 m)
24<li>VOLT:
25The peak RF voltage (DEFAULT: 0 MV).
26The effect of the cavity is
27<p>
28delta(<i>E</i>) = VOLT * sin(2 pi * (LAG - HARMON * <i>f<sub>0</sub> t</i>)).
29<p>
30<li>LAG:
31The phase lag [2pi] (DEFAULT: 0).
32<li>FREQ:
33The frequency [MHz] (no DEFAULT).
34Note that if the RF frequency is not given, it is
35computed from the harmonic number
36and the revolution frequency <i>f<sub>0</sub></i> as before. However,
37for accelerating structures this makes no sense,
38and the frequency is mandatory.
39<li>HARMON:
40The harmonic number <i>h</i> (no DEFAULT). Only if the frequency is not given.
41<!-- <li>BETRF:
42RF coupling factor (DEFAULT: 0).
43<li>PG:
44The RF power per cavity (DEFAULT: 0 MW).
45<li>SHUNT:
46The relative shunt impedance (DEFAULT: 0 MOhm/m).
47<li>TFILL:
48The filling time of the cavity T<sub>fill</sub>
49(DEFAULT: 0 microseconds). -->
50<li><font color=ff0000><i> Please take note, that the following
51MAD8 attributes: BETRF, PG, SHUNT and TFILL are currently not
52implemented in MAD-X!</i><
53<li><i> Note as well that twiss is 4D only. As a consequence the TWISS
54parameters in the plane of non-zero dispersion may not close as
55expected. Therefore, it is best to perform TWISS in 4D only, i.e. with
56cavities switched off. If 6D is needed one has to use the
57<a href="../ptc_twiss/ptc_twiss.html">ptc_twiss</a> command.
58</i></font>
59</ul>
60
61The RFCAVITY has attributes that will only become active in PTC:
62<ul>
63<li>n_bessel (DEFAULT: 0): <p>
64Transverse focussing effects are typically ignored in the cavity in
65MAD-X or even PTC. This effect is being calculated to order n_bessel,
66with n_bessel=0 disregarding this effect and with a correct treatment
67when n_bessel goes to infinty.
68<li>no_cavity_totalpath (DEFAULT: no_cavity_totalpath=false):<p>
69flag to choose if in a cavity the transit time factor is considered
70(no_cavity_totalpath=false) or if the particle is kept on the crest of
71RF voltage (no_cavity_totalpath=true).
72</ul>
73
74A cavity requires the particle energy
75(<a href="beam.html#energy">ENERGY</a>)
76and the particle charge
77(<a href="beam.html#charge">CHARGE</a>)
78to be set by a <a href="beam.html">BEAM</a> command
79before any calculations are performed.
80<p>
81Example:
82<pre>
83BEAM,PARTICLE=ELECTRON,ENERGY=50.0;
84CAVITY:   RFCAVITY,L=10.0,VOLT=150.0,LAG=0.0,HARMON=31320;
85</pre>
86The <a href="local_system.html#straight">straight reference system</a>
87for a cavity is a cartesian coordinate system.
88<p>
89<address>
90<a href="http://www.cern.ch/Hans.Grote/hansg_sign.html">hansg</a>,
91January 24, 1997
92</address>
93
94</body>
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