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Stabilization of long chains:<br />

the π/2 <strong>mode</strong><br />

Solution:<br />

Long chains of linac cells are operated in the π/2 <strong>mode</strong> <strong>mode</strong>, which is<br />

intrinsically insensitive to differences in the cell frequencies.<br />

Perturbing<br />

<strong>mode</strong><br />

ω<br />

0 6.67 13.34 20.01 26.68 33.35<br />

0<br />

π/2<br />

π<br />

k<br />

Operating<br />

<strong>mode</strong><br />

Perturbing<br />

<strong>mode</strong><br />

<strong>mode</strong> π/2<br />

2 2<br />

Contribution from adjacent <strong>mode</strong>s proportional to f − f with the sign !!!<br />

Contribution from equally spaced <strong>mode</strong>s in the dispersion curve will cancel<br />

each other.<br />

1<br />

0<br />

46

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