Linear accelerators

The highest-power operational proton linear accelerator is that of Los Alamos Meson Factory (LAMPF).

The LAMPF accelerator. The LAMPF accelerator accelerates protons up to 800 MeV. It is 800 m long. It provides 1ms bunches of protons with an intensity of 15 mA and with a repetition rate of 120 Hz. Correspondingly its duty cycle is 12%, and its average beam power 1.4 MW.

The accelerator comprises three parts:

1. The source and injector. The source can provide either H+ or H~ ions. The largest intensity of 30 mA is obtained with the H+ ions. The ions are accelerated at 750 kV by a Cockroft-Walton electrostatic accelerator. The continuous beam is then bunched at 201.25 MHz.

2. The 0.75 MeV protons are injected into a drift tube Linac (DTL or Alvarez). The DTL is 16.7m long. It accelerates protons up to 100 MeV. It works at a 201.25 MHz frequency. The Q value of the accelerating structures reaches 5 x 104. The drift tubes are enclosed in three tanks. Each tank shelters 165 drift tubes. Each tank is fed with an RF unit with 2.7 MW peak power. Beam focalization is achieved with 135 quadrupoles arranged in the focusing-defocusing-focusing-defocus — ing (FDFD) mode.

3. The 100 MeV protons are further accelerated up to 800 MeV in a side — coupled Linac (SCDTL). This is 726.9 m long. It works at a 805 MHz frequency. Only one out of four micro bunches is filled with particles. The Q value of the accelerating structures reaches 2.4 x 104. The 5000 cavities are enclosed in 104 tanks. The RF power is provided by 44 units with 1.25 MW peak power each. Beam focalization is achieved with 204 quadrupoles arranged in doublets.

The main characteristics of LAMPF are given in table 6.2. From the value of the shunt resistance and the phase angle of 64°, using equation (16.22) of Appendix III,

V2

P = ^ (6.21)

2Psh

one obtains a thermal RF power of approximately 10 MW, to be compared with a beam power of 12 MW,[44] and thus an RF-to-beam efficiency of 55%. The total power of the RF power units amounts to 65 MW, which gives a line-to-RF efficiency of 34% and a line-to-beam efficiency of 19%.