Choice of the accelerator type: Linac versus cyclotron

In principle both accelerator types can deliver the required proton beam for ADS applications. However, the nature of each — one compact unit for an isochronous cyclotron, a sequential modular structure for the linac — brings both advantages and disadvantages.

Due to its recirculation nature, a cyclotron is compact and cost effective. However, it lacks every form of redundancy which is crucial for fault tolerance. Hence, a cyclotron will not reach the wanted level of availability, and furthermore an upgrade of its beam energy is not a realistic option.

Linacs on the other hand, can be built as a sequence of many independent accelerating structures (RF cavities), which is a highly modular situation. It is this modularity that makes such a linac particularly well suited to tackle the availability issue. In case of failure of a single accelerating module, independently controlling the RF amplitude and phase of the adjacent modules creates the conceptual possibility of recovering the beam within a short time. Furthermore, increasing the final beam energy is obtained by merely adding accelerating modules.

For these reasons MYRRHA favours the linac option.


Linac versus cyclotron

Large space requirement (few hundred m long) but light Compact but heavy
Expensive  Cheaper in construction
Less efficient power conversion More efficient power conversion
Modularity provides redundancy No intrinsic redundancy
Upgradable in energy Difficult to upgrade in energy
Straightforward beam extraction  Difficult extraction and related beam losses
Capable of high beam current (100 mA) Modest beam current capability (5 mA)