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By using superconducting material to form the RF cavities, the efficiency of the accelerator is greatly improved. To remain superconducting, the cavities must be held at 2° K, which requires they be mounted inside cryomodules that provide heat insulation and refrigeration.
|Superconducting RF cavities are now commercially available.||Cryomodules in the Spallation Neutron Source at Oak Ridge National Laboratory.|
Further improvements in accelerator efficienty come from using magnetrons to power the RF cavities. Magnetrons are inherently oscillators, which makes it difficult to use many of them in an accelerator, as they normally oprerate independently, with different frequencies and phases. Recent innovations by Muons, Inc. have developed magnetrons that can be locked in frequency and phase to a low-level RF signal, with fine control over amplitude – just what is needed to use them to power an accelerator. These magnetrons are more efficient than traditional RF power supplies (klystrons, IOTs, and solid-state amplifiers). We expect the overall accelerator efficieny, from wall plug to beam power, to be about 50% – much higher than current designs (this includes the cryogenics).
The superconducting accelerator at the Spallation Neutron Source at ORNL generates 1.2 MegaWatts of beam power. But it operates at a 6% duty factor (i.e. beam is present only 6% of the time). Increasing the duty factor to 100% (i.e. continuous operation) is straightforward, as it does not affect the per-bunch beam dynamics. The Mu*STAR accelerator will use protons, not H-, significantly reducing losses and making this practical.