An 8 GeV Linac as the Booster Replacement in the Fermilab Power Upgrade: a Snowmass 2021 White Paper

Following the PIP-II 800 MeV Linac, Fermilab will need an accelerator that extends from that linac to the MI injection energy of ~8 GeV, completing the modernization of the Fermilab high-intensity accelerator complex. This will maximize the beam available for neutrino production for the long baseline DUNE experiment to greater than 2.5 MW and enable a next generation of intensity frontier experiments. In this white paper, we propose an 8 GeV Linac for that purpose. The Linac consists of an extension of the PIP-II Linac to 2.4 GeV using PIP-II 650 MHz SRF cryomodules, followed by a 2.4-->8.0 GeV Linac composed of 1300 MHz SRF cryomodules, based upon the LCLS-II cryomodules developed at Fermilab. The 8 GeV Linac will incorporate recent improvements in SRF technology. The research needed to implement this Linac is described.Comment: contribution to Snowmass 202

An 8 GEV Linac As The Booster Replacement In The Fermilab Power Upgrade

Increasing the Fermilab Main Injector (MI) beam power above ~1.2 MW requires replacement of the 8 GeV Booster by a higher intensity alternative. Earlier, rapid-cycling synchrotron and linac solutions were considered for this purpose. In this paper, we consider the linac version that produces 8 GeV H- beam for injection into the Recycler Ring (RR) or MI The new linac takes ~1 GeV beam from the PIP-II linac and accelerates it to ~ 2 GeV in a 650 MHz SRF linac, and then accelerates to ~8 GeV in an SRF pulsed linac using 1300 MHz cryomodules. The linac components incorporate recent improvements in SRF technology. This Booster Replacement linac (BRL) will increase MI beam power to DUNE to more than 2.5 MW and enable next-generation intensity frontier experiments.Comment: arXiv admin note: text overlap with arXiv:2203.0505

new evidence for thermal boundary resistance effects in superconducting 6 ghz cavities

Thermal boundary resistance and, more specifically, Kapitza resistance effects have been often considered as a possible source of "non ideal" superconducting accelerating cavity behavior, through the formation of a temperature difference between the inner cavity superconducting surface and the helium bath. However, in the present literature the general reported assessment is that such effects could be neglected, at least at low or moderate input power. In this communication we present new data on small test bulk Nb 6Ghz cavities, showing that when the cavity surface resistance (or the Q) is plotted as a function of the temperature at constant input power, a clear anomaly occurs at the Helium superfluid transition point Tλ reflecting the abrupt change of the thermal boundary resistance at that temperature. The data analysis shows that this anomaly is consistent with the typically measured values of the thermal boundary (Kapitza) resistance. Implications on the cavity optimization strategy are finally discussed