[knzhou]

This is a new proposal, fresh on the arXiv today, from a group of U.S. particle physicists. The introduction is very readable and lays out the mission clearly:

> We can now confidently claim that the “Standard Model” of particle physics (SM) is established. At the same time, we are more and more strongly persuaded that this SM is incomplete. [...] It is now common to describe the SM as an “effective” theory that should be derived from some more fundamental theory at higher energies. But we have almost no evidence on the properties of that theory.

> Our successes have become a liability in reaching this goal. Scientists from other fields now have the impression that particle physics is a finished subject. They question our motivations to go on to explore still higher energies. The scale of an energy frontier collider is also challenging to the young people in our field. They need to see qualitatively new capabilities realized during their active scientific careers. [...] That is where the urgency lies.

> [T]he entire C3 program could be sited in the United States. With the cancellation of the Superconducting Super Collider and the end of Tevatron operations the US has largely abandoned construction of domestic accelerators at the energy frontier. C3 offers the opportunity to realize an affordable energy frontier facility in the US. This may be crucial to realize a Higgs factory in the near term, and it will also position the US to lead the drive to the next, higher energy stage of exploration.

The main innovation is that they propose to use non-superconducting cavities, which allow much higher accelerating fields, cooled to increase their quality factor. The resulting shorter length dramatically decreases the cost, to an estimated $4 billion, which is 80% to 90% less than other proposals. Of course, $4 billion is no small amount of money, but for perspective that's about equal to the monthly budget of the National Institutes of Health, a third of the cost of the James Webb Space Telescope, or 2% of the total cost of the space shuttle.

[jamesmaniscalco]

I would expand on this to say that they propose to use an innovative cavity shape. Normal-conducting cavities can reach higher accelerating fields than superconducting cavities, but at much lower duty factors and with high voltage breakdown events. This new design would allow for lower power dissipation than typical normal-conducting structures, ultimately allowing higher RF duty factors.

There are still some downsides/tradeoffs compared to superconducting structures, including a much smaller beam aperture (5 mm diameter vs. ~100 mm for superconducting cavities), which disrupts the quality of the beam. Superconducting machines can also be run in continuous wave mode (100% duty factor), and state-of-the-art niobium cavities have been driven at ~50 MV/m in CW.

[spullara]

I dropped out of my theoretical particle physics Ph.D. program when the SSC was cancelled. Experimental results for the stuff I worked on was delayed 20 years.

[rob_c]

Don't worry the legacy of the LHC is likely that the SSC would not have given us much. (Unless there are funny resonances at 20TeV+)

[scrubs]

Agree. Had much the same thought. Ssc maybe have found higgs as predicted but nothing new. Now, that's not to give the CERN ppl a hard time. They tried and are trying very hard to go beyond SM but mom (mother nature) isn't making it easy for them. In the US I'm hoping neutrino work will give us the edge there

[01100011]

Where are we at with femtosecond laser driven accelerators? It seemed like there were promises of table-top accelerators in the near future.

[naasking]

I was just thinking that laser-driven plasma wakefield accelerators have produced some promising results recently. Particle physicists still seem stuck in the big accelerator mentality when maybe there are better uses for that money, even in their own field.

[bettysdiagnose]

I would say that 8km is actually quite small, and besides, LPWA has its own problems.

[naasking]

Of course it has its own problems, the question is whether a novel approach is likely to yield more novel insights than the standard approach for the past 50 years. Answer seems kind of obvious.