1. Introduction: FCC beam dumping system
The energy of 8 GJ in the FCC beams is impressive
Studies o hydrodynamic tunnelling: 8000 bunches travel more than 100 m (preliminary)
We manage to safely dump beam of up to 150 MJ
We have a lot of operational experience with LHC
A scaling of the LBDS might be possible, but we should also explore other options
Thinking outside the box, coming up with crazy ideas that, even if discarded, sometimes trigger other thoughts
These thoughts be considered as encouragement to consider other «crazy» ideas
Challenge of asynchronous beam dump
Challenge of dumping the beam in the beam dump block

2. FCC beam dumping system
Concentrate of designing a beam dumping system for top energy, if we can design the beam dumping system for top energy, it will also work for lower energy
Can we conceive a beam dumping system that will not generate asynchronous beam dumps?
If yes, consequences on triggering and parameters of beam dump kickers
If no, design protection systems accordingly (TCDQ like absorber, collimators must stand impact)
What is the damage potential of one single bunch at top energy with FCC parameters?
Depends on the beam size
What is the beam size that will allow to stop one bunch with light material (such as carbon) without damage?

3. No asynchronous beam dump
Wrong trigger to all kicker magnets to be avoided
Electronics safety system to prevent such wrong trigger
Coincidence of trigger signal with observation of abort gap, by beam monitors (BPM using sum signal)
Similar safety level as in airplanes ….not allowed to switch engine off, no failsafe status
Challenging, but I consider it to be possible…..

4. No asynchronous beam dump
Assume that spontaneous firing of one kicker magnet cannot be excluded
Amplitude must be limited, say, to very few sigma (one or two) for one kicker -> many kicker magnets are required, each with a limited kick strength
A similar failure case is considered for crab cavities of HL-LHC…..
Space between beam tail and collimators required – need to be monitored and interlocked, similar for as for HL-LHC
No direct retriggering of other kicker magnets
Triggering a synchronous dump a little later can be considered
At top energy, the total kick should be as small as possible….
Consequence if it goes wrong – what happens in case of asynchronous beam dump?
Depending on consequences, one asynchronous beam dump in, say, 20 years might be acceptable for a downtime of, say, 2-3 month

5. HL-LHC: Gaussian beam collimated at 4 
99.9% of protons
collimator
collimator
Example: a collimator is positioned at 4 , and we assume a dipole magnet failure. The beam starts to move, assume by 1.7 . All particles beyond 2.3  are lost.

6. Asynchronous beam dump
Wrong trigger to kicker magnets
Minimum number of bunches to hit material at top energy
Use orbit bump to reduce requirement on deflection angle for kicker magnets
Minimum rise time
At injection, lot of aperture is required
At top energy, aperture requirements are much smaller
Can this be used in the design of fast kicker magnets?
Is it possible to make kicker magnets that close during the energy ramp such as collimators?

7. Asynchronous beam dump
Maximise beam size: what is the maximum possible beta function at top energy?
Change of optics in beam dump insertion during energy ramp could be considered – increase beam size at top energy
Assume 25 ns bunch distance
5 us rise time = 200 bunches: difference of about 1 sigma / bunch
1 us rise time = 40 bunches: difference of about 5 sigma / bunch

8. Beam dumping block
Beam size at exit window with sigma of about 4 mm (window of carbon should survive, to be confirmed)
Corresponds to beta function of 400 km (why not?)
1m beta waist after 1000 m gives 1000 km
Beam can be stopped in gas, water, …. some material that is not too dense