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FCC – injector complex features…. …with a view to possible Fixed-Target beams B.Goddard 15/7/14. Outline. Initial assumptions Requirements, p re-injector performance, constraints HEB tunnel options and features SPS LHC FHC Comparison of idealised FT beam performance reach

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fcc injector complex features
FCC – injector complex features…

…with a view to possible Fixed-Target beams



  • Initial assumptions
    • Requirements, pre-injector performance, constraints
  • HEB tunnel options and features
    • SPS
    • LHC
    • FHC
  • Comparison of idealised FT beam performance reach
  • Potential issues
basic assumptions for fcc injectors
Basic assumptions for FCC injectors
  • Maximise CERN facility reuse
    • Add High Energy Booster (HEB) to present LHC injector complex
    • Not considering an “SPL/PS2-like” option to rebuild full complex
  • Take HL-LHC injector chain output for granted
    • 2.5e11 p+/bunch in 2 mm exy at 25 ns, maximum reach
  • FHC: 100 km collider length, 50 TeV/beam
    • 1e11 p+ per bunch, 25 ns spacing, need to fill ~11’000 bunches
  • Evaluate all HEB designs with 2-in-1 magnets, for filling times
    • May not be realistic for all options
    • Only one ring assumed for FT beams!
  • Filling times calculated assuming present injector complex cycle times (but with increased PS batches in SPS from 4 to 8…)
fhc injection considerations
FHC injection considerations
  • Minimum FCC filling time (on paper) should be of order of 10 minutes
    • Aim to keep this ‘in the shadow’ of FHC cycle time
    • To note: present LHC could fill both rings in under 10 minutes – on paper
  • Injection energy considered around 4 TeV
    • 3.2 TeVwould give same field ratio (collision/injection) as present LHC
    • 1.8 TeV gives same minimum field in T as present LHC
    • Lower than 4 TeV may penalise FCC (magnet aperture, instabilities, …)
an fhc injector chain
An FHC injector chain


0.16 – 2 GeV (x13)


0-160 MeV (H-)


2 – 26 GeV (x13)


26 – 450 GeV (x17)


0.450 – 4 TeV (x8)


4- 50 TeV (x13)

  • Plenty of them….
  • Starting point for injectors assumes re-use of existing LHC chain, up to and including SPS
    • New HEB: should reach 4TeV and fill FHC in around 10 minutes
  • Initial options for evaluation:
    • 7 km SC machine in SPS:
      • High-field 9 T NbTi (only if FHC injection at 2 TeV)
      • Very high field 18 T Nb3Sn (to reach 4 TeV)
    • 27 km existing LHC reuse
      • Ramp rate to increase by as much as possible: x5 reasonable target?
      • New 2-quadrant higher voltage powering, new QPS, remove low-b, …
      • Decommissioning of highly activated zones to study
      • ..or replacing LHC with low-cost SC or SF machine….?
    • 100 km NC/SF machine
      • 30-60 km of 2-in-1 iron dipole magnets, at least 1000 quadrupoles
some specific topics for studies
Some specific topics for studies
  • Minimum injection energy (field) in FHC
    • 1.8 TeV would open other options for HEB...but probably need 4 TeV
  • Maximum ‘flat-bottom’ time for FHC
    • Need to know if target of ~10 minutes is adequate
  • Feasibility of HEB in SPS tunnel (if 1.1/2.0 TeV is OK….)
    • Integration, ramp rate, 1 or 2 apertures…
  • Feasibility of LHC reuse for HEB
    • Lattice design for simplified 4 TeV synchrotron
    • Key question of ramping at ~50 A/s. Tests??
    • Availability (how often were there 4 consecutive LHC ramps??)
    • Decommissioning feasibility
  • Feasibility of HEB in 100 km tunnel
    • Beam dynamics at 450 GeV injection energy(space charge, impedance, IBS, …)
    • Basic lattice needed
  • Preliminary cost scaling for magnet systems for all options
  • Beam transfer, machine protection (both of these get difficult!)
heb options sps tunnel
HEB options – SPS tunnel

SPS tunnel: SC low-field can reach 1.1 TeV, but 3.2 TeV is tough

heb options lhc tunnel
HEB options– LHC tunnel

LHC tunnel: wide range of possibilities – including reuse of LHC

heb options fcc collider tunnel
HEB options – FCC collider tunnel

FCC tunnel: 2.0/2.5 T NC/SF with 0.33/0.27 filling-factor

baseline option
Baseline option?

Not yet defined…

….but reuse of existing LHC machine has strong “naturalness” arguments in favour, if technically feasible and cost competitive

….so, a digression on reuse of LHC….

to this
To this…?













RF: need to keep ring 1 and ring2 same length! Min. of 2 crossings








changes per ir 1 4
Changes per IR (1-4)
  • P1: extraction to collider:
    • removal of low-beta insertion, ATLAS, construction of floor through ATLAS cavern, civil engineering for junctions to new TLs to collider, installation of extraction system
  • P2: injection of B1 (no crossing)
    • removal of low-beta and ALICE, modification of injection system to inject into INNER ring (presently outer!)
  • P3: collimation – unchanged
  • P4: RF and new crossing
    • Addition of D2 magnets, plus required matching quadrupolesfor crossing (not at IP…)
changes per ir 5 8
Changes per IR (5-8)
  • P5: FODO transport, no crossing
    • removal of low-beta and CMS, construction of floor through CMS cavern, installation of FODO quads
    • Possible location for FT extraction system
  • P6: beam dump – unchanged
  • P7: collimation – unchanged
  • P8: Injection beam 2 (crossing)
    • removal/modification of low-beta and LHCb (2 options still open for crossing – medium beta, or with D2s only)
ft extraction insertion in lhc
FT extraction insertion in LHC

Depends on where transfer to FCC takes place, but would be either P1 or P5

Not yet looked at any details of extraction system requirements or possible layout

Likely to be not particularly straightforward to design conceptually….

pot estimates
PoT estimates
  • Simple methodology to compare options….
  • Limit peak power on targets to 2.0 MW
    • Maybe slightly pessimistic at this stage (or maybe not!)
  • Stored energy in beam given by FCC filling constraints
  • Adjust spill lengths to give 2.0 MW power
  • Subtract FCC filling time
  • 80% efficiency for FT physics
  • Total cycle length and protons per spill then give maximum PoT per year (if no other limitations)
pot from cycle length etc
PoT from cycle length etc.

e18-e19 p+/year at 4 TeV might be envisaged, in this respect at least….

extraction of ft beams from heb
Extraction of FT beams from HEB
  • Slow extraction assumed essential
    • For experiments (digesting ~e14 p+ in ~100 us…?)
    • For targets (20-700 MJ on target in ~100 us…?)
  • Will be technologically “challenging” for a machine at 4.0 TeV!

1/3 order slow extraction

Stable area in H phase space defined with 6-poles

Shrink area by approaching tune to 1/3 integer

Particles follow separatrices out across septum wire

Spiral step at (60 um) wire ~15 mm determines losses

  • Transverse losses typically 0.5 – 1.0 %
  • Sparking of Electrostatic septa and damage to wires is possible
  • Spill of 0.1 – 10 sec possible (longer if machine duty-cycle allows)

ZS septa in SPS

Anodes made of 2080x 60 um W/Re wires

5 individual anodes, aligned together over ~20 m

For ~300 kW average power, get >10 mSV/h activation…

possible limitations i
Possible limitations - i
  • Extraction system for 4 TeV
    • SPS works at 450 GeV
    • Space in lattice is ~100 m
    • Beam losses will be 10-20 kW in extraction region
      • Equipment performance, activation, radiation damage
    • Limiting elements are
      • Thin electrostatic septa (E field 100 kV/cm, 50 um diameter wires, 15 m active septum length)
      • Thin magnetic septa (5 mm thick, 7.5 kA current)
possible limitations ii
Possible limitations - ii
  • Distributed beam losses in SC magnet system
    • For re-use of present LHC, would appear *very* challenging to incorporate an insertion with 1% beamloss, while maintaining sufficient cleaning efficiency elsewhere
    • For [email protected] tunnel, even if HEB is NC or SF, would be sharing a tunnel with 16-20T dipoles….
      • Maybe need separate parallel extraction straight for HEB for some 2-10 km, for extraction plus beam cleaning….cost, layout, …
    • For [email protected], looks even more difficult to manage extraction losses, as the existing LSS are only 120 m long
other challenges
Other challenges…
  • 4 TeV beam transfer for slow-extracted beams
    • Losses may make SC magnets difficult, but huge bending radius with 2 T NC magnets!
  • Targetry for 4 TeV, 2 MW beams
    • 4 TeV beam likely to pose different difficulties compared to typical ~GeV energy of spallation sources
  • Shielding and experimental area design
  • Secondary beamlines
  • Very long spills…
    • Spill quality
    • Resonance and ripple control
    • POWER CONSUMPTION (HEB running most of time at top energy!)
    • Crystal extraction studies to look at
  • Too early for any real conclusions!
  • e18-e19 PoT/year at 4 TeV ‘could be envisaged’ from time-sharing arguments, depending on which HEB option
  • Need to look at feasibility of 4 TeVslow extraction from these HEB machines
    • Extraction concept, layout, technology
    • Losses, collimation, quenches, collider cross-talk
    • Spill quality and control
    • Targets
    • Beam transport
    • Experimental area
    • Power consumption, operability
lhc ramp rate and cycling limits
LHC ramp-rate and cycling limits

Factors which could limit the ramp rate for the LHC main dipoles and quadrupoles, between 0.5 and 3.8 T: 

  • Maximum voltage per magnet (and insulation to ground)?
    • “900 V for dipoles” (presently ~150 V for ramp-up)
  • Ramp-induced quench?
    • “LHC dipoles could probably work up to 100 A/s (10 times the nominal) from the dB/dtcapacity”
  • Effects on field quality?
    • “negligible at 10 A/s, the interstrand resistance is about 5 times larger than lower acceptable limit. I would expect visible effects (requiring compensation) at 5 times the present ramp-rate, say 50 A/s”
  • QPS sensitivity?
    • “this would be a real bugger. At present thresholds are around 100 to 200 mV, but we have magnets for which aperture compensation does not work well, not really clear why. It may be possible to double the detection threshold, but not much more (i.e. ramps at 20 A/s). Doing better will require new detection architecture”
lhc ramp rate and cycling limits1
LHC ramp-rate and cycling limits
  • Limitation on mechanical lifetime from cycling?
    • “Not that I know, but I guess that it should be analysed”
  • Power loss into cryo system?
  • Power drawn from network?
  • Eddy currents in beamscreen?

Additional factors:

  • Two-quadrants power converters will be needed for all circuits
  • Compensation rate for the corrector circuits. Higher dB/dt will imply larger band for the correction controls, higher voltage power supplies. The QPS of the correctors is not compensated, and already at the limit
  • Electrical lifetime at higher dielectric stress, not known
  • No need for the complication of IR\'s, should be better to change the layout in those areas
lhc ramp rate and cycling limits2
LHC ramp-rate and cycling limits

What improvement could be gained by realistic upgrades and what is the associated cost, for example:

  • Extra powering sectorisation of the arcs (plus SC links etc.)?
    • “Additional components required (feedboxes, shuffling modules) will have to fit in the space”
  • Cryopower upgrade?
    • “will be required, but some limits are "built-in" the system (e.g. pipe diameters and lengths, heat transfer surfaces, flow conditions)”
  • Replacement of beamscreen e.g. with additional cryo capacity;
    • “means removing the complete LHC from its feet”
  • Additional correction circuits/capacity?
  • New QPS?
lhc ramp rate and cycling limits3
LHC ramp-rate and cycling limits

What also limits the overall cycle time for LHC, between 0.5 and 3.8 T, and what could be done about these:

  • Minimum essential pre-cycle?
    • “can be removed”
  • Persistent current decay times?
  • Limits on d/dt(dI/dt) or d/dt(dB/dt)?

Could we be limited by the dipole/quadrupolelifetime?

  • What is the design lifetime of the dipoles/quadrupole?
  • Can we extrapolate already from the first years\' operation to validate or refine this?
  • How many \'healthy\' dipoles/quadrupoles would we expect to have at the end of HL-LHC operation?
  • Could we conceive of a new 3.2 TeV lattice running at e.g. 4.2 T with 10% fewer dipoles, to be used as spares/replacements,?
  • Can a refurbishment be foreseen?