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Faster ramps for the LHC magnets?

Faster ramps for the LHC magnets?. Attilio Milanese. 11 Feb. 2014. Faster LHC magnets?. Foreword

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Faster ramps for the LHC magnets?

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  1. Faster ramps for the LHC magnets? Attilio Milanese 11 Feb. 2014

  2. Faster LHC magnets? Foreword • This is a compilation of considerations and possible issues after quick discussions with several colleagues: M. Bajko, L. Bottura, M. Modena, E. Todesco, D. Tommasini, A. Verweij, L. Walckiers. • The focus is on the main bending magnets; the main quadrupoles do not seem more limiting. In the tunnel now • dI/dt = 10 A/s in the linear part, with smoothing at the ends • dI/dt limited by power converter voltage • inductance of a sector (154 magnets in series) Lsector = 15 H • the power converter can take about 190 V when powering • count ≈ 10 V for losses in current leads at nominal conditions • nominal current (11850 A, 8.33 T, 7 TeV) reached in ≈ 19 minutes Attilio Milanese

  3. Faster LHC magnets? Diode • the diode opens at 6 V, that is, 60 A/s Premature quench • overall consensus is that a single magnet can go without premature quenching at 100 A/s (or more) up to nominal Quench protection • already now after a quench the other dipoles in a string start going down at 120 A/s (at the beginning of the exponential) without triggering the QPS, which is still on • this is using 100 mV or 200 mV thresholds on voltage differences (200 mV when the aperture compensation doesn’t work well) • so 100 A/s would seem reasonable for QPS without major upgrades Attilio Milanese

  4. Faster LHC magnets? Cryo load • tentative scaling, from A. Verweij thesis, with Rc = 40 mW • this is one of the physical limits, the cryo upgrades would have to live with the hydraulic / thermal design of the current system • with an injection / ramp up / extraction / ramp down cycle there would be no time to breathe for the cryo Attilio Milanese

  5. Faster LHC magnets? Inductive voltage • maximum voltage per magnet in operating conditions is around 1 kV • the same powering scheme could be used till around 50 A/s • for faster dI/dt extra powering sectorisations of the arcs (jumpers…) seem unavoidable Field quality • ramp rate affects decay and snap-back at injection energy • looking at the measurements, it looks like the dipoles can go to 50 A/s with challenging (but possible) acrobatics to describe the dynamic effects, in particular on the sextupole component • faster than that, some other kind of compensations – is possible – would be required Attilio Milanese

  6. Faster LHC magnets? Other (just on the magnet side) • mechanical lifetime from cycling: fatigue issues? • compensation rates for corrector circuits, faster, with QPS working in an uncompensated mode • electrical lifetime at higher dielectric stress • superconducting magnets for the new transfer lines? Attilio Milanese

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