1. Andrzej SIEMKO, CERN/AT-MTM Slide 1 14th “Chamonix Workshop”, January 2005 Beam loss induced quench levels A. Siemko and M. Calvi Machine Protection Issues affecting Beam Commissioning

2. Andrzej SIEMKO, CERN/AT-MTM Slide 2 14th “Chamonix Workshop”, January 2005 Beam loss induced quench levels  When does the magnet quench? u Experience from other colliders u Transient vs. Continuous quench origins  Quench levels of various families of the main ring superconducting magnets  Outlook on further simulations and envisaged experiments  Conclusions Overview

3. Andrzej SIEMKO, CERN/AT-MTM Slide 3 14th “Chamonix Workshop”, January 2005 When does the magnet quench?  For LHC dipole inner cables typical maximum current at 6 T, 1.9 K: I=20 kA 7 T, 1.9 K: I=15 kA  For LHC dipoles at top energy T= 1.9K : Bmax= 8.58T, I=11850 A

4. Andrzej SIEMKO, CERN/AT-MTM Slide 4 14th “Chamonix Workshop”, January 2005 When does the magnet quench?  Quench = Transition from SC to normal state  Q   T If  T > Tc(B,I) - Tb  Quench Field [T] Current density  B  J Bc Temperature [K] Field [T]  T  T=temperature margin Tc Bc conductor limit SC normal SC normal

5. Andrzej SIEMKO, CERN/AT-MTM Slide 5 14th “Chamonix Workshop”, January 2005 Do the magnets quench during operations?

6. Andrzej SIEMKO, CERN/AT-MTM Slide 6 14th “Chamonix Workshop”, January 2005 Do the magnets quench during operations?  All three: Tevatron, HERA and RHIC machines demonstrated that the beam induced quenching happens  Integrated luminosity is by definition compromised by any type of quenches (downtime from recovery)  High luminosity operation can even be limited by beam induced quenching: u Tevatron is not far from such limitation. Luminosity increase requires continues amelioration of the collimation system and its efficiency in order to limit the beam loss to the magnets  Quench = Physical Transition from Luminosity to Unproductivity State (with frustration).

7. Andrzej SIEMKO, CERN/AT-MTM Slide 7 14th “Chamonix Workshop”, January 2005 Transient vs. steady-state sources of premature quenches  LHC main magnets operate at high overall current densities and by necessity are working in the quasi-adiabatic regime u Under this condition, the heat produced by the transient disturbance must be absorbed by the entalphy of the conductor and/or helium u enthalpy of liquid helium plays an important role in the enthalpy budget u for fast disturbances (<1ms) energy must entirely be absorbed by the enthalpy of the conductor u the so-called dry magnets (epoxy impregnated coils) are critical by definition (typically one order of magnitude smaller energy margin)

8. Andrzej SIEMKO, CERN/AT-MTM Slide 8 14th “Chamonix Workshop”, January 2005 Transient vs. steady-state sources of premature quenches u The temperature margin for the LHC main dipoles in case of the transient heat deposition: u At top energy an impact of lost ~10 6 -10 7 protons per meter is sufficient to dissipate 2·10 -3 J and to drive the conductor volume normal u The temperature margin for the continuous heat deposition is reduced:  For steady-state losses an allowed power deposition depends on the thermal budget at superfluid/normal helium bath (cooling capacity)

9. Andrzej SIEMKO, CERN/AT-MTM Slide 9 14th “Chamonix Workshop”, January 2005 Transient origins of heat deposition  Mechanical disturbances u Conductor motions u Structural disturbances: micro-fractures, cracks, etc.  Electrical disturbances u Non uniform current redistribution in Rutherford cables u Strain dependence of critical current, flux jumps  Energy release in the magnet due to the beam u Beam losses from non-perfect setting up of cleaning u Fast beam losses u Beam gas scattering

10. Andrzej SIEMKO, CERN/AT-MTM Slide 10 14th “Chamonix Workshop”, January 2005 Steady-state sources of heat deposition  Heat generated by electrical sources u For main dipole during ramp (R. Wolf)[J/m]  Hysteresis loss240  Inter-strand coupling (Rc = 7.5  )45  Inter-filament coupling (  = 25ms)6.6  Other eddy currents (spacers, collars..)4  Resistive joints (splices)30 u Total (per meter)~325  Energy release in the magnet due to the beam u Slow beam losses from non-perfect cleaning u Synchrotron radiation, Electron-cloud losses, Image current losses u Beam gas scattering  Insufficient cooling u by definition reduces temperature margin

11. Andrzej SIEMKO, CERN/AT-MTM Slide 11 14th “Chamonix Workshop”, January 2005 What is needed to calculate the temperature margins? u Magnet specific parameters at operational conditions:  Temperature, current, field map u Superconducting cable parameters

12. Andrzej SIEMKO, CERN/AT-MTM Slide 12 14th “Chamonix Workshop”, January 2005 Temperature margins of various families

13. Andrzej SIEMKO, CERN/AT-MTM Slide 13 14th “Chamonix Workshop”, January 2005 MB Magnet - Temperature Margin Profile

14. Andrzej SIEMKO, CERN/AT-MTM Slide 14 14th “Chamonix Workshop”, January 2005 MQY Magnet - Temperature Margin Profile  At high energies 2D calculations are relevant  At low energies problem starts to be 3 dimensional: possible quench recovery, minimum propagation zone  Matching of the temperature margin (minimum quench energy) profile with the beam loss profile is necessary to avoid large errors (usually overestimates)

15. Andrzej SIEMKO, CERN/AT-MTM Slide 15 14th “Chamonix Workshop”, January 2005 Not Only Magnets Can Quench ! Cold Mass of Connection Cryostats

16. Andrzej SIEMKO, CERN/AT-MTM Slide 16 14th “Chamonix Workshop”, January 2005 Towards Predictive Tool for Beam Induced Quench Levels Conclusions and Report are expected by Chamonix 15 S.C. Cable and Magnet as build Parameters Temperature Margin Profiles of Magnets Minimum Quench Energy Profiles for Magnets Beam Optics Halo Tracking and Loss Maps Beam Loss Profiles for Magnets Quench Levels Predictive Tool for Preventive Dump of the Beam Due to Beam Induced Quenches Other Transient and Steady State Sources of Energy Loss

17. Andrzej SIEMKO, CERN/AT-MTM Slide 17 14th “Chamonix Workshop”, January 2005 Workshop on beam generated heat deposition and quench levels for LHC magnets (3-4 March 2005)  The workshop is organized in the frame of the CARE-HHH-AMT network scope of assessing the stability margin of the ultimate LHC and validation of design for the LHC upgrade.  The workshop will address the implication of the LHC luminosity upgrade in terms of evaluation of the thermal transfer and superconductor stability, through modeling and experiments.  This workshop will address quench margins, for nominal and ultimate parameters, taking into account the as-built parameters for different type of magnets, different operating temperatures, spatial and temporal distribution of beam losses, and other beam related heat loads.  The experience on quench levels from magnet operation at CERN, and from beam and magnet operation at other labs will be presented.  Models and simulation tools (tools to calculate nuclear cascades, tools to predict quench levels) will be discussed and R & D actions will be identified.  The exchanges of information should provide a useful common starting point and make possible a profitable contribution by the various labs collaborating through CARE, LARP, etc.

18. Andrzej SIEMKO, CERN/AT-MTM Slide 18 14th “Chamonix Workshop”, January 2005 General Remarks  It is sure that magnets will suffer from beam induced quenching u A quench is bad for luminosity, but NO worry for magnet survival  Top energy and luminosity will depend on the performance of the weakest magnet and beam loss topology  Magnets will see all real quench sources only in the tunnel u Magnet specific quench sources are of importance near and at top energy u Beam induced quench sources will be an issue both at injection and top u Concurrence of both sources can not be excluded and will be seen by real magnets for the first time during commissioning

19. Andrzej SIEMKO, CERN/AT-MTM Slide 19 14th “Chamonix Workshop”, January 2005 Conclusions  An accurate prediction of the quench levels of the main ring superconducting magnets will allow only necessary, preventive dump of the beam, based on beam loss measurements with beam loss monitors before the magnet quench, thus limiting the downtime of the machine.  The particle energy deposition in the coils is calculated by using simulation programs like GEANT or FLUKA. The magnet quench levels as a function of proton loss distribution and magnet specific parameters can be estimated using codes like SPQR and ROXIE.  Until now only simplified analytical calculations have been done for the main magnet families.  An outlook on further simulations for the quench levels and envisaged experiments to validate the simulations was sketched.

20. Andrzej SIEMKO, CERN/AT-MTM Slide 20 14th “Chamonix Workshop”, January 2005 Acknowledgments Christine Vollinger, Nikolai Schwerg, Glyn Kirby, Arjan Verweij and Ruediger Schmidt for their help and contributions