Machine Protection Issues affecting Beam Commissioning * 07/16/96 Machine Protection Issues affecting Beam Commissioning Beam loss induced quench levels A. Siemko and M. Calvi *

Beam loss induced quench levels * 07/16/96 Beam loss induced quench levels Overview When does the magnet quench? Experience from other colliders Transient vs. Continuous quench origins Quench levels of various families of the main ring superconducting magnets Outlook on further simulations and envisaged experiments Conclusions *

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

When does the magnet quench? Quench = Transition from SC to normal state Field [T] Current density D B J Bc normal normal conductor limit Field [T] SC SC D T T=temperature margin Bc Tc Temperature [K] DQ  DT If DT > Tc(B,I) - Tb  Quench

Do the magnets quench during operations?

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: 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).

Transient vs. steady-state sources of premature quenches * 07/16/96 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 Under this condition, the heat produced by the transient disturbance must be absorbed by the entalphy of the conductor and/or helium enthalpy of liquid helium plays an important role in the enthalpy budget for fast disturbances (<1ms) energy must entirely be absorbed by the enthalpy of the conductor the so-called dry magnets (epoxy impregnated coils) are critical by definition (typically one order of magnitude smaller energy margin) *

Transient vs. steady-state sources of premature quenches * 07/16/96 Transient vs. steady-state sources of premature quenches The temperature margin for the LHC main dipoles in case of the transient heat deposition: At top energy an impact of lost ~106 -107 protons per meter is sufficient to dissipate 2·10-3 J and to drive the conductor volume normal 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) *

Transient origins of heat deposition * 07/16/96 Transient origins of heat deposition Energy release in the magnet due to the beam Beam losses from non-perfect setting up of cleaning Fast beam losses Beam gas scattering Electrical disturbances Non uniform current redistribution in Rutherford cables Strain dependence of critical current, flux jumps Mechanical disturbances Conductor motions Structural disturbances: micro-fractures, cracks, etc. *

Steady-state sources of heat deposition * 07/16/96 Steady-state sources of heat deposition Energy release in the magnet due to the beam Slow beam losses from non-perfect cleaning Synchrotron radiation, Electron-cloud losses, Image current losses Beam gas scattering Heat generated by electrical sources For main dipole during ramp (R. Wolf) [J/m] Hysteresis loss 240 Inter-strand coupling (Rc = 7.5 mW) 45 Inter-filament coupling (t = 25ms) 6.6 Other eddy currents (spacers, collars..) 4 Resistive joints (splices) 30 Total (per meter) ~325 Insufficient cooling by definition reduces temperature margin *

What is needed to calculate the temperature margins? Superconducting cable parameters Magnet specific parameters at operational conditions: Temperature, current, field map

Temperature margins of various families

MB Magnet - Temperature Margin Profile * 07/16/96 MB Magnet - Temperature Margin Profile *

MQY Magnet - Temperature Margin Profile * 07/16/96 MQY Magnet - Temperature Margin Profile Matching of the temperature margin (minimum quench energy) profile with the beam loss profile is necessary to avoid large errors (usually overestimates) At high energies 2D calculations are relevant At low energies problem starts to be 3 dimensional: possible quench recovery, minimum propagation zone *

Not Only Magnets Can Quench ! * 07/16/96 Not Only Magnets Can Quench ! Cold Mass of Connection Cryostats *

Towards Predictive Tool for Beam Induced Quench Levels * 07/16/96 Towards Predictive Tool for Beam Induced Quench Levels 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 Conclusions and Report are expected by Chamonix 15 *

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.

* 07/16/96 General Remarks It is sure that magnets will suffer from beam induced quenching 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 Magnet specific quench sources are of importance near and at top energy Beam induced quench sources will be an issue both at injection and top Concurrence of both sources can not be excluded and will be seen by real magnets for the first time during commissioning *

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.

Acknowledgments Christine Vollinger, Nikolai Schwerg, Glyn Kirby, Arjan Verweij and Ruediger Schmidt for their help and contributions