Observations with different bunch spacings LHC Heat Loads: Observations with different bunch spacings P. Dijkstal and G. Iadarola Many thanks to: B. Bradu, L. Mether, E. Metral, G. Rumolo, B. Salvant

Heat load evolution: scrubbing curve The different sectors are not following the same scrubbing curve Slope observed for the same heat load value are very different

Heat load evolution at 6.5 TeV When normalizing heat loads to intensity we find out that the curves are strongly correlated and they practically differ only for a constant offset Easiest interpretation: There is a source of heat load (most likely e-cloud in the dipoles) that is very similar for all arcs, and conditions in the same way in all sectors Plus there is another source of heat load which is different from sector to sector, scales ~linearly with intensity, and does not condition at all 2015 2016 Data are post processed to use the same calibration for all fills (thanks Philipp and Benjamin!)

Each color corresponds to cells with similar heat loads (within ~15 W) Heat load evolution at 6.5 TeV When normalizing heat loads to intensity we find out that the curves are strongly correlated and they practically differ only for a constant offset Easiest interpretation: There is a source of heat load (most likely e-cloud in the dipoles) that is very similar for all arcs, and conditions in the same way in all sectors Plus there is another source of heat load which is different from sector to sector, scales ~linearly with intensity, and does not condition at all This is true also at a cell by cell level Each color corresponds to cells with similar heat loads (within ~15 W) Data are post processed to use the same calibration for all fills (thanks Philipp and Benjamin!)

Heat load evolution: effect of energy ramp The heat load increase between injection and high-energy is practically the same for all sectors  mechanism responsible for difference between sectors is independent on energy HL6.5TeV - HL450GeV

Each color corresponds to cells with similar heat loads (within ~15 W) Heat load evolution: effect of energy ramp The heat load increase between injection and high-energy is practically the same for all sectors  mechanism responsible for difference between sectors is independent on energy Each color corresponds to cells with similar heat loads (within ~15 W) HL6.5TeV - HL450GeV

Heat load evolution: differences between sectors Heat load observations are compatible with the following scenario: There is a source of heat load (most likely e-cloud in the dipoles) that is very similar for all arcs, and conditions in the same way in all sectors On top there is another source of heat load which is different from sector to sector, scales ~linearly with intensity, is independent on energy and does not condition at all Can this second heat load source be an impedance? Important information to answer this question can be obtained comparing observations with different filling patterns Here we recollect the main observations, to be compared against detailed impedance estimates

Heat loads with different filling patterns We recollected analyzed the following fills performed with different kinds of filling patterns. The comparison is performed for beam parameters and heat load values measured after 2 h in stable beam For the sake of brevity, in these slides we focus on only on two sectors: Sector 23: example of high load sector Sector 34: example of low load sector The complete set of plots is available here

Heat loads with different filling patterns Measured data vs expectations from synchrotron radiation and resistive wall impedance Arc 23 Arc 34 Synchrotron Radiation Impedance (R.W.) Measured

Heat loads with different filling patterns Measured data vs expectations from synchrotron radiation and resistive wall impedance Arc 23 Arc 34 Synchrotron Radiation Impedance (R.W.) Measured Normalize to the number of bunches…

Heat loads with different filling patterns Measured data vs expectations from synchrotron radiation and resistive wall impedance Arc 23 Arc 34 Impedance (R.W.) Measured Normalize to the number of bunches and subtract contribution from synchrotron radiation

Heat loads with different filling patterns Measured data vs expectations from synchrotron radiation and resistive wall impedance Arc 23 Arc 34 +10% +20% Normalize to the number of bunches and subtract contribution from synchrotron radiation Then normalize all measurements w.r.t. the 100 ns case x14 Is it possible to construct an impedance that matches this quite peculiar behavior? (see consideration from Benoit HSC meeting 20 Feb)

Cell-by-cell plots at 6.5 TeV (only for S23 in these slides, complete set for all sectors can be found here)

Much larger than impedance and synchrotron radiation estimates 25 ns, 48 b/train, 601 b. Much larger than impedance and synchrotron radiation estimates Synchrotron Radiation Impedance (R.W.) Measured 100 ns, 685 b. Compatible with impedance and synchrotron radiation estimates

Much larger than impedance and synchrotron radiation estimates 25 ns, 48 b/train, 601 b. Much larger than impedance and synchrotron radiation estimates Synchrotron Radiation Impedance (R.W.) Measured Synchrotron Radiation Impedance (R.W.) Measured 100 ns, 685 b. Compatible with impedance and synchrotron radiation estimates Zoom: cell-by-cell structure is different

Much larger than impedance and synchrotron radiation estimates 25 ns, 48 b/train, 601 b. Much larger than impedance and synchrotron radiation estimates Synchrotron Radiation Impedance (R.W.) Measured Synchrotron Radiation Impedance (R.W.) Measured 50 ns, 296 b. Compatible with impedance and synchrotron radiation estimates

Much larger than impedance and synchrotron radiation estimates 25 ns, 48 b/train, 601 b. Much larger than impedance and synchrotron radiation estimates Synchrotron Radiation Impedance (R.W.) Measured 8b+4e, 529 b. Larger than impedance and synchrotron radiation estimates Cell-by-cell structure similar to 25 ns case

Cell-by-cell structure similar to 601b case 25 ns, 48 b/train, 601 b. Synchrotron Radiation Impedance (R.W.) Measured 25 ns, 48 b/train, 2200 b. Cell-by-cell structure similar to 601b case

Cell-by-cell structure extremely similar to 48b/train case 25 ns, 72 b/train, 2040 b. Cell-by-cell structure extremely similar to 48b/train case Synchrotron Radiation Impedance (R.W.) Measured 25 ns, 48 b/train, 2200 b.

Summary Heat load observations are compatible with the presence of a source of heat load which is different from sector to sector, scales ~linearly with intensity, is independent on energy and does not condition Information to identify this source can come from fills performed with different filling patterns In the high heat load sectors, the heat load increases by a large factor when moving from 100 ns or 50 ns to 25 ns beams. The increase is much smaller when moving from 600b (25 ns) to full machine and from trains of 48b to trains of 72b At a cell-by-cell level the 100 ns and 50 ns fills show loads that are compatible with impedance and synchrotron radiation (apart from a few outliers, measurement?) The cell-by-cell pattern observed with this schemes is different from the one observed with 25 ns The case of the 8b+4e beam is intermediate. Heat loads are significantly smaller than in the 25 ns case but still larger than impedance and syn. radiation, especially for the high load sectors (similarities are visible also in the cell-by-cell pattern)