Beam losses in the CLIC drive beam: specification of acceptable level and how to handle them ACE Michael Jonker

Beam loss detection and Radiation issues. (in the main tunnel) BLM system primary purpose: detection of onset of slow losses. Operational beam loss background levels: Tails on the beam entering the main linac and decelerators Interaction with residual beam gaz. Loss levels limits From Beam Physics: 0.1 % main beam, 0.1% each drive train From Radiation damage over the lifetime of CLIC (1MGy/year see following slides) Hence, these limits will define the required vacuum performance Resolution at operational background levels 20 % ? Dangerous level of beam loss when of DB or of MB is lost on an single aperture restriction. (Rough estimate needs further detailed simulations) Extended range for catastrophic (fast) losses: diagnostics only. (i.e. to better understand what happened, if ever something should happen)

Effect of beam in matter Note: in energy density in cupper for Melting : 400 J g -1, Structural yield 62 J g -1 MaterialCAlCuW LEP Beam (100GeV, 445 nC) Energy shower core [J g -1 ] Energy IB 0.1 mm 2 [J g -1 ] CLIC Main Pulse (1.5 TeV, 186 collimators) Energy shower core [J g -1 ] Energy IB 40  m 2 [J g -1 ] /bunch CLIC Main Pulse (2.8 GeV, 204 DR septum) Energy shower core [J g -1 ] Energy IB 125  m 2 [J g -1 ] /bunch CLIC Drive Train (2.4 GeV, nC) Energy shower core [J g -1 ] Energy IB 1 mm 2 [J g -1 ]

BLM Collection of Requirements (for the main tunnel) BLM system for detection of instabilities: Low end of dynamic range – 0.1% loss distributed over the main linac or a decelerator. – 20 % resolution High end of dynamic range – of main beam, of drive beam lost in a single aperture restriction (rf structure) – Details of failure mode at origin of loss not very important. – Resolution 7? sigma above background (or whatever is needed to reduce downtime from false alarms to less then 0.1 %). Good reliability & availability (to be defined, however, there are redundant diagnostics systems. BLM system for diagnostics of fast catastrophic losses extended dynamic range (with 10 2 for DB, 10 4 MB) – Full beam impact on an aperture restriction ? – 10 % resolution Reduced requirements on reliability and availability. Under discussion

More challenges Distinguish between beam losses in the same tunnel from: – Drive beam decelerator – Main beam – Transport lines – Beam turns – Beam dumps – Crosstalk Simulations (see following slides) Distinguish beam losses from other sources of radiation: – Synchrotron light – Photons from RF cavities – Wigglers, undulators – EM noise, etc. Investigate and document the radiation sources in tunnel (other than beam loss) BLM Collection of Requirements

Crosstalk: main beam – drive beam I S.Mallows, T.Otto: Radiation Levels in the CLIC Tunnel

Crosstalk: main beam – drive beam II  Signal to crosstalk ratios for equal fractional beam loss on one quadrupole of the main beam and drive beam (statistical uncertainty ~ 10%)  Higher loss on drive beam: main beam losses are shadowed!  Can spectral sensitivity help? S. Mallows, T. Otto

CLIC OMPWG Beam losses (DB 2.4 GeV) 2.4 GeV Lost before QP 1.5 TeV Lost in QP

S. Mallows, T. Otto, CLIC Two-Beam Module Review, September 2009

CLIC OMPWG Permitted fractional loss model (New model, Drive beam) Loss pointBeam dynamics Old estimate New Estimate in QP1.25 E-61.0 E-71.6 E-6 before QP1.25 E E-6 in PET1.25 E-6 Loss pointBeam dynamics Old estimate New Estimate in QP1.25 E-64.7 E-71.9 E-5 before QP1.25 E E-5 in PET1.25 E-64.8 E GeV 0.24 GeV Based on radiation limits of magnets during 10 years x 6 month operation. Regular magnet design (no rad hard)

CLIC OMPWG Permitted fractional loss model (New model, Main beam) Loss pointBeam dynamics Old estimate New Estimate in QP5 E-77.3 E-82.7 E-9 before QP5 E E-9 in AS5 E-79.1 E-9 Loss pointBeam dynamics Old estimate New Estimate in QP5 E-71.7 E-61.9 E-5 before QP5 E E-5 in AS5 E-74.8 E TeV 9 GeV Based on radiation limits of magnets during 10 years x 6 month operation. Regular magnet design (no rad hard)

Type of failures Failures causing slow onset of losses – Magnet system – Vacuum system (performance defined by tolerable operational losses) – Slow drifts (alignment, temperature, …) Next pulse permit and safe by design(2 ms) Failures causing fast losses (“in-flight” failures) – RF breakdown (effects on the beam under study) – Kicker misfiring (turn around kickers !) – Klystron trips (not applicable for DB) Protection by fixed masks (Impedance?)