1HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini Testing with beams in CTF3: breakdown kick and advanced diagnostics

Contents Two Beam test stand equipments and tools Beam used for structures RF diagnostics Energy gain / spread measurement and optimization RF power measurements BD detection Test bench for beam diagnostics Wake Field Monitors study Beam kicks study Beam shape distortion and multipolar field modeling Conclusion HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini2

HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini3 Drive beam (24 Amps) Probe beam (1 Amp) Quadrupoles Dipoles BPMs PMTs Correctors Screens Variable phase shifters & On/Off mechanisms RF couplers Water thermal probes and flow meters Ion analyzer FCU Wake Field Monitors Spectrometer lines The Two Beam Test Stand Franck Peauger - IRFU Germana Riddone

Operational models for beam optimization HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini4 For beam focusing: Current in quadrupoles -> beam enveloppe. For beam trajectory: Current in correctors -> beam position on BPMs From Quad scan… … to beam optimization.

Tuning frequency validation of the structures HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini55 LO = MHz LO = MHz LO = MHz LO = MHz LO = MHz LO = MHz RF output generated by a short beam pulse (3 ns: 5 bunches) is down-mixed with a local reference oscillator -> structure resonant frequency. Nominal tuning: GHz checked (accuracy < 1 MHz).

RF production with longer pulses HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini6 Pulse 150 ns LO = MHz Pulse 194 ns LO = MHz Extracted Faraday cup acts as a button pick-up RF output frequency forced by the probe beam pulse frequency RF output rising time = ACS filling time (65 ns) RF output rising time + sustain time = pulse length RF output falling time = ACS filling time (65 ns) Delays between the (RF couplers, Faraday cup, BPMs, PMTs, WFMs) -> instrumentation calibration

Energy gain measurement HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini7 Accelerated /non-accelerated beam -> dipole strength to be adapted Califes beam energy fluctuation +/- 2 MeV, period around 150 s (temperature oscillations ?) Sinusoidal function fit -> valid at least during 30 minutes Accurate measurement of the energy gain despite CALIFES beam energy fluctuations. Double pulsing method for energy gain lower than 30 MeV

Energy gain optimization HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini8 Inter-structures phase shifter position set for no acceleration whatever Drive Beam / Califes phase. This phase is then shifted by 180 deg -> accelerating crest. RF power control PETS On/Off mechanism Timing between drive beam pulse and probe beam pulse. 2 phase shifters (RF/ probe beam phase and inter-structures phase) Drive beam and probe beam detected by PMT Structures phase in opposition

Energy gain as function of RF power check HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini9 Phase scan Power fluctuations Energy gain lower than the nominal one -> uncertainties in the calibration of the RF chains ? Califes / Drive beam phase scanned over 360 deg of 12 GHz

Thermal method for RF power measurements HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini10 Water cooling circuit Finite differences thermal model of structure and cooling circuit. Inlet/outlet water temperature difference -> mean RF power deposited 10 % discrepancy factor found (power overvalued by the RF couplers) 0.02 o C

Reviewed power and energy spread HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini11 Structures performances much closer to the nominal Energy spread maximal at the zero crossing due the phase extension of the bunch on the 12 GHz period -> bunch length measurement method.

Reliable breakdown detection on 2 ACSs HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini12 Two criteria used: Reflected Power and Missing Energy Miss = Ener in – Ener out x attenuation Data are post processed with adaptative thresholds. Thresholds = mean  [ P Gauss (X>3.72  ) = ] Compromise between Detection prob. and False Alarm prob. A BD sometime triggers the other structure BD. Reflected power and Missing energy are data logged for each RF pulse Faraday cup and Photomultiplier tube activity also used to confirm BD

Test bench for beam diagnostics Rui Pan (PhD student), Electro- 0ptical Bunch Profile Measurement at CTF3 IPAC’13 MOPME077. HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini13 Inside CLEX optical tables for laser beam injection F. Cullinan (PhD student), J. Towner A Prototype Cavity Beam Position Monitor for the CLIC Main Beam, IBIC'12 MOPA18 Sophie Mallows(PhD student), A fiber Based BLM System Research and Development at CERN, HB2012 THO3C05 Position and beam charge linearity

Wake Field Monitors as BPMs HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini mm Two types of WFM installed on the structures : (HOMs: 18 GHz and 24 GHz). Resolution already better than 20  m. First successful results: realignment of the ACSs tank. Robustness with nominal 12 GHz RF power (42 MW) still under investigation F. Peauger - IRFU 18 GHz on diodes 24 GHz on log detectors WFM signals without 12 GHz RF power WFM signals with RF power WFM signals from a PB pulse

Breakdown beam kick study PhD research of A. Palaia HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini15 Average measured kick to the beam orbit : 29 +/- 14 keV Kicks angle measured not isotropic, not clear why cavity BPM CA.BPM0745V 0.68 mm 0.75 mm Screen MTV 790 w/o BDWith BD

Beam observed on MTV0790 HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini16 Hor. Position [mm] Vert. Pos. Beam kicks during acceleration observed, especially when beam is passing off-axis through the 12 GHz structures. Beam shape can also be distorted Horizontal beam kick during scan in horizontal positions within the ACSs Non-accelerated (left) and accelerated (right) beam shapes observed on the straight line screen, 4.75 m downstream the ACS accelerated non accelerated [mm]

Observation of octupolar shapes HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini17 Without RF power At zero-crossing (rising RF power side), 25 MW At zero-crossing (falling RF power side) On crests (accelerating or decelerating) Used of a non-focused beam to fully observe beam shape distortion -> full structure aperture covered (4.7 mm bore diameter). The octupolar beam shape changes from positive to negative at the RF crest phases.

Modeling of the octupolar fields HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini18 A. Grudiev Comparison b x =1V LF: i [mTm/m 2 ] PW: i [mTm/m 2 ] Dipolar field Quadrupolar field Sextupolar field Octupolar field Panofsky-Wenzel (PW) theorem Lorenz Force (LF) or

Consequences HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini19 for V z = 22.8 MV; P in = 46.5 MW TD24_vg1p8 f [GHz] Vz(x=0) [MV] i Vx [MV]0 b (2) [mTm/m]0 - 15i b (3) [Tm/m 2 ]0 b (4) [kTm/m 3 ] i ΔV after 5m for 180 MeV beam 18 V V~5 mm A. Grudiev Beam spots in the structureBeam spots on the screen

Conclusion A facility with a well controlled beam and a full set of diagnostics is an important tool for testing RF structures. In addition it attracts many users and PhD students who develop innovative diagnostics. But of course it requires significant resources for operation and maintenance. 20HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini I would like to thank all of them, CERN staff and collaborators, for their constant effort in running CTF3.

HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini21

Detail of the computations HG may 2013 TriesteTesting with beam in CTF3 - W. Farabolini22 Accelerating gradient: Accelerating voltage: Multipole expansion in vacuum only: Panofsky-Wenzel (PW) theorem: Gives an expression for multipolar RF kicks: Lorenz Force (LF): Gives an expression for kick directly from the RF EM fields: Which can be decomposed into multipoles: Equating the RF and magnetic kicks, RF kick strength can be expressed in magnetic units: A. Grudiev