ESS wire scanner Benjamin Cheymol www.europeanspallationsource.se 3 March 2015

Principle of wire scanner A thin wire is scanned through the particle beam while the secondary emission current, the signal from a calorimeter downstream, and the signal of the motor encoder are acquired simultaneously. Plotting either of the SEM or PMT signals against the encoder gives the beam profile.

Wire scanner in ESS linac 1 WS dual axis SEM mode 3 fast WS + 3 Dual axis WS in A2T Shower + SEM mode 4 WS dual axis SEM + shower mode 5 WS single axis SEM mode 3 variants of the system In total: 21 axis 44 channels for acquisition (+32 for fast wire scanner?)

Beam parameters in the ESS linac Evolution of the rms beam envelope along the linac (courtesy of M. Esharqi) The average beam sizes are 2 mm in both plane In operation, the pulse length is 2.86 ms and the repetion rate 14 Hz An iris positioned in the LEBT will allow a beam current varition from 6 mA to 62.5 mA.

Operation on ESS wire scanner Thermal load is an issue for interceptive device, beam duty cycle has to be reduced: A slow tuning mode (i.e. 100 μs, up to 62.5 mA, 1 Hz). A fast tuning mode (i.e. 10 μs, up to 62.5 mA, 14 Hz). Scan will be perform at constant speed (100 μm.s-1 to few mm.s-1) and in step by step mode Vertical and horizontal measurement separated to avoid cross talk

Warm linac WS Single movement at 45 deg. 33 μm Carbon wire Better thermal properties than tungsten Less signal Signal and thermal load has been estimated Maximum expected signal in MEBT (for Ibeam=62.5 mA): 180 μA to 400 μA depending on the beam sizes Maximum temperature during the scan (50 μs, 1 Hz): 900 K to 1900 K No thermionic emission effect on the signal Mechanical design No started yet, shared effort for MEBT-DTL wire scanner CERN LINAC4 wire scanner design can be used and adapted to our needs Maximum temperature on the wire during a scan as function of the wire position, beam energy is 3.63 MeV (MEBT)

Spoke-Wire Scanner Dual movement. 40 μm Tungsten wire Signal and thermal load has been estimated Maximum temperature during the scan (100 μs, 1 Hz): 1500 K to 1800 K Peak current: 60 to 90 μA (SEM mode) Mechanical design Hydroformed bellows, new design has to be done Electronic Electronic shall be similar to the MEBT/DTL wire scanners Expected signal at the exit of the first spoke cryomodule (blue line) and at the exit of the fourth spoke cryomodule (red line). On the right, the signals are plotted in logarithm scale.

Elliptical-Wire Scanner Detector geometry, in blue the scintillators and in black the beam pipe, the diameter of the beam pipe is 100 Same mechanical design as spoke wire scanner Detection of the SEM current from the wire Detection of hadronic shower created by the wire Monte Carlo simulation on going Gamma background might be an issue Error map for a 560 MeV beam Energy spectrum of proton reaching the detector surface. Estimated signal at the output of a typical photodiode coupled with a BGO scintillator.

Fast wire scanner (HEBT) Possibility of using a fast wire to measure beam profile in one pulse in HEBT Same mechanical design as the new CERN fast wire scanner Motion control design by CERN Carbon wire Detector geometry optimized Design of the new CERN flying wire scanner (courtesy of CERN BI group) Evolution of wire peak temperature during a scan at 560 MeV (solid line) and 2000 MeV (dashed line) for different wire velocity.

Mechanical design Small progress on this topic Warm linac wire scanner IKC from ESS Bilbao, agreement to be in place in few weeks Interface to be defined Cold wire scanner Some issues due to hydroformed bellows Looking fro IK partner, if not design will be done in house

Project planning Wire scanners have to be ready at the same time as the linac section : Warm linac commissioning (Q2 2018) Spoke commissioning (Q1 2019) Elliptical (medium β) commissioning (Q2 2019) Front end electronic is critical A full prototype of the system shall be ready by Q1 2017 Potential test of the WS at Saclay RFQ test

Potential beam test Test without beam is mandatory Potential beam test Can be done at Elettra or ESS Full vertical system has to be tested Potential beam test ESS LEBT commissioning Commissioning test box will allow the insertion of a single axis wire scanner 75 keV, only SEM mode tested CEA IPHI facility 3 MeV, 100 mA, CW RFQ Can be retuned with ESS beam parameter Other?