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

2. 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.

3. 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?)

4. 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.

5. 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

6. 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)

7. 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.

8. 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.

9. 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.

10. 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

11. 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

12. 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?