Use of Emittance measurements in LINAC2 and (future) LINAC4 at CERN

1. Use of Emittance measurements in LINAC2 and (future) LINAC4 at CERN Alessandra M. Lombardi LINAC2 and LINAC4 in the framework of CERN injectors LINAC4 beam dynamics: location of emittance growth, parameters for emittance control LINAC4 measurements: commissioning, operation

2. Present

3. Linac2 (1978 , upgraded 1993) • A Duoplasmaton ion source giving up to 300 mA of beam current. • Until 1993 the pre-injector was a 750 kV Cockcroft-Walton replaced by a 4-vane RFQ (RFQ2) with an injection energy of 90 kV and an output energy of 750 keV. • A three tank , 202.56 MHz drift tube linac with quadrupole focusing brings the beam energy to 50 MeV. • An 80 meter beam transport carries the linac beam to the 1.4 GeV PSB . LINAC is working well above the design current.

4. LINAC2 – measurements • Measurements line about 50m before injection into the booster used to verify the matching to the booster • Linac2 has been commissioned 30 years ago, upgraded in 1993, optics of the line changed in 1996 . Matching condition to the booster have not changed since 12 (30?) years.

5. Activities Linac4 (2008-2013)Goal : operational in 2013

6. Linac4 Layout 45keV 3MeV 3MeV 50MeV 102MeV 160MeV H- RFQ CHOPPER DTL CCDTL PIMS Drift Tube Linac 352 MHz 18.7 m 3 tanks 3 klystrons 4 MW 111 PMQuad Cell-Coupled Drift Tube Linac 352 MHz 25 m 21 tanks 7 klystrons 6.5 MW 21 EMQuads Pi-Mode Structure 352 MHz 22 m 12 tanks 8 klystrons ~12 MW 12 EMQuads RF volume source (DESY) 45 kV 1.9m LEBT Radio Frequency Quadrupole 352 MHz 3 m 1 Klystron 0.6 MW Chopper 352 MHz 3.6 m 11 EMquad 3 cavities Total Linac4: 80 m, 19 klystrons Beam Duty cycle: 0.1% phase 1 (Linac4) 3-4% phase 2 (SPL) (design for losses : 6%) 4 different structures, (RFQ, DTL, CCDTL, PIMS) Ion current: 40 mA (avg. in pulse), 65 mA (bunch)

7. Layout of the new injectors SPS PS2 ISOLDE PS SPL Linac4 LINAC4 to booster transfer line is 180 m long with two horizonthal bendings and one vertical

8. Linac4 Building Equipment building • Picture of the building • Picture of the the accelerator in the building Linac4 tunnel Linac4-Linac2 transfer line Low-energy injector Access building Vertical step (2.5 m) for compatibility with SPL

9. LINAC energy end-to-end

10. Emittance from the source to the injection foil

11. Emittance from the source to the injection foil 3 MeV, after chopping End of acceleration 0.25 µm : from the source

12. Emittance accelerator 30-40% emittance growth PATH

13. Emittance 0-3 MeV Symmetry x,y in LEBT, if source is symmetric Losses in the RFQ, emittance decreases Losses and emittance increase when matching to the DTL

14. Normalised transverse phase space LEBT in (45keV) RFQ in (45keV) Plot scale : 1cm X 2.5mrad RFQ out (3 MeV) DTL in (3MeV)

15. Emittance 3-160 MeV

16. Normalised transverse phase space Plot scale : 1cm X 2.5mrad CCDTL in (50MeV) PIMS in (100MeV) PIMS out (160MeV)

17. Emittance transfer lines

18. Challenges - general • The beam distribution is changing. The number of particles in one r.m.s. is changing. How to quantify emitt increase? • Space charge effects and coupling transverse- longitudinal influence the emittance : emittance depends on machine settings, emittance grows uncontrolled if the beam drifts for 10 X betalambda where βλ= 3.5 cm at 3 MeV ; 40 cm at 160 MeV We cannot use profiles to measure emitt • How to treat the halo without loosing information

19. Changing distribution PIMS output 160 MeV 50% of the beam in one rms RFQ input 45 keV 30% of the beam in one rms

20. Challenges • 0-3 MeV • Halo • LEBT : Possibly x,y correlation • MEBT : Emittance depends strongly on quad settings • 3-160 MeV • Transient effects can generate emittance increase • Alignment errors • 160 MeV to the booster • Extreme space charge effects at the beginning of the line • Detangle dispersion effects [dispersion of the centre is not the dispersion of the envelope !!!!] • Correlation x,y because of vertical bendings where the horizontal dispersion is not closed

21. Emittance measurements- if everything goes as planned • Critical for setting up in the energy range 0-3 MeV. • Should see only statistical fluctuations in the range 3-160 MeV • Should help set up the line and control the dispersion in the tranfer lines

22. Example: optimized matching to the RFQ vs. beam current

23. Space charge is important From 3 MeV to 160 MeV

24. Emittance measurements- calculated surprises • Alignment errors and gradient errors as budgeted should give an emittance increase with respect to nominal of 10% at 1 sigma • Transients, jitters : should be able to measure emittance of a slice of the beam in order to distinguish static errors from dynamics errors

25. Summary • Emittance measurements, together with transmission measurements, are essential for the correct set-up of the machine, and should be done after every stage of acceleration (3,50,100,160 MeV). • Emittance measurements at the end of the linac (160 MeV) are essential to diagnose problems during operations. • Emittance measurements at the current location of the LBE lines are necessary during commissioning and operation to verify the correct settings of the line and to deliver a matched beam to the PS booster. • Emittance measurements should be accurate to 5% both in emittance and twiss parameters (control of matching between acceleration stages).