1. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Gas Monitors for Transverse Distribution Studies in the LHC LHC Instrumentation Review Workshop CERN - 19-20/11/2001

2. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 ACKNOWLEDGMENTS Luminescence Review on behalf of colleagues involved in the topics : The Luminescence Profile Monitor of the CERN SPS G. Burtin, J. Camas, G. Ferioli, R. Jung, J. Koopman, R. Perret, A. Variola, J.M. Vouillot Ionisation of Rest Gas J. Koopman, G. Ferioli, M. Sillanoli + others (SL/OP…)

3. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Table of Contents Introduction Luminescence - spectrum - signal vs pressure - decay time - data Rest Gas Ionization - resolution - reproducibility - sensitivity in current - turn by turn operation Future Conclusion Proposed location in LHC

4. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Introduction Why gas monitors in LHC ? study of transverse distributions in the range 450 GeV  2 TeV -  650  m  1.25  m (  = 200 m) LHC Emittance workshop in July 2000 2 directions recommended : - Luminescence - Gas Ionization

5. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Luminescence Profile Monitor PRINCIPLE Uses the light emitted by gas molecules when they return to their ground state after having been excited by the beam: Nitrogen is a good candidate: high cross-section, low decay time, well pumped emits towards lower end of the visible spectrum

6. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Luminescence At 7 10 -5 Pa (5 10 -7 torr), the photon production corresponds to the N 2 + spectrum: ~ 60% of the light is within the bandwidth of a 400nm ± 35nm filter. The light production is linear with pressure: single step process with short decay time  suitable for profile measurements. The pressure can be used to increase the dynamic range of the detector. The pressure increase is negligible in the SPS: 5% for 6 10 -5 Pa (5 10 -7 torr) over 3 m Signal as a function of N2 pressure Spectrum

7. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Luminescence Measurement with Pb ions shows the bunch structure (131 ns) indicating a decay time compatible with the 60ns quoted in literature for low energy protons. This should generate negligible image broadening (~50  m FWHM) Decay time as a function of wavelength Decay is faster with the 400nm filter than with whole spectrum: afterglow up to 2-4  s. The batch structure is visible at 400nm. The profile measurements should hence be taken with the 400nm filter in place Decay time

8. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Luminescence – data 1 Single shot (20ms, i.e. 840 turns) vertical profile measurement at 6 10 -5 Pa (5 10 -7 torr) for 2 10 13 p (140 mA) at 450 GeV 3D image Side view (2D)

9. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Luminescence – data 2 Single shot (840 SPS turns) profiles at 8 10 -5 Pa ( 6 10 -7 Torr) with 9 10 8 (540 mA) Pb ions Single shot (840 SPS turns) at 6 10 -5 Pa (5 10 -7 Torr) for 2 10 13 p (140 mA) at 450 GeV   = 670  m   = 1070  m

10. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Luminescence – data 3 Single shot (20 ms) and statistically processed (10 cycles) measurements for low light density:  =4 700  m at 14 GeV at low pressure: 6 10 -6 Pa: same result as for 10 -4 Pa. Statistical data processing for Increased Sensitivity at 6 10 -6 Pa ( 5 10 -8 torr )

11. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Luminescence – data 4 Agreement with Wire Scanner as reference monitor – 17% ± 2% (wire scanner 244 m upstream  uncertainty) Integration Time ( beam energy “resolution” ) – 20 ms ( 0.8 GeV ) Normalised Sigma to observe V emittance blow-up Normalised Vertical sigma (mm ) Comparison with Wire Scanner SPS Fixed Target Cycle

12. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Rest Gas Ionization Profile Monitor

13. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Data Presentation

14. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Profile evolution during SPS cycle 34 GeV150 GeV312 GeV 430 GeV450 GeV

15. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 B field effect at 450 GeV 100% = 560 G B=40% B=100%B=80% B=60%

16. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Resolution Reproducibility

17. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Comparison Wire Scanner - Rest Gas Monitor Rest gas monitor data multiplied by 1.89 (theoretical optics ratio). At low energies discrepancies due to dispersive effects at the wire scanner. Then agreement within 3 % to 5% ( error of instruments + machine optics ).  Rest gas monitor discriminates variations < < 1 mm.

18. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Ultimate Resolution with present monitor With LHC type beam, ultimate resolution of present monitor is between 300  m and 400  m ( B = 560 G ) LHC beam, 48 or 72 bunches, 3.5 10 10 p to 4.5 10 10 p /bunch, 450 GeV Wire scanner dataIPM monitor data  m  m  m  m  WS /  IPM =2 OK  WS /  IPM =1 NOT OK

19. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Gaussian fit on data above 30% of maximum. Relative errors << 1% in general for rms values << 1 mm. Shrinking at 450 GeV due to beam extraction. Reproducibility three consecutive acceleration cycles

20. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Sensitivity in Current

21. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 One bunch - 870 SPS turns (20 ms) per profile 2 10 10 protons/bunch = LHC pilot * 4

22. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Ionization Profile Monitor One bunch of 2. 10 10 protons = LHC pilot bunch * 4 High resolution mode (870 SPS turns) - P = 10 -8 Torr One bunch of 6 10 9 protons = LHC pilot bunch

23. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 One bunch - 870 SPS turns (20 ms) per profile Limit with present monitor is LHC pilot intensity on 870 turns - vacuum: < 10 -8 T H2 S/N ratio : 3 to 4 Fixed noise pattern from camera (radiation) Possible improvements: new camera : noise /5  nominal: few turns - pilot: 100 turns ? at 10 -8 T H2

24. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 TURN by TURN Studies (injection, matching)

25. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Rest Gas Ionization Profile Monitor (3) Batch of 40 »LHC» bunches of 3.5 10 10 p. each - 3 mm /strip on 500 turns after injection into SPS SPS Turn by turn data (43 KHz)-P = 10 -8 Torr 1 mm H rms value evolution over 100 turnstime        Turn by turn average H position over 200 turns 5 mm

26. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Rest Gas Ionization Profile Monitor (4) One bunch of 3.5 10 10 p. - 3 mm /strip - on 200 turns after injection into SPS SPS Turn by turn data         Turn by turn H rms value evolution over 195 turns (screen left IN beam) 5 mm

27. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Ionization Profile Monitor– turn by turn data One batch (72 bunches) of 3.5 10 10 p / bunch 32 strips - 1 mm /strip - on 150 turns after injection into SPS Injection not matched Turn by turn H rms value evolution over 150 turnsTurn by turn average H position over 150 turns #150#170#180#200 #230#250#270#300 2 mm 4 mm

28. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Ionization Profile Monitor– turn by turn data One batch (72 bunches) of 3.5 10 10 p / bunch 32 strips - 1 mm /strip - on 150 turns after injection into SPS Matched injection Turn by turn H rms value evolution over 150 turnsTurn by turn average H position over 150 turns 2 mm 4 mm #150#170#190#210 #230#250#270#290

29. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Future – New IPM monitor installed in SPS (LSS5) next year B field *4 (2500 G) better resolution R. Perret, EST/ME

30. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Conclusion present monitor in SPS gives good results down to rms values of  500  m ( 3 TeV in LHC with  = 200 m) Can also be used in turn to turn mode: fully passive way of tuning the injection matching Expected improved resolution with new SPS monitor

31. C. Fischer – LHC Instrumentation Review – 19-20/11/2001 Proposed location in LHC: LSS4 One H&V monitor upstream D3 separator dipole quiet region (radiation), large beam separation > 300 mm (integration) Suitable optics:  H,V  250 m,   1.4 mm at 450 GeV RF system Q7 Q6 Q5D4 D3 IP4 D3 D4 Q5 Q6 Q7 H&V gas monitor beam 1 beam 2