Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 ELECTRON CLOUDS AND VACUUM EFFECTS IN THE SPS Experimental Program for 2004 J.M. Jimenez Thanks to my colleagues of the Vacuum Group for their contributions and their help in the preparation of this presentation And more generally to the AB/ABP, AB/OP, AB/RF, AB/BDI, AT/MEL, AT/ECR and TS/MME Groups for their help. See also in Session C: A. Rossi, “SEY and EC build-up with NEG Materials” V. Baglin, “Results of LHC type cryogenic vacuum systems subjected to ECE”

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Introduction – SPS Running with LHC-type beams Experimental set-ups and Main Results –Experimental set-ups: Cold and Variable Aperture Strip Detectors –Main results at 25 ns bunch spacing –Preliminary results at 75 ns bunch spacing Experimental program for 2004 –Questions which shall be answered –New detectors Conclusions Main topics

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Introduction SPS Running with LHC-type beams

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Different behavior between DF and FF Beam conditioning and bunch dependence observed but results not easily understandable Experimental Set-ups Pressure readings give indications…

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 80 K K Collecting plate (strips) Cold head Collecting strips Beam “pipe” (< 30 K) Thermal shielding (80 K) Experimental Set-ups Cold Strip Detector (30 K) Length of cold section = 600 mm

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Motor Moving plate RF contacts As seen by the beam… Experimental Set-ups Variable Aperture Strip Detector From 35 to 80 mm in height

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Electron cloud build up and thresholds –There is a threshold in the bunch intensity below which no activity is observed: p/b in a dipole field (DF) / p/b in field free region (FF) –At p/b in field free regions Build-up starts after 20 bunches in the first batch, immediately in batch 2 to 4 “Surviving” electrons are observed between batches Dependence on filling pattern (above threshold) –Linear dependence of the collected electron current and heat load with bunch intensity and with number of batches (filling factor) –> 550 ns spacing required between batches to decouple the effect of two successive batches on the build up Dependence on bunch length (during ramping from 26 to 450 GeV) –Initial increase of the collected electron current when the bunch length decreases at the beginning of the ramp, followed by a decrease at the end of the ramp, when the bunch length is the shortest (preliminary) Main Results at 25 ns Bunch Spacing Build-up, Thresholds, Filling Pattern and Bunch Length

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 e - cloud signal LHC beam signal 550 ns spacing Surviving e - Main Results at 25 ns Bunch Spacing Build-up measured using a shielded pick-up

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Main Results at 25 ns Bunch Spacing Build-up measured using a strip detector In field free conditionsIn dipole field conditions 26 mm

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 LHC Beam Screen Main Results at 25 ns Bunch Spacing Spatial Distributions in DF

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Heat load efficiency = HLE e - HLE (DF)= 1.7 × e - HLE (FF) E e ->180 eV located in the centre  faster beam conditioning observed 180 eV Dipole field 80 eV Field free Dipole field Main Results at 25 ns Bunch Spacing Energy and Spatial Distributions in DF/FF

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 COLDEX LHC LSS without NEG Main Results at 25 ns Bunch Spacing Effect of vacuum chamber height in DF/FF BS V BS r

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Ramp to 55 GeV Ramp to 450 GeV Main Results at 25 ns Bunch Spacing Detrimental effect of the ramp in Energy

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Main Results at 25 ns Bunch Spacing Detrimental effect of the ramp in Energy Pressure Variations

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 At RT in both DF and FF –Thresholds increased with beam time In DF: 3.0 ×10 10 p/b  8.0×10 10 p/b In FF: 5.0 ×10 10 p/b  > 1.3×10 11 p/b –Position of the 2 lateral strips independent from beam conditioning (expected) –Beam conditioning in FF faster than in DF –Vacuum cleaning/scrubbing observed:  P decrease by ~100 in DF and FF at RT Secondary Electron Yield (  ) measurements at RT in FF –  decreased down to 1.5 in FF –“Venting” to air reset the  to its initial value (as in the Lab) –“Memory” effect on a conditioned surface (faster conditioning as in Lab) –  drift without LHC-type beams  less than 4 h to recover the initial value Main Results at 25 ns Bunch Spacing Beam conditioning / Vacuum Scrubbing at 30 K and RT

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Main Results at 25 ns Bunch Spacing Pressure decrease resulting from both vacuum scrubbing and Beam conditioning

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 0 h 140 h Main Results at 25 ns Bunch Spacing Evolution of the Spatial Distribution during the Beam Conditioning 30 K/DF

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 The reduction of electron current versus cumulated beam time is significantly slower at 30K than at room temperature, but initial values are close. RT (VASD detector)30 K (CSD detector) (Values normalized to a circular tube of ID 35 mm) Main Results at 25 ns Bunch Spacing Beam conditioning: Evolution of Collected Electron Current in a Field Free

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 The reduction of electron current versus cumulated beam time seems also lower at 30K than at room temperature, but there is much less difference. Again, initial values are quite close. RT (VASD detector)30 K (CSD detector) Main Results at 25 ns Bunch Spacing Beam conditioning: Evolution of Collected Electron Current in a Dipole Field

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 In the SPS, the electron cloud-induced pressure rises are observed in the dipole field regions, arcs of the SPS  e - build up also seen with 50 ns bunch spacing in 2001 (using pressure gauges)  No signal in Field Free at RT (LSS) but there were already well conditioned Comparison between 25 and 75 ns bunch spacing in dipole field regions: –Smaller pressure rises  factor 4 –Smaller electron flux to the walls  factor 20 measured in a 30 K  Multipacting is still present with 75ns bunch spacing but at a much lower level.  Strip separation is different between the 25 and 75 ns bunch spacing (?) Preliminary results at 75 ns bunch spacing Comparison with the 25 ns Bunch Spacing

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Experimental program for 2004 Questions which shall be answered  According to the known values of the available cryogenic cooling capacity, what will be the maximum luminosity (bunch intensity/filling factor) which can be achieved at 75 ns and 25 ns bunch spacing  Are e - induced heat loads the only 1 st order limitations ? What about emittance growth and e-p instabilities ?  Confirmation of the beam conditioning efficiency measured on the cold surfaces in field free and dipole field  What about edge effects (limited length) ?  Vacuum performances in different electron multipacting conditions  What about the collimators halo ?  What about the transfer lines ? (build up after 20 bunches only)  Electron cloud build up and Heat load in a quadrupole field  …How reliable are the extrapolations from the SPS to the LHC ?

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Experimental program for 2004 Experimental Area SPS BA5 Strip2002 Baffle CSD MBA Pick-ups RFD QSD RGA MBB Pick-ups VASD

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Experimental program for 2004 New Detectors Cold Baffles to protect the Cold Strip (1) CSDCold Screen HP518 (LSS5)

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Experimental program for 2004 New Detectors Cold Baffles to protect the Cold Strip (1) Beam screen with collecting holes Heater RFD Cold Screen Heater Cold Strip Detector Cold Head Cold Screen inside the Baffle Cold Screens with Heaters RF Shields

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Strips covering half diameters with a 2 mm spatial resolution Chamber ID 95 mm Experimental program for 2004 New Detectors Strip Detector in a Quadrupole

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Experimental program for 2004 New Detectors Strip Detector in a Quadrupole Beam Screen with the collecting holes Beam Screen with the collecting stripes lithographed Kapton foil 1 mm resolution Spacers for the lithographed Kapton foil

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 SPS should be able to inject the LHC after 5 days of beam conditioning with 3 or 4 batches at 1.1x10 11 p/bunch No signal in the field-free regions (long straight sections), the electron cloud activity decreased below < A/m In the arcs (dipole field), electron cloud still “visible” with 4 batches injected  Pressure rises decreased by a factor > 100  Similarly to RF and HV devices, beam conditioning efficiency limited to the parameters used during the scrubbing  will not be effective if running conditions become more favourable Ultimate SEY value  = 1.5 reached after 4 days in the FF regions in the SPS:  Shows the multipacting threshold under these conditions  Is in good agreement with analytical calculations Upward drift of the SEY (  ) observed if the SPS is not operated with LHC- type beams is not an issue  Measurements confirmed that SEY recovered its initial value after 4 hours of operation with LHC-type beams. Conclusions (1) SPS as the LHC Injector

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Conclusions (2) LHC and the Electron Cloud Vacuum scrubbing (P decrease with beam time) is observed at RT in both DF and FF Beam conditioning is observed at RT and at 30 K in both DF and FF –Initial electron activity comparable at room and cryogenic temperatures –Electron activity decreases faster at RT than at cryogenic temperatures in FF regions, the difference is marginal in DF –75 ns bunch spacing results in a significantly lower activity (<1/10), but it is still present –Beam conditioning is limited by available cooling power / EC induced Instabilities Detrimental effect of the ramp in energy  bunch length shortening and beam orbit displacement

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Conclusions (3) LHC and the Electron Cloud To cope with the available cooling power:  Change the filling factor instead of reducing the bunch intensity since reducing the latter means displacing the strips in the chamber and changing the energy spectrum of the electrons  There still are questions: –Is the threshold the same as for SPS? –Influence of the reduced bunch length in LHC versus SPS? Preliminary estimation of the required beam conditioning time in LHC, pending to a better understanding of the behaviour of the cryogenic vacuum system.