Vacuum Devices for accelerator studies Bernard HENRIST CERN TE dept. – Technology Department VSC group – Vacuum Surfaces and Coatings OLAV III Oak Ridge July
OLAV III Oak Ridge July 2011 Outline Motivation: Why are we interested to study the electron cloud? Secondary Emission Yield (SEY) devices Electron Cloud (EC) devices 2
OLAV III Oak Ridge July 2011 Motivation: electron cloud High intensity bunched protons beams cause multipacting Dynamic pressure rise We need to understand and found solutions to deal with this phenomenon Key parameter: Multiplication factor - 3 = SEY = ESD P+
OLAV III Oak Ridge July 2011 SEY : principe of measurment e- AA Cage +45V eV SEY – Secondary Emission Yield = = Emitted electrons / Incident electrons Ib=Is+Ic ; =Ic/(Is+Ic) Ib Is Ic Ib Ic Is 4
OLAV III Oak Ridge July 2011 SEY : lab device Up to 13 samples Pulsed current Insulator measurement LabVIEW controlled 5 Up to 13 samples Cage (test for insitu measurements) Hemispheric energy analyser
OLAV III Oak Ridge July 2011 SEY: Results Measurments: Common UHV material Glow discharge (argon, nitrogen) Cleaning and storage effect Electron dose effect Photon dose (EPA) Cold surfaces (condensed gaz) Activation of NEG Insulators (BN, TiN, Al2O3,…) 6
OLAV III Oak Ridge July 2011 SEY: Cold surface LHC is 80% cold SEY measurement of cold surface correspond to measurement of condensed gas… The cold sample is placed in a warm system to have a known cold surface Differential pumping No insulator view by the electrons High insulation to be able to measure A on the sample 7 Cold baffle Electrically, insulated Sample ReFe t° RTD Vacuum barrier/ Thermal screen Phase separator Kapton/SS screens Cold Sample
OLAV III Oak Ridge July 2011 SEY – Photon dose Photon bombardement in EPA Translation and rotation of the sample Remote motions and SEY measurement 8 SEY Energy Photon conditioning SEY Measurement Synchrotronic light (from EPA)
OLAV III Oak Ridge July 2011 Electron cloud in SPS Experimental area in BA5 : 80 m deep – 150m cables SEY XSD – eXperimental Strip Detector SDNeg – Strip Detector with NEG coating CSD – Cold strip detector Pickups 9
OLAV III Oak Ridge July 2011 SEY in SPS In situ SEY Measurement Use of a half barrel sample Mesurement after a half turn rotation Rotation and translation motions Full remote from surface (150m) 10
OLAV III Oak Ridge July 2011 XSD – eXperimental strip detector Vacuum chamber in magnets Lithography on Kapton foil Transparency around 7% (laser drilled holes of 0.25 mm) 47 strips for profile measurement Use of liners for fast exchange RF fingers for impedance Pre-backeout of the kapton 11
OLAV III Oak Ridge July 2011 XSD Results In field free conditions In dipole field conditions 26 mm ECLOUD’04 - Jose Miguel Jimenez 12
OLAV III Oak Ridge July 2011 QSD - QuadStrip detector Round liner Half turn extraction Confirmation of the simulation based on the dipole measurements. 13
OLAV III Oak Ridge July 2011 SDNeg Activated NEG has a low SEY The liner was coated Water protection with additional neg chambers and cold baffles (80K) 14
OLAV III Oak Ridge July 2011 CSD – Cold strip Detector Cold strip detector reach 30K Temperature reach by the use of cold head in close loop with helium compressor Same effect at cold temperature but, strong effect induce by the condensed gas Use of two baffles around the detector Kapton heaters to drive temperatures PT100 temperatures measurements 15 Strip detector He compressors Cold head (<30K) CSDBaffle Cold heads Baffle Proton beam
OLAV III Oak Ridge July 2011 Pickup Pickup are often place behind a shielding grid to avoid to be influenced by the image current. 16 Proton beam Image current Unshielded pickup Shielded pickup
OLAV III Oak Ridge July 2011 EKD – Electron Kicker Detector Project for Christmas 2011 : EKD in SPS « Survivor electrons »: Stay excited between two batches The goal is to collect these « survivors» by a high tension kick between two plates… At the right moment… 17 3s3s 1s1s
OLAV III Oak Ridge July 2011 Conclusions Many devices have been built to study the SEY and EC – XSD still in operation (Carbon coating) It was demonstrated that scrubbing the surface is a way to reduce the multipacting EKD: a new system to improve the knowledge of batches interaction 18