Emittance (Profile) Measurements in the Proton Accelerators at DESY

Transcription

1 Emittance (Profile) Measurements in the Proton Accelerators at DESY Kay Wittenburg, MDI Deutsches Electronen Synchrotron Hamburg, Germany

2 Profile Monitors in the Proton Accelerators DESY III:» Wire Scanner, very old and new» Residual Gas Ionization (Prototype) PETRA II:» Residual Gas Ionization» New Wire scanners (LEP type) HERAp:» Residual Gas Ionization» Wire Scanners, old and new» (Synchrotron Radiation)

3 Residual Gas Ionization Profile Monitor in DESY III Prototype with no MCP Amplification by SIT Camera

4 Residual Gas Ionization Profile Monitor in DESY III Sensitivity at 10-8 mbar:» reliable signals from ma beam current using a sensitive SIT camera Resolution:» Primary electrons» Secondary electrons» Ions» Space charge» Optic (electrons and light)» Camera»...

5 1.17mm 1.19 mm

6 Residual Gas Ionization Profile Monitor in DESY III

7 Residual Gas Ionization Profile Monitor Ions Electrons Ions + Electrons The light electrons are much more sensitive to the space charge of the beam than the heavy ions

8 Simulation of space charge distortion without space charge with

9 Helmholtzcoil B focus : Cyclotron frequency = time of flight Wire Ø = 100 µm

10 Helmholtzcoil Test in Lab with a 100 mm wire B = 0 Tesla near resonance On resonance σ = 230 µm

11 DESY III Beam width versus momentum 1.5 mm offset

12 Measurement of the transversal energies of the Electrons / Ions E x = transv. Energy of particle Space charge

13 Distortion due to secondary emission from cathode Changing the cathode voltage

14 Distortion due to space charge of bunches Changing the grid voltage Space charge

15 Space Charge Correction by Th. Schotmann Dots = simulations Line = equation 700 µa Protons/bunch in HERAp

16 Distortion due to electron optic Potential lines in the IPM y=beam radius Profile distortion: focussing effect < 50 µm

17 Residual Gas Ionisation Profile Monitor in PETRA II and HERAp» Vacuum 10-9 mbar» Bunches => << ma» GeV/c» beam width << 1 mm, length 30-3 cm

18 First circulating beam in HERAp (1991) I p 0.01 µa (!) P vac»10-8 mbar FWHM»10 mm MCP dark current

19 Residual Gas Ionisation Profile Monitor in HERAp Continuous observation no absolute width measurement observation of changes at injection and ejection (PETRA)

20 Residual Gas Ionisation Profile Monitors at Petra II and HERAp Comparis on: W ire -scanner vs. Res.-Gas 2.5 horizontal : Petra curre nt/bunch [10e-6 A] * : c oastin g beam res.-gas wire-scanner Comparis on: Wire-Scanner vs. Res.-Gas 3 vertic al * + 51 * curre nt/bunch [10E-6 A] * * : c oastin g beam : P ETRA II res.-gas wire-scanner Ok. up to 220 µa/bunch (=ca Protons/bunch) incl. space charge correction

21 Fast Evolution of the normalized emittance and the beam width in DESY III measured with a linear sensor and a local gas bump. beam width σ [mm] momentum P [GeV/c] New measurement cycle every 400 ms DESY III: σ and εn versus Time Corrected to instrument "space charge" effect εn [π mm mrad] O : e n D : s - : P Cycle Time [ms] beam width σ [mm] momentum P [GeV/c] 10 first meas. cycle 9 8 DESY III: σ and ε n versus Time new cycle new cycle new cycle new cycle Corrected to instrument "space charge" effect ε n [π mm mrad] O : e n D : s - : P Cycle Time [ms]

22 Higher order mode losses in the IPM For the long proton bunches no problem

23 Wire Scanners at DESY Potentiometer /Ruler

24 Wire Scanner in DESY III» linear, pressed air» v = 1m/s» Carbon wire» Ø = 7 µm» Szintillator + Photomult. readout

25 Wire Scanner in DESY III

26 Wire Scanner in DESY III

27 Wire scanner in DESY III Position resolution of wire-scanner σ=59 µ m σ = 59 µmm Frequency x(fit) - x(meas.) [mm] measured position vs. linear fit

28 Wire Scanner in DESY III Wire - Temperature:» Calc. Tmax = C at I=160 ma Emittance blow up:» 10%/scan at 310 MeV to 0.01%/scan at 7.5GeV/c Beam losses:» <0.1 %/scan No broken or burned wire,no detectable beam loss or emittance blow-up!

29 Wire Scanner in HERAp Movement by pressed air Wire speed: 1 m/s Wire material : Carbon Wire diameter: 7 µm Signal: Scintillator + SEM

30 Wire scanners at HERAp Since start of HERA (1990) 3 broken or burned wire, no detectable beam loss or emittance blow up due to wire-scans! Increased background measured by the experiments. Specific Lumi agrees within 0-20% with experiments

31 Wire Scanners in HERAp - Fits

32 Single bunch emittance measurement with the HERAp wire scanner σ = 5.15 mm ε n π mm mrad p= 40 GeV

33 Trigger logic for the single bunch emittance measurement

34 The LEP Wire Scanner in all circular accel. and in TTF Advantages: Variable speed -> Tail measurements Small synchronization jitter Small size Very precise (<2 microns) Suitable for all accelerators in DESY

35 The LEP Wire Scanner in PETRAp

36 Triggered scan for TTF and DESY III Scans at 0.8 m/s Dt [ms] without Resistors with Resistors index of scan Synchronization jitter < 200 ms

37 Temperature of the wire (v=1m/s) Num. of part. Typ. Beam diam. Temp. after scan [C] Eqi. - Temp [Celsius] HERAp 1 *10^ mm HERAe 6.5 * 10^ mm PETRAp 4.8*10^12 2 mm PETRAe 1.5*10^ mm DESYIII 1.2*10^12 1 mm TTF fast 2.8*10^ mm TTF slow 2.8*10^ mm Melting temperature = 3500 ºC for Carbon = 1700 ºC for Quartz The wire in DESY III still exists with 200 ma = p In HERA 3 burned wires in the last two years

38 Wire Vibrations Wire mounting not fixed Black line = Fit of Gauss + Sinus White line = fit of real beam

39 Data from DESY III Simulation

40 Photomultipliers for wire scanners type sensitivity [microa/lm] ampl. Photom. Stages max lin. [ma] Diam. [mm] volt [kv] continuous curr. [ma] rise time [ns] used at R *10^5 Bi CERN PS XP 2243/B 160 2*10^5 tri CERN SPS/DESY XP 2203 B 165 4*10^6 tri Tevatron XP *10^8 Bi SLAC tri = trialkali Photokathode with lower resistance than bialkali Good linearity at high peak output

41 High peak current voltage divider

42 Synchrotron Radiation (edge effect) in HERAp

43 Synchrotron Radiation (edge effect) in HERAp The first spot of SR-light

44 Spatial Resolution microns Theoretical Spatial Resolution momentum Measurement with Laser and 3 slits (500 µm)

45 The End