Laser cooling of stored relativistic ion beams

Transcription

1 Laser cooling of stored relativistic ion beams full ion beam diagnostics M. Bussmann 1, F. Kroll 1, M. Löser 1, M. Siebold 1, U. Schramm 1 W. Nörtershäuser 2,3, C. Novotny 2,3, C. Geppert 2,3 D. Winters 3,4, Th. Kühl 2,3,5, C. Kozhuharov 3, Th. Stöhlker 3,4,5, M. Steck 3, C. Dimopoulou 3 T. Beck 6, B. Rein 6, Th. Walther 6, S. Tichelmann 6, G. Birkl 6 W. Wen 1,3,7, X. Ma 7 1 HZDR 2 Uni Mainz 3 GSI 4 Uni Heidelberg 5 HI Jena 6 TU Darmstadt 7 IMP-CAS

2 Motivation spectroscopy of high-z Li- and Na-like ions (SIS100/300, NESR) only cooling method for SIS study laser cooling without pre-electron cooling set up fluorescence detection to determine the lower limit of the longitudinal momentum ( p/p<10-7 ) study ordering of the ions in the beam at very low momentum spread use broadband pulsed laser cooling for fast cooling of many ions

3 The principle: laser cooling of relativistic ions C 3+ ion energy 122 MeV/u ( 0.47, 1.13) 2P transition 2S p =93 nm 0 =155 nm a =257 nm In our case, the cooling laser force must be counteracted by the restoring force of the `bucket when the ion beam is bunched.

4 Experimental setup (2004/2006) UV Laser Beam BPM Ions Ion Species: C 3+ Experimental Storage Ring at GSI Photomultiplier Schottky Electron cooler rest = laser / (1+ ) E beam = 122 MeV/u = 1.47 GeV ( = 0.47, = 1.13 ) f rev = MHz beam ~ 300 s (no cooling) Ar + ion laser (cw) SHG laser = nm Laser 2S 1/2 2P 1/2 rest = nm rest = 3.8 ns Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

5 Results of previous beamtimes Laser cooling of C 3+ at 122 MeV/u in the ESR in 2004 and : "simple" laser system for first tests on the 2s 2p ~155 nm 2006: scanning laser system to improve the cooling scheme measurement of 2S 1/2 2P 1/2 & 3/2 Uncertainty in absolute ion energy Schramm, Bussmann et al. (2S 1/2 2P 1/2 ) [nm] (2S 1/2 2P 3/2 ) [nm] ESR C 3+ experiment Theory (I. Tupitsyn, V. Shabaev) (39) (3) (39) (2) (26) (53).

6 What happens at small detuning? Schottky Schottky Signal vanishes (below 10-8, 4-5 orders) detuning Laser h = 20 I ion = 16 μa bunch length= m bunch width = 5.26 mm I ecool = 2 ma

7 Limitations at previous beamtimes pre-electron cooling was required laser force small momentum spread bucket frequency was scanned, not the laser Schottky detection is limited in sensitivity

8 Experiment improvements Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt UV Laser Beam BPM Ions Experimental Storage Ring at GSI new PMTs + channeltron Schottky new Schottky Electron cooler new BPM Pulsed / Scanning Laser Laser

9 Tools for the next beamtime new pulsed laser system (HZDR) new "fixed" CW laser (DL, 1024 nm) new "scanning" CW laser (ECDL, 30 GHz / ms) new Schottky pick-up system (pill-box design) new beam profile monitor (MCP - CCD / ms) new UV-PMTs and UV-channeltron (in vacuum) new data acquisition and control system (NI compact RIO)

10 New Schottky pick-up system Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt Two identical step motor drives for symmetrical frequency tuning Resonator, air filled ceramic gap dismountable assembly coupling loop cable

11 New beam profile monitor (BPM) horizontal vertical Play with - laser power- laser scanning- bucket frequency detuningbucket amplitude Vertical and Horizontal temperature

12 New optical diagnostics Ion beam Drift tube Laser beam fast scan of the velocity distribution HV (-5 5kV) PMT Moveable Photo-channeltron in vacuum trigger with bunching frequency TDC

13 gas jet target ion beam photo-channeltron detector (in vacuum) CaF2 viewports Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

14 channeltron cage with mesh "hat"

15 New data acquisition and control system Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt Controller Chassis Module HOST PC Slave Chassis Use LabView with network to control the system data transfer between the controller and the chassis, and between the controller and the host PC Save the data in controller or host PC

16 Nice results from cooled ion beams Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt Steck et al. ESR - Darmstadt T par 30 K T perp 4500 K Schramm et al. PALLAS - München

17 Laser cooling & spectroscopy SIS300 At the high velocities ( =25) in SIS300, laser cooling seems to be the only realistic cooling method. Laser cooling force ~ 3! Observers NESR CN DE ES FI FR GB GR IN IT PL RO RU SE

18 Laser cooling of Li-like ions at the SIS300 The transition wavelengths strongly depend on the atomic number Z! The Doppler boost of the SIS300 shifts wavelengths to `normal lasers! transition wavelength (nm) atomic number Z magnetic rigidity B (Tm) atomic number Z SIS300 NESR needs fast transition: 2S 1/2 2P 1/2 B U. Schramm, M. Bussmann et al.

19 Laser spectroscopy at the SIS300 Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt QED in lithium-like systems = s 2 2p 1s 2 2s ev x2 laser x-ray x2 Laser* ev ions Up to a factor 4 better resolution! ( E/E of the transition) x-ray micro-calorimeter ~10-5 kev resolution (now still ~10 x-ray -3 at few kev) detector crystal monochromator H. Backe, Hyp. Int. 171, 93 (2007). * 454 nm frequency doubled

20 Thank you for your attention! Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

21 EXTRA SLIDES Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

22 Linear-durchführung für Photo-channeltron Detektor CaF2 Fenster Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

23 cage with mesh reference line

24 channeltron connections, 15 March 2011 cage with mesh tail (signal) head (-HV) cage (bias) middle (ground) reference line Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

25 Linear-durchführung für Photo-channeltron Detektor CaF2 Fenster Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

26 New data acquisition and control system Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt Data files Pick-up Computer Data file GSI Network BPM Schottky Trigger Time Data file DAQ-CS CompactRIO Laser system Ion beam current High voltage drift tube Fluorescence rate Buncher

27 Labview interface: ion beam current readout a. Ion beam injection will be the trigger signal b. Display Ion beam current c. Online data fitting d. Display ion beam life-time e. Display ion number f. Save the data sheet for offline analysis t Iion I(t) I(0) exp( ) Nion f q e rev

28 Laser access and fluorescence detection 30m 6.5m C 3+ ions Laser light Fluorescence Detection section Moveable channeltron

29 Fluorescence detection: CaF2 viewports UHV CF63, 1.9" view Excimer 157 nm Transmission at 157 nm > 85% Max Bakeout 200 ºC Photomultiplier tube 9423B (51 mm diameter) CsI coated, MgF2 window spectral range: nm 157 nm: several percent dark count rate: 20 Hz Photo channeltron Mass Analyzer Products MAP , CEM 4869 cone CsI 26mm diameter

30 Photomultiplier tube for detecting UV light Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

31 Testing channneltron with deuterium lamp Counts(Hz) Position 1 of Lamp Position 2 of Lamp Position 3of Lamp Counts(Hz) HV=-1850V HV=-1950V HV=-2050V HV=-2150V HV=-2250V HV=-2350V HV=-2450V High Voltage add on the channeltron(v) Distance between Deuterium Lamp and Channeltron (m)

32 External Cavity Diode Laser Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt Cavities 26 GHz 100 Hz (we need ~ 3 GHz) to Amplifier Diode Laser + Grating

33 Fibre Amplifier Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt nm 2x SHG to 257 nm (we need < nm)

34 Advantages of compactrio Reconfigurable input and output modules (hardware) for different signals Small and stable embedded real time processor Rapidly design custom hardware reconfigurable FPGA chips provide the flexibility, performance, and reliability of custom hardware LabView graphical development tools for rapid development Control and communication via ethernet, complete system can be controlled by LabView (via network)

35 Injection Energy 400 MeV/u Spectroscopy at the ESR Experiment MeV/u

36 Schottky diagnostics at the ESR Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt pick-up local ion electrodes oscillator At the relativistic energies in the ESR (~50% of c), the Doppler shift is so large that only ONE laser can be used. Therefore, the cooling storage laser force will be FFT ring counteracted by the restoring force of the bucket when the ion beam is bunched. analyser image reject mixer

37 Electron cooler at the ESR I: ma U: kv momentum spread: p/p ~10-5 ion beam diameter: ~2 mm

38 Cooling: narrowing velocity, size and divergence uranium ions stored in the ESR 250 after 5 s Power [db/hz] electron cooling stochastic cooling after 3 s % -0.15% -0.05% 0.05% 0.15% 0.25% Injection p/p momentum distribution Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

39 Photograph of the ESR Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

40 How to access the ESR? 30m 6.5m C 3+ ions available view ports x - scraper Laser light y - scraper

41 Laser systems for laser cooling Ar + Laser (514 nm) # 1 Frequency doubling crystal frequency stabilised YB:YAG Ar + Laser pulsed (514 nm) (ns) # 2 frequency scan beating signal (MHz - GHz) Stabilised double-z resonator Frequency doubling crystal Stabilised double-z resonator merged UV laser beams (257 nm) Ion Ar + beam YB:YAG p ions p Fluorescence detection

42 Optical Schottky Diagnosis Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt Ion beam Drift tube fast scan of the velocity distribution trigger with bunching frequency HV (-5 5kV) Fluorescence Detection IN VACUUM! TDC

43 Laser cooling specifications Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

44 Ultralow Momentum Spread & Strong Coupling pure electron cooling pure laser cooling laser cooling + electron cooling (1 ma) Dashed lines: ~ N 1/6 ( IBS) Solid lines: ~ N 1/3 (space charge) 10 x smaller Momentum Spread Strong Coupling observed (Needed for Crystallization) 1 Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt

45 Schottky mass spectrometry (ESR) Danyal Winters 4th EMMI Workshop plasma physics 4 May 2011 Darmstadt ion pick-up electrodes local oscillator storage ring image reject mixer FFT analyser (velocity / circumference ) ( magnetic rigidity ) mass / charge

46 - + RF field ~

47