E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources1 Summary on „ABS‘s for Targets & Ion Sources“ Discussion Session Tuesday, , 16:00-18:00h Panel: D. Toporkov (BINP), M. Stancari (Ferrara), A. Nass (Erlangen-Jülich), A. Belov (INR), A. Zelenski (BNL), E. Steffens (Erlangen) Topics: Low-beta target section – A. Garishvili (Erlangen-Jülich) Luminescence BP monitor for RHIC jet – D. Trbojevic (BNL) Basic limitations of ABS intensity (Toporkov, Belov) Study of beam formation (Stancari, Nass) H 2 contamination in the RHIC jet, and how to measure it precisely (Zelenski) In addition, this topic was covered in several talks during the meeting!

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources2 The last 30 years of Atomic Beams ? ? M. Stancari (Ferrara)

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources3 Some Characteristics of Current Sources HermesNovos.Wisc.ANKERHIC Input (mbar l/s) B pt (T) d mag (cm) v drift (m/s) ~1530 T beam (K) ~18 length (m) d ct (cm) Intensity (10 16 atoms/s) 2 states Michelle Stancari Surprising: RHIC jet intensity about 1.7x the intensity of the other sources! Why ?

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources4 Understanding the ABS No real quantitative prediction or explanation of intensity into standard CT The high intensity of RHIC ABS (1.24·10 17 /s) is not explained (too much!) Important to refine the simulation programs to include - realistic starting distribution - tracking through magnets (the only well defined problem) - Intra-beam scattering (IBS) - distribution of lost atoms (defocussed and scattered) → calculation of H/H 2 density along axis (pressure bumps) To my knowledge, the only place where at present systematic simulation studies are performed, is Ferrara (Michelle Stancari & W. Kubischta)!? We have to put more effort into ABS simulation !

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources5 Contributing Effects Emittance at skimmer plane Formation of pressure bumps IBS Intra-beam scattering due to spread in velocity distribution Optimum flux into cell !! M. Stancari

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources6 Attenuation of the beam by residual gas - well understood process I(p) = I 0 *exp( -x*p/   p 0  ) Relative velocities of particles correspond room temperature Precise measurement of contributions of individual pumping stages possible by systematic variation of pressure via gas injection! See thesis F. Stock (Heidelberg 1994) and N. Koch (Erlangen 1999) For HERMES source total attenuation due to ‚homogeneous background‘ is about 10%. D. Toporkov

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources7 Still Missing Quantitative account for Intra-beam scattering - estimates exist indicating that it is important!

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources8 Assume  v/v max  0.25 and v max  2*10 5 cm/sec Take  ≈  1.5* cm -2 from attenuation atomic beam by 300K residual gas (for 20K beam temperature  should be larger). For given  we get   ·   cm s, resulting in: At Flux at/cm 2 s and distance x = 150 cm:  (150) ≈ 0.7  0 E. Steffens PST 1997 Estimates on IBS D. Toporkov Assume that losses occur by Single Scattering. For parallel beam and velocity spread  v one gets (x along beam):

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources9 Some Characteristics of Current Sources HermesNovos.Wisc.ANKERHIC Input (mbar l/s) B pt (T) d mag (cm) v drift (m/s) ~1530 T beam (K) ~18 length (m) d ct (cm) Intensity (10 16 atoms/s) 2 states Michelle Stancari Surprising: RHIC jet intensity about 1.7x the intensity of the other sources! Why ? Limit length of ABS!

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources10 Still Missing Quantitative account for Intra-beam scattering - estimates exist indicating that it is important! What about pressure bumps – a mystery ? - might lead to kind of ‚blocking effect‘

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources11 Characteristics the INR pulsed polarized proton source A. Belov (INR) ABS: –peak intensity of polarized atomic hydrogen beam is at/s –most probable velocity is cm/s Polarized proton beam: –peak current is 6 mA –polarization % –normalized emittance 2  mm mrad –rep. rate up to 10 Hz Unpolarized deutron current density mA/cm 2

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources12 Intensity of pulsed INR ABS A. Belov Linear! although measured at large distance Drops during pulse

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources13 Studies at INR (Moscow) A. Belov

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources14 Beam-skimmer interference A. Belov Density of pulsed atomic hydrogen beam decreases with decrease of the nozzle-skimmer distance while simulation (which does not take into account scattering of atoms) forecasts increase of density  Explanation: atomic beam forms gas “cloud” inside the skimmer and atomic beam attenuates due to scattering : beam-skimmer interference

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources15 Beam-skimmer interference simulation A. Belov When atomic beam passes through volume with restricted conductance - instability can arise for formation of gas “cloud” and attenuation of the beam incoming transmitted

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources16 Result of Simulation: Effect of Pressure Bump A. Belov looks familiar…

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources17 How dangerous are pressure bumps? Attenuation length a  a = [  loss ·  1 ] -1 Within a the beam is attenuated to 1/e. For  loss = cm 2 and a = 40cm (total magnet system) we get:  1 = 2.5·10 12 /cm 3 corresponding to about mbar So for 10% attenuation in the magnets we need an average pressure in the magnets of about 10  mbar (or mbar on 10% of this length). Just to set the scale…

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources18 Crude Estimates very preliminary – need to be checked! Assume tube of length L with conductance C* from center to the openings Assume  distribution with  0 as central density (→  0 = I*/C*) Assume that the flux of scattered atoms appears in the center: I* =  I ! Gives for intensity loss  I by the tube:  I = (L/2)  0  loss I Short calculation:  I = (L/2) (  I/C*)  loss I‘ I‘ = I‘ could be interpreted as kind of critical beam intensity (?). With C* = 10l/s, s = cm 2 and L = 5cm we get I‘ = 4·10 17 /s Does this mean that we are close to this limit – in particular for the pulsed sources? I I -  I

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources19 Conclusions Satifactory description of Atomic Beam Sources still lacking many observations! work on simulations in progress

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources20 Studies at HERMES N. Koch, A. Nass et al DSMC calculations

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources21 SpinLab ABS-1 Inlet Pressure Nozzle and Skimmer Chamber Pressures Beam Density and Time of Flight with QMA (both hydrogen atoms and molecules separately) M. Stancari (Ferrara)

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources22 Example of Simulation M. Stancari DSMC calculations

E. Steffens - PSTP 2007 (BNL)Summary ABS for Targets and Ion Sources23 Conclusions Satifactory description of Atomic Beam Sources still lacking many observations! work on simulations in progress - very important - compare with measurements on test benches and running sources! This will lead us to improved sources with higher output! I don‘t expect /s in the foreseeable future, but 3·10 17 /s is a resonable extrapolation for a strong development effort! Let‘s do it together!