Design and Properties of a Target for the MAGIX Experiment

Transcription

1 Design and Properties of a Target for the MAGIX Experiment Silke Grieser Westfälische Wilhelms-Universität Münster, Institut für Kernphysik New Vistas in Low-Energy Precision Physics (LEPP), Mainz, April 6th / 15

2 Design Requirements for the Target Windowless target Minimize background interaction Different target material: H 2, O 2, 3 He, Xe,... Pointlike interaction zone Target thickness constant in time Continuously adjustable and homogeneous spatial target density Target density: O ( 10 19) atoms cm 2 2 / 15

3 The Jet-Target baratron transfer part cold head warm stage cold stage turbomolecular pump nozzle 10 cm jet beam accelerator beam vacuum gauge 3 / 15

4 Volume Flow and Density Volume flow q V at normal conditions: q V = A p 0 MT0 T N p N ( 2 κ+1 ) κ+1 2(κ 1) κr A : Critical area of the nozzle p 0 and T 0 : Current pressure or temperature at the nozzle p N and T N : Normal pressure and normal temperature R: Universal gas constant M: Molecular mass κ: Heat capacity ratio Target density ρ T : ρ T = q V N A M M A beam v R T M A beam A beam and beam : Dimensions of the beam N A : Avogadro constant M M and M A : mass of gas molecul and atomar constituent v: Beam velocity 4 / 15

5 Volume Flow and Density Stagnations conditions at the nozzle for a constant volume flow Hydrogen Nozzle diameter: d = 30µm 5 / 15

6 Hagena parameter Hagena parameter Γ provides an empirical access to the prediction of cluster sizes Γ = kp ( ) dn 0 tanα 0.5 T Gas dependent constant k Stagnation pressure p 0 Temperature T 0 of the gas Nozzle diameter d n Expansion half angle α 0.5 Γ < 200: flow without cluster formation 200 < Γ < 1000: transition to cluster formation Γ > 1000: immense condensation of clusters 6 / 15

7 Hagena s scaling law Relation ( to the average cluster size N: Hagena s scaling law N = A Γ ) γn N 1000 Empirical Hagena parameter Γ, empirical values A N and γ N Esperanza 6. Mass distribution Köhler, of hydrogen PhD thesis cluster-jets2015, Münster cluster size / 10 5 atoms bar 8 bar 9 bar 10 bar Ñ(Γ ) N(Γ ) 1 10 Hagena parameter / 10 4 arb. units Figure 6.23.: Measured hydrogen cluster size (systematic uncertainties around 10 % excluded) of the selected isobars above 50 K as function of the Hagena parameter in double-log scale (with ˆk H2 = 184 [SDT98] and references therein, d n = 28 µm, and α1/2 = 3.5 degree). The grey solid line shows the expected cluster size N(Γ ) according to Hagena s scaling law (cf. Equation (6.21)) up to stagnation conditions within the vapour pressure curve. In addition, the grey dashed line presents a fit Ñ(Γ ) through the data via Equation (6.21) and varied parameter A N = 86 ± 3. The measured data and the predicted sizes agree by a factor of 2.6. Measured hydrogen cluster size as function of the Hagena parameter Grey solid line: Expected cluster size N (Γ ) (Hagena s scaling law) Grey dashed line: Fit Ñ (Γ ) through the data Measured data and the predicted sizes agree by a factor of / 15

8 Advantages of Cluster-Jets Directed jet flow Variable size and shape of cluster beam Effective size of target beam as small as possible Precise vertex reconstruction Small influence on the vacuum conditions in the accelerator High density in a distance of more than 2m from the nozzle Measurement which shows the best stagnation conditions in regards to Target size and shape Vacuum conditions in the accelerator 8 / 15

9 More elaborated Source Design Skimmer: Beam extraction and residual gas reduction Collimator: Size and shape of cluster beam 9 / 15

10 More elaborated Source Design Sperical joint to tilt the nozzle Narrowest inner nozzle diameter is point of rotation Extraction of highly intensive core beams rotation surface sliding surface Laval nozzle skimmer chamber skimmer 10 / 15

11 Cluster source - Beam structures Operation at highest densities liquid H 2 at the nozzle inlet Beam structures Highly intensive core beams Extraction of core beams by spherical joint 11 / 15

12 Cluster source - Beam structures Operation at highest densities liquid H 2 at the nozzle inlet Beam structures Highly intensive core beams Extraction of core beams by spherical joint 11 / 15

13 Cluster source - Beam structures Operation at highest densities liquid H 2 at the nozzle inlet Beam structures Highly intensive core beams Extraction of core beams by spherical joint 11 / 15

14 Cluster-Jet Target Cluster source - Beam structures Operation at highest densities liquid H 2 at the nozzle inlet Beam structures Highly intensive core beams Extraction of core beams by spherical joint 11 / 15

15 Specially Shaped Collimators cluster beam accelerator beam 700 µm Overlap between target beam and accelerator Collimator with round orifice beam small compared to the size of the target beam cluster beam accelerator beam 150 µm Collimator with slit orifice Target beam size as small as possible at same overlap region with accelerator beam Improvement of vacuum conditions in scattering chamber 12 / 15

16 Microscopic View of Collimators and Resulting Cluster Beams on MCP Detector Definition of target beam size and shape with collimators MCP images with expected beam shape and grid at approximately 5 m behind the collimator collimators phosphor screen MCP images Ø 0.5 mm 0.7 x x 0.19 mm 2 2 shaped and ionised cluster-jet beam Ø 22.5 mm max mm 5 m grid MCPs 13 / 15

17 Nozzle Shutter nozzle shutter opened cluster beam nozzle shutter closed cluster beam Useable as on/off switch A pulsed cluster beam is possible Reduced gas flow in interaction chamber Frequency of 10 Hz possible (limited by used linear motor) 14 / 15

18 Summary & Outlook Gas-jet targets fullfil all the requirements for Gas-Jet Target will be set up Possibility to switch into cluster-jet operation High density is feasible Directed cluster beam Variable size and shape of cluster beam Improvements of vacuum conditions Nozzle shutter as on/off switch Target production in progress... Target ready in summer / 15