Libresource View Page

{summary}

T1 I - Spectrometer
T1.1 1/ Requirements
The requirements of the spectrometer are:
- to measure electrons with kinetic energy from 0 to 30 eV
- to measure ion with kinetic energy from 0 to 10 eV with moderate mass resolution
- to be UHV compatible (<10^-9 mbar)
- to be easy to unmount and versatile: total length of the spectrometer should between 15-20 cm

T1.1 2/ Electrostatic Design
 [../images/Spectro_Elec_jpg|{image:../images/Spectro_Elec_jpg|align=right|width=300}] 
To improve the kinetic energy transmission of the spectrometer different strategies can be employed:
- use a uniform magnetic field to confine the radial motion of the electron along the Larmor radius. 
- use a non uniform electrical field either in the extraction region or after ("drift tube").
The use of magnetic field was simply discarded for many practical reasons. The possibility to apply a non uniform field in the extraction region was quickly investigated by shaping a field gradient with polynomial expansion. Simulation were performed using [http://www.simion.com/|Simion 3D software].  The result showed that one should shape as well the electrodes to have a complete control of the field gradient at the source point. From a practical point of view, such solution would also require a very careful alignment to know exactly the source location with respect to the field gradient. In the present case, a solution using a non uniform electrical field in the drift tube was used (see figure).\\
\\
 [../images/Spectro_Particle_jpg|{image:../images/Spectro_Particle_jpg|align=right|width=300}] 
The objective is to reach an extraction field (E V/cm) as low as possible. Using this units the ratio between the maximal kinetic energy of particles (Ekmax) and the E field should be around one. All solutions with a Wiley McLaren type spectrometer could not satisfy the mechanical constraint, namely the total length of the spectrometer: longer is the drift tube lower is the is ratio Ekmax/E. The l=2d condition has been broken and a dispersion of typically 350 ps/mm is noted.\\
The use of a mu-metal shielding against the earth magnetic field requires to have a grounded environment: a direct consequence is to have field penetration in the spectrometer. To minimize efficiently this effect, the size of the electrodes has to be at least twice larger than the spacing between electrodes, fixing thus the electrode outer diameter; the inner diameter being defined by the size of the detector.\\
Finally, one should be able to "zoom" to measure the low kinetic electrons with the highest resolution. The electrons with higher kinetic energy should then leave the spectrometer without producing noise. Therefore, a negative polarity for the spectrometer is preferable. Grids in the extraction region seems better then a simple metallic plate, however it can lead to a weak field penetration and two grids have been anticipated. Simulation with Simion software cannot properly take into account such field penetration and an alternative would be to perform simulation with the [http://www.electronoptics.com/| CPO software]. \\


\\

T1.1 2/ Mechanical Design
 [../images/Spectro_Mechanical_jpg|{image:../images/Spectro_Mechanical_jpg|align=center|width=500}] 

T1 II - Electrical Connectivity
 {table} Solution | Advantages | Inconvenients
Coaxial (1) | simple / cheap | vacuum uncertain / E fields not so flexible
Multi pin (2) | E fields flexible / good vacuum | expensive / rather complex
{table}

T1.1 1- Coaxial connectors
 {table} Coaxial type | No of Pins |  Price (euro)
MHV  (grounded shield - single ended)| 4| 274 
SHV-5 (recessed) | 4| 421 
 {table}
- 1*10 Push-on connectors:  46 euros
- 10 m Kapton 5kV : 82 euros
- 50 Resistances 1% Phoenix 1 MOhm : 1.75 euros
- 50 Resistances 1% Phoenix 7.5MOhm : 1.75 euros

T1.1 2 - Multi pin connectors (16 pins minimum)

 {table} Feed Through | No of Pins | Unitary Price (euro)| Quantity | Total (euro)
 12 kV|7|654|3|1962 
 5 kV|8|341|2|682
 5 kV (weldable)|1|34|16|544
2.5 kV |10|284|2|568
 {table}

- 4*10 Push-on connectors:  4*46=184 euros
- 10 m Kapton 5kV : 82 euros
Conception

ls://dev.artenum.com/community/mathieu/development/3DMomentum/3Dies/conception
