3 MV Tandetron

3 MV Tandetron

The 3 MV Tandetron Accelerator, manufactured by High Voltage Engineering Europe B.V., was installed and commissioned in 2012 and is mainly dedicated to applied research [1]. This installation is fully equipped to perform studies of materials with accelerated ion beams (IBA - Ion Beam Analysis), ion implants (IIB - Ion Implantation Beamline) and radiation resistance tests for various types of advanced materials, as well as measurements of effective reaction sections (CSM -Cross-Section Measurements), of interest in nuclear astrophysics.

The 3 MV tandetron has three experimental lines, each with a reaction chamber containing all the necessary equipment:
- IBA studies: charged particle detectors for rutherford backscatter spectrometry (RBS) and recoil atom analysis (ERDA), SDD detectors for X-rays used in characteristic particle-induced X-ray spectroscopy (PIXE), semiconductor detectors (HPGe - Hyperpure germanium) for γ radiation (PIGE) and Markus ionization chamber used in the dosimetry required for radiobiology experiments.
The IBA line also contains a set of four electrostatic quadrupoles, with the help of which the ion beam can be focused up to a diameter of the order of microns.
- implantation / irradiation experiments with ion beams: electrostatic ion beam sweep system in the XY plane (17x17 cm2), with four Faraday cups that can determine the fluency with an accuracy better than 98%.
- Effective Reaction Section (CSM) Determinations: HPGe Detectors, Si Detectors for Charged Particles, Collimation System and Faraday Cups for Optimizing Ionic Optics and Accurate Determination of Beam Electric Current

Lentilă electrostatică pentru microfascicul

3D CAD representation of the electrostatic lens used to obtain the microfeam: 1. support plate; 2. ceramic insulators; 3. quadrupole electrodes.[2]

3 MV Tandetron
Main subsystems of the 3 MV Tandetron accelerator

To make it possible to apply an acceleration voltage of up to 3 MV, the inside of the tank in which the acceleration column is immersed is filled with sulfur hexafluoride (SF6) at a pressure of 6 bar. (SF6) is strongly electronegative, absorbing free electrons produced by micro-discharges, the dielectric properties of this gas are thus 2.5 times better than those of air, having a dielectric constant at 25 oC and 1 bar of 1.00204.
Being a tandem electrostatic accelerator, the high voltage is applied to the middle of the acceleration column, and its ends are connected to earth. The two sections of the acceleration column are made up of a succession of conductive cylinders (metal), separated by insulating cylinders (glass), glued tightly so that the pressure inside the column can be maintained in the range 10-7 - 10-5 mbar. The metal cylinders are connected to each other by means of resistors of 300 MΩ, thus creating a voltage divider with the role of ensuring a uniform electric field.

Schiță Tandetron 3 MV

Schematic representation of the 3 MV Tandetron accelerator with indication of the main subsystems

Canal de schimb de sarcină cu Na
Na charge exchange channel for α particle beam

1. Dual ion injector

Source of negative ions with Cs sputtering effect (model 860A):

- Electrode extraction
- Manually operated vacuum valve
- Einzel type electrostatic lenses
- Y-axis electrostatic deflector

Duoplasmatron ion source (model 358):

- Electrode extraction
- Sodium exchange channel
- Magnet analyzer at 90o

Cuptor pentru încălzire Na
Sodium furnace

2. T-shaped Tandetron accelerator for medium beam currents:

Q-snout electrostatic lens
Pressurized vessel
Acceleration column
Voltage divider
Gas stripping channel (Ar) and recirculation for medium beams Electrode extraction Electrod extracție
Carousel for carbon stripping foils

Generator de înaltă tensiune (3 MV) de tip Tandetron
Tandetron type high voltage generator for medium current beam

3. Tandetron type high voltage generator for medium current beam

HV multiplier and rectifier
HV stabilization and control system with GVM (Generating Voltmeter)
Capacitive load handling system

4. Radiation protection screen for bremsstrahlung radiation
5. Set of three electrostatic quadrupoles
6. Deflector magnet (ports at: 10o, 20o, 30o and 45o)

Power supply with the possibility of changing the polarity
Vacuum chamber with water-cooled walls
Faraday cup on the port of 0o

7. Beam line and reaction chamber equipped for IBA studies

• Micrometrically adjustable image slots along (X&Y) axis
• X-axis electrostatic deflector
• Y axis electrostatic deflector
• (X&Y)-axis micrometrically adjustable object slots
• Electrostatic quadrupole for microfeam applications
• Electropneumatically operated Faraday cup
• Beam Profile Monitor (BPM)
• Cylindrical vacuum chamber (h = 500 mm, Φ = 400 mm)
• Beam Profile Monitor (BPM)
• Target support controlled by 4 motors
• Fixed (165o) and mobile (10o-150o) charged particle detector
• Electronic modules and power supplies:
      • Preamplifier
      • Spectroscopic amplifier
      • Voltage source
      • Data acquisition system with MCA Fastcom and MPANT
      • NIM rack with power supply
• CCD video camera (x7)
• Liquid nitrogen trap
• Carousel for foils (used at ERDA)
• Retractable SDD detector for PIXE
• HPGe retractable detector, cooled with liquid nitrogen for PIGE
• Beam extraction system in the air, with XYZ automated target support (radiobiology, in-air PIXE)

8. Beam line with reaction chamber for implantation and irradiation with ion beams

• Electrostatic beam sweep system (17x17 cm2)
• BPM monitoring with 4 Faraday cups with secondary electron suppression
• Sample carousel with manual operation
• Sample holder heated up to 800 oC
• Sample holder cooled with liquid nitrogen
• Beam stop

9. Reaction chamber beam line for effective section measurements

• Cylindrical vacuum chamber (h=500 mm, φ=400 mm)
• Fixed target support
• Mobile detector support (10o-150o)
• 11 ports
• Collimator system
• 2 Faraday cups

Examples of ionic species* that can be accelerated at 3 MV Tandetron
Accelerated particle Energy up to MeV (estimated values) Beam current up to eµA
1H 6 30**
4He*** 9 1
6Li 12 0.25
7Li 12 0.1
10B 18 5
11B 18 20
12C 20 80
13C 20 10
14N 20 0.5
16O 20 50
19F 20 0.05
26Mg 20 0.2
27Al 20 1
28Si 25 70
31P 25 70
58Ni 25 20
63Cu 25 20
75As 25 10
197Au 5 10

The values in the table above for energy and current are maximum values and cannot be met simultaneously.

Note:With he exception of noble gases, all stable elements in the periodic table can be accelerated.

* For more details regarding the beam currents that can be obtained using the 860A source, please see R. Middleton, A Negative Ion Cookbook
** This value of the proton beam current can only be obtained from the duoplasmatron source (358).
**** The alpha particle beam is obtained only from the duoplasmatron source.


[1] I Burducea et al., Nuclear Instruments and Methods in Physics Research B, 2015
[2] C Podaru et al., Nuclear Instruments and Methods in Physics Research B, 2013