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Experimental Setup



Figure: Experimental setup (status: Oct. 09)

 

The experimental setup of MATS (see also presentation (pdf, 9.81 MB) of Daniel Rodríguez) is a unique combination of an electron beam ion trap (EBIT) for charge breeding, ion traps for beam preparation, and a high-accuracy Penning trap system for mass measurements and decay studies. Each subsystem is a versatile tool itself and allows different high-accuracy experiments resulting in a broad physics output.

Short remarks to the subsystems

For detailed information see the Technical Design Report (pdf, 7.27 MB)

RFQ ion beam cooler and buncher

The first stage of MATS will be a second-generation cooler/buncher consisting of an open, cylindrical electrode geometry for the transverse RF field and tapered insertion electrodes for the longitudinal field. The system will be operated at cryogenic temperature which offers a potential gain of two orders of magnitude over a room temperature system. The RFQ is the connection between MATS and the gas catcher of the low energy branch of the Super-FRS. It is required to match the beam emittance of the radioactive ions to the quite small acceptance of the EBIT electron beam, to guarantee high injection efficiency.
Since molecular isobars cannot be suppressed sufficiently in standard RF quadrupoles, a multi-turn time-of-flight (MR-TOF) mass separator can be used instead.
As an alternative to isobar separation by time-of-flight, an "ion circus" could be used, which is formed from a classic (linear) radiofrequency quadrupole mass filter by bending it into a continuous circle.

Charge breeding electron beam ion trap (EBIT)

In addition to create high charge states in a very short time (charge breeding), the EBIT should be equipped with a high-resolution X-ray spectrometer to carry out spectroscopic measurements sensitive to nuclear size effects.
The charge breeding EBIT proposed here follows the Heidelberg EBIT design closely, which will also be used at the TITAN spectrometer. The Heidelberg EBIT can provide a maximum electron beam current of 535 mA, a beam diameter in the confinement region of about 70 μm, which corresponds roughly to a current density of 14000 A/cm^2. At the maximum electron beam energy of 50 kV, the EBIT can in principle produce bare ions up to Xe54+, and He-like ions across the periodic table. It also makes use of a laser ablation ion source to load the trap with ions from solid elements. In this way, independent measurements, calibrations, and tests of the preparation and precision trap can fully exploit its capabilities during off-line times.

Magnetic multi-passage spectrometer (MPS)

A MPS could be utilized as q/A separator to select the desired charge to mass ratio for injection into the Penning trap system. It consists of an electro-magnet with circular pole shoes and four ports where electrostatic lenses, which can be operated as mirrors, are installed.

Preparation Penning trap

The preparation Penning trap will be used to provide the precision Penning trap and others with a cooled beam of highly-charged ions. Since highly-charged ions cannot be cooled by buffer gas collisions we have to implement other cooling techniques. The most promising techniques are electron cooling and sympathetic laser cooling. The preparation trap will be installed in a superconducting magnetic solenoid of about 7 T. In order to reach the necessary vacuum conditions to store highly-charged ions for an extended period of time, the trap needs to be kept at liquid helium temperature of 4K. Here a static cryogenic vacuum (XHV, < 1E-15 mbar) will be reached by cryopumping. This allows also for improved in-trap detection via image currents for the diagnosis of the cooling process.

Measurement Penning trap

The combination of high-accuracy mass measurements with in-trap decay spectroscopy will require a new trap design. The trap needs to provide an excellent harmonic trapping potential while being a very open structure for the escape of the decay products. The high-accuracy mass measurements require a minimized uncertainty in the frequency determination, the magnetic field of the superconducting magnet needs to be as high (B >= 7 T), homogeneous (<= +/- 0.1 ppm measured over a 10 mm diameter spherical volume), and stable (δBt x 1/B <= 1E-9 / h) as possible. At the same time, the planned in-trap decay experiments require sufficient space inside the bore, so that the bore diameter needs to be about 160 mm or larger. For mass spectrometry either a destructive time-of-flight cyclotron resonance or a non-destructive Fourier transform ion cyclotron resonance detection will be used. For in-trap spectroscopy an electron conversion detector setup will be installed.

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