The HV platforms system consists of two platforms working at the same 250 kV voltage in separated rooms.

Most of the radioactivity is generated and confined in the first platform area. This platform (platform A in fig.1) house the target-ion source assembly, the pre-separator and is contained in a shielded pit.

The radioactivity level in the second platform area is much lower, this platform (platform B) house the charge exchange cell and the first stage of the isobaric mass separator. The platforms are at the same 250 kV voltage and are connected by a high voltage conduit.

Considering the peculiarity of the design and construction of HV platforms and the good results obtained with the a 450 kV platform used for our Tandem preinjector (built by ourselves) we have decided to design by ourselves the two HV platforms for the EXCYT Project. Instead, we have commissioned to National Electrostatic Company (USA) the construction of the high voltage conduit. Fig.1 and Fig.2 shows the HV platform system.

(b)

(a)

Fig1- A plan (a) and a front (b) view of the HV platforms

Fig.2- A render view of the HV platform system

The POISSON simulations (fig.3,4) show that the electrical gradients are appropriate to prevent sparks and electrical instabilities. These simulations show that the maximum electric field is at the interface air-ultra weight molecular polyethylene after the field termination rings (fig.4). For a platform voltage of 250 kV this field reaches 10 kV/cm.

Both the platforms are already installed at LNS.

The high-voltage conduit, that connect the two platforms, is capable of carrying the beam pipe and electrical cables through a 1 meter thick shield wall (the free space will be filled with concrete or iron).

The conduit consists of two concentric pipes: a continuous, electrically conductive, inner pipe and a continuos fiber glass/epoxy outer pipe with flanges that extend into the 250 kV platforms by few centimeters. The space between these two pipes is filled with 2 atm of SF₆ insulating gas.

Moreover, within the span of the shield wall the fiber glass/epoxy tube is covered by stainless steel tube, which ends with the field termination rings.

Fig.3- Electrostatic simulation with POISSON code of the first platform with the HV conduit.

Fig.4- Equipotential lines at the end of the HV conduit.

The conduit has been tested successfully at NEC factory in the middle of June 1999 and it is already installed at LNS.

Accelerating tubes

With the HV conduit, we have purchased three acceleration tubes from NEC.

The first tube is used to transport ion beams (A<48) with maximum energy of 100 Mev/amu from the beam line of our superconducting cyclotron at ground potential to 250 kV platform (platform A in fig.1). This tube consists of three sections of 90 kV NEC tube.

A second 75 kV NEC general purpose is used to insulate the target-ion source complex, which is at 50 kV with respect to the platform voltage.

The third tube is used to accelerate low intensity radioactive ion beams, at a total energy of 300keV (50+250 keV), from 250 kV platform to ground potential. This tube consists of 4 sections of the 75kV NEC general purpose tube.

All the tubes have passed their tests at the NEC factory and are already installed at LNS.