• The Start-Veto Detector Device of the HADES Spectrometer

Two identical 8-strip polycrystalline CVD-diamond detectors of octagonal shape are placed 75 cm downstream respectively 75 cm upstream of the HADES target. The downstream detector shall veto all particles with no reaction with target nuclei to provide a start signal with a rate of 10 ⁷ particles/s. The widths of the strips are optimized such that a coincidence of one start strip with 3 veto strips is sufficient for a veto efficiency of 96.5%. To keep multiple scattering and secondary reactions low the detectors have a thickness of 100 µm only.

The outer dimensions of the detectors (left) are 25 mm and 15 mm   matching the beam spot in this position. They are mounted on ceramic pcb's and every strip is connected via a 50 W   micro-stripline to DBA amplifiers. An excellent intrinsic time resolution of s _i = 29 ps is achieved with ⁵² Cr ions of 650 MeV/amu (right).

• The Focal Plane Detector of the Magnet Spectrometer at Atomic Physics Cave A

   

The largest polycristalline CVD-diamond detector world wide in use is a 60x40 mm² strip detector designed for atomic physics experiments in cave A. The experimental setup including germanium detectors for X-ray and g - spectroscopy and the dipole magnet is sketched on the left drawing. According to their q/A, particles are bend and detected on different positions of a plane (the 'focal plane') of the dipol magnet. The position-sensitive diamond strip detector placed there, has a thickness of 200 µm and a substrate electrode devided in 32 strips with a length of 38 mm and a pitch of 1.8 mm (right).

Beam Diagnostics Applications

• Spill- and Bunch-Structure Monitors / Beam-Loss Monitors

Diamond samples of a size of 1x1 cm² are being used for spill- (resp. spill-loss-) monitoring at the SIS and for bunch-structure measurements commissioning the High-Current Injector Linac of GSI. The photographs below show the top view (growth side) of the monitors on the left and the bottom view (nucleation side) on the right. The fully metallized backside of the ceramic pcbs at ground potential is connected with broad brass springs to the nucleation side (right) whereas the growth side electrode at high voltage potential (left) is connected to the pin of an rf-suitable coaxial connector (SMA).

Bunch Structure: d=distance from the last magnet.	Bunch Structure, tuning the rf-amplitude (Urf)

In order tostudy the longitudinal focusing of the beam ToF spectra are measured. The start signal was given by the accelerator and the individual stops by three diamond detectors placed in different distances along the beamline.   

• SIS spill structure studies (slow extraction) using ¹² C beams with an intensity of 10 ⁹ ions/spill    (P. Moritz et al.)

A 2 ms sequence of a ¹²C spill is shown. The traces are recorded with a digital sampling storage oscilloscope. Each marked region of a previous trace (the blue in A, the black in B and the pink in C) is zoomed in the following trace.  

• Beam-Intensity Monitors

In addition to the 1x1 cm² dot design described above, a 9-strip diamond detector (A = 30x30 mm², d  = 330 µm (left)) and a 16-pad detector (A = 20x20 mm², d = 120 µm (middle)) are in use. The choice of interdigital structured electrodes as shown on the right pictures has various advantages: The amount of electronic channels needed is reduced to a single one. The capacitance of thin large- area detectors is dynamically defined by the strip distance providing thus narrow pulses and, again, a high count-rate capability. Measurements of slow ions stopped in a few microns of diamond detectors of a common design, suffer from the polarisation occured in the diamond bulk. Interdigital electrodes allow a charge collection within the range of the particles. Large area detectors (A = 2x2 cm², A = 3 x 3 cm²) of a thickness of 120 µm are under development (right).

Various Designs of Beam-Intensity Monitors

• High-Intensity Bunch Monitoring (fast extraction)

In a cooperation between GSI and the University of Karlsruhe ( Deutsche Patentanmeldung Nr. 102 12 223.7) microstrip CVD diamond detectors are being developed able to measure burst by burst the beam intensity, the beam profile and the beam time structure of highly focused and bunch-compressed beams in high-luminosity accelerator facilities. The bunch monitors operate in current-integrating mode.

The picture shows ¹²⁴Xe bunches of 223 A MeV extracted in a 'four-packet' mode into the HHT Cave of GSI as recorded with a 80 µm thick diamond strip detector of varying strip width. The beam intensity in this case is 1.7x10 ⁹ ions/bunch and the beam spot on the detector about 1.8 mm in diameter. No distortion has been detected after the beam tests.     

Tumor Therapy with Carbon Ions at GSI

• Position-Sensitive Carbon-Ion Dosimeter

We propose the use of pad- resp.pixel CVD-diamond detectors in order to define the equivalent dose deposited in the tumor volume via precise single-particle counting. The applied dose D is then given by the total number N of ¹²C ions impinging the 'tumor volume' V = m / r times the energy deposit DE of a single ion in this volume (rel. 1) :

D [MeV/kg] = (DE / r*V ) * N            (1)

Pulse-height distribution of carbon ions of 11.5 MeV/amu in a 80 µm thick diamond detector. The clear separation of the 12C-ion distribution from the electronic noise allows a precise counting of all ions above a threshold at e.g. channel 100.	Prototype Dosimeter: A 16-pad detector of a thickness of 100 µm.