Munich MP-tandem Research Articles

The Stern–Gerlach polarized ion source for the Munich MP-tandem laboratory, a bright source for unpolarized hydrogen and helium ion beams as well

The design of our source of negatively charged, intense and brilliant DC beams of polarized hydrogen and deuterium ions was motivated by the excellent performance of the HERMES atomic beam source and the successful operation of a polarized ion source at TUNL. Deviating from their 30 K atomic beam technology we combine an 80 K atomic beam source (ABS) with subsequent ionization in an electron cyclotron resonance (ECR) plasma. In a separate unit, negative ions are obtained by successive two electron pickup from cesium in a vapour jet target. Our ABS provides a flux of 6.4 × 10 16 atoms / s for hydrogen and of about 5 × 10 16 atoms / s for deuterium into a compression tube of 10 mm diameter and 100 mm length. Polarized negative D - ⇒ / H - ⇒ ion beams of about 9 μ A / 15 μ A with an emittance of 20 π mm rad eV have been observed. After tandem acceleration we have polarized beam intensity of 2 μ A on target of the Q3D spectrograph. The measured vector polarizations of the D ⇒ and H ⇒ ion beams are 72% and 67%, respectively, in accordance with expectations from source operation data. Using an external gas inlet for the ECR region, intense beams of unpolarized 1 H - , 2 D - , 3 He - , and 4 He - ions are obtained.

Setup for materials analysis with heavy ion beams at the Munich MP tandem

A system has been installed for thin film analysis with two different techniques: Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA). The mass resolution of heavy ion RBS is demonstrated on multilayers of YBaCuO using 30 MeV 16O beams. The essential component of the ERDA system is an ionization detector with 7.5 msr solid angle and particle as well as position resolution. Depth resolution better than 10 nm and sensitivity below 1014 atcm2 could be achieved in ERDA of Al/Cu multilayers with 200 MeV Au ion beams. Angular resolution is sufficient to see blocking patterns of recoils from a Si single crystal.

Stripper foil requirements for optimum ion transmission at the Munich MP-tandem

The transmission of several ion beams ( 1H, 2H, 16O, 32S, 58Ni, 107Ag, 127I, and 197Au) through the Munich MP-tandem were measured as a function of stripper foil thickness, ion injection limitation, and analyzed charge state at 10 MV terminal voltage. These data offer the possibility to optimize the stripper foil thickness for the specific experimental requirements. In addition the knowledge could be broadened, how to choose the ion injection limitation conditions in order to achieve a high yield of the analyzed heavy ion charge state and a long lifetime of the carbon stripper foil.

Major maintenance of the Munich MP-tandem

Several measures have been taken to restore the voltage performance of the Munich tandem. 1. All accelerator tubes were reconditioned by sandblasting, new electrodes and diaphragms were inserted and preassembled groups of tubes were baked in high vacuum. 2. All other vacuum components were cleaned, baked in high vacuum and partly pressure leak tested outside the tandem. 3. High voltage tests were performed with tubes. Without portico voltages up to 16 MV were obtained, with portico up to 17.5 MV. 4. Some modifications (e.g. infrared light links) were introduced. The shutdown lasted 6 months. In March 1987 beam operation was resumed at moderate terminal voltages, interrupted by intervals of soft conditioning.

Structure studies of carbon foils with the aim to improve the ability for heavy-ion stripping

Slackened carbon stripper foils of 3 to 5 μg/cm 2 produced by vacuum evaporation-condensation were graphitized by annealing at about 3300 K with a pulsed laser beam (1.06 μm). An average crystal size of 10 nm was measured by electron diffraction. The texture of the 002-plane is parallel to the surface of the foil as known from slightly annealed carbon foils. Radiation damages caused by high doses of heavy ions dramatically change the crystal structure. Electron diffraction patterns reveal newly formed graphite crystals with their 002-plane perpendicular to the texture. Compared to carbon foils of the same kind, but not graphitized, a lifetime prolongation of a factor of two was achieved for such foils tested in the terminal of the Munich MP tandem. The slope of the curve for heavy-ion transmission through carbon stripper foils varies for foils of the same kind and for different ion-beam conditions.

The “portico” in the Munich MP-tandem

A “portico” was installed with the aim of preventing spark damage to column components and of increasing the terminal voltage. First experiences: no spark damage is observed, especially deconditioning of accelerating tubes by sparks has disappeared. No significant increase in terminal voltage due to axial effects has been attained.

A simple subnanosecond high energy buncher for the Munich MP-tandem

A simple and inexpensive postacceleration buncher is described. It provides heavy ion pulses of around 300 ps for several target positions.

The three-harmonics double-drift buncher at the munich heavy ion postaccelerator

A three-harmonics double-drift buncher has been developed and constructed to increase the intensity of the heavy ion beams from the postaccelerator at the Munich MP tandem. This buncher consists of three γ/4 coaxial line resonators which are operated at the frequencies ƒ, 2ƒ and 3ƒ (ƒ resonance frequency of the postaccelerator). The buncher resonators are positioned at the high energy side of the tandem, the resonators ƒ and 2ƒ about 20 m, the 3ƒ-resonator 17.5 m before the postaccelerator. The intensity of the target currents is increased by a factor 2–3 with the help of this harmonic buncher compared to the currents obtained with the old buncher, consisting of one single γ/4 resonator.

Laser treated carbon stripper foils

Procedures to graphitize conventionally prepared carbon foils are described. Self-supporting carbon foils of 2–6 μg/cm 2 were heat-treated in a high vacuum system by direct bombardment of electrons or light from a Nd: YAG laser. The stripper foils were installed in the terminal of the Munich MP-tandem accelerator and bombarded with negative ions of 10.6 MeV on a beam-spot size of approximately 7 mm 2. The quality of different stripper foils with different thicknesses was determined with respect to the beam intensity of the most probable charge state.

Improved performance of the Munich MP tandem: A status report

Operating experience and some of the modifications introduced during the last two years are reported. During the past year the terminal voltage obtained in test runs, the voltage used during experiments and the operating efficiency of the accelerator have improved considerably. The spectrum of ions available in routine operations has been extended to include 14C, 30Si, 36S, 48Ca and 60Ni beams.

A picosecond bunching system at the Munich MP-tandem accelerator

A picosecond bunching system was installed at the Munich MP-tandem accelerator. The resonator of the buncher consists of a sphere (diameter 1.65 m) and two axial cones with a total shunt impedance of 14 MΩ and a Q-factor of 2.8×10 4. The performance of the system was tested in time-of-flight experiments with heavy ions. Time resolutions of 75 ps (fwhm) for 18O, 95 ps (fwhm) for 32S and 110 ps (fwhm) for 58Ni were achieved with Si surface barrier detectors.

The Munich Heavy Ion Postaccelerator

The post accelerator in the Munich MP-tandem laboratory is a linear radio-frequency accelerator of the Interdigital-H-structure (IH). This structure has a particular high shunt impedance for particle velocities in the range 0.05 < ..beta.. < 0.10c. In this velocity range the effective shunt impedance is empirically well described by Z/sub eff/=13(+-1)M..cap omega../m...beta../sub -0.84/. The drift tube configuration is changeable in order to adjust the structure to the different particle velocities of the ion beams from the tandem accelerator. The eigenfrequency of different configurations varies between 55 and 80 MHz. With an applied rf-power of 50 kW in continuous operation it is possible, to increase the energy of the ion beam by a factor of 1.5 to 2. Acceleration tests were performed with ..cap alpha..-particles from a radioactive /sup 241/Am ..cap alpha..-source. The ..cap alpha..-particles were accelerated with 50 kW rf-power from 4.1 MeV to 14.9 MeV. A beam of /sup 32/S ions from the tandem with charge state 14+ was accelerated from 100 MeV to 160 MeV with an applied rf-power of 40 kW.

On the production of A 14C beam for tandem accelerators

The production of a low-current 14C beam (5 nA) and the acceleration in the Munich MP tandem is described. The beam has been produced from Fe 3 14C pellet used in an off-axis back-sputter geometry of a cesium-beam sputter source. Only 1 mCi (= 0.225 mg) of 14 C is needed to deliver a 14C beam for several days (≥100h).

The Munich Heavy Ion Post Accelerator

The post accelerator in the Munich MP-tandem laboratory is a linear radio-frequency accelerator of the Interdigital-H-structure (IH). This structure has a particular high shunt impedance for particle velocities in the range 0.05 ß < 0.106. In this velocity range the effective shunt impedance is empirically well described by Z<_eff=13(±1)M&#x003A9;/m·ß<sup-0.84</sup>. The drift tube configuration is changeable in order to adjust the structure to the different particle velocities of the ion beams from the tandem accelerator. The eigenfrequency of different configurations varies between 55 and 80 MHz. With an applied rf-power of 50 kW. in continuous operation it is possible, to increase the energy of the ion beam by a factor of 1.5-2. Acceleration tests have been performed with &#x022C9;-particles from a radioactive ²⁴¹Am &#x022C9;-source. The &#x022C9;-particles were accelerated with 50 kW rf-power from 4.1 MeV to 14.9 MeV. A beam of ³²S ions from the tandem with charge state 14+ was accelerated from 100 MeV to 160 MeV with an applied rf-power of 40 kW.

The diagnostic and control system for the converted MP-Tandem at Munich

2014 The diagnostic and control system for the Munich MP-Tandem is based on two bundles of acrylic light pipes running in the column structure from both ends of the tank to the dead sections and to the terminal. These light guides transmit all control signals for lenses, beam steerers, foil strippers and variable apertures as well as the readings of beam currents, charging currents, column currents, ionization currents, pump currents and voltages, and alternator frequencies. Details of the mechanical and electronic design are presented. Before the system has been installed, parts of it have passed various high voltage and radiation tests. It has gone in operation in june 1976. Operating experiences and test results are reported. REVUE DE PHYSIQUE APPLIQUEE TOME 12, OCTOBRE 1977, PAGE

A power shaft for the Munich MP-tandem

A power shaft for the Munich MP-tandem

Study of the104Ru(d, p)-reaction at 14 MeV

The reaction104Ru(d, p) was investigated with high resolution (5 keV) at the Munich MP tandem using the Q3D spectrograph in conjunction with the precision time-of-flight system. The ground stateQ-value was determined as Q=3,684.5±1 keV. Proton spectra were measured at 7 angles in the range of 6.1°–65°. 19 levels could be identified in the excitation energy range 0–730 keV. Transferredl-values and spectroscopic factors of these levels were derived with the aid of DWBA calculations.

High voltage tests with the MP-Tandem at Munich

As part of the conversion programme of the Munich MP-Tandem accelerator a Pelletron charging system has been installed and high voltage tests have been performed without acceleration tubes. Preliminary experience and test results are reported. In pure SF 6 the Pelletron chains delivered the guaranteed charging current of 100 μA per chain at 14 MV terminal voltage. A maximum terminal voltage of 16.1 MV was achieved at an SF 6 pressure of 0.76 MN/m 2. Earlier tests were carried out with a 30% SF 6/70% N 2 mixture at pressures up to 1.2 MN/m 2. The comparison indicates, that in pure SF 6 spark damage of components is less likely than in an SF 6 mixture.

The Munich MP tandem

This paper describes some of the unique features of the Munich MP tandem facility. The improved voltage stabilizing system using the liner-terminal capacity and a time-of-flight system for absolute calibration and monitoring of the tandem beam energy with an absolute accuracy of 1.5 × 10 −5 are discussed. Results of their performances are presented. The improved voltage stabilizing system has been tested by means of the time-of-flight system. The residual ripple at the terminal was measured to be less than 260 V fwhm. The time-of-flight system allowed the establishment of an accurate calibration energy in the tandem range by measuring the first T = 3 2 resonance in 12C(p,p) 12C to be (14230.75±0.2) keV. The Munich MP tandem conversion and upgrading program, initiated in 1973, is discussed in some detail. It includes installation of NEC-components into our HVEC MP tandem accelerator. Finally we present plans to add a small energy booster to our MP tandem in order to increase the energy of the heavy ion beams presently available in our laboratory. It is designed to allow, typically, post-acceleration of Ni-ions from about 100 MeV to 200 MeV.