HITRAP: A Facility for Experiments with Trapped Highly Charged Ions

HITRAP is a planned ion trap facility for capturing and cooling of highly charged ions produced at GSI in the heavy-ion complex of the UNILAC-SIS accelerators and the ESR storage ring. In this facility heavy highly charged ions up to uranium will be available as bare nuclei, hydrogen-like ions or few-electron systems at low temperatures. The trap for receiving and studying these ions is designed for operation at extremely high vacuum by cooling to cryogenic temperatures. The stored highly charged ions can be investigated in the trap itself or can be extracted from the trap at energies up to about 10 keV/q. The proposed physics experiments are collision studies with highly charged ions at well-defined low energies (eV/u), high-accuracy measurements to determine the g-factor of the electron bound in a hydrogen-like heavy ion and the atomic binding energies of few-electron systems, laser spectroscopy of HFS transitions and X-ray spectroscopy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Testing atomic structure theories with high accuracy mass measurements on highly charged ions

The mass of a highly charged ion is the sum of the mass of the nucleus, the mass of the electrons and the electronic binding energies. High accuracy mass measurements on highly charged ions in a sequence of different charge states yield informations on atomic binding energies, i.e., the ionisation potentials. In our contribution we discuss the possibility of determining atomic binding energies of highly charged ions to better than 20 eV via cyclotron frequency measurements in a Penning trap. At this level of accuracy different contributions to the binding energies, like relativistic corrections, Breit corrections and QED corrections, can be measured. This revised version was published online in August 2006 with corrections to the Cover Date.     

Recent Progress with the SMILETRAP Penning Mass Spectrometer

The Penning trap mass spectrometer SMILETRAP has been considerably improved during the last two years. The helium pressure has been carefully stabilized and is now independent of irregular air pressure. The temperature of the hyperboloidal precision trap is stabilized to ±0.03°C. Remaining temperature instabilities are compensated by changes in the current of a warm coil surrounding the precision trap. The frequency synthesizer is now locked to GPS. This means that it is much easier to accurately measure resonances during several days. The improvements have demonstrated that in mass doublet measurements with an excitation time of 1 s it is possible to determine the mass of ions with q/A=1/2 at an uncertainty to a few times of 0.1 ppb, using selected rather than cooled ions. In routine measurements lasting for one day it is possible to reach a mass uncertainty of 1 ppb. The masses of the following particles and atoms have been measured with uncertainties in the region 0.3–2 ppb: p, ³H, ³He, ⁴He, ²²Ne, ²⁸Si, ³⁶Ar, ⁷⁶Ge, ⁷⁶Se, ⁸⁶Kr and ¹³³Cs. It has also been shown that though we are using a warm bore the trap pressure is sufficiently low to prevent electron capture from the rest gas for excitation times of 3 s and for ion charges as high as 50+. This revised version was published online in July 2006 with corrections to the Cover Date.     

Observing a single hydrogen-like ion in a Penning trap at T = 4 K

We describe how a single hydrogen-like ion (C⁵⁺) is prepared, cooled with the method of resistive cooling and non-destructively detected with the image-current technique in a cryogenic Penning trap at T = 4 K. The storage time for C⁵⁺-ions in the cryogenically pumped vacuum chamber is longer than six months. The experimental techniques of preparing, cooling and detecting highly-charged ions in a Penning trap are relevant for precision experiments such as g-factor measurements, mass spectroscopy and laser spectroscopy. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Canadian Penning Trap Spectrometer at Argonne

The Canadian Penning Trap (CPT) mass spectrometer is a device used for high-precision mass measurements on short-lived isotopes. It is located at the ATLAS superconducting heavy-ion linac facility where a novel injection system, the RF gas cooler, allows fast reaction products to be decelerated, thermalized and bunched for rapid and efficient injection into the CPT. The CPT spectrometer and its injection system will be described in detail and its unique capabilities with respect to its initial physics program, concentrating on isotopes around the N=Z line with particular emphasis on isotopes of interest to low-energy tests of the electroweak interaction and the rp-process, will be highlighted. This revised version was published online in July 2006 with corrections to the Cover Date.     

Direct mass measurements of Hg and Au: A new route to the neutrino mass determination?

The study of nuclear electron capture (EC) offers an exciting alternative for the determination of the neutrino mass. Whereas only tritium and ¹⁸⁷Re can be used in the case of β-decay experiments involving the anti-neutrino, a potentially large number of EC-nuclides can be used in experiments involving the monochromatic neutrino. This alternative to β  -decay experiments requires an accurate measurement of QEC$Q_{\mathit{EC}}$-values of appropriate candidates. In the present work we initiate a search for such a candidate and determined the QEC$Q_{\mathit{EC}}$-value of the electron capture in ¹⁹⁴Hg by direct mass measurements of ¹⁹⁴Hg and ¹⁹⁴Au. The new QEC$Q_{\mathit{EC}}$-value of 29(4) keV determined by the ISOLTRAP Penning-trap mass spectrometer at ISOLDE/CERN forbids the K-capture for ¹⁹⁴Hg. However, it allows a determination of the neutrino mass by a combination of a micro-calorimetric measurement of the de-excitation spectrum from L-capture in ¹⁹⁴Hg and a comparable QEC$Q_{\mathit{EC}}$-value remeasurement by high-precision Penning trap mass spectrometry.     

A cooler ion trap for the TITAN on-line trapping facility at TRIUMF

We present simulations of electron and proton cooling of highly charged ions in a Penning trap, including the potentially detrimental effects of radiative, dielectronic, and three-body recombination in electron cooling. We show a preliminary design for a cooler trap accommodating both electron and proton cooling, which will be a component of the TITAN ion-trap facility under construction at TRIUMF for precision mass measurements of short-lived radioactive nuclei.      

The HITRAP project at GSI: trapping and cooling of highly-charged ions in a Penning trap

A decelerator will be installed at GSI in order to provide and study heavy nuclei without or with only few electrons at very low energies or even at rest. Highly-charged ions will be produced by stripping at relativistic energies. After electron cooling and deceleration in the Experimental Storage Ring (ESR) the ions are ejected out of the storage ring at 4 MeV/u and further decelerated in a combination of linear accelerator structures operated in reverse. Finally, they are injected into a Penning trap where the ions are cooled to 4 K by electron cooling in combination with resistive cooling. From here, the ions can be transferred in a quasi DC or in a pulsed mode to different experimental setups. This article describes the technical concepts of this project focused on the Penning trap.      

Temperature dependence of the electric field gradient in GaN measured with the PAC-probe 181Hf

A radial inhomogeneous magnetic field produced by counter-propagating currents in anti-Helmholtz configuration coils has been superimposed to a Penning trap. The confinement properties of electrons in such a trap have been studied experimentally. Without the radial B-field we find a number of operating conditions where instabilities occur, arising from higher order contributions to the quadrupolar trapping field. When we apply the radial field the trap properties remain essentially unchanged until the strength of this field at the boundary of the electron cloud is of the same order as the homogeneous Penning field. Then a sudden breakdown in the confinement appears. The experiments have been performed in low magnetic fields. The equations of motions of the trapped particles can be cast in a dimensionless form and our results can be considered as independent of the field strength. Contribution was presented at the TCP06, Vancouver Island, 2006.     

Mass measurements in the endpoint region of the rp-process at SHIPTRAP

The Penning-trap mass spectrometer SHIPTRAP was designed for precision mass measurements of radionuclides produced in fusion–evaporation reactions. The latest measurement campaign covered heavy nuclei (A>90) related to the astrophysical rapid proton capture process. The masses of 34 neutron-deficient radionuclides have been measured since February 2006 with relative uncertainties between 5×10⁻⁸ and 1×10⁻⁷. Furthermore, the use of an octupolar RF excitation for the time-of-flight ion-cyclotron-resonance technique was investigated and an increase of the resolving power by a factor of ten was observed in agreement with simulations. This will allow to resolve isomeric states with excitation energies of a few 10 keV only.      

Penning阱中的量子跃迁

对极低温下囚禁在Ｐｅｎｎｉｎｇ阱中的单个离子在受到外部扰动时出现的不稳定现象作了量子处理。首先，求解了系统的薛定谔方程，并根据所得的波函数性质，得出了阱内的量子跃迁规则，然后，在此规则下，定量描述了离子在受到扰动后的不稳定表现。     

Time Characteristics of the Ion Beam Cooler-Buncher at JYFL

A beam cooler for low-energy ion beams was constructed to improve the ion optical properties of radioactive ion beams produced at the IGISOL facility in Jyväskylä. The beam cooler is a buffer gas filled RF-quadrupole. The delay properties and the possibility to accumulate a continuous IGISOL beam and release it in short bunches is discussed.     

A high-current electron beam ion trap as an on-line charge breeder for the high precision mass measurement TITAN experiment

The precision of atomic mass measurements in a Penning trap is directly proportional to the charge state q of the ion and, hence, can be increased by using highly charged ions (HCI). For this reason, charge breeding with an electron beam ion trap (EBIT) is employed at TRIUMF’s Ion Trap for Atomic and Nuclear science (TITAN) on-line facility in Vancouver, Canada. By bombarding the injected and trapped singly charged ions with an intense beam of electrons, the charge state of the ions is rapidly increased inside the EBIT. To be compatible with the on-line requirements of short-lived isotopes, very high electron beam current densities are needed. The TITAN EBIT includes a 6 Tesla superconducting magnet and is designed to have electron beam currents and energies of up to 5 A and 60 keV, respectively. Once operational at full capacity, most species can be bred into a He-like configuration within tens of ms. Subsequently, the HCI are extracted, pass a Wien filter to reduce isobaric contamination, are cooled, and injected into a precision Penning trap for mass measurement. We will present the first results and current status of the TITAN EBIT, which has recently been moved to TRIUMF after assembly and commissioning at the Max-Planck-Institute (MPI) for Nuclear Physics in Heidelberg, Germany.     

Beam diagnostic developments at the cooler synchrotron COSY-Jülich

New developments of beam diagnostic devices and methods at the cooler synchrotron and storage ring COSY at the Forschungszentrum Jülich are described. A Schottky-pickup was tested and installed. The new pickup consists of four diagonally arranged plates which can be combined by means of relays to measure either in the horizontal or in the vertical plane. A new method for resonant tuning of the Schottky-pickup for transversal measurements was realized. A tune meter was developed for real-time tune measurements in the acceleration ramp and is used as routine diagnostic tool. Based on the developed bunch synchronous tracking generator an on-line phase space measurement was realized. For beam profile measurements a residual-gas ionization beam profile monitor was installed in the COSY-ring and tested. To measure the beam quality in case of fast and slow extraction a universal spill detector was developed and tested in the extraction beam line.     

Motional frequencies in a planar Penning trap

A Penning trap consisting of concentric ring electrodes on a substrate and a magnetic field perpendicular to the substrate plane has been loaded with electrons. In order to demonstrate the performance of the trap we have measured the motional frequencies of the trapped electrons. Frequencies, line shape and width agree well with simulations. Miniaturization of the device is at hand which opens novel possibilities for application in quantum computing. Contribution presented at the TCP06, Vancouver Island, 2006-09-21     

Direct mass measurements of exotic nuclei at the FRS-ESR facility at GSI

An overview of direct mass measurements of exotic nuclei at the FRS-ESR facility at GSI is given. The nuclides are produced at relativistic energies by projectile fragmentation and fission, separated in-flight at the fragment separator FRS and injected into the storage ring ESR. Mass measurements are performed using Schottky and Isochronous Mass Spectrometry, which both allow for high precision measurements with single-ion sensitivity. Recent experimental developments are summarized, and examples for measurement results are given, including applications in nuclear structure physics and astrophysics, comparisons with mass predictions, and the search for new isotopes and isomers. Further research potential will be available at next-generation fragment-separator-storage-ring facilities such as the Super-FRS-CR-NESR complex at the future FAIR facility.     

潘宁阱中电子等离子体稳态的数值模拟

应用粒子模拟方法研究了电子束潘宁阱中的非中性等离子体的稳定状态及其定标关系，数值模拟结果表明，给定电子的初始分布和外场条件后，潘宁阱中可以出现聚心状态的电子等离子体，中心电子密度可达10倍布里渊密度；电子密度分布与理想的I／r^2关系有差别，阱中的电子数越多，差别越大。系统趋于稳定状态的弛豫时间反比于阱中的电子总数而正比于外加电场强度。     

用离子阱经H2++H2碰撞反应碰撞反应制备H4+

用Ｐｅｎｎｉｎｇ型离子阱经碰撞反应Ｈ２＾＋＋Ｈ２→Ｈ４＾＋产生稳定的Ｈ４＾＋,主要的反应产物是Ｈ３＾＋,但十分明显地观测到Ｈ４＾＋信号。Ｈ４＾＋在阱中稳定存在时间长达０．１ｓ量级,远比Ｋｉｒｃｈｎｅｒ等人测量的１０＾－６ｓ量级长,最后讨论了生成Ｈ４＾＋的反应过程机制。