An experiment to focus transversely and simultaneously axially bunch a space charge neutralized K+ ion beam has been carried out at LBNL. The principal objectives of the simultaneous bunching and focusing experiments are to control the beam envelope, demonstrate effective neutralization of the beam space- charge, control the velocity tilt on beam, understand effects of net defocusing, field imperfections, limitations on minimal spot size such as emittance and aberrations and to quantify the longitudinal phase space. A demonstration of increased axial compression and a reduction in spot size compared to earlier measurements is presented.

/pdf/bunching-and-focusing-of-an-intense-ion-beam-for-target-8j339wge2x.pdf

Bunching and focusing of an intense ion beam for target heating experiments

The High Current Experiment (HCX) is used to study beam transport and accumulation of electrons in quadrupole magnets and the Neutralized Drift-Compression Experiment (NDCX) to study beam transport through and accumulation of electrons in magnetic solenoids. We find that both clearing and suppressor electrodes perform as intended, enabling electron cloud densities to be minimized. Then, the measured beam envelopes in both quadrupoles and solenoids agree with simulations, indicating that theoretical beam current transport limits are reliable, in the absence of electrons. At the other extreme, reversing electrode biases with the solenoid transport effectively traps electrons; or, in quadrupole magnets, grounding the suppressor electrode allows electron emission from the end wall to flood the beam, in both cases producing significant degradation in the beam.

/pdf/electrons-in-a-positive-ion-beam-with-solenoid-or-quadrupole-1gl9xz3prv.pdf

Electrons in a Positive-Ion Beam with Solenoid or Quadrupole Magnet Transport

The High Current Experiment (HCX) is used to study beam transport and accumulation of electrons in quadrupole magnets and the Neutralized Drift- Compression Experiment (NDCX) to study beam transport through and accumulation of electrons in magnetic solenoids. We find that both clearing and suppressor electrodes perform as intended, enabling electron cloud densities to be minimized. Then, the measured beam envelopes in both quadrupoles and solenoids agree with simulations, indicating that theoretical beam current transport limits are reliable, in the absence of electrons. At the other extreme, reversing electrode biases with the solenoid transport effectively traps electrons; or, in quadrupole magnets, grounding the suppressor electrode allows electron emission from the end wall to flood the beam, in both cases producing significant degradation in the beam.

Electrons in a positive-ion beam with solenoid or quadrupole magnetic transport

/pdf/electrons-in-a-positive-ion-beam-with-solenoid-or-quadrupole-3s8w7ftpsa.pdf

Electron cloud eﬀects on an intense ion beam in a four solenoid lattice J.E. Coleman Department of Nuclear Engineering, University of California at Berkeley, 4155 Etcheverry Hall, MC 1730, Berkeley, CA 94720, USA. P.A. Seidl, E. Henestroza, P.K. Roy, and J.L. Vay Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA-94720, USA. I. Haber University of Maryland, College Park, MD 20742-3511, USA. A.W. Molvik and W.M. Sharp Lawrence Liveremore National Laboratory, Livermore, California 94550, USA. D.R. Welch Voss Scientiﬁc, Albuquerque, NM 87108, USA. (Dated: July 16, 2007) The Solenoid Transport Experiment (STX) at LBNL successfully demonstrated the transport of a space-charge dominated ion beam in a two-solenoid lattice. Initial experiments showed a strong dependence of electron cloud eﬀects on solenoid ﬁeld strength. A current-reducing aperture, two solenoids and in-bore diagnostics were added to the two-solenoid lattice in order to study electron cloud eﬀects more closely. Experiments were conducted with a 10 µs, singly charged potassium ion bunch at an ion energy of 0.3 MeV and currents of 26 mA and 45 mA. A qualitative comparison of experimental and calculated results are presented, including a comparison of the eﬀects of manip- ulating electrons on the beam dynamics, quantifying beam-induced gas desorption, ionization, and electron eﬀects. PACS numbers: 52.59.Sa, 41.75.Ak, 41.85.Lc, 41.85.Ja, 29.27.Bd, 29.30.Aj, 34.50.Dy, 79.20.Rf I. INTRODUCTION Space-charge dominated ion beams used in the low en- ergy end of an accelerator to drive fusion targets face a number of unique challenges. One of particular interest to the general accelerator community is beam degrada- tion due to electron cloud and gas eﬀects [1–10]. Mismatched portions of a beam, such as beam halo, photons hitting the beam pipe, and anything that ob- structs the path of the beam, desorbs gas and elec- trons [11–14]. The desorbed gas expands into the beam path close to the sound speed and subsequently becomes ionized [15]. In some cases the electron and ionized neu- tral densities can approach the beam density and sig- niﬁcant changes in the charge collected on diagnostics, emittance growth, and ﬂuctuations in the beam envelope are seen [16, 17]. For solenoid transport of space-charge dominated ion beams the predominantly axial ﬁelds in the center of the magnets and the radial ﬁelds in between magnets pro- vide an easier means for electrons to be pulled in by the beam potential and stay there. These ﬁelds also present diﬃculties in suppressing electrons when intercepting the beam with diagnostics. The ion species used for the STX on the Neutralized Drift Compression Experimental beamline (NDCX) was a singly charged, 300-kV, 26-45 mA potassium ion beam [17–19]. A solenoid ﬁeld close to 3 T was necessary in the ﬁrst magnet to match or overcome the beam space charge force. The exact tune used in the lattice was cho- sen based on the desired envelope and to avoid scraping. This included compensating for beam halo and centroid motion. II. FOUR-SOLENOID EXPERIMENT Two more solenoids were added to the two-solenoid lat- tice on the NDCX beamline (Fig. 1). The two additional solenoids were also 50-cm long, had an identical construc- tion to those used in the two-solenoid experiment, and the spacing in between all of the magnets was about 9 cm [17, 20]. The observation that intercepting the beam in a strong magnetic ﬁeld aided electron cloud and gas eﬀects in degrading the beam quality in the two-solenoid experiment was accounted for in this four-solenoid lat- tice. So the same 29-cm drift distance was used between the exit of the four-solenoid lattice and the intercepting diagnostics. Initial tests with the four-solenoid lattice were done with a current-reducing aperture that reduced the 45- mA beam to 26 mA. The focusing lattice in Figure 2(a) was chosen to give the desired envelope for the 26-mA beam in Figure 2(b). All of the same diagnostics used in the two-solenoid experiment were used here [17]. De- spite having the additional drift distance from the trans-

Electron cloud effects on an intense ion beam in a four solenoid lattice

The Solenoid Transport Experiment (STX) at LBNL successfully demonstrated the transport of a space-charge dominated ion beam in a two-solenoid lattice. Initial experiments showed a strong dependence of electron cloud effects on solenoid field strength. A current-reducing aperture, two solenoids and in-bore diagnostics were added to the two-solenoid lattice in order to study electron cloud effects more closely. Experiments were conducted with a 10 {micro}s, singly charged potassium ion bunch at an ion energy of 0.3 MeV and currents of 26 mA and 45 mA. A qualitative comparison of experimental and calculated results are presented, including a comparison of the effects of manipulating electrons on the beam dynamics, quantifying beam-induced gas desorption, ionization, and electron effects.

/pdf/electron-cloud-effects-on-an-intense-ion-beam-in-a-four-3ll6fo85rb.pdf

/pdf/electron-cloud-effects-on-an-intense-ion-beam-in-a-four-3mgyj25cdg.pdf

Voss Scientific, Albuquerque, Nm , Usa.

Papers

Electron cloud effects on an intense ion beam in a four solenoid lattice

Electron cloud effects on an intense ion beam in a four solenoid lattice

Electron cloud effects on an intense ion beam in a four solenoid lattice - eScholarship