• Y. Hao, J. Kewisch, V. Litvinenko, E. Pozdeyev, V. Ptitsyn, D. Trbojevic, N. Tsoupas
  BNL, Upton, Long Island, New York

In this paper, we an­a­lyzed the linac op­tics de­sign re­quire­ment for a mul­ti-pass en­er­gy re­cov­ery linac (ERL) with one or more linacs. A set of gen­er­al for­mu­la of con­strains for the 2-D trans­verse ma­trix is de­rived to en­sure de­sign op­tics ac­cep­tance match­ing through­out the en­tire ac­cel­er­at­ing and de­cel­er­at­ing pro­cess. Mean­while, the rest free pa­ram­e­ters can be ad­just­ed for ful­fill­ing other re­quire­ments or op­ti­miza­tion pur­pose. As an ex­am­ple, we de­sign the linac op­tics for the fu­ture MeR­HIC (Medi­um En­er­gy eRHIC) pro­ject and the op­ti­miza­tion for en­larg­ing the BBU thresh­old.

• E. Wang, I. Ben-Zvi, A. Burrill, J. Kewisch, T. Rao, Q. Wu
  BNL, Upton, Long Island, New York
• D. Holmes
  AES, Medford, NY
• E. Wang
  PKU/IHIP, Beijing

RF elec­tron guns with strained super lat­tice GaAs cath­odes can pro­duce high­er bright­ness and lower emit­tance po­lar­ized elec­tron beams, due to the high­er field gra­di­ent at the cath­ode sur­face com­pared with DC guns. The vac­u­um in the gun must be bet­ter than 10^-11 torr to ob­tain a suf­fi­cient cath­ode life time with high quan­tum ef­fi­cien­cy (QE). Such high vac­u­um can­not be ob­tained eas­i­ly in a nor­mal con­duct­ing RF gun. We re­port on an ex­per­i­ment with a su­per­con­duct­ing RF (SRF) gun, which can main­tain a vac­u­um of near­ly 10^-12 torr be­cause of cryo-pump­ing at the tem­per­a­ture of 4.2K . The GaAs cath­ode was ac­ti­vat­ed by Cs'O treat­ment with a QE of 3% and ex­hibits a long life­time in a prepa­ra­tion cham­ber. This cath­ode will be used in a 1.3 GHz - cell SRF gun to mea­sure the de­struc­tion of the QE by ion and elec­tron back-bom­bard­ment.

• E. Wang, I. Ben-Zvi, A. Burrill, J. Kewisch, T. Rao, Q. Wu
  BNL, Upton, Long Island, New York
• D. Holmes
  AES, Medford, NY
• E. Wang
  PKU/IHIP, Beijing

Su­per­con­duct­ing RF (SRF) elec­tron guns de­liv­er high­er bright­ness beams than DC guns be­cause the field gra­di­ent at the cath­ode is high­er. SRF guns with metal cath­odes have been suc­cess­ful­ly test­ed. For the pro­duc­tion of po­lar­ized elec­trons a Gal­li­um-Ar­senide (GaAs) cath­ode must be used, and an ex­per­i­ment to test this type of cath­ode is under way at BNL. Since the cath­ode will be nor­mal con­duct­ing, the pri­ma­ry con­cern is cath­ode-driv­en heat load. We pre­sent mea­sure­ments of the elec­tric re­sis­tance of GaAs at cryo­genic tem­per­a­tures, a pre­dic­tion of the heat load, and ver­i­fi­ca­tion by mea­sur­ing the qual­i­ty fac­tor of the gun with and with­out the cath­ode.

• G. Wang, M. Blaskiewicz, A.V. Fedotov, Y. Hao, J. Kewisch, V. Litvinenko, E. Pozdeyev, V. Ptitsyn
  BNL, Upton, Long Island, New York

We pre­sent our stud­ies on var­i­ous as­pects of the beam dy­nam­ics in 'race­track' de­sign of the first stage elec­tron-ion col­lid­er at RHIC (eRHIC), in­clud­ing trans­verse beam break up in­sta­bil­i­ties, elec­tron beam emit­tance growth and en­er­gy loss due to syn­chrotron ra­di­a­tion, elec­tron beam loss­es due to Tou­schek ef­fects and residue gas scat­ter­ing, beam-beam ef­fects at the in­ter­ac­tion re­gion and emit­tance growth of ion beam due to elec­tron bunch to bunch nois­es. For all ef­fects con­sid­ered above, no show­stop­per has been found.

• I. Ben-Zvi, R. Calaga, H. Hahn, L.R. Hammons, E.C. Johnson, A. Kayran, J. Kewisch, V. Litvinenko, W. Xu
  BNL, Upton, Long Island, New York

A pro­to­type am­pere-class su­per­con­duct­ing en­er­gy re­cov­ery linac (ERL) is under ad­vanced con­struc­tion at BNL. The ERL fa­cil­i­ty is com­prised of a five-cell SC Linac plus a half-cell SC pho­to-in­jec­tor RF elec­tron gun, both op­er­at­ing at 703.75 MHz. The fa­cil­i­ty is de­signed for ei­ther a high-cur­rent mode of op­er­a­tion up to 0.5 A at 703.75 MHz or a high-bunch-charge mode of 5 nC at 10 MHz bunch fre­quen­cy. The R&D fa­cil­i­ty serves a test bed for an en­vi­sioned elec­tron-hadron col­lid­er, eRHIC. The high-cur­rent, high-charge op­er­at­ing pa­ram­e­ters make ef­fec­tive high­er-or­der-mode (HOM) damp­ing manda­to­ry, and re­quires to de­ter­mi­na­tion of HOM tol­er­ances for a cav­i­ty up­grade. The nio­bi­um cav­i­ty has been test­ed at su­per­con­duct­ing tem­per­a­tures and has pro­vid­ed mea­sured dipole shunt impedances for the es­ti­mate of a beam breakup in­sta­bil­i­ty. The fa­cil­i­ty will be as­sem­bled with a high­ly flex­i­ble lat­tice cov­er­ing a vast op­er­a­tional pa­ram­e­ter space for ver­i­fi­ca­tion of the es­ti­mates and to serve as a test bed for the con­cepts di­rect­ed at fu­ture pro­jects.

Slides

• C. Montag, L. Ahrens, M. Bai, J. Beebe-Wang, M. Blaskiewicz, J.M. Brennan, K.A. Brown, D. Bruno, R. Connolly, T. D'Ottavio, K.A. Drees, A.V. Fedotov, W. Fischer, G. Ganetis, C.J. Gardner, J.W. Glenn, H. Hahn, M. Harvey, T. Hayes, H. Huang, P.F. Ingrassia, J.P. Jamilkowski, A. Kayran, J. Kewisch, R.C. Lee, D.I. Lowenstein, A.U. Luccio, Y. Luo, W.W. MacKay, Y. Makdisi, N. Malitsky, G.J. Marr, A. Marusic, M.P. Menga, R.J. Michnoff, M.G. Minty, J. Morris, B. Oerter, F.C. Pilat, P.H. Pile, E. Pozdeyev, V. Ptitsyn, G. Robert-Demolaize, T. Roser, T. Russo, T. Satogata, V. Schoefer, C. Schultheiss, F. Severino, M. Sivertz, K. Smith, S. Tepikian, P. Thieberger, D. Trbojevic, N. Tsoupas, J.E. Tuozzolo, A. Zaltsman, A. Zelenski, K. Zeno, S.Y. Zhang
  BNL, Upton, Long Island, New York

Dur­ing the sec­ond half of Run-9, the Rel­a­tivis­tic Heavy Ion Col­lid­er (RHIC) pro­vid­ed po­lar­ized pro­ton col­li­sions at two in­ter­ac­tion points with both lon­gi­tu­di­nal and ver­ti­cal spin di­rec­tion. De­spite an in­crease in the peak lu­mi­nos­i­ty by up to 40%, the av­er­age store lu­mi­nos­i­ty did not in­crease com­pared to pre­vi­ous runs. We dis­cuss the lu­mi­nos­i­ty lim­i­ta­tions and po­lar­iza­tion per­for­mance dur­ing Run-9.